bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnosis of Voltage Losses of the Proton Exchange Membrane Water Electrolyzer with Nonlinear Frequency Response Method
Authors: Milicic Tamara , Muthunayakage Kasun , Vu Hoang Thanh , Zivkovic Luka A. , Ritschel Tobias Kasper Skovborg , Vidakovic-Koch Tanja
Published: August 2024

Proton exchange membrane water electrolyzer (PEMWE) takes a central place in the hydrogen economy as a crucial technology for green hydrogen production. However, this technology still faces challenges, such as the cost of the materials, performance losses at high current densities, and durability. To overcome these obstacles, better comprehension of the phenomena occurring in the PEMWE is necessary. Typical electrochemical methods, such as polarization curves and high-frequency response measurements, lack detailed information about the individual contributions to the overall voltage losses and cannot point out the causes of the performance shortcomings. Therefore, the development of advanced diagnosis techniques for PEMWE is of importance both for the state of health analysis during the operation, as well as for the testing of new materials.

In this work, a nonlinear frequency response (NFR) method was applied for the diagnosis of a lab-scale PEMWE. The NFR method represents an extension of the electrochemical impedance spectroscopy to the nonlinear domain by investigating the second-order frequency response function (FRF) in addition to the first-order FRF (equivalent to the impedance) [1]. Typical features corresponding to processes occurring in the PEMWE were observed in both the first- and the second-order FRFs. The experimental observations were interpreted based on a simple nonlinear model. The features observed at frequencies higher than 0.1 Hz were attributed to the electrochemical half-reactions, while a high current density feature observed at lower frequencies, could be attributed to the mass transport. During the analysis, the first-order FRF (impedance) was found not to be sensitive enough for the discrimination of the different sets of parameters and the second-order FRF had to be included for better parameter identification. The obtained parametrized model is dynamic and nonlinear and, thus, it can be utilized for model predictive control of the PEMWE and optimization of the overall green hydrogen production system.

[1] Vidaković-Koch, T., Miličić, T., Živković, L.A., Chan, H.S., Krewer, U., Petkovska, M., Cur. Opin. Electrochem., 2021, 30, 100851
Highly Durable Compositionally Variant Bifunctional Tetrametallic Ni–Co–Mn–Fe Phosphide Electrocatalysts Synthesized by a Facile Electrodeposition Method for High-Performance Overall Water Splitting
Authors: K. Allam Nageh
Published: August 2024

In the recent few decades, the demand for green sources of energy that are clean and sustainable became very essential to reduce the greenhouse and global warming problems. Consequently, there is an increasing demand to identify nonprecious, cheap bifunctional electrocatalysts for water splitting. Herein, nanosheets of different earth-abundant Ni, Co, Mn, and Fe combinations are electrodeposited over commercial Ti mesh and tested for the overall water splitting. The bare Ti mesh requires overpotentials of −486.6 mV at −10 mA cm–2 and 534.5 mV at 10 mA cm–2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. However, the electrodeposited catalysts show much higher catalytic activity for both HER and OER with overpotentials of −300 and 279 mV at −10 and 10 mA cm–2, respectively, lowering the overpotential needed to drive the OER by 50%. Nevertheless, to enhance the electrocatalytic performance of the fabricated catalysts, they are phosphidized using different phosphorous precursors. The resulted NiCoMnFe–P catalysts exhibit much lower HER overpotential (−200 mV at −10 mA cm–2), which is 40% lower than that needed by the bare Ti mesh. For the overall water splitting, a cell voltage of 1.71 V is recorded to achieve a current density of 10 mA cm–2. Lastly, the stability test of the overall device reveals very high stability with current retention of 90% over 22 h of continuous electrolysis. Furthermore, the synergy between the metallic components in the absence and presence of P is elucidated using density functional theory calculations, revealing optimized G
H* and G
H2O* for the HER reaction over the P-top site of the MnFeCoNiP catalyst. In addition, the calculations explain the superiority of the NiCoMnFe catalyst over the NiCoMnFeP counterpart for the OER.
Investigation of the Activity and Stability of Manganese-Based Electrocatalysts for the Electrochemical Oxidation of Water and Small Organic Molecules in Acidic Electrolyte
Authors: Lucato Cassio L.P. , Lima Fabio H.B.
Published: August 2024

