Powering Tomorrow: Fuel Cells and Energy Storage
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The demand for energy storage is increasing alongside worldwide population growth. Simultaneously, the need to transition to sustainable and clean energy sources is more urgent than ever before.
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VOLUME 17 • NUMBER 3
Material
Matters™
Molecular Solar Thermal
Energy Storage Systems
(MOST) – Design, Synthesis,
and Application
Nanostructured Catalyst for
Direct Alcohol Low
Temperature Fuel Cells
How to Best Store Electrical
Energy
Polymer
Electrolyte
Membrane
(PEM)
Powering
Tomorrow:
Fuel Cells and
Energy Storage
The Life Science business of Merck operates
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About the Cover
The demand for energy is
increasing at an unprecedented
rate. At the same time, the need
to transition to sustainable and
clean energy sources is more
urgent than ever before. This
issue highlights some exciting
research technologies proposed
to solve the challenges of
powering the future sustainably,
including solar energy storage, fuel
cells, and flow batteries. An image of
a fuel cell is displayed in the top right
corner. A schematic representation of a fuel cell converting hydrogen
and oxygen gas into electricity and water is shown in the middle. Our
Material Science team is dedicated to advancing energy technologies with a
comprehensive portfolio of innovative materials to empower breakthroughs.
VOL. 17 • NO. 3
Material Matters™
Introduction
Polymer
Electrolyte
Membrane
(PEM)
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Welcome to the final issue of Material Matters for 2022, focused on novel materials and innovative platforms for
renewable energy. Due to the growing need for energy, technologies that can convert electricity from a renewable
source into a chemical fuel for storage (and vice versa) are increasingly vital. While there are many challenges
facing the widespread use of renewable energy, among the most critical are cost-effective, sustainable energy
storage and conversion systems. Unlike fossil fuels, renewables don’t generate electricity on demand. Although
batteries have long been considered one of the most effective energy storage methods, the environmental
impacts of large-scale battery use remain a significant challenge requiring inventive solutions. As technology
progresses, the future development of renewable systems depends on energy storage.
In the first article, Professor Moth-Poulson (ICREA, Spain) looks at Molecular Solar Thermal Energy Storage
(MOST) Systems, also known as solar thermal fuels (STF), as a promising approach for solar energy harvesting
and storage. MOST systems play a crucial role in current renewable energy research by combining sunlight's power with molecular
materials' ability to store energy. This article highlights the advantages of some of these candidates by detailing their synthesis
and demonstrating how each can be tuned to increase their efficiency.
In the second article, Professor Neto (Cidade Universitária, Brazil) presents their perspective on fuel cell material development
with a focus on ethanol and glycerol for direct alcohol fuel cells. Enormous advances have been made for the utilization of
glycerol in catalytic processes, and it currently offers great potential for renewable energy generation. Additionally, the
author discusses anion exchange membrane developments and challenges.
In the final article, Professor Stimming (Newcastle University, United Kingdom)
discusses his novel innovations using polyoxometalates (POM) ions with multiple
redox centers. These compounds can be applied to a modified redox flow battery
concept which uses two liquids for electrodes in an electrochemical cell. POMbased battery systems have many advantages for electricity storage including
capacity, power, ease of operation and transport, durability, sustainability, and
eventually, low costs.
Each article is accompanied by a curated list of related products available
from Merck. For more information and additional product offerings,
please visit us at SigmaAldrich.com/matsci. Do you have any new product
suggestions or new ideas for future Material Matters™ Please contact us at
SigmaAldrich.com/technicalservice.
Megan Muroski, Ph.D.
Global Product Manager
– Nanomaterials and
Energy
1
Material Matters
VOL. 17 • NO. 3
™
Table of Contents
Your Material Matters
Nicolynn Davis, Ph.D. Articles Head of Material Sciences and F&F
Molecular Solar Thermal Energy Storage Systems 3
(MOST) – Design, Synthesis, and Application
Nanostructured Catalyst for Direct Alcohol 11
Low-Temperature Fuel Cells
How to Best Store Electrical Energy 16
Featured Products
Materials for MOST 9
A selection of materials suitable for Molecular Solar
Thermal Energy Storage Systems (MOST)
Proton Exchange Membrane (PEM) Fuel Cells 14
A list of exchange membrane materials for fuel cells
Solid Oxide Fuel Cells (SOFCs) 19
A list of materials for use in SOFCs
Fuel Cell Membranes 19
A selection of membrane materials for fuel cells
Lead sulfide-based quantum dots can absorb and emit light
across the near-infrared (NIR) and short-wave infrared (SWIR)
wavelengths in the electromagnetic spectrum. Quantum dot
technology has been intensively researched and developed for
commercial application in photodetectors, photovoltaics, and
infrared light emitters.
The semiconductor band gap of lead-sulfide (PbS) quantum dots
can be controlled by the particle size, whereby longer wavelength
absorbing materials denote larger nanoparticles. The excitonic
absorption peak wavelength can ascertain the characteristics of
the quantum dot and is observed as a strongly absorbing peak
at a slightly higher energy than the absorption onset. Defined as
the full width at half maximum (FWHM), a narrow peak indicates a
monodisperse ensemble of nanoparticles. This is highly desirable
in applications where a flat energy landscape, a narrow energy
distribution, and the formation of superlattices yield improved
performance.
Alongside superior optical performance through synthesis,
Quantum Science Ltd. surface science has developed robust
materials that can withstand prolonged exposure to high
temperatures. This serves as a strong indicator that the materials
are resistant to shorter periods of elevated temperatures during
post-processing in device fabrication.
Some potential applications of infrared PbS quantum dots include:
1. Infrared photodetectors based on solution processing of PbS
nanoparticles that have reported photon conversion efficiencies
of over 80%, giving excellent sensitivity in short-wave infrared
(SWIR).1
2. Photovoltaics using PbS quantum dots that can exploit the
infrared spectrum not easily accessible using traditional
solar cells. This is advantageous as half of the solar energy
reaching the earth is in the infrared region. These devices
can be designed as single-junction solar cells or multijunction
“tandem” cells.2
3. Infrared light-emitting diodes (LEDs) that find application in
several areas, such as surveillance and security, night vision,
biomedical imaging, and spectroscopy.3
References
(1) Vafaie, M.; et al. Matter 2021 4 (3), 1042–1053. DOI:10.1016/j.
matt.2020.12.017
(2) Choi, M. J.; et al. Nat. Commun., 2020, 11 (1), 1–9. DOI:10.1038/
s41467-019-13437-2
(3) Pradhan, S. et al. Nat. Nanotechnol. 2019, 14 (1), 72–79. DOI:10.1038/
s41565-018-0312-y
Name Cat. No.
Infrared PbS quantum dots, λmax 1550 nm, 100 mg/ml in
toluene
925535
Infrared PbS quantum dots, λmax 1350 nm, 100 mg/ml in
toluene
925543
Catch
the sun
Product Category list:
• Organic Photovoltaic (OPV) Donors and Acceptors
• Dye-Sensitized Solar Cell Materials
• Perovskite Materials
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3
Material Matters
VOL. 17 • NO. 3
™
250
photochemistry
hv1
∆1, cat,. hv2
∆H‡
stability ∆' ∆Hstorage
& availability
heat
release
Sexcited
So
energy
storage
Energy
Reaction coordinate
thermal
catalytic
i
iii
v
iv
ii
A)
A B
B)
Molecular Solar Thermal Energy
Storage Systems (MOST) – Design,
Synthesis, and Application
Helen Hölzel1 and Kasper Moth-Poulsen1,2,3*
1 Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Kemigården
4, 412 96 Gothenburg, Sweden
2
The Institute of Materials Science of Barcelona, ICMAB-CSIC, 08193, Bellaterra, Barcelona, Spain
3
Catalan Institution for Research & Advanced Studies, ICREA, Pg. Lluis Companys 23, Barcelona, Spain
*
E-mail: kasper.moth-poulsen@chalmers.se
Introduction
With worldwide population growth, the global energy demand
has drastically increased and will rise by an average of 1.3%
annually until 2040.1
Currently, this challenge is not merely
addressed by conventional energy sources such as oil, coal, gas,
or nuclear power, but also by renewable energy sources such
as wind and solar energy. The demand for renewable energy
sources has been increasing even during the economic crisis due
to lockdowns caused by the global pandemic, Covid-19.2,3 The
renewable energy share, among the total energy mix, increased
to 5.7% in 2020 outnumbering nuclear energy at 4.3%.3
The
growth for wind and solar energy was 238 GW in 2020, which
is 50% more than any single year in history. The sun, being
most abundant among renewable energy sources, delivers
around 235 Wm-2 on average.4
Typically, energy from the sun is
used directly for heating or electric power production; however,
as renewable energy continues to grow as part of the energy
mix, efficient energy storage becomes a growing challenge. A
promising approach for solar energy harvesting and storage is
the concept of molecular solar thermal energy storage (MOST)
systems also known as solar thermal fuels (STF). Solar energy
is used to drive the chemical reaction of a molecule, usually
referred to as a molecular photoswitch, leading to an energy-rich
metastable isomer, which stores the energy. The energy can
later be released on demand, controlled thermally, catalytically,
or through irradiation with selected wavelengths of light. In this
article, we introduce the requirements for a MOST system, the
structures of different photoswitches, their general charging
and discharging mechanisms, highlight the accessibility of the
material by synthetic production, and describe possible uses of
the stored energy.
Molecular Solar Thermal Energy Storage
(MOST) Systems
In general, MOST systems should feature at least four functional
principles as illustrated in Figure 1A. A MOST system is based
on a photochemical reaction such as isomerization, dimerization,
or rearrangements. During the photochemical reaction, photon
energy is converted to chemical energy by converting the parent
molecule, A to a high-energy meta-stable photoisomer, B (Figure
1). B should have a high-energy storage density compared to
A, and depending on the application, should feature a suitable
storage half-life (t1/2). The back-reaction process should result in a
release of energy as heat and can be activated by either thermal
activation, a catalytic system (catalyst or electrochemistry),
or light. The last but most important principle is the stability
and availability of the system. This includes a simple way
Figure 1. A) Schematic depiction of features of a MOST system and B)
the MOST operation cycle, i) absorption from parent molecule to an excited
state, ii) absorption from the meta-stable state, iii) photoconversion, iv)
thermal or catalytic back-conversion, v) cyclability. Reproduced from
reference 5, copyright 2022 Elsevier B.V.
4 Molecular Solar Thermal Energy Storage Systems (MOST) – Design, Synthesis, and Application
of molecule preparation, which requires economic feasibility
regarding applications. Further, the molecule should be stable for
longer periods, and withstand several cycles of operation. To meet
all these principles, molecular design is the most crucial point.
