Understanding and addressing impedance scattering in low-temperature electrolysis

Energy dispersive X-ray spectroscopy (EDX) and electron diffraction and high-resolution electron microscopy are used to study the composition and structure of anode and cathode deposits formed during the high temperature (950°C) electrolysis of the Y-Ba-Cu-O system and low temperature (450°C) electrolysis of the Y-Ba-Cu-K-O system. It is found for the first time that an oxide with the YBa2Cu3Oy structure (123 phase) is synthesized during the high temperature electrolysis of Y0.02Ba0.30Cu0.70Oy and Y0.02Ba0.25Cu0.75Oy melts. The 123 phase is not synthesized during low temperature electrolysis, where melts are formed from Y2O3, BaO2, CuO, and KOH. Two new Pt-containing oxides with hexagonal structure are found in the products of high temperature electrolysis.

The U.S. Department of Energy (DOE) is supporting a wide range of research and development efforts that fall under the umbrella of low temperature electrolysis (LTE). These efforts range from early stage R&D on cell components to demonstrating the effectiveness of integrating MW-scale electrolyzer systems with the electric grid to provide ancillary services. LTE is included in multiple initiatives led by the Fuel Cell Technologies Office (FCTO) at DOE’s Office of Energy Efficiency and Renewable Energy (EERE). Low temperature electrolysis is one of four pathways being supported under DOE’s HydroGEN Energy Materials Network (EMN) Consortium on Advanced Water Splitting Materials (AWSM) for H2 production. The HydroGEN EMN offers an extensive collection of materials research capabilities at 6 core national laboratories for addressing AWSM R&D challenges in efficiency, durability, and cost. The LTE work supported under HydroGEN includes early stage R&D in membranes and catalysts for both PEM and AEM electrolysis. Low temperature electrolysis also has a role in DOE’s H2@Scale energy system vision. This initiative is bringing together diverse stakeholders to advance affordable wide-scale hydrogen production, transport, storage, and utilization to unlock revenue potential and value across multiple sectors. The use of low-cost electricity to affordably split water into hydrogen and oxygen is central to implementation of the H2@Scale concept. Work is also being carried out on electrolyzer manufacturing, benchmarking, protocol development, and technoeconomic analysis. An overview of FCTO-supported activities related to these initiatives and topics, and the role of LTE in them, will be provided.

In low temperature electrolysis, anion exchange membrane (AEM) systems combine the advantages of alkaline and proton exchange membrane (PEM) electrolysis in generating high purity hydrogen and reducing material costs from catalysts and component coatings [1]. Recent studies in AEM electrolysis have focused on improving cell performance, minimizing catalyst dissolution and mitigating ionomer/membrane degradation with different operating conditions. Ionomers play a critical role in the electrode because they provide ion conductivity, enhance mechanical support, and create preferred morphologies for electrolyte and produced gas to move [2, 3]. Optimizing catalyst-ionomer interactions by varying ionomer content, chemistries, and forms can accelerate the development of AEM electrolysis in terms of performance enhancement, cost and lifetime.In this work, different forms of ionomer (powdered and dispersed) with two polymer backbones were evaluated in AEM electrolysis cell testing. Ni- and Co-based oxides and IrO2 were applied as anode catalysts. In Figure 1, the anodes with powdered ionomer outperform the dispersed samples. With Co3O4 catalyst, the overpotential can be improved by 0.9 V at 1 A/cm2 (iR-free voltage of Co3O4 with powdered ionomer: 1.68 V at 1 A/cm2). By electrochemical diagnostic and modeling methods, the improved performance with powdered ionomer is attributed to better reaction kinetic from more active area between catalysts and ionomers, less ohmic overpotentials due to better contact between the electrode and the transport layer and preferred transport properties with higher porosity created by powdered ionomer. Scanning electron microscopy data verifies that the anodes with powdered ionomer provide more homogeneous distribution of catalysts and ionomer in the electrode, while dispersed samples have the issues of agglomerates and uneven coverage of catalysts, which could worsen the catalyst utilization and trigger mass transport issues.[1] Ayers, Katherine, et al. "Perspectives on low-temperature electrolysis and potential for renewable hydrogen at scale." Annual review of chemical and biomolecular engineering 10 (2019): 219-239.[2] Lee, Sol A., et al. "Anion exchange membrane water electrolysis for sustainable large‐scale hydrogen production." Carbon Neutralization 1.1 (2022): 26-48.[3] Favero, Silvia, Ifan EL Stephens, and Maria‐Magdalena Titirci. "Anion Exchange Ionomers: Design Considerations and Recent Advances‐An Electrochemical Perspective." Advanced Materials 36.8 (2024): 2308238. Figure 1

