bluuebunny/crossref_metadata_2025 huggingface dataset:
Garnet Nb-Doped Li7La3Zr2O12 Ceramic Electrolyte and Its Composite Electrolyte for Solid-State Lithium Batteries
Authors: Lu Wanzheng , Xue Mingzhe , Zhang Cunman
Published: July 2021

Lithium ion batteries (LIBs) have world-widely emerged as energy storage devices for electronic products, electric vehicles, energy storage systems and special purpose devices. LIBs are increasingly expected to be provided with a shorter battery charging time, a longer battery life and the better battery security for industrial development and social demand. However, most conventional LIBs with active organic liquid electrolytes have suffered from several issues, especially high safety risk and low energy density. Therefore, continuously improving conventional LIBs and designing new-type lithium batteries are extremely urgent. Solid-state lithium batteries (SSLBs) are recognized as the promising candidates of next generation lithium batteries with good safety and high energy density. Solid-state electrolytes (SSEs) as the most critical component in SSLBs largely lead the future battery development. To obtain the SSEs with good overall performance is a prerequisite to realize the potential of SSLBs. Garnet Li7La3Zr2O12 (LLZO) ceramic SSEs have the great potential for SSLBs, owing to high ionic conductivity, wide stable potential window and good electrochemical stability against lithium metal. However, so far, LLZO ceramic SSEs still suffer from critical issues of poor air stability and hard machinability, greatly limiting their practical application. Hence, in this work, the cubic garnet Nb-doped LLZO, Li6.5La3Zr1.5Nb0.5O12, ceramic electrolyte is synthesized by a simple sol-gel process. Stability and mechanical properties of as-synthesized Li6.5La3Zr1.5Nb0.5O12 ceramics are explored in detail. Directly polishing and assembling Li6.5La3Zr1.5Nb0.5O12 ceramic pellets in analog batteries are applied to investigate electrochemical behaviours. In addition, the flexible composite membrane composed of Li6.5La3Zr1.5Nb0.5O12 particles and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix is successfully prepared through tape casting method. The composite membrane shows good machinability. When the composite membrane as electrolyte is applied in the lithium metal cell, good electrochemical performances are exhibited. The composite membrane integrating hard inorganic Li6.5La3Zr1.5Nb0.5O12 ceramics with soft polymer achieves a gain effect of “1+1 > 2”. This work may be helpful for next forward-looking studies of garnet LLZO family SSEs and their extensions.
Sulfur and Nitrogen Co-Doping Bismuth-Based Catalysts for Selective Electroreduction of CO2 to Formate
Authors: Shao Xiaolin , Liu Yuyu , Zhang Jiujun
Published: July 2021

Since the greenhouse effect is an urgent problem, the conversion of greenhouse gas CO2 into valuable chemicals and low-carbon fuels by electrocatalysis is a promising way and has attracted comprehensive attention. In recent years, metal sulfides have shown catalytic performance for electrocatalytic reduction of CO2. However, the existing catalysts still face the problems such as insufficient activity, poor conductivity and low stability. Here, we synthesized a bismuth-based catalyst doped with sulfur by electroreducing Bi2S3 precursor, which is obtained by one-pot hydrothermal reaction, and simultaneously modified catalyst with nitrogen atoms using N,N-Dimethylformamide (DMF) as nitrogen source. The experimental results show that maximum faradaic efficiency of formate can reach 85% at -0.96V (vs. RHE) with the largest current density of 30mA/cm2 and a long-term tolerance in reduction process. Combined with other experimental results, the better catalytic performance is mainly attributed to the improvement of the electron structure on the surface of the catalyst by sulfur and nitrogen co-doping. This work not only provides a simple way of sulfur and nitrogen co-doping, but also explores the transformation of Bi2S3 during electrochemical reduction, further providing an idea for the design of catalysts from metal sulfides.
Facile Synthesis of Nanoporous Pb-Based Catalyst for CO2 Electrochemical Reduction
Authors: Sun Xueliang , Liu Yuyu , Zhang Jiujun
Published: July 2021

Electrochemical reduction of CO2 (ERCO2) is a promising way for the direct production of useful low-carbon fuels, which can simultaneously alleviate the energy crisis and the greenhouse effect. The most important to realize highly efficient catalytic reaction for ERCO2 is to develop a high-powered catalyst. In this paper, we facbricated a nanoporous Pb-based catalyst on a copper substate by Pb and Zn electrodeposition at a constant current (50 mA/2´2cm2), and then chemically etching of Zn in sodium hydroxide solution. The surface morphology, composition and polycrystalline structure of nanoporous Pb-based electrodes were characterized by SEM, XPS and XRD. By changing the experiment conditions including the concentrations of Zn in electroplating solution and chemical etching time, the catalytic performances of as-prepared catalysts for formic acid/formate production were changed subsequently. When the Pb-based electrode fabricated in electroplating solution (molar ratio: 100:20 for Pb:Zn) was chemically etched in NaOH aqueous solution for 8 hours, the Faraday efficiency achieved a highest value of 95.3% at applied potential 1.8 V vs Ag/AgCl, which was attributed to the rougher surface, better electron conductivity and larger electrochemical surface area and thus more favour for ERCO2 relative to the others. Moreover, the nanoporous catalyst exhibited a good stability and there was no obvious inactivation after 12-h electrolysis in 0.5 M KHCO3 solution. The results reveal that the nanoporous Pb-based catalyst possesss highly catalytic performances.
A High-Performance Continuous Flow MEA Reactor for Electroreduction CO2 to Formate
Authors: Liu Peixuan , Qiao Jin Li
Published: July 2021