Before design and synthesis come into play, it is necessary
to understand the energy landscape and steps of the energy
storage process in more detail, to extract the most ideal concept
fitting the requirements to create efficient systems.5–7 The
process consists of four main steps and a few side processes
(Figure 1B). Exposure to light should excite molecule A from
its ground state (S0) to its excited state (Sexcited) via photon
absorption (i). To use the photons provided from solar irradiation,
the system should absorb light between 300–800 nm,8
as
50% of the incoming photons are within this range.5 Through
photoconversion (iii) the excited molecule ends up in a metastable high energy photoisomer B. This process strongly depends
on the photoisomerization quantum yield Φiso. Preferably, the
photoisomerization should happen via one photon with a quantum
yield close to 1. The molecule should then remain in this state,
for longer periods indicated by the half-life time (t1/2). Depending
on the application, t1/2 should be long enough to store the energy
for days, months, or years at room temperature.8
However,
t1/2 depends on the rate of the back-reaction (iv) and is thus
intimately related to the thermal back-reaction barrier ΔH‡
. As
the meta-stable isomer should store energy, the ΔHstorage, which
is the energy difference between the two isomers, should be as
high as possible. To release the energy, the back-conversion (iv)
can be triggered either catalytically, thermally, electrochemically,
or for some compounds also photochemically. Especially the latter
trigger might display a competing absorption process (ii) and
should be avoided or suppressed. In the best case, the spectral
overlap should be small. The trigger should be as efficient as
possible to release the energy when required. Considering this
is a circular process, the final, important factor is the cyclability
(v) of charging and discharging of the MOST material. Within this
cycle, there should be no degradation (or less degradation) and no
material fatigue should be observed. Real-life applications should
apply sustainability practices, meaning the material should be
harmless for the environment and humans. These requirements
are very specific and difficult to address in a single molecular
system, creating a challenge to find the “ideal system” to apply
in real-life applications. Nevertheless, the search steadily reveals
important molecular features and progress in performance in all
aspects previously mentioned. In the following sections, we will
introduce different molecular systems that are being studied and
how molecular design has been used to improve their function.
Photoswitches as MOST Materials
Through the years several different molecular systems have
been investigated and suggested as MOST candidates.5,6 Three
main molecular systems are gaining increasing interest: the
norbornadiene/quadricyclane (NBD/QC), the E/Z-azobenzene
(E/Z-AZO), and the dihydroazulene/vinylheptafulvene (DHA/VHF)
isomers (Figure 2).
However, while the overall goals for the use of those systems as
MOST are similar, there are some differences in the charging and
discharging mechanisms as well as molecular design principles
for each compound class. For the NBD/QC system the molecule
is excited through either direct irradiation or via the use of a
photosensitizer. The chemical reaction that occurs after excitation
is a [2+2] cycloaddition (Figure 2A). Unsubstituted NBD itself only
absorbs in the UV region, therefore different design strategies
have been used to optimize the system for solar absorption.9
The quadricyclane molecule has a high internal strain and can
store around 0.1 MJ mol-1.10 For some optimized compounds
storage energy densities of up to 1 MJ kg-1 are reported.7,11 The
azobenzene system can be switched from its E/trans-isomer
to its Z/cis-isomer via irradiation at the respective wavelength
(Figure 2B).6
However, the amount of stored energy of the
parent Z-azobenzene (0.041 MJ mol-1) is around half the value
of QC,12 and full conversion is challenging to achieve due to the
photochemical equilibrium. The Z-isomer converts back to the
E-isomer via light irradiation in the visible range. This competition
can be mitigated using a bandpass filter for device applications13 or
by molecular engineering.14 The DHA molecule can be converted
to VHF through a photoinduced ring-opening reaction. Initially,
the s-cis form is formed which then changes into the more stable
s-trans conformer (Figure 2C).15 The VHF usually possesses redshifted absorption compared to DHA, similar to azobenzene, but is
photochemically inactive, and thus no competing back-conversion
of the visible spectral range occurs. To date, most parent
molecules cannot store energy efficiently; therefore, structural,
and molecular design strategies are employed to modify and
optimize the properties.
Molecular Design Strategies
Addition of substituents to red-shift the absorption profile of
the parent molecule A is an important objective for storage
of a large fraction of the solar energy spectrum. Herein, we
exemplify some strategies for the NBD molecule.9
Attaching
corresponding functionalities and substituents to the parent
Figure 2. Examples of currently investigated MOST systems and
conversion processes. A) norbornadiene NBD/ quadricyclane QC couple,
B) E-/Z-azobenzene couple, C) dihydroazulene DHA/ vinylheptafulvene VHF
couple.
250
A) Norbornadiene (NBD)/ Quadricyclane (QC)
C) Dihydroazulene (DHA)/ Vinylheptafulvene (VHF)
B) E-IZ-Azobenzene
5
Material Matters
VOL. 17 • NO. 3
™
360
250
450Donor
NBD 1
NBD 4 NBD 4
NBD 5 NBD 6
QC NBD
QC 4
QC 4
NBD 2 NBD 3
Acceptor
Bulky substituent
A)
D) E)
B) C)
1.0
0.5
0.0
2
0
-2
-4
200
175
150
125
100
75
50
25
0
1.0
0.5
1.0
0.5
300 350
0 25 55 75 100
0 40 80 120 160 0 100 200 300
81 86
125
400 450
Absorbance (a.u.)
Cycle number Temperature (°C)
An/Ao
Heat flow (kj°C-1mol-1)
Energy (kj/mol)
Diehedral angle (degree)
0 100 200 300
Diehedral angle (degree)
molecules using a donor-acceptor pair, lowers the HOMO-LUMO
gap of the system. Hereby two design approaches can be used.
One approach is the introduction of donor and acceptor groups at
the two different double bonds of the NBD system (Figure 3A).16
These types of push-pull systems, NBD 1, rely on the principle
of homoconjugation which promotes communication and charge
transfer through space. However, this may be accompanied
by an increase in molecular weight which reduces the energy
storage density. Another approach is a push-pull architecture
on one double bond of the molecule (Figure 3B, for example,
NBD 2).11 This results in a better match with the solar spectrum
via bathochromic shifting of the absorption profile but may lead
to reduced energy storage time t1/2.
Dimeric donor-acceptor type systems, NBD 3, can lead to even
further red-shifting of the absorption band and provide enhanced
charge transfer through the bridge (Figure 3C).17 Accompanied
by the general design of multi-photoisomeric architectures, which
feature two or more photoswitchable units. Each moiety can
exhibit different thermal back-conversion barriers and thus lead
to several switching events in one molecule so that the overall
energy storage density increases even though the molecular
weight also increases.18 Therefore, one of the most promising
approaches to date, utilizes two concepts: the extension of
the conjugation within the system and the introduction of
electron-donating and electron-accepting groups. Aryl and
acetylene units attached to the molecular core typically led to
a better match with the solar spectrum and show enhanced
p-conjugation. However, this increases the molecular weight
drastically, especially in the case of aryl units.19 To counter this,
one of the substituents can be replaced by a low molecular
weight functionality with electron-withdrawing properties.20
This could result in very promising candidates such as NBD 4
(Figure 3D) which not only lead to bathochromic shifting of the
absorption but also a higher energy density, as well as improved
and persistent stability, withstanding many cycles of charging
and discharging.21 Unfortunately, in this case, a lowered t1/2 was
observed.20 Extension of storage times for NBDs was observed
by the addition of bulky substituents to the carbon bridge or the
introduction of ortho-aryl substituents (compare NBD 5 and NBD
6, Figure 3E). Both approaches lead to steric repulsion effects
directly impacting the back-reaction barrier.11,22
Similar Design strategies are applied for other MOST systems,
e.g. azobenzenes and DHA (Figures 4A and 4C). In a recent
study, substituents on the azobenzene units had stark effects on
their properties (storage times, absorption profiles, isomerization
quantum yield, etc.), e.g. donor-acceptor motifs or introduction of
ortho-substituents, especially fluorinated azobenzenes (Figure 4A
and 4B).6
Leading to exceptional extended half-life times caused
by less electron density in the azo-bridge, thus stabilizing the
Z-form.6
Further half-life and red-shifting of absorption can be
influenced by introducing various amino-functionalities with
different p-donation properties; hence stronger donors lead to
more visible range spectral overlap while weaker donors ensure
longer storage times (Figure 4B).23 Replacement of the phenylsubstituents in azobenzenes by using heteroaryls (Figure 4B),
such as triazoles and pyrazoles have an impressive effect on the
Figure 3. A–C) Different NBD donor-acceptor motifs with examples, D) example for a low-molecular weight NBD with red-shifted absorption and full
conversion, high cyclability, and good heat release, E) strategy to improve half-life by introduction of bulky substituents or change in the dihedral angle
using ortho-substituents. Figures reproduced from references 11, 20 and 21, copyright 2016 Wiley-VCH Verlag GmbH&Co. KGaA, 2018 Wiley-VCH Verlag
GmbH&Co. KGaA, and The Royal Society of Chemistry 2017.
6 Molecular Solar Thermal Energy Storage Systems (MOST) – Design, Synthesis, and Application
conversion, revealing complete conversion from Z to E in most
of the cases.6,14,24 In the case of bis-pyrazole systems, less steric
hindrance within the molecule and the position of substitution
of the heteroaryl moiety, effects the thermal back-reaction and
thus the half-life of the system, due to different stabilization
via intramolecular interactions.14 Azobenzenes have also been
investigated as phase-change materials for MOST applications.25
DHA molecules are also influenced by substituents (Figure 4C),
especially with the introduction of donor-acceptor units at the C2,
C3, or C7 positions, for example, with functionalities attached
to phenyl groups.15,26,27 Hereby, longer half-lives and red-shifting
of absorption were achieved, especially when using cyano-based
substituents at C7.28 Variations from one cyano group at C1 using
a hydrogen atom or methyl group influence the back-reactions
barrier,29 while computations reveal that annellation of a benzene
unit at the C2–C3 will increase the energy density.30
Synthesis and Preparation
The preparation of MOST materials is strongly dependent on the
molecular system and the accompanying structural composition.
In the case of NBDs, synthesis occurs primarily using two
approaches: palladium-catalyzed cross-coupling reactions, or
Diels-Alder reactions (Figure 5). The first synthesis pathway starts
from the commercially available 2,5-norbornadiene (Cat. No.
8.20918) 1 (Bicyclo[2.2.1]hepta-2,5-diene, Cat. No. B33803)
which reacts with brominating agents, like 1,2-dibromoethane
2, (Cat. No. 240656),31,32 or by using a lithiation followed by
quenching with electrophiles, such as p-toluenesulfonyl halide,
to form a halogenated species 2.33 These molecules can then
undergo cross-coupling reactions such as Sonogashira or Suzuki
reactions using palladium catalysts (Figure 5A). With this
approach, several 2,3-substituted NBDs 3 were synthesized.11,20
The second approach includes the use of cyclopentadiene (CP) 6
and substituted acetylene 7 in a [4+2] cycloaddition reaction, here
a Diels-Alder reaction (Figure 5B). However, this electrocyclic
reaction requires specific electronic properties of both reactants.