Water electrolysis is a crucial process for hydrogen production, providing a clean and sustainable method for H2 production. Iridium-based catalysts are particularly effective in promoting the oxygen evolution reaction (OER) that takes place at the anode of electrolyzers. The unique properties of iridium make it well-suited for this purpose, but its high cost becomes a bottleneck in making water electrolysis economically viable on a large scale. Manganese-based electrocatalysts have emerged as promising candidates for the OER, mainly due to their earth abundance, low toxicity, and activity. It has been shown that manganese oxide can operate stably in acid, in a restricted potential window, where the formation of permanganate ions is avoided. Thus, for practical application, the stability must be improved, so a larger potential window can be employed. To address this challenge, some approaches have emerged from combining a catalytically active, but instable oxide, with the one that is stable, but inactive for the OER. In the presentation, we will show the results of activity, stability, and faradaic efficiency (FE) for O2 formation for water electro-oxidation on manganese oxide, and on manganese oxide combined with antimony, tin, titanium, niobium, and silicon oxide. The faradaic efficiencies, determined via EC-MS (Electrochemistry coupled to mass spectrometry) measurements revealed that manganese antimonate and pure manganese oxide have the highest values for O2 formation, with the former presenting higher stability at high overpotentials. We will discuss the obtained trends in stability and FEs for the other synthesized oxides. Additionally, for these two most efficient electrocatalysts, EC-MS measurements were conducted for the electrochemical oxidation of some small organic molecules, such as formic acid, methanol, ethanol, and ethylene glycol (electrochemical reforming for H2 production). The results showed that the selectivity for the electro-oxidation of water and/or of the organic molecule (monitoring the formation of CO2) strongly depends on the catalyst composition and on the number of carbon atoms of the molecule. We will further discuss, in the presentation, the factors that govern the selectivity and stability for each case. The obtained results of this study may be helpful for developing more efficient, selective and, mainly, more stable earth-abundant electrocatalysts for electrolyzers.
Defect Engineering of WO3 by Rapid Flame Reduction for Efficient Photoelectrochemical Conversion of Methane into Liquid Oxygenates
Authors: Woo Ho Kun , Gautam Ankit Kumar , Barroso-Martínez Jaxiry , Baddorf Arthur , Zhou Kai , Choi Yoon Young , He Jiajun , Mironenko Alexander , Rodriguez Lopez Joaquin , Cai Lili
Published: August 2024

Photoelectrochemical (PEC) conversion is a promising way to utilize methane (CH4) as a chemical building block without harsh conditions. However, PEC CH4 conversion to value-added chemicals remains challenging due to the thermodynamically favorable over-oxidation of CH4. Here, we report WO3 nanotubes (NTs) photoelectrocatalysts for PEC CH4 conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, the oxygen vacancies of WO3 NTs were carefully controlled. The optimally reduced WO3 NTs suppressed over-oxidation of CH4 showing high total C1 liquid selectivity of 69.4% and production rate of 0.174 μmol⋅cm-2⋅h-1. Scanning electrochemical microscopy revealed that oxygen vacancies can restrain the production of hydroxyl radicals, which in excess could further oxidize C1 intermediates to CO2. Additionally, band diagram analysis and computational studies elucidated that oxygen vacancies thermodynamically suppress over-oxidation. This work introduces a strategy to understand and control the selectivity of photoelectrocatalysts for direct CH4 conversion to liquids.
(Invited) Novel Anodic Oxide Nanotube Array Architectures for Solar Photoelectrochemical Fuel Generation
Authors: Varghese Oomman K
Published: August 2024

Electrochemical anodization has progressed from its level as a low-cost commercial technique to fabricate corrosion and abrasion resistant compact oxide coatings to the status of an effective method for growing a variety of oxide nano-architectures, particularly nanorods, nanowires, nanotubes, nanoporous films, and nanoflowers. Among these structures, self-organized vertically aligned nanotubes of oxide semiconductors have been demonstrated to possess interesting electrical, optical and mechanical properties. As in the case of most low dimensional materials, these structures also possess high surface area. Nevertheless, their unique properties applicable to solar energy conversion processes such as photoelectrochemical (PEC) fuel generation arise primarily from their vertical orientation, their ability to keep the charge carriers always in the vicinity of the surface and the pathways they offer for facile charge transport. They can form heterostructures with other low dimensional materials and function synergistically to enhance the efficiency of the PEC processes. Anodic nanotube arrays of only a few oxide semiconductors have been discovered so far; however, expanding the list further has been proven difficult. Recently, we have developed a few novel nanotubular semiconductors promising for PEC fuel generation. This presentation provides the details of their fabrication process and performance as photocatalysts for solar fuel generation.
(Invited) Controlling Electric Fields and Hydration at Electrochemical Junctions Using Surfactants
Authors: Dawlaty Jahan M , Maitra Anwesha , Pennathur Anuj , Tseng Cindy
Published: August 2024

Tuning the electrostatics and the water structure at the nm and sub-nm scales are two important frontiers towards the broader goal of controlling reactivity at interfaces. Surfactants offer a way to influence both the electrostatics and hydration of an electrochemical interface. Here we report measurements of local electric fields generated between layers of surfactants and an electrode without application of an external potential. We estimate the value of the electric field by measuring the vibrational frequency shift of a well-defined Stark probe that is adsorbed on the electrode. The field generated by the common quaternary ammonium surfactants in aqueous media is estimated to be in the order of 1 V/nm. We show that modest quantities of surfactants (50 mM) can produce polarizing fields similar to those produced by an electrode poised at -0.8 V vs. Ag/AgCl. Furthermore, we show that under electrochemical conditions, surfactants offer a way of modulating the water content near the electrode. In a mixture of water and DMSO, there are two forces that act upon the surfactants to drive them to the interface: they hydrophobic forces and the electrostatic forces from the electrode. We measure the surfactants at the interface as a function of these variables using surface enhanced IR spectroscopy, and arrive at quantitative comparisons between these two effects. These results help in understanding the design principles of modifying interfacial reactions via tailored surfactants.
(Invited) Following Energy Transduction from Light Absorption to Product Formation in Photoelectrocatalysis
Authors: Maitra Anwesha , Belman-Wells Livia , Huang Chengye , Nalige Sanjana , Hart Stephanie , Utterback James , King Alex J , Sayer Tom , Bhattacharyya Srijan , Mendes Jocelyn , Weber Adam Z. , Cushing Scott K , Montoya-Castillo Andres , Ginsberg Naomi S.
Published: August 2024