The electrochemical reduction of carbon dioxide reduction reaction (CO2RR) to liquid fuels and industrial chemicals represents a promising approach to the environmental remediation of carbon emissions and utilizing intermittent renewable electricity. However, the traditional device of electrolysis CO2 is seriously limited by low CO2 solubility, large PH gradient and high ohmic resistance due to the large distance between two electrodes, which is not applicable to industrial production. Herein, we demonstrate a high-performance continuous flow membranes electrode assembly (MEA) reactor based a self-growing Cu-Sn bimetallic electrocatalysts in the liquid-phase to electroreduction of CO2 to formate. We then via testing different electrolyzer structure explore the best performance of the flow MEA reactor, and compare with H-type cell. Notably, the reactor is designed not only greatly increase current density (66.41 mA cm-2) at -1.11 VRHE, but also maintain high Faraday efficiency (89.56%), and that can effective separation of the gaseous/liquid production. And then, we achieve the production rate of 1 L CO2 to formate (163 μmol h -1 cm-2) at working electrode at -0.97 VRHE and cell voltage at 3.17 V after 20 hours electrolysis. This present study provides a novel reactor can maximize the use of catalyst activity for electrochemical CO2RR and other emerging electrochemical catalysis research.
Modeling Water and Thermal Transients Inside Proton Exchange Membrane for Vehicle Application Fuel Cells
Authors: Wang Qianqian , Li Bing , Tang Fumin , Zheng Jim P. , Ming Pingwen
Published: July 2021

Dynamic performance of proton exchange membrane fuel cells (PEMFCs) is very important for vehicle application. However, limited by the structure and dimension, it is still difficult to understand the internal transient behaviors by experiment. In this work, two-phase, non-isothermal, transient models are developed to investigate the water and thermal transients inside the membrane and their influences on the performance of fuel cells. Firstly, the simulation result and the experimental data are compared. The simulation result basically accords with the experimental data because it captures well the overshoot and downshoot of output voltage as current step changes, which are mainly related to the evolution of membrane water content (λ). A driving protocol is then set up to simulate a real vehicle running on the road with consideration of starting, variable load acceleration, overload running, etc. During the simulation, we observe a power overshoot as the current step changes during overload running, which is caused by membrane dehydration at high temperature. To decrease the temperature, the influences of loading speed and coolant temperature are investigated, respectively. The results indicate that reducing loading speed can relieve the power overshoot to some extend, while the reduction of coolant temperature during loading can fundamentally avoid the high temperature and membrane dehydration, and thus improve fuel cell output performance. Lastly, based on an inverse relationship hypothesis between λ and the glass transition temperature of membrane (Tg), the dynamical changes of Tg are explored. It is found the membrane temperature will exceed its glass transition temperature if operation temperature is higher than 105 ℃ during overload running, which may result in polymer melting.
(Invited) Amorphization Mechanism of SrIrO3: How Oxygen Redox Initiates Ionic Diffusion and Structural Reorganization
Authors: Wan Gang , Fong Dillon , Feng Zhenxing , Zhou Hua , Suntivich Jin
Published: July 2021

The oxygen evolution reaction (OER) is integral to nearly all material and fuel electrosyntheses. However, very little is known about the structural evolution of the OER electrocatalyst, especially the amorphous layer that forms from the crystalline structure. In this contribution, we discuss our investigation of the interfacial transformation of the SrIrO3 OER electrocatalyst. The SrIrO3 amorphization is initiated by the lattice oxygen redox, a step that allows Sr2+ to diffuse and O2- to reorganize the SrIrO3 structure. This activation turns SrIrO3 into a highly disordered Ir octahedral network with Ir square-planar motif. The final SryIrOx exhibits a greater degree of disorder than IrOx made from other processing methods. The presented results demonstrate that the structural reorganization facilitated by coupled ionic diffusions is essential to the disordered structure of the SrIrO3 electrocatalyst.
Quantifying the Density and Mobility of Mobile Ions in Solid Electrolytes By Transient Current Measurements
Authors: Futscher Moritz H. , Sastre Jordi , Romanyuk Yaroslav E.
Published: July 2021

Solid electrolytes are a key component in enabling new technological advances for rechargeable batteries by mitigating many of the challenges associated with the use of liquid organic electrolytes. One of the key properties of solid electrolytes is their ability to transport ions between the anode and the cathode. This ion migration is usually characterized by measuring the ionic conductivity by means of impedance spectroscopic measurements. However, the ionic conductivity is proportional to both the density and the mobility of mobile ions. Only the mobility represents the actual velocity of the mobile ions.