Hydrogen has unique advantages as an energy carrier due to its high energy density and abilities in long-term storage and to convert between chemical bonds and electricity. [1] Although hydrogen currently has a small role in energy pathways, decreasing electricity prices can allow for significant growth. Anion-exchange-membrane water electrolysis (AEMWE) holds promise for reaching reduced hydrogen production cost targets, particularly from a materials perspective, and is the primary technology pathway being studied under Low Temperature Electrolysis in the HydroGEN Energy Materials Network (EMN). In AEMWE, it has been critical to explore the impact of materials and their integration on performance and durability, thereby demonstrating and enhancing use opportunities. [2] While platinum group (PGM) -free components, including catalysts and transport layer/separator coatings are readily available that can achieve high performance at a reduced cost, individual properties and their interactions create integration challenges.[3] Specifically in performance, the inclusion of ionomer and pore structures can be more complicated than for acidic systems and the use of PGM-free materials can add difficulties in electronic and ionic transport. While AEMWE can become extremely durable when targeted for low-cost applications, additional loss sources including ionomer oxidation, materials passivation (catalyst, transport layer, separator) further complicates identifying and separating irreversible loss mechanisms, and in developing accelerated stress tests. This presentation includes an overview of efforts in AEMWE and focuses on materials choices, catalyst-ionomer-transport layer interactions, and the variety of integration strategies being employed in the HydroGEN EMN.

Stability of catalyst materials during operation is essential for long-term operation of large-scale chemical reactors. This is particularly true for costly electrochemical reactors and their harsh reaction conditions in terms of potential and pH, as for instance also occurring during low temperature electrolysis. Fundamental studies can provide quick and deep insights into material performance, optimized operation conditions, or degradation mechanism and extent, which altogether can contribute to the development of improved materials and membrane-electrode assemblies. In this presentation I will show recent results with a special focus on catalyst dissolution during oxygen and hydrogen evolution in electrolysis. I will discuss denominators for the assessment of stability of novel materials, degradation mechanism, measurement artifacts and pitfalls, as well as the relevance of the results for reactor operation.

As part of any overall strategy for environmental sustainability, a source of renewable hydrogen is needed, as a chemical feedstock as well as part of the portfolio of energy storage solutions. Currently over 95% of hydrogen is made from fossil fuels through natural gas reforming or coal gasification. However, water electrolysis has decreased significantly in capital cost and increased in scale. At the same time, renewable electricity costs have also dropped, especially in periods of high capacity, providing a potential pathway for competitively priced “green” hydrogen from water splitting. Still, continued materials and manufacturing research is essential to achieve cost parity with fossil fuels and produce renewable hydrogen at scale. As new materials are developed, it is important to make accurate comparisons to a common baseline, to understand the potential for improvement over existing technology and to compare different pathways. Currently, research on electrolysis materials published in the scientific literature tends to be scattered across a range of test conditions and configurations, making these comparisons difficult. For example, catalysts may be tested with a range of membranes, at different temperatures, with different counter electrodes, and different electrolytes. In addition, test configurations can impact performance and cause variation in results even for the same materials. Having a standard baseline set of conditions can ground the results, even if additional tests are also performed to look at benefits of specific conditions for specific materials. There are currently efforts in both Europe and the United States to select common standards and define test parameters and configurations for low temperature electrolysis. The U.S. Department of Energy is funding a team to coordinate similar work across all of the major water splitting pathways: low temperature electrolysis (primarily ion exchange membrane-based), high temperature electrolysis (primarily solid oxide), solar thermochemical water splitting (STCH), and direct photoelectrochemical water splitting (PEC). This talk will describe status of this project, including a workshop held in October 2018 and follow up work for specific materials tests.