The ability to track how energy is transduced and transported in its various forms is critical to achieve a full understanding of key factors to optimize photoelectrocatalysis. Toward this end, we employ various forms of in situ optical scattering and reflectance microscopy that reveal the spatiotemporal evolution of both photogenerated charge carriers in semiconductor photoelectrodes on ultrafast time scales and electrochemical products as they diffuse from an electrode with sub-mM sensitivity and sub-ms time resolution. Thermal transport can also be resolved to clarify dissipation and thermal management. I will show structure-transport relationships in candidate photoelectrode transition metal oxides and show how a related approach also enables investigation of solution phase reaction products and their transport, even as a function of electrode irregularities.
Measuring Charge Selective Contacts on Semiconducting Photocatalyst Particles
Authors: Kaufman Aaron James , Boettcher Shannon W. , Shen Meikun
Published: August 2024

Water splitting could replace steam-methane reforming, a carbon intensive process, to generate hydrogen for energy storage, fertilizer production, and many other industrial processes. Photoelectrochemical (PEC) overall water splitting (OWS), for example, produces hydrogen from water, without wires or applied voltages, via a clean and renewable energy source, sunlight. To do so, PEC particles or photocatalysts (PC) must absorb light, and selectively collect the generated carriers, either electrons or holes, at specific sites which drive reduction or oxidation reactions, respectively. While theoretical solar to hydrogen (STH) efficiencies are at least 18%, state-of-the-art PCs are below 3%. Despite the extreme efforts screening and tuning semiconductor photocatalysts, a thorough understanding and control of electronic properties of the semiconductor-electrocatalysts (sem|cat) interface is limited.

Here, we use advanced electrochemical methods (dual-working electrode), scanning probe microscopy (conductive-AFM) and ambient-pressure XPS to measure and understand the origins of the electrochemical driving force (gradient in electrochemical potential) developed at complimentary electrocatalysts on photocatalyst particles. We use the dual-working electrode geometry on a high-quantum-yield wide-bandgap perovskite oxide, SrTiO3, to demonstrate the adaptive nature of electrocatalysts, Pt and CoOx, as they accumulate electrons and holes respectively. The cooperativity of half-reaction kinetics and adaptive sem|cat barrier height will be demonstrated along with the influence of crystal termination, which we argue is commonly overemphasized. Finally, a new contactless method of measuring the photovoltage at chemically distinct catalysts sites will be presented. Measured photovoltage induced shifts to element specific core levels in ambient pressure XP spectra in the dark and under illumination directly probe interfacial mechanisms operando. In sum, the introduced techniques and their findings demonstrate the underlying mechanisms and the degree that they play, enabling directed research of photocatalyst systems under one dominant engineering condition, charge selective

Figure 1
(Invited) Systems of Microenvironments for CO2 Reduction into Liquid Products
Authors: Houle Frances
Published: August 2024

The Liquid Sunlight Alliance (LiSA), a project in the DOE Fuels from Sunlight Energy Innovation Hub, has as its mission the co-design of assemblies of microenvironments that function together to convert natural sunlight and components of air into liquid fuels. Drawing on lessons from natural photosynthetic systems, these assemblies couple multiple interacting components to convert CO2 and water into energy-dense chemical products. This talk will highlight recent progress by the team, including development of distinctive cascaded photo-driven systems, and the underlying science advances required to refine their performance.
(Invited) Ternary Oxide Semiconductors and Alloys for Photoelectrochemical Applications: Hope and Reality
Authors: Rajeshwar Krishnan , Rawat Abhishek , Danladi Fahad
Published: August 2024

This perspective talk focuses on the history and status of new materials with targeted application in solar energy conversion. Specifically, photoelectrochemical energy conversion/solar water splitting and wide bandgap oxide semiconductors and alloys for solar windows and displays are the two targeted application areas. The Cu-M-V-O family of oxide semiconductors will be discussed in this talk. Both synthetic aspects and chemical composition-property-performance correlations will be presented.