Using lithium phosphorus oxynitride (LiPON), we show how measuring the temperature-dependent current transients can be used to independently quantify both the mobility and the density of mobile ions in solid electrolytes. By changing the mobile ion density in Li7La3Zr2O12 (LLZO) solid electrolyte by co-sputtering LLZO and Li2O, we show how samples that seem to have the same ionic conductivity can still differ in ionic mobility. Finally, we employ this method to quantify the effects of Al and Ga doping on the ion migration in LLZO solid electrolytes. The proposed approach in quantification of mobile ions can be extended to other solid electrolytes for a better understanding of ion migration and the influence on battery performance.
Electrochemical Properties of High-Temperature Polymer Electrolyte Thin Films
Authors: Venugopalan Gokul , Briceno-Mena Luis A , Bhattacharya Deepra , Romagnoli Jose A , Arges Christopher G.
Published: July 2021

Electrode binders based on ionomer chemistries have a profound impact on the performance of polymer electrolyte membrane (PEM) fuel cells. High temperature PEM fuel cells (HT-PEMFCs) typically use phosphoric acid (H3PO4) imbibed polymers or polymers without ionic moieties as the binder (e.g., PTFE). The former materials hinder gas reactant transport and compromise electrode kinetics, while the latter materials suffer from severe ohmic penalties in the electrode layers. The ionomer binder limitations for HT-PEMFCs stymie power density and lead to poor utilization of the costly platinum catalyst.

This talk presents our work probing the electrochemical properties of high-temperature ionomer thin films. The polymer electrolytes investigated are phosphoric acid imbibed polycations as well as phosphonated polymers. Thin films are examined because they mimic the structure found in electrode layers and they can be interrogated with interdigitated electrode (IDE) arrays featuring nanoscale electrocatalysts. The IDE platform is useful for drawing definitive conclusions about the electrochemical behavior of ionomer binder materials without being muddled by the complexity of bulk electrodes. Our work has shown that phosphonated ionomers display better hydrogen diffusivity and hydrogen oxidation reaction kinetics than acid imbibed polycations. The phosphonated ionomers can match the anhydrous proton conductivity of acid imbibed polymers provided they contain electron withdrawing moieties in the polymer. The final part of the talk presents Machine Learning (ML) tools (e.g., support vector regression, density-based clustering, and self-organized maps) that use data from IDEs and single-cell polarization. The ML bridges materials properties to device performance and is poised to accelerate the timeline for realizi
Bifunctional CuMoS4 for Green Energy Production
Authors: Choi Jonghyun , Morey Kinsey , Gupta Ram K
Published: July 2021

The growing need for energy and sustainability issues demand green energy production. Research in this field needs better materials that can efficiently produce energy. Modified electrode materials with better electrochemical properties that can work as bifunctional materials to produce energy are much needed. In this work, copper-molybdenum sulfide synthesized using a self-assembled synthetic route was dip-coated onto nickel foam for energy generation (hydrogen and oxygen via water splitting). For water splitting applications, CuMoS4 displayed an overpotential of 207 mV to reach a current density of 10 mA/cm2 for hydrogen evolution reaction (HER). The Tafel slope associated with the HER activity of this material was 118 mV/dec. The overpotential needed to reach a current density of 10 mA/cm2 for oxygen evolution reaction (OER) was 270 mV. The OER activity of copper-molybdenum sulfide showed a Tafel slope of 82 mV/dec. Moreover, the material showed great stability over a long period water splitting reaction. CuMoS4 produced results comparable to many other materials in literature and has promising results for applications for water splitting.
Nanostructured Nickel-Cobalt Oxide and Sulfide for Green Energy Production Using Waste Water
Authors: Choi Jonghyun , Ndambakuwa Wadzanai , Ndambakuwa Yustinah , Fernando Ganga , Mishra Sanjay R , Perez Felio , Gupta Ram K
Published: July 2021

With the advancement in technology, demand for green energy production is increasing year by year. To meet the increasing demand for green energy, there has been continuous research in a bid to find better materials and efficient ways to generate energy. Transition metals such as Fe, Mo, Ni, etc. based materials have shown great potential to be used as electrocatalysts for water splitting, and the urea oxidation reaction (UOR). In this work, nanostructured nickel-cobalt oxide and nickel-cobalt sulfide were synthesized using a facile hydrothermal method for their applications in water splitting and UOR. It was observed that the properties of nickel-cobalt oxide improved significantly after converting it to nickel-cobalt sulfide. Nickel-cobalt sulfide showed an overpotential of 282 mV while nickel-cobalt oxide displayed an overpotential of 379 mV to generate a current of 10 mA/cm2 , towards oxygen evolution. After introduction of 0.33 M urea, the potential for oxidation of urea for both nickel-cobalt oxide and nickel-cobalt sulfide is decreased to 1.34 V.
Phase Engineering of Metal Oxides for Enhanced Energy Application
Authors: Nkhama Alfred , Gupta Ram K
Published: July 2021