Usually, it involves 4p-electrons of the diene and 2p-electrons of
the dienophile. To match the electronic requirements, the HOMO
of the diene and the LUMO of the dienophile need to overlap. This
is even more favored when the dienophile carries an electronwithdrawing group (EWG, e.g. COR, COOR, CN) which facilitates
the reaction by lowering the LUMO energy. Using the EWG group
on the acetylene, the reaction with the reactive and electron-rich
diene can be carried out easily, to result in NBDs 8. Also, depending
on the starting material this reaction can be performed neat,
without involving any solvent. As shown previously, this synthesis
route can be efficient for the preparation of various types of
NBDs.11 However, this approach also gives rise to challenges since
the cyclopentadiene is unstable and usually forms an equilibrium
with its dimer, dicyclopentadiene 9 (DCPD, Cat. Nos. 8.03038
or 454338). CP can be regained from DCPD 9 via a retro DielsAlder reaction, through thermal cracking (Figure 5C). For NBDs
requiring a higher temperature for synthesis, both reactions can
be carried out in a combined fashion.
Most synthetic approaches were carried out in batches, which
becomes impractical when upscaling is required. Therefore,
another method gaining attention comes into play: flow chemistry.
Recently, a continuous flow method that combines both the DielsAlder and Cracking in one step was developed using a tubular
flow reactor allowing for the preparation of larger quantities
(Figure 5D).34 Herein, a commercially available dienophile, ethyl
phenylpropiolate (Cat. No. E45309), CP 6, and DCPD 9, were
used for screening and optimization of the reaction in a 5 mL
360
250
450
• Variation of substituents (e.g. donor-acceptor motifs)
• Ortho substituents (e.g. F)
• use of other aryl units, e.g. heteroaryls
Variation of substituents in different positions
A)
C)
B)
Donor
Acceptor
Aryl unit
Donor-acceptor motifs
t1/2: 700 d 1000 d 681 d 0.3 d 445 h 1.2 s
Figure 4. A) Examples for variation of azobenzene, B) concrete examples and influence on the half-life, C) numbered DHA molecule and examples
for variation.
7
Material Matters
VOL. 17 • NO. 3
™
stainless steel coil reactor. Optimized conditions were then applied
to various substituted acetylenes 10 to synthesize differently
functionalized NBDs 11. The method shows that it is possible
to upscale and produce around 100 g of NBD in a few hours.
Applications need larger amounts of material, which makes this
method very valuable.
Azobenzene systems can be synthesized via various approaches.35
The most common are Azo coupling and the Mills reaction. Azo
coupling uses a diazonium salt as electrophile prepared from
a primary amine with NaNO2
(Cat. No. 901903 or 563218)
in acidic media, and an electron-rich partner, such as arene
derivatives decorated with electron-donating groups, while the
Mills reaction includes a nitroso-derivative which is typically
reacted with aniline in glacial acetic acid. DHA molecules have been
prepared mainly through three pathways.36 The first approach
follows a [8+2] cycloaddition between 8-methoxyheptafulvene and
dicyanoethylenes, the latter prepared from malononitrile (Cat. No.
M1407) and carbonyl compounds. The second method directly
starts from tropylium tetrafluoroborate (Cat. No. 164623) which
either first reacts with a dicyanoethylene compound or a carbonyl
derivative and then with malononitrile. This subsequently leads
to the formation of a VHF molecule that reacts under heat to the
corresponding DHA compound. The third route which primarily
results in a substituted 7-membered ring relies on the utilization
of tropone derivatives which forms the VHF, form but via
condensation with dicyanoethylenes, which can then be converted
to the DHA form using heat.
Energy Release in MOST Systems
MOST systems are unique energy systems in the sense that they
offer energy capture, storage, and release in a single, emissionfree system. The challenge is to design devices that make
use of these attractive properties while mitigating challenges
with low energy storage efficiency and energy density. In one
implementation, a liquid MOST system is first pumped through a
solar collector, and later, a heat release device containing a fixed
bed catalytic system is used to trigger the heat release (Figure 6A
left). In this way, chemical energy from the QC to NBD conversion
was used to increase the temperature in the device from ambient
temperature to 85 °C (Figure 6A right).37 This heat release can
also be used to heat water in a hybrid device (Figure 6B).21
Electrochemistry can also be used to trigger heat release. In this
way, the initial oxidation of QC leads to the conversion of several
molecules by a local radical mechanism (Figure 6C).38 Research
shows this reaction works reversibly both in solution and in solidstate and offers an attractive way of controlling energy release.
Other systems feature hybrid combinations of MOST and phase
change materials to allow for continuous thermal heat storage
and release over extended periods (Figure 6D).39 The co-location
of the energy capture storage and release together with the
semitransparency of most systems allows for unconventional
applications, such as the possible integration of the MOST system
into functional windows40,41 where the MOST system is intended to
regulate the daily variation of solar influx, where in many cases,
strong solar influx at noon leads to strong heating, whereas
energy loss through windows at night need heating (Figure 6E). A
functional MOST system may in the future be used in this way to
control indoor climates.
Figure 5. Synthetic approaches of norbornadienes as MOST material. A) Lithiation and Halogen exchange starting from norbornadiene, option for
replacement of bromine with nitrile via substitution, and with subsequent cross-coupling reactions. B) Diels-Alder reaction between cyclopentadiene and
activated acetylene. C) Dicyclopentadiene cracking to cyclopentadiene under thermal conditions. D) Recently developed combined cracking and Diels-Alder
flow method to norbornadienes.
360
250
450
A)
D)
Lithiation and
Halogen
exchange
Diels-Alder
One step two reactions Cracking
+
Diels-Alder Reaction
+
1
6
10 9 11
7 8 9 6
2 2
4 5
X2
X1 R'
CN
EWG
BPR
EWG
EWG
EWG
R
Ar
2
∆
R
Ar
CI
CN
R''
R''
Sonogashira
or Suzuki
cross-coupling R'= R'' for X1 = X2 = Br
R'/R'' = arylacetylene, aryl
R” = arylacetylene, aryl for X1 = Br, X2 = CI
X = Br, or CI
substitution
with CuCN
Sonogashira
or Suzuki
cross-coupling
B) C)
8 Molecular Solar Thermal Energy Storage Systems (MOST) – Design, Synthesis, and Application
Summary
MOST systems were first proposed for energy storage more than
100 years ago.42 Recently, increased efforts have been carried out
to improve the functionality of molecular photoswitches for solar
energy storage. Herein we have introduced the features of MOST
systems and presented design principles that have been used
to increase energy storage density, efficiency, and availability,
we have highlighted key examples of synthesis from literature.
With increasing awareness of challenges with traditional energy
production and geographic uneven distribution of fossil fuels,
we hope that new, emission-free solar energy systems can be
developed since the sun shines on all areas of the planet.
References
(1) (2019), I. E. A., World Energy Outlook 2019 (OECD)
(2) (2021), I. E. A., World Energy Outlook 2021 (OECD)
(3) Statistical Review of World Energy. BP Statistical Review of World Energy
2021, 70th ed Full report – Statistical Review of World Energy 2021
(bp.com)
(4) Ognjen S. Miljanic, J. A. P., Solar Energy. In Introduction to Energy and
Sustainability, 1st ed.; Wiley-VCH: 2021; pp 451–468.
(5) Wang, Z. et al. Joule 2021, 5 (12), 3116–3136. DOI:10.1016/j.
joule.2021.11.001.
(6) Dong, L. et al. Chem. Soc. Rev. 2018, 47 (19), 7339–7368. DOI:10.1039/
C8CS00470F.
(7) Bren, V. A. et al. Russ. Chem. Rev. 1991, 60, 451–469. DOI:10.1070/
RC1991v060n05ABEH001088.
(8) Börjesson, K. et al. ACS Sustain. Chem. Eng. 2013, 1 (6), 585–590.
DOI:10.1021/sc300107z.
(9) Orrego-Hernández, J. et al. Acc. Chem. Res. 2020, 53 (8), 1478–1487.
DOI:10.1021/acs.accounts.0c00235.
(10) Lennartson, A. et al. Tetrahedron Lett. 2015, 56 (12), 1457–1465.
DOI:10.1016/j.tetlet.2015.01.187.
Figure 6. Examples of energy release and devices for conversion. A) Illustration of a heat release device and corresponding device plot. B) Illustration of
a hybrid device used to heat water. C) Plots of energy conversion of several molecules by a local radical mechanism. D)Illustration of hybrid combinations
of MOST and phase change materials allowing continuous thermal heat storage and release over time. E) Plot of a 24H cycle using MOST in a functional
window. Figures reproduced from references 21, 37–39, 41, copyright The Royal Society of Chemistry 2019, The Royal Society of Chemistry 2017, The Royal
Society of Chemistry 2020, 2019 Elsevier Inc., and 2022 by Elsevier Ltd.
(11) Jevric, M. et al. Chem. Eur. J. 2018, 24 (49), 12767–12772. DOI:10.1002/
chem.201802932.
(12) Taoda, H. et al. J. Chem. Eng. Jpn. 1987, 20 (3), 265–270. DOI:10.1252/
jcej.20.265.
(13) Wang, Z. et al. Adv. Sci. 2021, 8 (21), 2103060. DOI:10.1002/
advs.202103060.
(14) He, Y. et al. Angew. Chem. Int. Ed. 2021, 60 (30), 16539–16546.
DOI:10.1002/anie.202103705.
(15) Broman, S. L.; Nielsen, M. B. Phys. Chem. Chem. Phys. 2014, 16 (39),
21172–21182. DOI:10.1039/C4CP02442G.
(16) Yoshida, Z.-i. J. Photochem. 1985, 29 (1), 27–40. DOI:10.1016/0047-
2670(85)87059-3.
(17) Mansø, M. et al. Org. Biomol. Chem. 2018, 16 (31), 5585–5590.
DOI:10.1039/C8OB01470A.
(18) Mansø, M. et al. Nat. Commun. 2018, 9 (1), 1945. DOI:10.1038/
s41467-018-04230-8.
(19) Gray, V. et al. Chem. Commun. 2014, 50 (40), 5330–5332. DOI:10.1039/
C3CC47517D.
(20) Quant, M. et al. Chem. Eur. J. 2016, 22 (37), 13265–74. DOI:10.1002/
chem.201602530.
(21) Dreos, A. et al. Energy Environ. Sci. 2017, 10 (3), 728–734. DOI:10.1039/
C6EE01952H.
(22) Jorner, K. et al. J. Mater. Chem. A 2017, 5 (24), 12369–12378.
DOI:10.1039/C7TA04259K.
(23) Kuntze, K. et al. Photochem. Photobiol. Sci. 2022, 21 (2), 159–173.
DOI:10.1007/s43630-021-00145-4.
(24) Fang, D. et al. J. Am. Chem. Soc. 2021, 143 (36), 14502–14510.
DOI:10.1021/jacs.1c08704.
(25) Shi, Y. et al. J. Mater. Chem. A 2021, 9 (15), 9798–9808. DOI:10.1039/
D1TA01007G.
(26) Broman, S. L. et al. Chem. Eur. J. 2013, 19 (29), 9542–9548.