Acknowledgements. This work was primarily supported by the National Science Foundation UTA/NU Partnership for Research and Education in Materials (NSF DMR-2122128).
(Invited) Soapy Molecules for Photocatalysis in Soft Membranes: A Multidisciplinary Approach Towards Solar Fuels
Authors: Bonnet Sylvestre
Published: August 2024

Natural photosynthesis takes place at lipid bilayers. Although major progress has been achieved in understanding how it works, science is still unable to re-create an efficient, lipid-based photocatalytic membrane that can generate solar fuels. To understand what happens when a photocatalytic system is embedded in a soft membrane, a multidisciplinary approach is needed. In this presentation I will discuss how to synthesize and characterize “soapy” photosensitizers and catalysts that can be used to functionalize soft interfaces. Using these molecules, my group has been able to study water oxidation and proton reduction in liposomes and foams. To understand the influence of the soft matter interface on photocatalysis, and notably compare it to homogeneous conditions, it is necessary to measure the diffusion of molecules in the membrane as well as electron transfer rates using time-resolved spectroscopy. On the one hand these studies highlighted the exceptional lifetimes of a selection of spectroscopically visible photoreduced and photooxidized catalytic intermediates; on the other hand, full understanding of the role of the soft interface on photocatalysis is still hindered by the spectroscopic invisibility of other intermediates, as well as by the challenge of modelling photocatalytic interfaces.

Figure 1
(Invited) 14.8% Quantum Efficient Gallium Phosphide Photocatalyst for Hydrogen Evolution
Authors: Becker Kathleen , Xiao Chengcan , Assavachin Samutr , Kundmann Anna , Osterloh Frank E
Published: August 2024

Gallium phosphide is a well-established photoelectrode material for H2 or O2 evolution from water, but particle-based GaP photocatalysts for H2 evolution are very rare. To understand the reasons, we investigated the photocatalytic H2 evolution reaction (HER) of suspended n-type GaP particles with iodide, sulfite, ferricyanide, ferrous ion, and hydrosulfide as sacrificial electron donors, and using Pt, RhyCr2-yO3, and Ni2P HER cocatalysts. A record AQE of 14.8% at 525 nm was achieved after removing charge trapping states from the GaP surface, adding a Ni2P cocatalyst to reduce the proton reduction overpotential, lowering the Schottky-barriers at the GaP-cocatalyst and GaP-liquid interfaces, and adjusting the electrochemical potential of the electron donor. The work showcases the main factors that control charge separation in suspended photocatalysts, and it explains why most known HER photocatalysts in the literature are based on n-type and not p-type semiconductors.

Figure 1
Adjusting the Catalytic Performance of MIL-88B(Fe/Co) through Structural Transitions
Authors: He Xiang
Published: August 2024

Metal-organic frameworks (MOFs) are a family of highly porous materials, which are composed of metal-based nodes and organic ligands. Thanks to the large surface areas and tunable chemical functionalities, MOFs are emerging as excellent catalysts for the sector of renewable energy. Of particular interest, the structures of certain MOFs are highly flexible, allowing for reversible structural transitions upon the stimuli from various external sources. Such stimuli-responsive behaviors of MOFs create new opportunities to design functional materials for switchable catalysis. Nevertheless, the exploration of the flexible MOF-based catalysts is still at a nascent stage. Herein, to advance the fundamental understanding of how the dynamic behaviors of flexible MOFs could affect the catalytic performance, first-principles calculations were carried out using the density functional theory, where a bimetallic MOF, MIL-88B(Fe/Co), was selected as a model structure. Results showed that the lattice contraction can result in twisted ligands as well as the rotary metal nodes, which subsequently lead to variations of the free energy diagrams for the oxygen evolution reaction, demonstrating the critical role of structural flexibility in determining the energy barriers during the elementary steps. Further analysis using the pair distribution function and electron localization function confirmed the rigid short-range order of MOFs during the structural transitions, as well as the tunable guest-host interactions upon lattice contraction/expansion, which could be responsible for the observed differences in the energy barriers during catalysis. Overall, the findings from this work offer new insights into the catalyst design for the modulated production of renewable fuels.

Reference: CrystEngComm, 2023, 25, 6441 - 6448
(Invited) Changes in Electric Double-Layer Structures Under Localized Surface Plasmon Excitation
Authors: Minamimoto Hiro , Shiga Futa , Mizuhata Minoru
Published: August 2024

For the visible light energy conversion, the localized surface plasmon resonance (LSPR), which is the collective oscillations of free electrons, should be promising. With the excitation of LSPR, the highly localized electric field generates in the vicinity of metal nanostructures. It is interesting that various unique photo-response properties, such as chemical reactions or molecular excitations, can be observed due to the enhancement of light-matter interaction.[1] To understand and control such mediated chemical reactions or electrochemical reactions, the precise understanding about the electrified interfaces of plasmonic nanostructures should be required.

