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An anode electrode concept of thin catalyst-coated liquid/gas diffusion layers (CCLGDLs), by integrating Ir catalysts with Ti thin tunable LGDLs with facile electroplating in proton exchange membrane electrolyzer cells (PEMECs), is proposed. The CCLGDL design with only 0.08 mg

Membrane (PEM)-based electrolysis provides an ideal near-term technology to address the growing energy storage demands as intermittent renewable energy becomes more prevalent. While proton exchange membrane (PEM) systems are often viewed as preferred solutions to legacy KOH systems due to the lack of corrosive electrolyte, small footprint, dynamic operating range and ability to generate hydrogen at differential pressure, they still present capital cost challenges. In particular, the platinum group metal catalysts and valve metals for separator and flow field construction required for stability in the acidic environment become a significant cost driver at scale. Alkaline exchange membrane (AEM)-based electrolysis is therefore viewed as a potential replacement to the current PEM systems as a means of driving down the high capital cost. This cost reduction is accomplished by replacing the typical high cost catalyst and materials of cell construction with lower cost metals that would corrode in the acidic PEM environments, but are stable in the alkaline chemistries. In theory, this approach is highly promising, but testing of the current state-of the art has shown the technology gaps between the two platforms in terms of stability, durability, and operating electrical efficiency. Modeling has shown that savings realized in capital cost are typically off-set by an increase in operating expense resulting from the lower activity of the non-PGM catalysts and poor conductivity of the AEM. Additionally, thermal instability of the AEMs require stacks to be operated at lower temperatures than a typical PEM system, impacting conductivity further and slowing kinetics. Recent activities have looked at improving the mechanical properties, through the addition of mechanical reinforcements, to support pressurized operation, while operating temperature and varied concentrations of liquid electrolyte to the water feed have been explored to operationally evaluate the impact on performance and durability. The latter of these operating parameters have been shown by some groups to be effective in reducing cell operating potentials and providing overall voltage stability. However, this solution adds management and additional maintenance of handling the caustics typically used. Efforts at Proton continue to show improvements in short duration operational tests under milder conditions and potential pathways to achieve targets required to compete with incumbent technology. In this talk, some of the advancements achieved and how these have impacted the cost of the hydrogen will be discussed, as well as the longer-term targets that need to be reached in order to be a viable commercial application. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the AEM electrolysis technology cost, show the critical areas to focus on to establish equivalence with current PEM systems and what is required to go beyond. Figure 1

Proton exchange membrane (PEM) electrolysis and anion exchange membrane (AEM) electrolysis are both able to directly produce high purity hydrogen from electricity and water. Key benefits of electrolysis using polymer membrane separators include a quick response rate, enabling load following, and ability to operate with high differential pressure. Operation under differential pressure allows for simultaneous electrolysis and electrochemical compression, simplifying overall system design. The development and stack integration of new, high performance electrolysis materials must include consideration of operating range and durability under differential pressure to maintain the technologic benefits. PEM electrolyzers are commercially available on the megawatt scale and produce hydrogen fuel that is increasingly cost competitive with fossil fuel in select parts of the world. Better utilization of low cost electricity from renewable energy (wind and solar) is one route to additional hydrogen cost reductions, for which a wide current operating range is beneficial. Thinner membranes, more active catalysts, and better electrode design enable high currents at acceptable cell efficiencies. Performance and durability data will be presented on state-of-the-art PEM electrolyzer materials operating under differential pressure. AEM electrolyzers are not currently commercially available, but promise membrane, catalyst, and balance of stack cost reductions. To begin to compete with PEM technology, performance and durability need to be improved. This work focuses on membrane stability under differential cell pressure and material integration into high performance AEM electrolyzers.