A recent ongoing technological breakthrough in numerous fields including eco-friendly energy, electronics, transportation, defense, and security, etc. is immensely challenged by the inadequate capability of energy devices. Deliberate efforts in researches that could lead to obtaining reliable energy devices are being carried out applying diverse approaches. In this study, the structure of the materials has been considered and examine its impact on electrocatalysis and hence its green fuel production capability. The porous NiFe-oxide nanocubes (NCs) system is generated from a NiFe Prussian analog metal-organic framework. In 1M KOH, the nanocubes demonstrate overpotentials of 54 mV and 298 mV for HER and OER, respectively to deliver a current of 10 mA/cm2 whereas the spherical NiFe-oxide nanoparticles (NPs) of similar composition showed respective overpotentials of 187 mV and 258 mV for HER and OER. The incredible catalytic performance of NiFe-NCs is attributed to the exposure of active sites at the edges and vertices of NCs. Moreover, both the NPs and NCs showed interesting property changes after being sulfurized. Sulfurized nanocubes (NCs-S) demonstrated overpotentials of 177 mV and 241 mV whilst sulfurized nanoparticles (NPs-S) showed overpotentials of 152 mV and 216 mV for HER and OER, respectively. On top of that, the electrochemical measurements in 3M KOH showed the increase of the specific capacitances of NCs and NPs after sulfurization from 69 to 604 F/g and from 185 to 514F/g, respectively, at a current density of 1 A/g. Our study suggests that a facile sulfurization process could significantly improve catalytic activities of metal oxides.
Renewable Energy Powered Water Electrolysis for Hydrogen and Oxygen Generation with Non-Precious Catalysts
Authors: Li Jiangtian , Chu Deryn
Published: July 2021

Renewable energy powered electrochemical conversion reactions for chemical fuels is in urgent demand to address the energy and climate crises. Hydrogen, as a high-power-density energy carrier, can deliver or store huge amount of energy for many applications. Electrochemical water splitting to produce hydrogen and oxygen is an appealing sustainable approach using natural water and renewable energy resources like sun, wind and hydro power. The benchmark electrocatalysts for hydrogen evolution reaction and oxygen evolution reaction are noble metal Pt- and Ir/Ru-based materials, respectively. Nevertheless, the scarcity and the high cost of these precious catalysts severely hinder their widespread applications. Developing earth abundant, non-precious electrocatalysts has been one long-term target, but still remains a great challenge. This presentation will show our research efforts in designing and synthesizing transition metal-based electrocatalysts for hydrogen evolution, oxygen evolution or bifunctional water electrolysis, as well as in constructing the water electrolyzer cell powered by solar energy.
Probing the Local pH during HER on TiO2 Promoted Co-Mo Electrocatalysts
Authors: Wang Cheng , Podlaha Elizabeth J.
Published: July 2021

The HER catalytic performance of electrodeposited Co-Mo thin film electrocatalysts in base can be improved by incorporating nano-TiO2 particles into the metal matrix.1-2 The HER overpotential was significantly reduced, and the exchange current density was substantially higher compared to its Co-Mo counterpart. The embedded TiO2 particles were found to also affect the partial current density of metal deposits during the electrodeposition process. To further probe the influence of the TiO2 particles on both the HER and the electrodeposition, the local pH was investigated. The Co-Mo and Co-Mo-TiO2 thin films were deposited onto copper mesh electrodes from a sulfate-citrate electrolyte with particles suspended in the electrolyte. The HER activity was evaluated in a 1 M NaOH electrolyte at room temperature. The surface morphology was characterized by SEM, and deposit composition was assessed by XRF and EDS. With an in-house designed, 3D printed experimental setup, the local pH of the cathode was monitored during galvanostatic deposition and HER electrolysis. During the electrodeposition process, the trend of local pH change with and without TiO2 particles are the same, consistent with their similar HER partial current densities. During the HER electrolysis, as the current density increases, the local pH value of Co-Mo without particles increases considerably, while the local pH value of Co-Mo-TiO2 remains unaltered. This result suggest that TiO2 particles can buffer the electrode surface and is an important factor in improving the HER catalytic performance.

Wang, C.; Bilan, H. K.; Podlaha, E. J., Electrodeposited Co-Mo-TiO2 Electrocatalysts for the Hydrogen Evolution Reaction. Journal of The Electrochemical Society
2019,
166 (10), F661-F669.

Wang, C.; Podlaha, E. J., Communication-Electrodeposited Co-Mo-P-TiO2 Composites Electrocatalysts for the Hydrogen Evolution Reaction. Journal of the Electrochemical Society
2020.
Cu3p/N-Doped Carbon Catalyst with One-Step Synthesis Method for Hydrogen Evolution Reaction of Alkaline Water Electrolysis
Authors: Kim HyoWon , Lee Yongju , Song DongHoon , Kwon YongKeun , Kim Eom Ji , Cho EunAe
Published: July 2021