Especially in the electrochemical system, the electric double layer is formed due to the difference in electrochemical potential between the metal interface and solution. The study of the surface potential is important for the design of chemical reactions because the surface potential at the liquid-solid interface is dependent on the physical properties of the systems. The zeta potential which is the potential of the slipping surface near the Stern layer of the diffusion layer could provide such information. From this point of view, in this study, we investigated the electric double-layer structures through the examination of the zeta potential under LSPR excitation condition. To obtain the zeta potential, we have performed the streaming potential method using Au nanoisland structures under visible light illuminations to excite the LSPR. It was interesting that the zeta potential was drastically changes under the visible light illumination conditions. This zeta potential change indicates the changes in the electric double layer structures through the excitation of LSPR. Through the investigations of incident wavelength dependence or the substrate dependences, the effects for the LSPR excitations on the electric double layer structure have been revealed. The present work would provide the fundamental knowledge about the effect on the LSPR excitation at solid-liquid interfaces.

[1] H. Minamimoto et al., Acc. Chem. Res., 2022, 55(6), 809.
(Invited) The Oxidation Mechanism of Cu with Operando X-Ray Spectroscopy Techniques
Authors: Garcia-Esparza Angel , Sokaras Dimosthenis , Yano Junko
Published: August 2024

Artificial photosynthesis capable of the CO2 reduction reaction (CO2RR), with solar energy as external excitation energy and water (H2O) as the electron and proton source, has been considered an attractive method to achieve a sustainable energy cycle, since it allows direct solar-to-chemical energy conversion. To design such systems, X-ray techniques play an important role for gaining the fundamental understanding needed to tailor its components and assemblies, by providing their chemical and structural information. For example, Cu is unique in the electrocatalytic conversion of CO2/CO to C2+ products, but with poor selectivity and durability. To understand the redox behavior of Cu under operation conditions, we have utilized surface-sensitive hard X-ray techniques to investigate the interaction of metal catalytic surfaces with electrolytes under operando conditions. Modulation excitation spectroscopy has proven to be an effective approach to enhance diluted signals. We discuss current challenges of studying artificial photosynthetic systems.
(Invited) Charge Separation and Stabilisation in Photocatalyst Materials for Solar Driven Water Splitting
Authors: Durrant James
Published: August 2024

In photocatalytic systems for solar energy conversion, a key challenge for efficient operation is the efficient separation and stabilisation of photogenerated charges, and thereby the minimisation of undesired recombination losses. This challenge is particularly great for photocatalytic systems because of the long charge lifetimes required to drive catalysis A further consideration is to minimise the energy losses required to drive this charge separation. My talk will cover examples of recent work from my group addressing aspects of this challenge. I will start by considering the role of polaron localisation / relaxation in driving charge separation in metal oxides, and quantification of the energetic loss associated with this polaron formation. Kinetic competion between polaron formation and ligand field state mediated charge recombination will be highlighted as the key challenge limiting the performance of many visible light absorbing metal oxides. The roles of metal oxide dielectric constant, surface facet energies, traps, ‘photocharging’ and heterojunctions in aiding charge separation in metal oxides will be discussed, drawing on examples from BiVO4 and SrTiO3. I will then go on to discuss charge separation and stabilisation in alternative photocatalyst materials, including organic semiconductor nanoparticles and metal-organic frameworks, highlighting the observation of remarkably long lived charge photogeneration in both systems and their relevance to the efficiency photocatalytic performance.
(Invited) Resolving Catalytic Mechanism at an Electrode Surface: Thermodynamics & Kinetics of Reaction Steps
Authors: Cuk Tanja
Published: August 2024

Computationally, often the energetics of intermediate reaction steps differentiate the efficiency of heterogeneous catalysts for product evolution. Yet, when compared to experiment, kinetic models are applied. For example, a material’s activity measured by one rate of product evolution is plotted as a function of the calculated formation energies of intermediate chemical forms. A critically important reaction for which this dichotomy between experiment and theory exists is the oxygen evolution reaction (OER) from water. In the laboratory group, we employ time-resolved optical and vibrational spectroscopy to deconstruct OER into its individual reaction steps on an electrode surface. In the presentation, I will describe the experimental methodology and the chosen model system, the n-doped SrTiO3/aqueous interface. I’ll show how these experiments identify both the rates and energetics of the first reaction step, the release of a proton and electron from an absorbed water species, denoted by OH* or O*. A recent success was to isolate a Langmuir isotherm of the intermediate population arising within < 2 ps on the SrTiO3 surface. The intermediate population is of trapped holes measured by emission from the conduction band into unoccupied states in the middle of the semi-conductor bandgap. The isotherm is tuned by the pH of the electrolyte. The pH-dependent formation of these intermediates are connected to their pH-dependent decay at microsecond timescales, presumably related to later reaction steps of OER. I'll also present work on the side of vibrational spectroscopy that looks at how the potential energy surface of a particular trapped hole, the terminal oxyl radical, arises in time through the spectral kinetics of its normal mode. A growing area is to apply the particular experimental methodology to a surface of similar electronic structure but diverse crystal geometries, namely polymorphs of TiO2.
(Invited) Perovskite/Perovskite Tandem Photoelectrodes for Unassisted Water Splitting
Authors: Yan Yanfa , Song Zhaoning
Published: August 2024