DOI:10.1002/chem.201300167.
(27) Kilde, M. D. et al. Eur. J. Org. Chem. 2017, 2017 (6), 1052–1062.
DOI:10.1002/ejoc.201601435.
(28) Mogensen, J. et al. Eur. J. Org. Chem. 2019, 2019 (10), 1986–1993.
DOI:10.1002/ejoc.201801776.
(29) Cacciarini, M. et al. Chem. Eur. J. 2015, 21 (20), 7454–7461.
DOI:10.1002/chem.201500100.
(30) Skov, A. B. et al. Chem. Eur. J. 2016, 22 (41), 14567–14575. DOI:10.1002/
chem.201601190.
360
250
450
Thermocouple 2
NBD out
MOST
fluid in MOST fluid out
Water out
Stored heat
Readily available
heat
ηMOST=1.1%
11 W m-2
ηSWH=80%
800 W m-2
MOST
Water
Photons
EAM1.5=1000 W m-2
≤880 W m-2
≤88%
Water in
Silica
Quartz
Plastic
QC in Thermocouple 1
Vacuum System Catalyst
Syringe pump
T2
T1
Recycling
vial
A)
C) D) E)
B)
60
40
20
0
10
5
0
-5
-10
1.0
0.8
0.6
0.4
0.2
0
1000
Temperature activated (T>TThreshold)
UV
0 250 500 750
0
-1.0
-0.88 Vfc
-0.88 Vfc
-0.42 Vfc
1.72 Vfc
-0.5 0.0 0.0 1.0 1.5
100 800 1200
∆T (°C) ∆c (mM)
∆R/R
= 2%
potential [Vfc]
NBB'
2195 cm-1
QC'
2220 cm-1
Consumption
of QC'
Oxidation
of NBD'
Formation
of NBD'
NBD'
NBD'
NBD'
NBD
MSM
Solar Irradiation
MSM
L-PCM
L-PCM
Silica Aerogel
Silica Aerogel
Temperatue
Hot
Cold
Anti-Reflective Glass
HTF out
HTF in
HTF L-PCM
open: night
closed: day
open: day
closed: night
HOPG
Pt(111)
Daytime Night time
24 hour cycle
MOST Energy density
NBD'
hν
QC'
QC'
QC'
QC
2220
2250 2200
Wavenumber [cm-1]
Storage Capacity
70
60
50
40
30
20
10
0
-10
0.1 MJ/kg
0.4 MJ/kg
1 MJ/kg
Heat release
30% wt. of MOST
Storage
0 12 16 20 24 28 32
Net Stored Flux (W/m2)
Time (h) Cycle
2150
2195
Decomposition
Time (s)
Maximum temperature measured: 63.4 °C
9
Material Matters
VOL. 17 • NO. 3
™
(31) Kenndoff, J. et al. J. Am. Chem. Soc. 1990, 112 (16), 6117–6118.
DOI:10.1021/ja00172a031.
(32) Tranmer, G. K. et al. Can. J. Chem. 2000, 78 (5), 527–535. DOI:10.1139/
v00-047.
(33) Lennartson, A. et al. Synlett 2015, 26 (11), 1501–1504.
DOI:10.1055/s-0034-1380417.
(34) Orrego-Hernández, J. et al. Eur. J. Org. Chem. 2021, 2021 (38), 5337–
5342. DOI:10.1002/ejoc.202100795.
(35) Merino, E. Chem. Soc. Rev. 2011, 40 (7), 3835–3853. DOI:10.1039/
C0CS00183J.
(36) Lubrin, N. C. M. et al. Eur. J. Org. Chem. 2017, 2017 (20), 2932–2939.
DOI:10.1002/ejoc.201700446.
(37) Wang, Z. et al. Energy Environ. Sci. 2019, 12 (1), 187–193. DOI:10.1039/
C8EE01011K.
(38) Waidhas, F. et al. J. Mater. Chem. A 2020, 8, 15658–15664. DOI:10.1039/
D0TA00377H.
(39) Kashyap, V. et al. Joule 2019, 3 (12), 3100–3111. DOI:10.1016/j.
joule.2019.11.001.
(40) Petersen, A. U. et al. Adv. Sci. 2019, 6 (12), 1900367. DOI:10.1002/
advs.201900367.
(41) Refaa, Z. et al. Appl. Energy 2022, 310, 118541. DOI:10.1016/j.
apenergy.2022.118541.
(42) Weigert, F. Berichte der deutschen chemischen Gesellschaft 1909, 42 (1),
850–862. DOI:10.1002/cber.190904201136.
Materials for MOST
Name Form Description Cat. No.
Cerium(IV) oxide 20 wt. % colloidal dispersion in 2.5%
acetic acid
30-50 nm avg. part. size 289744-500G
nanoparticle dispersion, 10 wt. % in H2O <25 nm particle size 643009-100ML
nanopowder <25 nm particle size (BET) 544841-5G
544841-25G
<50 nm particle size (BET)
99.95% trace rare earth metals basis
700290-25G
700290-100G
powder <5 µm, 99.9% trace metals basis 211575-100G
211575-500G
99.995% trace metals basis 202975-10G
202975-50G
solid ≥99.0% 22390-100G-F
Cerium(IV) oxide-gadolinium doped nanopowder, contains 10 mol %
gadolinium as dopant
<500 nm particle size 572330-25G
nanopowder, contains 20 mol %
gadolinium as dopant
<100 nm particle size 572357-25G
Cerium(IV)-zirconium(IV) oxide nanopowder <50 nm particle size (BET)
99.0% trace metals basis
634174-25G
634174-100G
Lanthanum strontium cobalt ferrite powder composite cathode powder, LSCF/GDC 704253-10G
LSCF 6428 704288-10G
Lanthanum strontium manganite powder LSM-20, ≥99% 704296-10G
LSM-35 704261-10G
solid composite cathode powder, LSM-20/GDC10 704237-10G
Nickel(II) oxide nanopowder <50 nm particle size (TEM)
99.8% trace metals basis
637130-25G
637130-100G
637130-250G
powder -325 mesh, 99% 399523-100G
powder and chunks 99.99% trace metals basis 203882-20G
203882-100G
solid ≥99.995% trace metals basis 481793-5G
481793-25G
Strontium oxide powder 99.9% trace metals basis 415138-10G
415138-50G
Strontium peroxide powder 98% 415200-100G
Vanadium(III) oxide powder and chunks 99.99% trace metals basis 463744-5G
463744-25G
Vanadium(V) oxide powder 99.95% trace metals basis 204854-1G
204854-5G
204854-25G
Yttrium(III) oxide nanopowder <50 nm particle size 544892-25G
powder 99.99% trace metals basis 205168-10G
205168-50G
205168-250G
99.999% trace metals basis 204927-10G
204927-50G
nanoparticle dispersion
10 wt. % in isopropanol
<100 nm (DLS)
≥99.9% trace metals basis
702048-100G
Zirconium(IV) oxide-yttria stabilized nanopowder ≤100 nm particle size 572322-25G
nanopowder
contains 8 mol % yttria as stabilizer
<100 nm particle size 572349-25G
powder <100 nm particle size 544779-25G
submicron powder 99.9% trace metals basis
(purity excludes ~2% HfO2)
464228-100G
464228-500G
R&D Highlight
2D Layered Perovskites
References:
1) Dou, L.; Wong, A. B.; Yu, Y.; Lai, M.; Kornienko, N.; Eaton, S. W.; Fu, A.; Bischak, C. G.; Ma, J.; Ding, T.; Ginsberg, N. S.; Wang, L-W.; Alivisatos,
A. P.; Yang, P. Science 2015, 349, 1518. DOI: 10.1126/science.aac7660
2) Yuan, M.; Quan, L. N.; Comin, R.; Walters, G.; Sabatini, R.; Voznyy, O.; Hoogland, S.; Zhao, Y.; Beauregard,E. M.; Kanjanaboos, P.; Lu, Z.;
Kim, D. H.; Sargent, E. H. Nat. Nanotechnol. 2016, 11, 872. DOI: 10.1038/NNANO.2016.110
3) Shao, Y.; Liu, Y.; Chen, X.; Chen, C.; Sarpkaya, I.; Chen, Z.; Fang, Y.; Kong, J.; Watanabe, K.;Taniguchi, T.; Taylor, A.; Huang, J.; Xia, F.
Nano Lett. 2017, 17, 7330. DOI: 10.1021/acs.nanolett.7b02980
4) Cao, D. H.; Stoumpos, C. C.; Farha, O. K.; Hupp, J. T.; Kanatzidis, M. G. J. Am. Chem. Soc. 2015, 137, 7843. DOI: 10.1021/jacs.5b03796
5) Raghavan, C. M.; Chen, T.-P.; Li, S.-S.; Chen, W.-L.; Lo, C.-Y.; Liao, Y.-M.; Haider, G.; Lin, C.-C.; Chen, C.-C.; Sankar, R.; Chang, Y.-M.; Chou,
F.-C.; Chen, C.-W. Nano Lett. 2018, 18 (5), 3221. DOI: 10.1021/acs.nanolett.8b00990
Solution Processable Materials
The recent discovery that single-layer 2D perovskites can
be prepared using solution processing techniques1 has been
followed by enormous research into optoelectronic applications
of 2D perovskites including light emitting diodes (LEDs),2
phototransistors,3 and solar cells,4 and lasers.5
Direct and Tunable Bandgap
Photoluminescent 2D perovskites have a direct bandgap
with a narrow emission peak that changes depending on
the layer thickness and the choice of amine and halide. We
offer an excellent portfolio of the most popular 2D perovskite
compositions for photoluminescence based devices.
Improved Moisture Stability
Solar cells fabricated with 2D perovskites have improved stability
in moist air compared to 3D perovskites.4
Formula Cat. No. Layer
Thickness
(RNH3)2(MeNH3)n−1 PbnX3n+1
R X n
(BA)2PbI4 910961 n=1 Bu I 1
(BA)2PbBr4 910953 n=1 Bu Br 1
(PEA)2PbI4 910937 n=1 PE I 1
(PEA)2PbBr4 910945 n=1 PE Br 1
(BA)2(MA)Pb2I7 912816 n=2 Bu I 2
(BA)2(MA)2Pb3I10 912557 n=3 Bu I 3
(BA)2(MA)3Pb4I13 914363 n=4 Bu I 4
(BA)2(MA)4Pb5I16 912301 n=5 Bu I 5
BA = n-butylammonium; PEA = 2-phenylethylammonium;
MA =methylammonium, Bu=n-butyl, PE=2-phenylethyl
SigmaAldrich.com/perovskite
11
Material Matters
VOL. 17 • NO. 3
™
Nanostructured Catalyst for Direct
Alcohol Low-Temperature Fuel Cells
Priscilla J. Zambiazi, and Rodrigo F.B. de Souza, Almir Oliveira Neto*
Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, Av. Prof. Lineu Prestes, 2242 Cidade Universitária,
CEP 05508-900 São Paulo, SP, Brazil
*
Email: aolivei@usp.br
Introduction
At a time when the world is committed to changing its energy
matrix, fuel cells are back on the scene as a promising source
of energy. Fuel cells can convert chemical energy into electrical
energy efficiently. Conceptually, fuel cells are very similar to
the Daniell cell, which is often taught in introductory chemistry
courses. In a Daniell cell, the anode (usually a metal like zinc) is
oxidized and the oxidized metal ions dissolve into the electrolytic
solution while metal ions at the cathode surface are reduced.