Hydrogen energy is in the spotlight to resolve the imbalance in the supply and demand for renewable energy. Water electrolysis is an eco-friendly method of producing hydrogen, and it is necessary to develop a high-efficiency, low-cost hydrogen evolution reaction (HER) catalyst. This study presents a copper phosphide/N-doped carbon (Cu3P/N-C) catalyst with relatively abundant reserves and low cost. This catalyst is synthesized in a one-step process involving phosphorization of copper and cyclization of polyacrylonitrile (PAN). By adding PAN to the phosphorus precursor, the Cu3P particles are electrically and physically connected, providing improved electrical conductivity and structural integrity of the Cu3P electrode. The disordered N-doped carbon structure formed under the influence of the phosphorus source induces a synergistic effect with the extended electrochemically active surface area (ECSA), increasing HER activity. The P to PAN ratio is optimized to achieve the best HER activity, and Cu3P/N-C prepared in copper foam exhibits HER overpotentials of 211.1 and 301.8 mV at 10 and 50 mA cm-2 current densities in 1 M KOH solution. At a current density of 10 mA cm-2, the HER overvoltage remained stable between 211.1 and 222.1 mV for 24 hours.
(Invited) Exploring Synergistic Effects for High Performance Catalysts of Electrolytic Water Splitting
Authors: Senthil Raja Duraisamy , Cheng Chih-Chieh , Lu Shih-Yuan
Published: July 2021

Hydrogen plays a key role in deep decarbonization to tackle the two–degree–scenario (2DS) set by the Paris Climate Agreement. It has been proposed that decarbonization through hydrogen economy could achieve half of the reduction in carbon dioxide emission required to realize the 2DS. Presently, the most popular and economical commercial process for H2 production is steam–methane reforming, which uses fossil fuels as the raw material and produces comparable amounts of CO2 as the by–product. It is definitely an environmental unfriendly and a non–sustainable H2 production process, and development of green H2 production is in urgent need. In this regard, renewable energy driven electrolytic water splitting has been gaining rapidly increasing popularity and is considered by many the most promising green H2 production process for future hydrogen economy infrastructure. It is also considered a necessary energy storage approach to resolve the detrimental unreliability and intermittency issues of renewable energies. The high cost of electricity however severely limits the prevailing of this technology, and cost–effective highly efficient and stable electrocatalysts, aiming to reduce the necessary working potential for cost competiveness, are critically important for the prevailing of the technology. For catalyst development, unary systems have been exhaustively explored and multi–component systems have advanced drastically, benefitting from the synergistic effects between constituent components. Engineering synergistic effects of multi-component catalysts is thus one key for breakthrough catalyst design. Here, several recent examples from our lab are presented to illustrate the strategy.
Surface Modification of TiO2 with Metal Oxides for Water Splitting
Authors: Nolan Michael , Rhatigan Stephen
Published: July 2021

The photocatalytic oxidation of water to molecular oxygen is a key step in the water splitting reaction. The development of robust catalysts with high efficiency in this half-reaction is crucial for achieving technological application of water splitting. Density functional theory studies predict that alkaline earth metal oxide modified TiO2 can enhance water activation and the free energies of oxygen evolution reaction (OER).

DFT simulations were performed on extended rutile (110) and anatase (101) surfaces modified with alkaline earth oxide (AEO) nanoclusters of composition (MO)4 and (MO)12 to explore coverage and dispersion effects in the nanocluster modification of TiO2
1. We use the VASP5.4 code with a cut off energy of 400 eV, the PW91 approximation to the exchange-correlation functional and the DFT+U approach to describe the partially occupied 3d states in reduced TiO2, with U = 4.5 eV.

We use models of rutile (110) modified with MgO nanoclusters of composition (MgO)4 and (MgO)12 to model dispersion/coverage effects. The nanoclusters bind strongly the rutile surface, forming new interfacial bonds. Computed formation energies of oxygen vacancies show that these heterostructures are easily reducible, with reductions of ca. 2 eV in the cost of forming oxygen vacancies, with electron localization on the TiO2 substrate. The computed free energy for the OER steps , using the standard computational model for structures without and with surface hydroxyls shows that moderating stability of the *OH intermediate in the water oxidation steps, reduces the overpotential compared to pure rutile (110) and competitive with hematite. The most favourable water adsorption mode for OER is at the MgO-rutile interface.

Work on other surface modified TiO2 materials includes CeO2 and MnOx, where these are also reducible and activate water to produce hydroxyls. Comparison is made with experimental results from collaborators.
High Performance Low PGM Alkaline Membrane Water Electrolysis
Authors: Strasser Derek James , Xu Hui , Kabir Sadia , Shi Wenjuan , Rojas-Carbonell Santiago , Yan Yushan , Wu Gang , Shi Qiurong
Published: July 2021

Development of water electrolysis technology is critical to the future of clean energy consumption and storage. Alkaline membrane water electrolysis is very attractive owing to the high energy density of the hydrogen produced and, more importantly, the possibility of lowering system cost by significantly lowering or completely replacing platinum group metal (PGM) catalysts with less expensive metals such as nickel and iron. Replacing perfluorinated membranes with much less expensive hydrocarbon based materials such as oxidation-resistant alkaline membranes and ionomer that are stable under water electrolysis operating conditions will also improve system costs and durability requirements. Previous research has focused on alkaline electrolyzers operating with KOH supporting electrolyte.1 To date, it is clear that alkaline membrane electrolysis is still low technology readiness leveltechnology with reported limitations such as membrane/ionomer durability, non-PGM catalyst performance and durability and previously mentioned, operation with a supporting electrolyte, such as KOH to achieve performance, which adds significant cost to design a corrosion resistant device.