The bandgap tunability and low-temperature processing make halide perovskites excellent candidates for achieving efficient and cost-effective tandem devices for solar cells and solar-driven water electrolysis devices. Here, we report our progress on fabricating perovskite/perovskite tandem cells consisting of two solution-processed perovskite subcells for unassisted water-splitting applications. The perovskite/perovskite tandem photoelectrodes are achieved by monolithically integrating a wide-bandgap (1.7 – 2.1 eV) Pb-based mixed-halide (Br-I) perovskite top subcell and a narrower-bandgap (1.25 - 1.55 eV) bottom subcell based on Pb-based or mixed Pb-Sn iodide perovskites. Varying the halide perovskite composition for each subcell enables us to tailor the photovoltaic performance of the tandem devices. We demonstrate that perovskite/perovskite tandem solar cells can deliver open-circuit voltages of more than 2 V. The high photovoltage provides a sufficient overpotential to drive unassisted photoelectrochemical (PEC) water splitting with a solar-to-hydrogen conversion efficiency of more than 15%. After applying water-impermeable encapsulants, the perovskite/perovskite photoelectrodes can successfully operate in an aqueous environment and enable a long operational lifetime.
(Invited) Semi-Monolithically Integrated Photoelectrochemical Devices for Unassisted Water Splitting
Authors: Gaillard Nicolas
Published: August 2024

Photoelectrochemical (PEC) water splitting has the potential to become an efficient method for renewable hydrogen production. However, the efficiency, projected cost, and durability of lab-scale systems are not yet at the level required to make this technology economically feasible. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group demonstrated that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into multi-junction stacked PEC device. In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites compatible with the stacked multi-junction integration scheme. We present specifically results on EGtunable Cu(In,Ga)S2, CuGa(S,Se)2 and order vacancy compound CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of bandgap tunable MgZnO n-type buffer layers. Finally, we introduce the concept of semi-monolithic tandems, a new integration scheme where wide- and narrow-bandgap chalcopyrites are first integrated on separate substrates, then exfoliated, and finally bonded together to create fully functional multi-junction PEC devices.
A Flow Battery Path to Long Duration Energy Storage
Authors: Guarnieri Massimo , Manfrin Marcello , Zingales Antonio
Published: August 2024

Solar and wind sources are expected to replace fossil fuels in powering grids, but they are intermittent and non-dispatchable, thus requiring electric energy storage to provide reliable power delivery according to load profile. A dramatic growth in storage capacity is forecasted in to face these issues, up to 1.25 TW and 5 TWh by 2050. Pumped hydro is today the largest-capacity form of grid energy storage worldwide, but it is not expected to grow much, due to geographical and environmental issues. Batteries are often indicated as the solution of choice, notably the dominating Li-ion batteries (LIBs), which are expected to continue to expand. However, their use is limited by economically convenient discharge durations, which do not exceed 4 hours, and raw material costs dynamics. Like other batteries, they present issues e.g. life duration, safety and self-discharge. On the other hand, several studies indicate that to achieve full decarbonization Long Duration Energy Storage (LDES) will be essential, i.e. systems with discharge times above eight hours. Flow Batteries (FBs) have the potentials to provide this performance. In this framework, flow batteries (FBs) are emerging as a competitive option for LDES and several other services. They provide independent sizing of energy and power, thus allowing for long discharge times at full power. Their most developed version, the vanadium FB, exhibits very long life, virtually no self-discharge, operation at room temperature and pressure and absence of fires and explosion hazards. The presentation will discuss their potential and challenges and the undergoing research to improve their performance and competitiveness.

References

S. Department of Energy. Long Duration Storage Shot. https://www.energy.gov/eere/long-duration-storage-shot, 2021.

Long Duration Energy Storage Council. Net-zero power: Long duration energy storage for a renewable grid, technical report, 2021.

Jeremy Twitchell, Kyle DeSomber, and Dhruv Bhatnagar. Defining long duration energy storage. Journal of Energy Storage, 60 (2023):105787.

Sanchez-Diez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, “Redox flow batteries: status and perspective towards sustainable stationary energy storage”, J. Power Sources, 481, (2021) 228804.

Trovò, M. Rugna, N. Poli, M. Guarnieri. Prospects for industrial vanadium flow batteries, Ceram. Int., 49 (14), (2023) 24487-24498.

Trovò, V. Di Noto, J. E. Mengou, C. Gambaro, M. Guarnieri. Fast Response of kW-Class Vanadium Redox Flow Batteries, IEEE Trans. Sustain. Energy 12, (2021) 2413–2422.