Anode Catalyst Durability in Low Temperature Electrolysis and the Impact of Hydrogen CrossoverShaun Alia,1 Kimberly S. Reeves,2 Haoran Yu,2 Elliot Padgett,1 Deborah Myers,3 David Cullen2 1 Chemical and Material Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 3 Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IllinoisHydrogen has unique advantages as an energy carrier, with a high energy density and abilities for long term storage and conversion between electricity and chemical bonds. Although hydrogen currently has a significant role in transportation and agriculture, its use in energy consumption overall has been limited, particularly in the case of electrochemical water splitting. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for an opportunity for greater use.(1) While load-following renewable power sources can reduce feedstock cost, further cost reductions can be achieved by reducing the platinum group metal (PGM) content.(2) Efforts are needed to understand and mitigate electrolyzer degradation, particularly when accounting for lower PGM loadings and intermittent operation.Previous efforts have developed anode catalyst-specific accelerated stress tests for intermittent operation that focused on catalyst layer changes and interfacial loss with standard material sets. (3) Under cycled testing between open circuit and operating potentials, performance losses primarily appeared through kinetics and were accompanied by anode catalyst dissolution, migration, and interfacial tearing. Performance losses were further aggravated by a reduced anode catalyst loading or a thinner catalyst layer, an increase in cycling frequency, and an increase in cell potential.In this study, the impact of hydrogen crossover on anode catalyst durability during device shutdown was evaluated and found to significantly increase performance loss through catalyst reduction and higher dissolution kinetics when operation resumed. Large drops in kinetics accounted for the majority of cell performance changes and corresponded to increased anode catalyst migration and aggregation within the catalyst layer. Compared to intermittent operation, however, ohmic losses disproportionately grew and higher rates of interfacial tearing were found ex-situ, particularly when simulated shutdowns incorporated brief periods of water deprivation and drying. While various anode catalyst types were evaluated for their potential in materials mitigation, high loss rates were found in all cases. Sub-stoichiometric oxides may be a driver for performance losses due to increase subsurface metal dissolution once near-surface oxides are reduced. Understanding catalyst layer degradation and the impact of shutdowns is critical to developing catalyst- and device-level accelerated stress tests and forming operational mitigation strategies.[4][1] B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018).[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual Review of Chemical and Biomolecular Engineering, 10, 219 (2019).[3] S. M. Alia, S. Stariha and R. L. Borup, J. Electrochem. Soc., 166, F1164 (2019).[4] Electron microscopy was performed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Low temperature electrolysis (LTE) is the most promising method for fully renewable hydrogen production. However, to compete with current hydrogen production methods (which produce CO2), substantial cost reductions and efficiency improvements are necessary. Of the various LTE technologies, liquid alkaline (LA) electrolysis is the most mature. It has proven large scalability and can operate with all earth-abundant materials. However, most conventional LA electrolyzers are limited to lower current density operation than newer LTE technologies.Most LA electrolyzers operate with uncatalyzed Ni anodes, despite the existence of many highly active catalysts for oxygen evolution in alkaline conditions. This is because catalyzed systems require constant operation, as the catalyst layers degrade and delaminate rapidly upon exposure to the reverse polarization conditions experienced during system shutdown. This limitation prevents the integration of catalyzed electrodes, as even a single unexpected plant shutdown causes significant efficiency and cost losses. Further, this prevents fully catalyzed LA electrolyzers from directly operating with renewable power sources with large power fluctuations. Therefore, the development of reverse-current tolerant catalyst layers is essential to enable high-efficiency renewable energy powered LA electrolyzers.This talk will detail the mechanisms of electrode degradation during electrolyzer system shutdown. Our findings reveal anode catalyst layers fail through a combined electrochemical and mechanical degradation mechanism. I will discuss key differences in the cathode versus anode operating environments that explain the difference in reverse current tolerance. Considering these results, I will highlight priority research and development directions for developing anode and cathode catalysts for renewable-powered LA electrolyzers.

Low temperature electrolysis (LTE) is a very promising technology that can support the decarbonization of the energy sector through the production of hydrogen from water using renewable energy sources. For the introduction of LTE at scale several advances are required such as the reduction of voltage losses and platinum group metal (PGM) loadings without sacrificing the current lifetimes of 60000+ hours. Thrifting these PGM materials will be one essential step to reduce the component cost. In LTE systems PGM materials are used as catalysts, i.e. IrOx on the anode and platinum (Pt) supported on high surface carbon on the cathode, and also as protective coatings of the titanium base anode PTLs. At the acidic conditions and high potentials of the anode titanium develops an oxide layer that passivates the material surface with regards to its thermal and electrical conductivity and hampers the functionality of the LTE device. The literature shows that this process can be prevented by applying a protective PGM layer to the PTL. In this presentation we discuss the effect of PTL coating thickness on cell performance and contact resistance. PTL coatings were systematically varied by physical vapor deposition and the resulting PTL materials were subsequently measured using in-situ and ex-situ diagnostics and a range of operating conditions. Results will be discussed in detail during the presentation and indicate that the PTL / catalyst layer interface is key to high performance electrolysis performance. Note that PTL materials were additional characterized at the nano scale with techniques such as ToF-SIMS, STEM-EDS, FIB, SEM, EDS. These results will be reported in separate talks.