In this study, we have developed an alkaline membrane water electrolyzer which operates with pure water and employs non-PGM anode catalyst. Initial focus was to demonstrate membrane and ionomer performance and durability during electrolyzer operation without the use of added electrolyte. We have demonstrated for the first time 500 hours of cell operation with pure water at 500 mA/cm2 and a cell potential of 1.7 V using standard PGM catalysts indicating significant durability. Replacing the iridium oxide with PGM-free catalyst and operating the electrolyzer with pure water will lead to significant cost saving both in catalyst materials and allow for less expensive stainless-steel current collectors. More recently, an alkaline water electrolyzer with iron and nickle based PGM-free based anode catalysts has demonstrated promising performance while operating on pure water.

Reference

Abbasi, R., Setzler, B. P., Lin, S., Wang, J., Zhao, Y., Xu, H., Pivovar, B., Tian, B., Chen, X., Wu, G., Yan, Y., A Roadmap to Low‐Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers. Mater.2019, 31, 1805876
(Invited) High-Temperature Alkaline Water Electrolysis Using Composite Ceramic-Molten Hydroxide Membrane
Authors: Lattimer Judith , Xu Hui , McCatty Steve , Mohan Yamini , Singh Prabhakar , Rahman Muhammad Anisur , Aphale Ashish
Published: July 2021

Hydrogen production from water electrolysis for mobile and energy storage applications is attractive due to its high efficiency, fast ramp rates, and potential for the clean energy economy. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials (membrane, catalyst, and bipolar plates) and electricity consumption of the commercial electrolysis systems. We have developed a high temperature alkaline electrolyte-based water electrolyzer (HTAWE) that operates at 350-550 °C, enabling high reaction rates while limiting thermal degradation compared to solid oxide cells operating above 700 °C. This water electrolyzer is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. This HTAWE can simultaneously reduce the electrolyzer cost (by adopting cheap material) and improve energy efficiency (by enabling high-temperature operation).

Using an innovative new SrZrO3-based matrix, we have demonstrated exceptional water electrolysis performance using both single and binary hydroxide mixtures. We successfully achieved sustained cell performance of 1.35 V at a current density of 1,000 mA/cm2 with area specific resistance (ASR) 0.1 Ohm-cm2 across the cell at furnace temperature 500 °C. We were also able to demonstrate cell performance of 1.45 V at a current density of 1,000 mA/cm2 with ASR of <0.2 Ohm-cm2 across the cell at a furnace temperature 400 °C. Furthermore, we have demonstrated stable cell performance for >1000 h of continuous operation at 1 A/cm2 with ASR of 0.2 Ohm∙cm2 across the cell.
Enabling Efficient Water Splitting with Advanced Materials Designed for High pH Membrane Interface
Authors: Kendrick Ian , Gerhardt Michal , Weber Adam Z. , Rojas-Carbonell Santiago , Wang Lan , Yan Yushan , Mukerjee Sanjeev
Published: July 2021

This research focuses on durable, high-performance materials and interfaces for advanced water splitting, enabling a clear pathway for achieving <$2/KgH2 (on scale) via anion exchange membrane (AEM)-based electrolysis. We aim to advance this goal via an improved fundamental understanding of both hydrogen and oxygen evolution reactions (HER/OER) leading to platinum group metal (PGM)-free catalyst materials. Here, we use NiFeCo and NiMo as OER and HER catalysts, respectively, in a full alkaline electrolysis cell. A thermally stable, multi-cation AEM is used to operate the cell at elevated temperatures thereby lowering the operating potential by increasing the kinetics of the respective catalytic reactions. The transition metal catalysts, paired with this novel AEM, have been used to achieve an operating potential of 1.79 V at 1 A/cm2. This potential is 300 mV lower than similar electrolysis cells equipped with PGM-based catalysts. We have also demonstrated the efficacy of the less caustic potassium carbonate solution as a replacement for potassium hydroxide as an electrolyte. By using a carbonate-based electrolyte, the hydroxide ion required for the anodic reaction is continuously replenished by re-establishing an equilibrium with water. This consideration, coupled with the reduced alkalinity of the carbonate solution, yields an electrolysis cell capable of sustained operation with minimal increase in operating potential.
(Invited) Membrane Coated Electrocatalysts for Seawater Electrolysis
Authors: Baxter Amanda F. , Beatty Marissa , Bhardwaj Amar , Esposito Daniel V.
Published: July 2021

One obstacle to the widespread adoption of water electrolysis powered by renewable sources is the availability of highly pure water required by conventional electrolyzers. This is particularly true for hot, dry coastal regions which have access to seawater and great potential for harvesting solar and wind energy, but where fresh water is often scarce. Additionally, seawater makes up 97% of the water on Earth, and although desalination is possible, it adds cost to the electrolysis system. Thus, direct seawater electrolysis could be a more cost effective approach to hydrogen production that doesn’t strain fresh water resources. However, direct seawater electrolysis is challenging due to the large concentration of Cl- ions, which can be detrimental to electrocatalyst stability and is a reactant for the undesirable chlorine evolution reaction (CER) that competes with the oxygen evolution reaction (OER) at the anode. Mitigating the CER is important because Cl2 is toxic and harmful to the environment.