Trovò, N. Poli, M. Guarnieri. New strategies for the evaluation of Vanadium Flow Batteries: testing prototypes, Cur. Opin. Chem. Eng. 37, (2022) 100853.
BiVO4-Decorated Graphite Felt as Highly Efficient Negative Electrode for All-Vanadium Redox Flow Batteries
Authors: Kabtamu Daniel Manaye , Huang Zih-Jhong , Ou Yun-Ting , Wang Chen-Hao
Published: August 2024

Recently, discovering high-performance electrocatalytic materials for vanadium redox flow batteries (VRFB) has been one of the most crucial tasks. This paper successfully fabricates low-cost plate-like bismuth vanadate (BiVO4) material through a simple one-step hydrothermal route, employed as an electrocatalyst to adorn the graphite felt (GF) for use as the negative electrode in VRFB. The experimental results show that BiVO4-3h exhibits the optimal electrocatalytic activity and reversibility for the vanadium redox couples among all samples. The energy efficiency of the VRFB cell assembled with BiVO4-decorated GF as the negative electrode is found to be 75.42% at 100 mA cm−2, which is about 10.24% more efficient than that of the cell assembled with heat-treated graphite felt (HT-GF) electrode. The possible reasons for the activity enhancement can be ascribed to the existence of oxygen vacancies in the BiVO4 lattice structure and the relatively high surface area of BiVO4, which provide more active sites for facilitating the vanadium redox reactions. Furthermore, the BiVO4-GF electrode obstructs the competitive irreversible hydrogen evolution reaction on the negative side of the cell, and it also has better wettability. Impressively, BiVO4-GF as the negative electrode shows good stability over 100 cycles.
Electrolyte Gradients and Capacity Drop in Large Flow Battery Tanks: From Experiments to Fluid-Dynamic Investigations
Authors: Prieto-Diaz Pablo Angel , Marini Giacomo , Rugna Matteo , Trovo Andrea , Zatta Nicolò , Concheri Gianmaria , Savio Gianpaolo , Vera Marcos , Guarnieri Massimo
Published: August 2024

A study of the effects of electrolyte flow inside the tanks on electrical performance of an industrial-size Vanadium Redox Flow Battery (VRFB) is presented. The concentration of electrolytes feeding the stacks of VRFBs is crucial in determining the device voltage and overall power performance. Usually, the assumption of perfect mixing in the tanks is assumed, but the hydraulic behavior of large VRFB can deviate significantly from this assumption depending on the electrolyte flow rate, stochiometric factor and geometry of the tanks. In this study, the State of Charge (SoC) measurements have been analyzed, starting from the signal produced by an Open Circuit Voltage (OCV) cell. An experimental campaign has been conducted during charge/discharge roundtrip cycles at different current levels and constant stoichiometric factor. Building on the delay in the voltage response of the battery, a fluid-dynamic model was developed to study how the hydraulic behavior of electrolytes inside tanks influences the electrolyte concentration and, consequently, the SoC of the electrolyte that feeds the stack and the electrical time response of the battery. The model indicated that a stratification of charged electrolyte is responsible for this delay resulting in an initial voltage plateau. A different hydraulic behavior was found in each tank and in each charge/discharge phase. These results highlight the tank role in the industrial-scale VRFB performance.

References

Sanchez-Diez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, “Redox flow batteries: status and perspective towards sustainable stationary energy storage”, J. Power Sources, 481, (2021) 228804.

Kurilovich, A. Trovò, M. Pugach, K. J. Stevenson, M. Guarnieri. Prospect of Modeling Industrial Scale Flow Batteries – from Experimental Data to Accurate Overpotential Identification, Renew. Sust. Energ. Rev. 167, (2022) 112559.

Trovò, V. Di Noto, J. E. Mengou, C. Gambaro, M. Guarnieri. Fast Response of kW-Class Vanadium Redox Flow Batteries, IEEE Trans. Sustain. Energy 12, (2021) 2413–2422.

Trovò, M. Rugna, N. Poli, M. Guarnieri. Prospects for industrial vanadium flow batteries, Ceram. Int., 49 (14), (2023) 24487-24498.

Maggiolo, A. Trovò, M. Guarnieri, “Reactant Flow in Flow Batteries”, in L. Cabeza (ed.), Encyclopedia of Energy Storage, vol. 4, pp. 231-242. Oxford: Elsevier. March 2022.

A. Prieto-Díaz, S. E. Ibáñez, M. Vera. Fluid dynamics of mixing in the tanks of small vanadium redox flow batteries: Insights from order-of-magnitude estimates and transient two-dimensional simulations, Int. J. Heat Mass Transf. 216, (2023) 124567.

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Figure 1
Elucidating Degradation of Aqueous Organic Redox Flow Batteries by Electrochemical Impedance Spectroscopy
Authors: Zeng Chao , Kim Soowhan , Fu Yucheng , Chen Yunxiang , Bao Jie , Xu Zhijie
Published: August 2024

Redox flow batteries, facilitating the dissociation of energy and power, emerge as a promising avenue for electrochemical electricity storage. A shift from vanadium flow batteries to those employing aqueous organic electroactive species is evident due to the latter's advantageous features, such as diverse design possibilities through functionalization, reduced cost, non-toxicity, and improved availability. Despite expectations that organic redox flow batteries can surpass a lifespan of 10 years or 2000 cycles, their practical long-term performance faces challenges arising from electrode, membrane, and organic species degradation.