Similarly, in a fuel cell, molecules (for example, H2
and O2
) are
inserted into the device and are oxidized and reduced at the
electrodes.1
Conceptually, the hydrogen fuel cell is one of the cleanest energy
sources, consuming only hydrogen and oxygen and releasing only
water; however, hydrogen fuel cells face technological challenges.
For example, producing, storing, and transporting hydrogen is
still expensive and incurs considerable risks, even though the
technology to accomplish these processes has greatly evolved.
In addition, the loss of gas during storage and transport remains
a challenge.2
One strategy to overcome this problem was the adoption of
hydrogen-generating devices, such as thermo-reformers, to
generate hydrogen on demand for use in the fuel cell.3–4 The
downside to this strategy is that the power generation system
occupies more volume due to this extra device.
Figure 1. Diagram of the Daniell Cell and the Hydrogen Fuel Cell devices.
360
250
Electrons
V
Electricity
Salt Bridge
Fuel H2 O2
H2O Fuel H2
e- e- e- eMetal Electrode
Metal Electrode
Cathode
Reduction
Anode
Oxidation
Anode
Gas Diffusion Layer
Gas Diffusion Layer
Proton Exchange Membrane
Cathode
Ions Metallic
in Solution
Ions Metallic
in Solution
Daniell Cell vs Fuel Cell Systems
12 Nanostructured Catalyst for Direct Alcohol Low-Temperature Fuel Cells
Direct Alcohol Fuel Cells
Among the possibilities of fuels of a PEM-FC, alcohols are the
most deeply studied, the main ones being methanol, ethanol,
and glycerol.
Direct Methanol Fuel Cells
Direct alcohol oxidation cells started with the simplest alcohol,
methanol, which is a liquid that is easy and cheap to store and
transport, and has a high energy density of 6.09 kWh kg-1, including
an existing distribution network due to being an industrial input.5
Initial studies identified platinum (Pt) as a promising catalyst for
the methanol oxidation reaction (MOR), but two main obstacles
quickly emerged: 1) Pt is expensive and 2) Pt in MOR is prone to
poisoning by carbon monoxide.
Fortuitously, the beginning of studies on the methanol oxidation
reaction (MOR) happened concomitantly with the development of
new methods for preparing nanostructured materials. Researchers
found that nanostructured materials as catalysts for MOR may
offer a solution to both of the obstacles faced by traditional Pt
catalysts. The findings on nanostructure platinum galvanized
interest in studying direct methanol fuel cells (DMFC). One
strategy that emerged to address the catalytic poisoning was to
use reactive oxygen species (ROS), made by the water activation
product, to constantly remove some of this catalytic poison.
A second strategy, adopted from research on the electrolysis
reaction, soon followed, to add other metals such as ruthenium
(Ru) together with Pt that would act in a bifunctional mechanism
(Figure 2). In this mechanism, the ROS reacts with the strongly
adsorbed CO on the electrode surface oxidizing it to CO2.6
During this period, not only the addition of a second, sometimes
a third, and even a fourth metal was studied, but also the optimal
composition, which, in addition to increasing the activity of the
catalyst, also reduced the use of platinum in the catalyst. One
particularly successful catalyst developed in this period is PtRu
in the composition 50% in atoms among the metals, which to
this day is still considered the benchmark for MOR, even though
superior materials have already been presented in the literature.6
Researchers developed another way to obtain ROS for CO
removal, by adding rare earth oxides to the catalyst. These rare
earth oxides, such as ceria, act as an oxygen buffer near the
surface of the material. By changing its oxidation state easily
according to the presence or absence of oxygen near its interface,
ceria creates a chemical environment on the electrode surface
that favors CO oxidation.7
Yet another approach is to tailor the Pt catalyst. For example,
changing the platinum D-band density decreases the CO
adsorption energy and limits catalytic poisoning. This strategy is
based on the insertion of a metallic heteroatom in the crystalline
structure of platinum, obtaining alloys, the named electronic
effect.8
The CO oxidation at low overpotentials can also be
achieved by selecting preferred platinum faces, for example, lowindex crystalline planes, which have adequate surface energy to
carry out the oxidation of CO and water at low overpotentials.
Similarly, the same effect can be obtained by creating surface
defects as reported by Ramos et al.9
Direct Ethanol Fuel Cell
Studies with alcohols have expanded to the oxidation of ethanol,
as a substitute for methanol, because it is less toxic, has an
energy density greater than that of methanol (8.02 kWh kg-1), and
mainly to be a renewable fuel obtained from biomass. The use of
alcohol with a slightly longer chain brought with it the problems
of methanol and a new challenge, the breaking of the C-C bond.
Pt-based electrocatalysts were not efficient for this purpose;
however, the alloy PtSn 3:1 was appointed as the benchmark due
to the high powers obtained.10
Even the PtSn alloy does not show the complete oxidation of alcohol
to CO2
, and in search of these scientists began a new search for
solutions that could help to overcome this challenge. One of the
options found was the addition of Rh to the catalyst because
this metal has an electron affinity for the C-C bond.11 However,
studies that explored this option showed only an increase in CO2
generation, but this was reflected in smaller currents. This fact
combined with the high costs of Rh reduced the use of this noble
metal as the catalyst for the ethanol oxidation reaction.
Another strategy adopted was the use of catalysts with steps
and terraces to break the C-C bond. However, these stepped
and terraced materials tend to restructure to more stable
forms, which makes it difficult to maintain the effect in the long
term. In addition, stepped and terraced materials are difficult
to synthesize, which discourages the application of this kind of
material on a large scale.
Figure 2. Bifunctional mechanism of the methanol oxidation on the platinum surface catalyst.
360
250
450
OH-
-H+, -e- -H+, -e- -H+, -e- -H+, -eOH- OH- OHPlatinu
m
Surface
CH3OH
CH OH 3
CH
O3
CH
O2
CH
O
CO
CO2 + H+
13
Material Matters
VOL. 17 • NO. 3
™
One of the additional challenges that ethanol brings is that the
partial oxidation of ethanol yields stable products like acetaldehyde
and acetic acid. On the one hand, the incomplete oxidation of
ethanol reduces the energy density that can be utilized, which
is a drawback, but on the other hand, these products do not
strongly adsorb to the catalyst and do not function as catalytic
poisons. The most active catalysts for the ethanol oxidation
reaction normally affect the kinetics of acetaldehyde or acetic
acid formation, which can go through several oxidation pathways12
as shown in Figure 3. To date, catalyzing the partial oxidation of
ethanol is much better understood than the slow step of breaking
the C-C bond.
Direct Glycerol Fuel Cell
With the popularization of biodiesel, the production of glycerol
grew beyond what the market needed, transforming this alcohol
from a commodity to an environmental problem. Being another
fuel from biomass, this alcohol with its three hydroxyls has the
breaking of the C-C bond facilitated by the steric effect of the
oxidation of any of the three functional groups, but, like methanol,
it has similar problems with CO.
Usually, the potency densities obtained by the oxidation of glycerol
are lower than those of the other alcohols already presented, but
the diversity of products formed during the oxidation of glycerol
opened the eyes of the scientific community to the possibilities
of co-generation of energy and chemicals.13 Figure 4 shows the
reaction pathways of glycerol oxidation.14
Anion Exchange Membrane Fuel Cells
Around 2010 the development of anion exchange membranes
brought the possibility of carrying out the oxidation of alcohols
in an alkaline medium and with that some advantages, such as
greater ease in the oxidation of alcohols whose hydroxyls are
more easily deprotonated, the alkaline medium also reduces the
possibility of intermediates to be formed during oxidation. Since
aldehydes are unstable at high pH and most importantly, many
metals that only activate water at neutral pHs become active at
high pH in the oxidation of alcohols. One such metal is Pd, which
is around 30 times more abundant than platinum. Other transition
metals also appeared as viable, such as Ni, Cu, Au, Ag.15
Studies on the oxidation of alcohols in the alkaline medium have
gone into great depth in the last few decades, but anion exchange
membranes have not evolved at the same rate as catalysis, and
are still not very durable.16 The alkaline medium suffers from
another type of catalytic poisoning, the coverage of the site by
the deposition of solid carbonate deposited on the catalytic layer,
this carbonate from the precipitation of CO and CO2
in an alkaline
medium prevents the arrival of new alcohol molecules to the
catalytic surface.
Opportunities and Outlook
Nanostructured materials made it possible to study lowtemperature fuel cells, especially those fueled with alcohol, which
brings the possibility of obtaining renewable energy from alcohols
such as ethanol and glycerol. Anion exchange membranes brought
the possibility of decreasing the dependence of Pt on the catalyst,
but they need to evolve to increase durability.
Figure 3. Schematic representation of the pathways of ethanol oxidation on the metallic catalytic surface.
Figure 4. Reaction mechanism of glycerol oxidation in an acidic environment to produce different products.
360
250
450
CH3
CH3
CH3 CH3
Step 1 CH3
Step 2 Step 3 Step 4 Step 5
H2O
H2O OH H2O
H2C H3C
OH HO
H H
O H
O
O O O
C C
C C
C
OHOHOHOH-
-
O
OHeee360
250
450
Glycerol
2e- 4e2e2e- 2eGlyceric acid
Glycolic acid
Formic acid
Hydroxypyruvic acid
Glyceraldehyde
1,3 dihydroxyacetone
14 Nanostructured Catalyst for Direct Alcohol Low-Temperature Fuel Cells
Regardless of cell type, for ethanol and glycerol, the most active
catalysts are not those that promote complete oxidation of
alcohol, which implies a lower use of energy density, however,
makes it possible to obtain chemically stable partially oxidized
products. This allows the cells to do something beyond their initial
purpose of generating energy, but rather the co-generation of
energy and chemicals.
References
(1) Brusso, B. C. IEEE Ind. Appl. Mag. 2021, 27 (5), 8–13. DOI: 10.1109/
MIAS.2021.3086965.
(2) Singla, M. K.; Nijhawan, P.; Oberoi, A. S. Environ. Sci. Pollut. Res. 2021,
28 (13), 15607-15626. DOI:10.1007/s11356-020-12231-8. Wu, W.; Pai,
C.-T.; Viswanathan, K.; Chang, J.-S. J. Clean. Prod. 2021, 300, 126959.
DOI:10.1016/j.jclepro.2021.126959.
(3) Boettner, D. D.; Moran, M. J. Proton exchange membrane (PEM) fuel cellpowered vehicle performance using direct-hydrogen fueling and on-board
methanol reforming. Energy 2004, 29 (12), 2317-2330. DOI:10.1016/j.
energy.2004.03.026.