Our group has shown that ultrathin semi permeable oxide overlayers can be designed to modulate transport of reactants to the active catalyst at the buried interface. Thus, the oxide overlayer acts as a membrane, rendering the material a membrane coated electrocatalyst (MCEC). An additional advantage of the MCEC architecture compared to conventional electrocatalysts is enhanced stability. The overlayer can act as a glue holding catalyst particles in place, which we have shown comparing SEM images before and after chronoamperometry in 0.6 M NaCl. This work describes how MCECs can be applied to seawater electrolysis to i) improve catalyst stability and ii) enable selectivity for OER over CER by impeding transport of Cl- ions to the buried interface.
Carbon Nanostructures-Transition Metal Oxide Hybrid As Bifunctional Electrocatalyst
Authors: Devi Hemam Rachna , Bisen Omeshwari Yadorao , Chen Zhong , Nanda Karuna Kar
Published: July 2021

The keen to replace coal and petroleum-based energy with renewable and environment friendly resources has persuaded the research in energy conversion and storage devices like metal-air batteries, fuel cell and electrolyzers. Oxygen electrochemistry that includes oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are sluggish reactions. RuO2/IrO2 and Pt-C are promising candidates in terms of the catalytic performance for OER and ORR, respectively. However, stability and the cost hinder its usage for large scale commercial applications. Therefore, rational designing of electrocatalyst that can overcome these sluggish reactions accounting their economic factor is important. Moreover, designing bifunctional catalyst remains a challenging issue till now. Carbon based materials have been extensively known for ORR whereas transition metal oxides show promising OER. 1
2 In this regard, we have synthesized a hybrid consisting of one-dimensional carbon nanostructures supported on Co-Ni oxide that shows efficient OER and ORR activity with low overpotential (OER), E1/2 (ORR), excellent stability and durability. The low Tafel slope for both OER and ORR reveals favorable reaction kinetics. Importantly, the hybrid offers ∆E (Ej=10 -E½) of 0.80 V that shows the promising bifunctional behavior. The overall study indicates that the hybrid catalyst is as potential candidate for OER/ORR and hence, expected to serve the energy storage device like metal-air batteries.

References

(1) Devi, H. R.; Nandan, R.; Nanda, K. K. Mechanistic Investigation into Efficient Water Oxidation by Co-Ni-Based Hybrid Oxide-Hydroxide Flowers. ACS Appl. Mater. Interfaces
2020, 12 (12), 13888–13895.

(2) Nandan, R.; Devi, H. R.; Kumar, R.; Singh, A. K.; Srivastava, C.; Nanda, K. K. Inner Sphere Electron Transfer Promotion on Homogeneously Dispersed Fe-N XCenters for Energy-Efficient Oxygen Reduction Reaction. ACS Appl. Mater. Interfaces
2020, 12 (32), 36026–36039.
(Invited) Photo-Electrochemical Hydrogen Production Systems Using III-V Semiconductors: Challenges in Scaling-up from an Electrode to a Device
Authors: Deutsch Todd G , Young James , Klein Walter , Steiner Myles
Published: July 2021

While III-V semiconductors have achieved the highest photo-electrochemical solar-to-hydrogen conversion efficiencies, they are remarkably unstable during operation in a harsh electrolyte. The first part of this talk will focus on the degradation mechanism of inverted metamorphic mulijunction (IMM) III-V cells and surface modification strategies aimed at protecting them from photocorrosion. We applied noble metal catalysts, oxide coatings by atomic layer deposition, and MoS2 in an effort to protect the GaInP2 surface that was in contact with acidic electrolyte. We also grew epitaxial capping layers from III-V alloys that should be more intrinsically stable than GaInP2. The ability of the various modifications to protect the IMM’s surface was evaluated by operating at each electrode at short circuit for extended periods of time.

The second part of this talk will identify the challenges encountered while scaling the IMM III-V absorber areas of from ~0.15 cm2 up to 16 cm2 and incorporating them in a photoreactor capable of generating 3 standard liters of hydrogen in 8 hours under natural sunlight. To successfully scale photo-electrochemical water-splitting technologies from bench to demonstration size requires addressing predictable and unpredictable complications. Despite using Comsol multiphysics to model our photoreactor and identify suitable specifications for a prototype, several practical issues were uncovered during testing that led to multiple iterations of photoreactor design between the initial and final generations. Several bottlenecks that ranged from counter electrode composition and orientation to bubble management needed redress in order to meet our performance targets. Ultimately, the demonstration-scale system was able to generate nearly twice the target volume of hydrogen in an 8-hour outdoor trial.
(Invited) Understanding the Mechanism of (photo)Electrochemical Transformations in Functional Architectures for Artificial Photosynthesis
Authors: Toma Francesca Maria
Published: July 2021

Stable and efficient catalytic architectures are a prerequisite for artificial photosynthesis. In order to achieve sustainable energy conversion and storage into chemical bonds, it is instrumental to understand the chemical transformation of these catalytic architectures under operating conditions. Our group uses different strategies to understand how the performance of a (photo)electrode is impacted by chemical transformations during operation. Specifically, we look at how functional, chemical, and structural heterogeneity over different length scales influences macroscopic performance and stability. Here, we will show how we combine photoelectrochemical measurements with atomic force microscopy based techniques, and scanning transmission X-ray microscopy to gain a complete understanding of different material systems, such as bismuth vandate, copper oxide, and gallium nitride, for their application in artificial photosynthesis.
(Invited) Insights and Strategies for Electrochemical Valorization of Lignin
Authors: Yang Cheng , Stephenson Corey , Maldonado Stephen
Published: July 2021