The intricate interplay of various degradation factors during full cell cycling results in observable capacity decay over cycles. Effectively mitigating degradation necessitates the dissection of these factors to identify the limiting component. Electrochemical impedance spectroscopy (EIS) emerges as a potent diagnostic tool capable of pinpointing and disentangling the sources of resistance within an electrochemical device. Through deconvolution of different factors, EIS allows for the quantitative measurement of resistance evolution throughout full cell cycling, reflecting degradation through changes in resistance. Consequently, by monitoring resistance evolution with EIS, the degradation rates of individual factors can be calculated.

This study employs an alkaline aqueous organic redox flow battery with 2,5-di-tert-butyl-1,4-dihydroxybenzene sulfate (DHPS) as anolyte and ferrocyanide as catholyte for demonstration. EIS measurements are conducted at various cycles, and three distinct resistance components (charge transfer, ohmic, and mass transport) are identified as functions of cycle numbers. Subsequently, the degradation rates of crucial electrochemical parameters, such as reaction rate and mass transport coefficient, are quantified, providing essential inputs for subsequent modeling endeavors.
Molecular Engineering for Organic Redox-Flow Batteries
Authors: Malapit Christian
Published: August 2024

Recent advances in organic redox-flow batteries have made them a viable option for grid scale energy storage as they can increase energy density through molecular engineering. Here, we present the importance of molecular engineering as a key factor in the development of novel redox-active organic molecules (ROMs). Importantly, this presentation will highlight the design and synthesis of these molecules and how they are tuned to obtain optimal properties necessary for ROMs that will improve key performance needed in organic-based redox-flow batteries. This talk will feature two distinct classes of compounds as ROMs and will systematically describe their development and application to redox-flow batteries.
(Invited) Transport Limits for Zinc Aqueous Electrolyte Batteries: Investigation over Multiple Length Scales
Authors: Takeuchi Esther S. , Marschilok Amy C. , Takeuchi Kenneth J.
Published: August 2024

Large scale grid level storage would benefit from low cost environmentally sustainable batteries. A system class under investigation is rechargeable zinc anode batteries utilizing aqueous electrolytes. These systems hold promise due to their potential for safe low-cost scalable energy storage. Consideration of the systems over various length scales is warranted due to the complexity of the possible reactions and pernicious parasitic processes. Further, the diversity and intricacies of these battery systems inherently reduce the probability of optimization experiments alone resulting in marketable products.

Many of the fundamental issues influencing ion and electron transport and electron transfer and how the transport phenomena evolve under flux are not yet fully undefined. More complete understanding demands multiple characterization approaches used in concert, to tie together information gathered at the local or atomic level and the mesoscale with systems level performance from electrochemical impedance spectroscopy (EIS), galvanostatic cycling (GC), and related techniques. This presentation will provide insight into probes of the reaction mechanisms, evolution of zinc interfaces, methods to determine limitations of cathode function at high rate, and impact of the findings on the electrochemical behavior of the batteries.
Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries
Authors: Miliante Caio Miranda , Gourley Storm William D , Adams Brian D , Higgins Drew , Rubel Oleg
Published: August 2024

Continued efforts towards the decarbonization of the power sector through an uptake of renewable energy generation, namely solar and wind, play a key role in the fight against climate change. However, due to their variable nature, the simultaneous implementation of energy storage solutions capable of ensuring a reliable delivery of energy at any time of day is of the utmost importance. Aqueous rechargeable zinc-ion batteries (RZIBs) are a promising technology for this end. Offering several advantages over lithium-ion batteries in terms of cost, environmental impact, and material abundance, the investment in RZIB research continues to grow. However, the realization of commercial RZIBs is currently hindered by the lack of cathode materials with adequate performance for long-term storage solutions. This is the case for manganese (e.g., MnO2, Mn2O3, Mn3O4) and vanadium (e.g., V2O5, VO2) based oxides, which exhibit considerable capacity fade during realistic charge and discharge times. While simple transition metal oxides (MyOx, M=transition metal) are one of the most studied classes of materials for RZIB cathodes, a literature survey shows that there are still many unexplored redox active elements and redox pairs which may be employed in next-generation RZIBs. Therefore, to accelerate the discovery of these novel cathode systems, we mapped the theoretical Zn intercalation potential for simple oxides from 12 different transition metals using Density Functional Theory (DFT) calculated thermodynamic properties. The screened elements were chosen upon considering their commercial availability, toxicity, price, and existence of previously reported structures containing zinc. During the present analysis, the feasibility of Zn intercalation for each system was accounted for by analyzing the atomic arrangement in the charged and discharged phases. Experimentally obtained Pourbaix Diagrams were also used to probe the electrochemical stability of the cathodes in aqueous solution, with the possibility of electrolyte degradation (oxygen or hydrogen evolution reaction) and competing reactions (metal dissolution or solid phase change) also considered. Experimental validation of the computationally predicted potentials was also done for select materials. The result for the 35+ redox pairs evaluated in this study provides a clear roadmap for the future development of RZIBs cathodes.