(4) Assumpção, M. H. M. T.; Piasentin, R. M.; Hammer, P.; De Souza,
R. F. B.; Buzzo, G. S.; Santos, M. C.; Spinacé, E. V.; Neto, A. O.;
Silva, J. C. M. Appl. Catal. 2015, 174–175, 136–144. DOI:10.1016/j.
apcatb.2015.02.021. Nandenha, J.; Fontes, E. H.; Piasentin, R. M.;
Fonseca, F. C.; Neto, A. O. J. Fuel Chem. Technol. 2018, 46 (9), 1137–
1145. DOI:10.1016/S1872-5813(18)30046-X. Braesch, G.; Wang, Z.;
Sankarasubramanian, S.; Oshchepkov, A. G.; Bonnefont, A.; Savinova,
E. R.; Ramani, V.; Chatenet, M. J. Mater. Chem. A 2020, 8 (39), 20543–
20552, 10.1039/D0TA06405J. DOI:10.1039/D0TA06405J.
(5) Ai, T.; Bao, S.; Lu, J. Front. Chem. 2021, 9. DOI:10.3389/
fchem.2021.667754.
(6) Lu, S.; Li, H.; Sun, J.; Zhuang, Z. Nano Res. 2018, 11 (4), 2058–2068.
DOI:10.1007/s12274-017-1822-x.
(7) Wang, Q.; Liu, Z.; An, S.; Wang, R.; Wang, Y.; Xu, T. J. Rare Earths
2016, 34 (3), 276–282. DOI:10.1016/S1002-0721(16)60025-X.
(8) Lu, C.; Lee, I. C.; Masel, R. I.; Wieckowski, A.; Rice, C. J. Phys. Chem. A
2002, 106 (13), 3084–3091. DOI:10.1021/jp0136359.
(9) Ramos, A. S.; Santos, M. C. L.; Godoi, C. M.; de Queiroz, L. C.;
Nandenha, J.; Fontes, E. H.; Brito, W. R.; Machado, M. B.; Neto, A. O.;
de Souza, R. F. B. Int. J. Hydrog. Energy 2020, 45 (43), 22973–22978.
DOI:10.1016/j.ijhydene.2020.06.105.
(10) De Souza, R. F. B.; Parreira, L. S.; Rascio, D. C.; Silva, J. C. M.;
Teixeira-Neto, E.; Calegaro, M. L.; Spinace, E. V.; Neto, A. O.; Santos,
M. C. J. Power Sources 2010, 195 (6), 1589–1593. DOI:10.1016/j.
jpowsour.2009.09.065.
(11) Bai, J.; Xiao, X.; Xue, Y.-Y.; Jiang, J.-X.; Zeng, J.-H.; Li, X.-F.; Chen, Y.
ACS Appl. Mater. Interfaces 2018, 10 (23), 19755–19763. DOI:10.1021/
acsami.8b05422.
(12) Marinkovic, N. S.; Li, M.; Adzic, R. R. Top. Curr. Chem. 2019, 377 (3),
11. DOI:10.1007/s41061-019-0236-5.
(13) Fontes, E. H.; Ramos, C. E. D.; Ottoni, C. A.; de Souza, R. F. B.; Antolini,
E.; Neto, A. O. Renew. Energ. 2021, 167, 954–959. DOI:10.1016/j.
renene.2020.12.026.
(14) Liang, Z.; Villalba, M. A.; Marcandalli, G.; Ojha, K.; Shih, A. J.; Koper,
M. T. M. ACS Catal. 2020, 10 (23), 13895–13903. DOI:10.1021/
acscatal.0c04131.
(15) Fontes, E. H.; Piasentin, R. M.; Ayoub, J. M. S.; da Silva, J. C. M.;
Assumpção, M. H. M. T.; Spinacé, E. V.; Neto, A. O.; de Souza, R. F. B.
Mater. Renew. Sustain. Energy 2015, 4 (1), 3. DOI:10.1007/s40243-
015-0043-z.
(16) Dekel, D. R. J. Power Sources 2018, 375, 158-169. DOI:10.1016/j.
jpowsour.2017.07.117.
Proton Exchange Membrane (PEM) Fuel Cells
Name Form Description Cat. No.
Aquivion® D83-06A 20% dispersion in water 6% polymer content in lower aliphatic alcohols and water 802603-50ML
802603-500ML
Aquivion® D83-24B 24% dispersion in water PFSA eq. wt. 830 g/mole SO3H 802654-25ML
802654-250ML
Aquivion® D72-25BS 25% dispersion in water PFSA eq. wt. 720 g/mole SO3H
stabilized CF3 polymer chain ends
802549-25ML
802549-250ML
Aquivion® D79-25BS PFSA eq. wt. 790 g/mole SO3H
contains CF3 polymer chain ends as stabilizer
802565-25ML
802565-250ML
Aquivion® D79-25BS-Li PFSLi eq. wt. 790 g/mole SO3Li
stabilized CF3 polymer chain ends
802573-25ML
Aquivion® D98-25BS PFSA eq. wt. 980 g/mole SO3H
contains CF3 polymer chain ends as stabilizer
802557-25ML
802557-250ML
Aquivion® P87S-SO2F 2mm cylindrical pellets PFSF eq. wt. (870 g/mole SO2F)
contains CF3 polymer chain ends as stabilizer
802530-50G
Aquivion® P98-SO2F PFSF eq. wt. 980 g/mole SO22F 802662-50G
Aquivion® pellets P87-SO2F PFSF eq. wt. 870 g/mole SO2F 915327-50G
Aquivion® PW79S coarse powder PFSA eq. wt. 790 g/mole SO3H
contains CF3 polymer chain ends as stabilizer
802611-25G
Aquivion® PW79S-Li PFSA eq. wt. 790 g/mole SO3Li
stabilized CF3 polymer chain ends
802581-10G
Aquivion® PW87S PFSA eq. wt. 870 g/mole SO3H
contains CF3 polymer chain ends as stabilizer
802646-25G
Aquivion® PW98 PFSA eq. wt. 980 g/mole SO3H 802638-25G
Disodium bis(4-chloro-3-
sulfophenyl)sulfone
crystals 97% 730882-5G
Platinum on silica granular extent of labeling: 1 wt. % loading 520691-25G
520691-100G
Poly(2-vinylpyridine-co-styrene) average Mn ~130,000
average Mw ~220,000 by LS, granular
184608-50G
Aquivion® E98-05S membrane sheet, L x W 31 cm x 31 cm contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 980 g/mole SO3H
802700-1EA
Aquivion® E87-12S membrane sheet, L x W x thickness
18 cm x 18 cm x 120 µm
contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 870 g/mole SO3H
802786-1EA
Aquivion® E98-15S membrane sheet, L x W x thickness
18 cm x 18 cm x 150 µm
stabilized CF3 polymer chain ends
PFSA eq. wt. 980 g/mole SO3H
802751-1EA
Aquivion® E87-05S membrane sheet, L x W x thickness
18 cm x 18 cm x 50 µm
contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 870 g/mole SO3H
8027191EA
Aquivion® E98-05 PFSA eq. wt. 980 g/mole SO3H 802670-1EA
15
Material Matters
VOL. 17 • NO. 3
™
Name Form Description Cat. No.
Aquivion® E98-09S membrane sheet, L x W x thickness
18 cm x 18 cm x 90 µm
contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 980 g/mole SO3H
802735-1EA
Aquivion® E87-12S membrane sheet, L x W x thickness
31 cm x 31 cm x 120 µm
stabilized CF3 polymer chain ends
PFSA eq. wt. 870 g/mole SO3H
802514-1EA
Aquivion® E98-15S membrane sheet, L x W x thickness
31 cm x 31 cm x 150 µm
contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 980 g/mole SO3H
802778-EA
Aquivion® E87-05 membrane sheet, L x W x thickness
31 cm x 31 cm x 50 µm
PFSA eq. wt. 870 g/mole SO3H 915866-1EA
Aquivion® E87-05S contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 870 g/mole SO3H
802727-1EA
Aquivion® E98-05 PFSA eq. wt. 980 g/mole SO3H 802697-1EA
Aquivion® E98-09S membrane sheet, L x W x thickness
31 cm x 31 cm x 90 µm
contains CF3 polymer chain ends as stabilizer
PFSA eq. wt. 980 g/mole SO3H
802743-1EA
Platinum black powder fuel cell grade, ≥99.9% trace metals basis 520780-1G
520780-5G
Platinum cobalt on carbon extent of labeling: 30 wt. % Pt3Co loading 738565-1G
Platinum on graphitized carbon extent of labeling: 10 wt. % loading 738581-1G
Platinum on graphitized carbon extent of labeling: 20 wt. % loading 738549-1G
Platinum on graphitized carbon extent of labeling: 40 wt. % loading 738557-1G
Platinum-ruthenium alloy on
graphitized carbon
extent of labeling: 20 wt. % Pt loading
extent of labeling:10 wt. % Ru loading
738573-1G
Poly(vinylphosphonic acid) 661740-1G
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16
Advantages of Electrochemical Systems
Historically, energy storage to power vehicles and electrical grids
has relied on converting chemical energy to mechanical and
electrical energy by a heat process using the Carnot cycle. This
process often involves burning fossil fuels to generate heat and
converting heat to mechanical energy, as in a typical heat engine.
Unfortunately, this process is inefficient, as shown by the maximum
theoretical efficiency of only 64% and actual efficiencies only at
30-40%. In addition, burning fossil fuels generates environmentally
damaging waste products, including CO2
, methane, and nitrous
oxide. Consequently, scientists have sought more efficient and
cleaner energy storage and conversion processes.
Electrochemical systems have tremendous promise for storing
energy and converting energy to workable forms. Efficiencies
of electrochemical systems typically can be 40-60% and even
greater than 85% in newer technologies. In addition, some
electrochemical systems, like the polyoxometalate-based redoxflow batteries discussed here, operate with a near 100%
atom economy and operate without generating any chemical
waste directly. These aspects give electrochemical systems an
advantage compared to heat engines.
Advances in Fuel Cells
One promising type of electrochemical system is the hydrogenbased fuel cell. Assuming hydrogen as a fuel, fuel cells can offer
high efficiencies for electricity production of 50–60% compared to
a heat engine of 30–40%. Current stack operations yield power
densities of 6kW/L and more. If goals of 1 W/cm2
@0.8V (single
cell) become feasible, the efficiencies will be pushed to 70–80%.
Hydrogen-based fuel cells are very attractive for energy conversion
because they are much more efficient and environmentally
cleaner than heat engines. Still, hydrogen-based fuel cells do
have limitations for energy storage. First, using hydrogen as an
energy storage medium means converting electricity to hydrogen
and back to electricity. Because this involves two conversions with
losses at each conversion, the efficiency of the storage process
drops to only 35–45%. Second, hydrogen fuel cells are expensive.