Electrochemically driven organic reactions offer several advantages for the realization of abundant and inexpensive chemical feedstocks and fuels. In this presentation, advances in both oxidative and reductive transformations germane to the valorization of lignin are presented. First, a comprehensive description of the reactivity of electrochemically-generated PINO radicals for electrocatalytic oxidation of benzyl alcohols is reported. A combination of voltammetric, chronoamperometric, and computational results are shown that detail the proton-coupled electron transfer behavior of NHPI for the generation of PINO radicals. The dependence of the base used with NHPI is shown, with an optimal pKa for subsequent electrocatalytic oxidation of lignin cogeners. Second, the fragmentation of beta-O-4 linkages in lignin through electrochemical reduction pathways are discussed. Data are shown that suggest fragmentation is possible with selectivity at judiciously chosen reaction driving forces. Selectivity and conversion yields are shown for a variety of conditions, with an emphasis on aspects that pertain to the rate-limiting mechanistic aspects. Time permitting, efforts to couple these insights with photoelectrochemical systems will be discussed.
(Invited) Understanding Multi-Component Transport and Reaction Phenomena in Bipolar Membranes Used for Electrosynthesis
Authors: Bui Justin C. , Bell Alexis T. , Weber Adam Z.
Published: July 2021

Bipolar membranes (BPMs), which have long seen usage in electrodialysis reactors for the generation of acid and base, have recently demonstrated potential to become critical components in electrochemical synthesis devices. Because they can operate under large pH gradients, BPMs enable favorable environments for electrocatalysis at the individual electrodes. Critical to the implementation of BPMs in these devices is understanding the kinetics of water dissociation that occurs within the BPM junction as well as the co- and counter-ion crossover through the BPM, which both present significant obstacles to developing efficient and stable BPM-devices for electrosynthesis applications. Prior work has modeled ion transport in bipolar membranes in neutral salt solutions for electrodialysis. However, no model exists for the BPM under the harsh applied pH gradients that would be present in electrosynthesis, and there is significant need to explore the effects of the internal hydration on the lifetime and performance of BPMs in such environments. Additionally, a mechanistic understanding of water dissociation catalysis will be required to develop interfacial catalysts that enable the high current density operation required for scalable electrosynthesis of fuels.

In this talk, we discuss modeling methodologies and physics inherent in BPMs and present our recent model of ion transport and water dissociation catalysis in BPMs across the pH scale. Specifically, we simulate multi-ion transport for a BPM with various electrolyte combinations on each side of the membrane, demonstrating the significance of co- and counter-ion crossover in BPMs operating under harsh pH gradients. We then investigate effects caused by hydration gradients that occur due to internal ion-exchange and examine potential methods for improving performance and mitigating crossover. Finally, we examine the impact of the interfacial water dissociation catalyst and perform sensitivity analysis on the key properties (catalyst point of zero charge and pKa) that dictate catalyst performance. These results provide information that is critical to developing a comprehensive understanding of multi-component phenomena in BPMs and to informing the design and implementation of BPMs in next-generation devices for the numerous electrosynthesis chemistries that benefit from operation under an applied pH gradient.
Novel Perovskites Containing Ba, Mg, Ca, Nb, Fe and Ta for Electrochemical Oxidative Coupling of Methane
Authors: Ramaiyan Kannan , Denoyer Luke H , Benavidez Angelica , Garzon Fernando H
Published: July 2021

Methane is the major component of many gas sources such as natural gas and shale gas and more than 500 million tons of methane is produced every year. Unfortunately, most of it is burnt as an energy source due to difficulties in converting it into easily transportable fuels. Oxidative and non-oxidative coupling of methane (OCM and NOCM) has been actively researched to produce ethylene and higher olefins from methane although catalysts with commercially viable conversion rates have not been developed yet.[1] Electrochemical OCM (EC-OCM) is gaining attention due to its ability to regulate the oxide ion flux that will help reduce the over-oxidation of methane while also helping to activate methane.[2] Fe based catalysts have been shown to activate methane in both OCM and NOCM although suffer from coking related durability challenges. We have developed two novel perovskites comprising Ba, Ca, Mg, Nb and Ta where incorporation of Fe in the crystal lattice has resulted in mixed ionic electronic conductivity. Their physical and chemical properties are evaluated using TGA, XRD, XPS and FT-IR measurements. We further examined these catalysts for EC-OCM along with structural and chemical stability characterizations. Both these perovskites show very good chemical stability in methane under EC-OCM conditions. TGA under methane environment further reveal adsorption of methane on our perovskite material at about 600°C. Ethylene production was observed to increase with increasing Fe content in the perovskite structure. In this presentation we report our findings on the application of both perovskites towards EC-OCM and discuss potential future directions.

References

Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017.

Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.