Hydrogen is an important part of any discussion on sustainability and reduction in emissions across major energy sectors. In addition to being a feedstock and process gas for many industrial processes, hydrogen is emerging as a fuel alternative for transportation applications. Renewable sources of hydrogen are therefore required to increase in capacity. Low-temperature electrolysis of water is currently the most mature method for carbon-free hydrogen generation and is reaching relevant scales to impact the energy landscape. However, costs still need to be reduced to be economical with traditional hydrogen sources. Operating cost reductions are enabled by the recent availability of low-cost sources of renewable energy, and the potential exists for a large reduction in capital cost withmaterial and manufacturing optimization. This article focuses on the current status and development needs by component for the low-temperature electrolysis options.

We have developed a method that involves the generation of a “cation pool” using low-temperature electrolysis, and then its reaction with nucleophiles under non-oxidative conditions. This one-pot method solves problems associated with conventional oxidative generation of cations and their in situ reaction with nucleophiles, and provides an efficient method for direct oxidative carbon−carbon bond formation. As an example of this method, generation of cation pools from carbamates by low-temperature electrolysis (−72 °C) and their reactions with carbon nucleophiles such as allylsilanes, enol silyl ethers, and enol acetates were examined and the desired products were obtained in good yields. Aromatic compounds and 1,3-dicarbonyl compounds can also be utilized as carbon nucleophiles. The present method was also applied to combinatorial parallel synthesis using a robotic synthesizer.

Techno-economic assessment of hydrogen-based energy storage systems in determining the optimal configuration of the nuclear-renewable hybrid energy system

Hydrogen has several attributes that provide advantages compared to other storage options, including high energy density, viability as a long-term storage solution, and an ability to convert between electricity and chemical bonds. (1) Although hydrogen’s role in in energy pathways has been limited to transportation and agriculture, decreasing electricity prices and electrolyzer cost reduction can allow for growth. While cost reduction through proton exchange membrane electrolysis will in part rely on platinum group metal (PGM) thrifting and economies of scale, anion exchange membrane (AEM) -based electrolysis holds additional promise due to the high pH environment, enhanced durability, and the enabling of PGM-free materials. (2)Within the HydroGEN Energy Materials Network (EMN), investigations of low temperature technologies have been developing an improved understanding of AEM electrolyzers. Efforts have included a focus on durability, including understanding degradation mechanisms and the durability of different components, establishing a loss rate and status for AEM electrolysis, and determining the resulting impact on electrolyzer lifetime. In AEM electrolysis durability, the largest durability consideration has typically been catalyst-ionomer interactions and how polymer oxidation at high potential can result in loss of site-access and interfacial contact. (3) Other concerns, however, include passivation losses, cathode contributions, and poor catalyst/transport layer and interfacial properties and their changes over time. Additionally and with materials variability, the dissolution and migration of other elements occurs. By separating the degradation of different components and processes, broader community recommendations are provided in the development of catalyst layers, transport layers, and polymers, as well as guidance on integration approaches of those materials.

N-Acyliminium ions having a piperidine skeleton were attractive because the functionalized piperidines frequently show interesting biologically properties. The “indirect cation pool method” 1) is useful to prepare a solution of synthetically valuable N-acyliminium ions having a protecting group that is labile under acidic conditions, because organic cations can be generated and accumulated under neutral conditions. In this presentation we demonstrated utilities of highly enantiomerically enriched chiral N-Acyliminium ions bearing a piperidine skeleton, which are generated by the indirect cation pool method. Almost enantiomerically pure chiral precursor 2 was prepared by using the enantioselective lithiation strategy using chiral diamine 1 (Scheme 1).2) N-Acyliminium ion pool 3 was then irreversibly generated from 2 by the treatment of ArS(ArSSAr)+, which was generated by low temperature electrolysis (Scheme 2). The reaction of 3 with allylstannane gave trans isomer in high diastereomer and enantiomer ratios. In contrast, the coupling between 3 and allylmagnesium bromide afforded cis isomer in high stereoselectivity. As a result, we could selectively synthesized two 1) Suga, S.; Matsumoto, K.; Ueoka, K.; Yoshida, J. J. Am. Chem. Soc. 2006, 128, 7710-7711. Matsumoto, K.; Suga, S.; Yoshida, J. Org. Biomol. Chem. 2011, 9, 2586-2596. 2) Coldham, I.; O’Brien, P.; Patel, J. J.; Raimbault, S.; Sanderson, A. J.; Stead, D.; Whittaker, D. T. E. Tetrahedron: Asymmetry 2007, 18, 2113–2119. Figure 1