Hydrogen fuel needs specific storage conditions, such as highpressure tanks and/or cryogenic temperatures. Building hydrogen
storage at scale requires significant capital investment considering
the components, the electrolyzer, the fuel cell, and other
components. Third, hydrogen is highly flammable, which poses
safety hazards. The flammability, combined with the difficulties
of storing hydrogen, significantly limits the use of hydrogen as a
mobile fuel.
Alternatives: Li-Ion and Other Concepts
An alternative electrochemical system, a battery, is much better
suited to energy storage. Typical battery storage efficiencies,
including the entire cycle, are around 80%, nearly double that
of today’s hydrogen fuel cell. Two battery systems, among many
more, should be briefly mentioned here. The Li-ion battery has
become quite ubiquitous because of its excellent properties. These
batteries are used in portable electronics, automotive applications,
and stationary purposes. For example, a Li-ion battery of 85kWh
in a Tesla Model S car has a volume and weight of 263 L and 400
kg, respectively (excluding protective housing, BMS, and power
conditioning), which can yield a range of up to 450 km.
But Li-ion batteries have downsides: One downside of the Li-ion
battery is that the raw materials used in the battery are available
only in a few countries (similar to oil) with all the polito-economic
consequences associated. Another downside is that the battery
lifetime (load/unload cycles) is short, and methods to recycle the
valuable battery components are still in their infancy. In addition,
technical improvements, like the faster charge-discharge rate and
increased gravimetric capacity, are needed. One notable downside
of lithium-ion batteries is their safety. Under certain operation
conditions, but also in standby mode, a thermal run-away can
occur, or by other adverse conditions, the batteries can burn
How to Best Store Electrical Energy
Ulrich Stimming*
Chemistry - School of Natural and Environmental Sciences, Newcastle University,
Newcastle upon Tyne NE1 7RU, United Kingdom
*
Email: Ulrich.Stimming@newcastle.ac.uk
17
Material Matters
VOL. 17 • NO. 3
™
very stable, capable of withstanding more than 20,000 chargedischarge cycles without significant degradation; (4) Because
POMs have delocalized electron density, electron transfer is
very fast (e.g., for PV14, it is 104
times faster than for the V ion
itself); and (5) POMs are made of environmentally benign and
inexpensive materials.
An RFB battery based on POMs offers high energy density
and high-power density at the same time. Coupled with the
advantages of inexpensive and environmentally benign materials,
POM-based RFBs have applications in three fields: mobility, power
grid, and decentralized storage.
Mobility
Mobility is currently a hot topic regarding electrification. For
automobile battery solutions, Li-ion batteries are presently
favored. There are various challenges with the technology, as
already noted, but limited resources for materials, limited power
capabilities, and missing infrastructure are the most severe ones.
Some of these challenges are so severe that using lithium-ion
batteries in electric trucks is questionable. With the one liquid
POM-RFB, we can achieve energy densities at par with Li-ion, but
power densities are up to 50% higher than with Li-ion.
or even explode. Many incidents have been described. Recently
an ocean freighter bringing electric cars from Europe to North
America burned out and sank, with steel walls melting in the high
heat of the fire induced by the Li-ion batteries.
Another type of battery is the redox flow battery (RFB). A redox
flow battery, like any battery, converts chemical energy to
electrical energy. In a redox flow battery, two solution-phase
chemical components are pumped passed current collecting
electrodes on separate sides of an ion-selective membrane. The
redox chemistry at the electrodes’ surfaces results in a flow of
electrons through an external circuit accompanied by ion transfer
through the membrane. The chemical potentials of the chemical
components determine the cell voltage. At the same time, the
energy capacity depends on the electrolyte volume, and the
power depends on the surface area of the electrodes.
Unlike a traditional battery, like a Li-ion battery, where storage
and conversion both occur in one entity of the battery cell, the
electrode, in an RFB, the converter and the container for the
“fuel” are separated. This separation of energy and power has
advantages regarding the design of such systems, e.g., doubling
the capacity of the battery is possible by simply doubling the size
of the tank. (Doubling the capacity of a Li-ion battery is much
more costly and cumbersome.) In addition, unlike traditional
batteries, in an RFB, only a few percent of the total stored energy
is connected electrochemically at any one time, which limits the
risk of a runaway or uncontrolled energy release. Because flow
can easily be stopped during a fault condition, the vulnerability to
runaway is significantly reduced. Still, RFBs have their limitations.
For example, the most common type of redox flow battery, the
vanadium-based RFB, is limited to a low energy density because
the redox process only involves one electron per ion. In addition,
it offers a low power density because of the slow rate constant of
the process. Finally, vanadium-based RFBs use a highly corrosive
and environmentally damaging liquid for operation.
Converting Problems to Advantages in Redoxflow Batteries Using Polyoxometalates (POMs)
Chemical Characteristics
It is highly desirable to have an energy and power capability
similar to Li-ion batteries and the flexibility of an RFB concept but
with safe and environmentally benign materials and processes.
A possibility to achieve this is to use polyoxometalates (POMs)
as redox systems in an aqueous solution close to neutral pH.
POMs are complex ions with multiple redox centers of the same
or different metals. For example, SiW12, which has the formula
of [SiW12O40]4-, is an approximately spherical cluster of tungsten
atoms bound to oxygen and a central silicon atom (Figure 1).
Similarly, PV14 (Figure 2), which has the formula [PV14O42]9-, is
a cluster of vanadium atoms bound to oxygen and a central
phosphorus atom. In an RFB, POMs offer several advantages over
dissolved metals like vanadium: (1) POMs can deliver multiple
electrons, (2) POMs offer relatively high solubilities (often >0.5
M), which enables higher energy content; (3) POMs are typically
Figure 2. Model of PV14.
Figure 1. Model of SiW12.
250
250
18 How to Best Store Electrical Energy
The following example illustrates the situation: If you take a Li-ion
battery in a Tesla Model S vehicle of 85 kWh, the whole system
has a volume and mass of 263 L and 400 kg, respectively. A
one-liquid POM system of the same capacity has a volume of 200
l and a mass of 400 kg. The resulting specific values are 0.21
kWh/kg for both and 0.43 kWh/L (POM) and 0.32 kWh/L (Tesla).
Considering the power capabilities, the comparison is 0.38 kW/
kg and 0.75 kW/L (POM) and 0.21 kW/kg and 0.31 kW/L (Tesla),
respectively (see Table 1). Considering even some variations in
numbers, performance data are at par, with a somewhat better
power density for the POM system.
However, the most striking advantage for RFBs in mobile energy
storage applications is that the charging process consists of
exchanging the spent solution with a fresh one, comparable to the
current process of refueling your car with gasoline. This process
is faster than the slow charging times for current LIB batteries.
It could leverage the existing fuel storage and distribution
infrastructure, in contrast to LIB battery technology, which
requires new infrastructure and capital investment to create the
infrastructure. The RFB concept also enables electric-powered
trucks to avoid extra weight problems with scaled-up lithium-ion
batteries and their long charging times.
Power Grid
RFBs can also find use in storing energy to stabilize the power
grid. In most countries, power plant capacity is laid out to cover all
peak loads that can occur in the electric grid. The most common
ones are the typical morning and evening peaks. Providing
extra electricity during peak times requires large amounts of
electricity and fast response. The state-of-the-art vanadiumbased RFBs are too slow to respond to the changes in the grid,
but POM-based RFBs have power capabilities about 104 times
larger than vanadium-based RFBs. This allows for large electricity
transfers in the sub-ms regime, a necessity for a fast frequency
stabilization of the electric grid. A rough estimate shows that,
e.g., in Germany, 20 to 30% of the power plants could be shut
down due to this enormous load leveling effect. Beneficial for
the environment, this could be a shutdown of most coal-fired
power plants. In addition, such storage power stations provide
grid stability by integrating renewable energy resources. Due to
the extremely low self-discharge rates, it can provide a constant
supply to the grid from unstable sources like solar or wind power
over days or weeks.
Decentralized Storage
RFBs may provide a solution to decentralized energy storage
as well, energy off grids. In an area of increased importance,
the local building-related energy storage based on PV and/or
small wind turbines, this concept can be beneficial. An RFB is
comparable in performance to Li-ion batteries and is much safer
because the risk of uncontrolled energy release is significantly
reduced. In addition, RFBs may offer longer lifetimes and lower
costs.
Conclusions
We advanced to an essential level in the current search for the
holy grail of electricity storage. While validation is still needed,
the POM-based battery systems tick the boxes of many aspects
important for electricity storage, like capacity, power, ease of
operation and transport, durability, sustainability, and, eventually,
low cost of storing electricity. There may be better systems in the
future. Still, this technology allows us to broadly introduce and
use energy storage for many applications making fossil fuels more
and more obsolete.
References
(1) Friedl, J.; Al-Oweini, R.; Herpich, M.; Keita, B.; Kortz, U.; Stimming, U.
Electrochim. Acta 2014, 141, 357. DOI:10.1002/celc.201701246
(2) Al-Oweini, R.; Bassil, B.; Friedl, J.; Kottisch, V.; Ibrahim, M.; Asano, M.;
Keita, B.; Novitchi, G.; Lan, Y.; Powell, A.; et. al. Inorg. Chem. 2014, 53,
5663. DOI:h10.1021/ic500425c
(3) Haider, A.; Ibrahim, M.; Bassil, B. S.; Carey, A. M.; Viet, A. N.; Xing, X.;
Ayass, W. W.; Minambres, J. F.; Liu, R.; Zhang, G.; et. al. Inorg. Chem.
2016, 55, 2755. DOI:10.1021/acs.inorgchem.5b02503
(4) Chen, H-Y.; Friedl, J.; Pan, C-J.; Haider, A.; Al-Oweini, R.; Cheah, Y. L.;
Lin, M-H.; Kortz, U.; Hwang, B-J.; Srinivasan, M.; Stimming, U. Phys.
Chem. Chem. Phys. 2017, 19, 3358. DOI:10.1039/C6CP05768C
(5) Friedl, J.; Holland-Cunz, M. V.; Cording, F.; Panschilling, F. L.; Wills, C.;
McFarlane, W.; Schricker, B.; Fleck, R.; Wolfschmidt, H.; Stimming, U.
Energy Environ. Sci. 2018, 11, 3010. DOI:10.1039/C8EE00422F
(6) Holland-Cunz, M. V.; Cording, F.; Friedl, J.; Stimming, U. Front. Energy
2018, 12, 198. DOI:10.1007/s11708-018-0552-4
(7) Friedl, J.; Pfanschilling, F. L.; Holland-Cunz, M. V.; Fleck, R.; Schricker, B.;
Wolfschmidt, H.; Stimming, U. Clean Energy 2019, 3, 278. DOI:10.1093/
ce/zkz019
(8) Litricity – liquid electricity - https://litricity.de/
POM system or battery gravimetric energy
density /kWh/kg
volumetric energy
density /kWh/L
gravimetric power
density /kW/kg
volumetric power
density / kW/L
POM 1 0.21 0.43 0.38 0.75
POM 2 0.20 0.31 0.35 0.56
Tesla 85kWh battery 0.21 0.32 0.21 0.31
Table 1. Energy and power densities of battery systems [Litricity, patent application to EPO]
19
Material Matters
VOL. 17 • NO. 3
™
Solid Oxide Fuel Cells (SOFCs)
Name Form Purity Cat. No.