This work analyzes pressurized, tubular, proton-conducting, ceramic reversible fuel cells (PreTProCRFC) for efficient, low-cost energy storage. PreTProCRFC have the potential to facilitate low carbon energy economies and power-to-gas applications. In the power-to-gas concept, excess electricity from wind turbines and solar photovoltaic arrays is sent to high temperature electrolyzers, like the PreTProCRFC, that store energy as hydrogen (H2) and oxygen (O2) for short or long durations (> 4 hours). When electricity is needed, the PreTProCRFC runs as a fuel cell and consumes the stored H2 and O2 to generate electricity. In this way, PreTProCRFCs have the potential to significantly augment the growth of renewables globally. This research analyzes the potential for PreTProCRFCs as viable short or long-term energy storage devices. This work develops thermodynamic and techno-economic analyses (TEA) for these PreTProCRFC systems and identifies cost drivers important to their R&D and commercialization path. This work also explores the value propositions presented by pressurized, tubular designs, for different segments of the energy storage market.Approach:This work is conducted in close collaboration with project partners Special Power Sources Inc. (SPS), which currently manufactures tubular ceramic fuel cells for research and niche energy applications, and Kansas State University (KSU), which is developing novel, proton-conducting ceramic materials. To execute this research, Gaia works with SPS and KSU to identify and analyze cell, stack, and system engineering performance data. Gaia then develops and deploys custom computer models and data sets that include, but are not limited to, chemical engineering process plant designs of PreTProCRFC systems and detailed TEA models. Gaia also builds on existing U.S. DOE modelling tools, such as the H2A H2 production analysis modelling tools and existing DOE electrolysis case studies.Results:Modelling results indicate that the primary cost drivers for the lifecycle energy storage costs of PreTProCRFC systems include, but are not limited to,(1) the system’s ramp rate in fuel cell mode (i.e. the electric power output per unit time);(2) the system’s ramp rate in electrolysis mode (i.e. the electric power input per unit time);(3) the quantity of effective heat reuse between exothermic fuel cell modes and endothermic electrolysis modes;(4) the efficiency of thermal storage between fuel cell and electrolysis modes;(5) the electricity consumed per unit of hydrogen produced in electrolysis mode;(6) the electricity consumed per unit of oxygen produced in electrolysis mode;(7) the capital costs of the stack;(8) the capital costs of the surrounding balance of plant (BOP) subsystems;(9) the electrolysis outlet pressures for hydrogen and oxygen; and(10) the marginal increase in system cost with higher electrochemical outlet pressures.Regarding (1) and (2), when connected to the electricity grid, and receiving intermittent renewable electricity to store, PreTProCRFC systems need the capability to respond rapidly. Electricity storage devices that can either receive and/or supply electricity more quickly can demand a higher premium ($/kWh price). In particular, the electricity balancing market is a submarket within the overall electricity market responsible for reconciling instantaneous differences in electricity supply and demand, and, consequently, sees the highest prices. The proposed SPS PreTProCRFC stack design is tubular, with less total sealant area, and with a close match of stack material thermal expansion coefficient, so it is expected that this design will more readily electrically ramp compared with other designs. (A main failure mechanism of high temperature electrochemical systems under fast-ramping conditions is mechanical cracking of the stack’s materials, due thermal expansion coefficient mismatches.)Regarding (3), (4), (5), and (6), a unique feature of high temperature electrolysis (compared with low temperature electrolysis) is that electricity consumption by the electrolyzer can be displaced by heat consumption, in a one-to-one ratio. In a PreTProCRFC system, heat released during the exothermic fuel cell reaction can be stored and reused to provide heat for electrolysis. Efficient design of this heat reuse subsystem is crucial to the PreTProCRFC system achieving high round-trip efficiencies, a necessity for the energy storage market.Regarding (7) and (8), primary cost drivers for PreTProCRFC system also include stack capital costs, stack power density, and system BOP costs. Over time, stack capital costs are estimated to decline more rapidly with R&D and more high volume manufacture, compared with BOP capital costs, because the BOP already incorporates many mass-produced components.Regarding (9) and (10), the SPS PreTProCRFC stack is also unique in that it has the capacity to supply hydrogen and oxygen at pressure. Model results indicate that electrochemical compression has the most compelling cost advantage over mechanical compression in the lower pressure range included in the proposed stack design.