Tris(cyclopentadienyl)yttrium(III) solid 99.9% trace metals basis 491969-1G
Zirconium(IV) oxide-yttria stabilized nanopowder 92% ZrO2 basis 572349-25G
Tetrakis(dimethylamido)zirconium(IV) solid ≥99.99% trace metals basis 579211-5G
Zirconium(IV) oxide-yttria stabilized solid 99.9% trace metals basis 774049-1EA
Zirconium yttrium alloy solid 99.9% trace metals basis (excluding ≤1% Hf) 774057-1EA
Fuel-Cell Membranes
Proton-Exchange Membranes
Name L x W (cm) Thickness (μm) Cat. No.
Xion PEMAquivion®-720
5 x 5 5 PEM3A0522-1EA
5 x 5 10 PEM3A1022-1EA
5 x 5 20 PEM3A2022-1EA
5 x 5 30 PEM3A3022-1EA
5 x 5 50 PEM3A5022-1EA
10 x 10 5 PEM3A0544-1EA
10 x 10 10 PEM3A1044-1EA
10 x 10 20 PEM3A2044-1EA
10 x 10 30 PEM3A3044-1EA
10 x 10 50 PEM3A5044-1EA
15 x 15 5 PEM3A0566-1EA
15 x 15 10 PEM3A1066-1EA
15 x 15 20 PEM3A2066-1EA
15 x 15 30 PEM3A3066-1EA
15 x 15 50 PEM3A5066-1EA
Xion PEMAquivion®-830
5 x 5 5 PEM3B0522-1EA
5 x 5 10 PEM3B1022-1EA
5 x 5 20 PEM3B2022-1EA
5 x 5 30 PEM3B3022-1EA
5 x 5 50 PEM3B5022-1EA
10 x 10 5 PEM3B0544-1EA
10 x 10 10 PEM3B1044-1EA
10 x 10 20 PEM3B2044-1EA
10 x 10 30 PEM3B3044-1EA
10 x 10 50 PEM3B5044-1EA
15 x 15 5 PEM3B0566-1EA
15 x 15 10 PEM3B1066-1EA
15 x 15 20 PEM3B2066-1EA
15 x 15 30 PEM3B3066-1EA
15 x 15 50 PEM3B5066-1EA
Xion PEMDyneon-725
5 x 5 5 PEM1A0522-1EA
5 x 5 10 PEM1A1022-1EA
5 x 5 20 PEM1A2022-1EA
5 x 5 30 PEM1A3022-1EA
5 x 5 50 PEM1A5022-1EA
10 x 10 5 PEM1A0544-1EA
10 x 10 10 PEM1A1044-1EA
10 x 10 20 PEM1A2044-1EA
10 x 10 30 PEM1A3044-1EA
10 x 10 50 PEM1A5044-1EA
15 x 15 5 PEM1A0566-1EA
15 x 15 10 PEM1A1066-1EA
15 x 15 20 PEM1A2066-1EA
15 x 15 30 PEM1A3066-1EA
15 x 15 50 PEM1A5066-1EA
Name L x W (cm) Thickness (μm) Cat. No.
Xion PEMDyneon-800
5 x 5 5 PEM1B0522-1EA
5 x 5 10 PEM1B1022-1EA
5 x 5 20 PEM1B2022-1EA
5 x 5 30 PEM1B3022-1EA
5 x 5 50 PEM1B5022-1EA
10 x 10 5 PEM1B0544-1EA
10 x 10 10 PEM1B1044-1EA
10 x 10 20 PEM1B2044-1EA
10 x 10 30 PEM1B3044-1EA
10 x 10 50 PEM1B5044-1EA
15 x 15 5 PEM1B0566-1EA
15 x 15 10 PEM1B1066-1EA
15 x 15 20 PEM1B2066-1EA
15 x 15 30 PEM1B3066-1EA
15 x 15 50 PEM1B5066-1EA
Xion PEMNafion™-1000
5 x 5 5 PEM2A0522-1EA
5 x 5 10 PEM2A1022-1EA
5 x 5 20 PEM2A2022-1EA
5 x 5 30 PEM2A3022-1EA
5 x 5 50 PEM2A5022-1EA
10 x 10 5 PEM2A0544-1EA
10 x 10 10 PEM2A1044-1EA
10 x 10 20 PEM2A2044-1EA
10 x 10 30 PEM2A3044-1EA
10 x 10 50 PEM2A5044-1EA
15 x 15 5 PEM2A0566-1EA
15 x 15 10 PEM2A1066-1EA
15 x 15 20 PEM2A2066-1EA
15 x 15 30 PEM2A3066-1EA
15 x 15 50 PEM2A5066-1EA
Xion PEMNafion™-1100
5 x 5 5 PEM2B0522-1EA
5 x 5 10 PEM2B1022-1EA
5 x 5 20 PEM2B2022-1EA
5 x 5 30 PEM2B3022-1EA
5 x 5 50 PEM2B5022-1EA
10 x 10 5 PEM2B0544-1EA
10 x 10 10 PEM2B1044-1EA
10 x 10 20 PEM2B2044-1EA
10 x 10 30 PEM2B3044-1EA
10 x 10 50 PEM2B5044-1EA
15 x 15 5 PEM2B0566-1EA
15 x 15 10 PEM2B1066-1EA
15 x 15 20 PEM2B2066-1EA
15 x 15 30 PEM2B3066-1EA
15 x 15 50 PEM2B5066-1EA
20 How to Best Store Electrical Energy
Anion-Exchange Membranes
Name L x W (cm) Thickness (μm) Cat. No.
Xion AEMPention-72-5CL
5 x 5 5 AEM2A0522-1EA
5 x 5 10 AEM2A1022-1EA
5 x 5 20 AEM2A2022-1EA
5 x 5 30 AEM2A3022-1EA
5 x 5 50 AEM2A5022-1EA
10 x 10 5 AEM2A0544-1EA
10 x 10 10 AEM2A1044-1EA
10 x 10 20 AEM2A2044-1EA
10 x 10 30 AEM2A3044-1EA
10 x 10 50 AEM2A5044-1EA
15 x 15 5 AEM2A0566-1EA
15 x 15 10 AEM2A1066-1EA
15 x 15 20 AEM2A2066-1EA
15 x 15 30 AEM2A3066-1EA
15 x 15 50 AEM2A5066-1EA
Xion AEMPention-72-15CL
5 x 5 5 AEM2B0522-1EA
5 x 5 10 AEM2B1022-1EA
5 x 5 20 AEM2B2022-1EA
5 x 5 30 AEM2B3022-1EA
5 x 5 50 AEM2B5022-1EA
10 x 10 5 AEM2B0544-1EA
10 x 10 10 AEM2B1044-1EA
10 x 10 20 AEM2B2044-1EA
10 x 10 30 AEM2B3044-1EA
10 x 10 50 AEM2B5044-1EA
15 x 15 5 AEM2B0566-1EA
15 x 15 10 AEM2B1066-1EA
15 x 15 20 AEM2B2066-1EA
15 x 15 30 AEM2B3066-1EA
15 x 15 50 AEM2B5066-1EA
Name L x W (cm) Thickness (μm) Cat. No.
Xion AEMDurion II-LMW
5 x 5 5 AEM1A0522-1EA
5 x 5 10 AEM1A1022-1EA
5 x 5 20 AEM1A2022-1EA
5 x 5 30 AEM1A3022-1EA
10 x 10 5 AEM1A0544-1EA
10 x 10 10 AEM1A1044-1EA
10 x 10 20 AEM1A2044-1EA
10 x 10 30 AEM1A3044-1EA
15 x 15 5 AEM1A0566-1EA
15 x 15 10 AEM1A1066-1EA
15 x 15 20 AEM1A2066-1EA
15 x 15 30 AEM1A3066-1EA
Water-Exchange Membranes
Name L x W (cm) Thickness (μm) Cat. No.
Xion WEMHydrex-200
5 x 5 30 WEM1A3022-1EA
5 x 5 50 WEM1A5022-1EA
10 x 10 30 WEM1A3044-1EA
10 x 10 50 WEM1A5044-1EA
15 x 15 30 WEM1A3066-1EA
15 x 15 50 WEM1A5066-1EA
Name Specifications Cat. No.
2.0 M LiPF6 in EC/DMC=50/50 (v/v) in ethylene carbonate and dimethyl carbonate 809357
2.0 M LiPF6 in EC/EMC=50/50 (v/v) in ethylene carbonate and ethyl methyl carbonate 809365
2.0 M LiPF6 in EC/DEC=50/50 (v/v) in ethylene carbonate and diethyl carbonate 809349
2.0 M LiPF6 in DMC in dimethyl carbonate 809411
2.0 M LiPF6 in EMC in ethyl methyl carbonate 809403
2.0 M LiPF6 in DEC in diethyl carbonate 809543
2.0 M LiPF6 in PC in propylene carbonate 809470
Name Specifications Composition Cat. No.
Lithium nickel manganese cobalt oxide loading >80%, thickness 25–50 μm LiNi0.33Mn0.33Co0.33O2 765163
Lithium nickel cobalt aluminum oxide loading >80%, thickness 12–25 μm LiNi0.8Co0.15Al0.05O2 765171
Lithium manganese nickel oxide loading >80%, thickness 25–50 μm Li2Mn3NiO8 765198
Lithium manganese oxide loading >80%, thickness 25–40 μm LiMn2O4 765201
Lithium titanate spinel loading >80%, thickness 25–50 μm Li4Ti5O12 765155
Electrolyte
Anode Cathode
Discharge
Charge
Discharge Charge
Li+ Li+
Li+
e – e –
Li+
Li+ Li+
Li+ Li+
Li+
Li+
Li Li+ +
Li+
Li+
Li+
Electrolyte Solutions
H2O < 15 ppm, HF < 50 ppm, APHA < 50
Electrode Sheets
Aluminum substrate, size 5 in. × 10 in.
Applications of lithium-ion batteries (LIBs) extend from
modern electronics to automobiles. Order ready-to-use
electrolyte solutions and electrode sheets in battery grade
to fabricate your LIB.
Product Highlight
To find out more, visit
SigmaAldrich.com/LIB
Make Your Own
Lithium-Ion Batteries
Silicon Anode Materials
for High-capacity Cathode Research
With a capacity over 1300 mAh/g, our silicon composite
formulation is well suited for use as a counter electrode
for new high capacity cathode materials.
Test your batteries longer with our silicon composite anodes.
Unlike some silicon-based electrode formulations, our 3D porous
conductive polymer prevents capacity loss during the charge/
discharge cycles.
SigmaAldrich.com/si-anode
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MK_BR11901EN 12/2022
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