Proton exchange membrane water electrolyzers (PEMWEs) are the major components of the green source of high-purity hydrogen for chemical applications as well as energy storages. However, some technical and economic problems have restricted their widespread development. One of the principal technical issues hampering the extensive use of PEMWEs is hydrogen crossover. The produced hydrogen in the PEMWE cathode compartment is typically stored at high pressure through either an external compressor or electrochemical compression with high pressure PEMWEs which leads to a high overall efficiency [1-3]. However, some produced hydrogen passes through the proton exchange membrane restricting the cell performance, especially when operating under pressure [1, 4]. The hydrogen crossover also causes a serious safety hazard in the anodic compartment where the oxygen is produced because the lower explosion limit of hydrogen in oxygen content is about 4 vol.%. It has been shown that a mitigation strategy is needed to reach this value with a safety margin of 2 vol.% [4, 5]. Although several mitigation strategies have been utilized, the integration of a recombination layer incorporated directly into the membrane has shown the best performance. Recently, Klose et al. [4] showed that integrating Pt nanoparticles as a recombination layer with Pt loading of 0.02 mg cm-2 between a NR-212 and a N115 membrane of a PEMWE can significantly overcome the safety issue. The results indicated no hydrogen in oxygen after 245 hours at 1 A cm-2 which demonstrates the Pt recombination layer effect on hydrogen crossover reduction. However, a strong increase for hydrogen in oxygen content was observed at higher current densities (>1 A cm-2). Thus, a further investigation is still needed to achieve a better recombination layer by optimizing Pt nanoparticles distribution or the position of the recombination layer. In this work, a novel electrode fabrication method, reactive spray deposition technique (RSDT), was employed to deposit a Pt recombination layer directly introduced into the membrane. The microstructural characteristics of the Pt recombination layer were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thereafter, the stability and cell performance of a full RSDT catalyst coated membrane (86 cm2) were investigated using diagnostic tests including polarization analysis, cyclic voltammetry, and electrochemical impedance spectroscopy. The results revealed significant stability for 1000 hours at 1.8 A cm-2, 50 °C, 400 psi hydrogen pressure with lower catalyst loading compared to commercial membrane electrode assemblies (MEAs) and > 65% reduction in hydrogen crossover. References [1] M. Schalenbach, M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Pressurized PEM water electrolysis: Efficiency and gas crossover, International Journal of Hydrogen Energy, 38(35), (2013), 14921-14933. [2] K. Onda, T. Kyakuno, K. Hattori, K. Ito, Prediction of production power for high pressure hydrogen by high-pressure water electrolysis, Journal of Power Sources, 132(1–2), (2004), 64-70. [3] B. Bensmann, R. Hanke-Rauschenbach, I. K. Pena Arias, K. Sundmacher, Energetic evaluation of high pressure PEM electrolyzer systems for intermediate storage of renewable energies, Electrochimica Acta, 110, (2013), 570-580. [4] C. Klose, P. Trinke, T. Bohm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, S. Thiele, Membrane Interlayer with Pt Recombination Particles for Reduction of the Anodic Hydrogen Content in PEM Water Electrolysis, Journal of Electrochemical Society, 165(16), (2018), F1271-F1277. [5] H. Janssen, J.C. Bringmann, B. Emonts, V. Schroeder, Safety-related studies on hydrogen production in high-pressure electrolysers, International Journal of Hydrogen Energy, 29(7), (2004), 759-770.

Commercial water electrolysis technologies, including proton exchange membrane electrolysis (PEMWE), are the only renewable hydrogen generation technologies that can achieve the U.S. Department of Energy (DOE) cost targets within the next ten years at the required scale, based on the supply chain maturity and materials performance. In particular, membrane and electrode modifications have enabled the use of advanced electrolysis membranes to achieve the efficiency targets, while nanoengineered alloy catalyst layers (CLs) have been pursued to meet the cost and efficiency targets. These advancements have been achieved by building the basic understanding to allow the successful technical development and include: (1) Mechanical and chemical understanding of membranes in liquid water below 90oC; (2) Characterization of as-deposited electrodes and MEAs after operation; (3) Water management in the anode catalyst layer, dependence on catalyst loading and porous transport layer form factor; and (4) Long-term degradation rate and stability of engineered alloy Ru-Ir alloy nanocatalysts in well-defined anode catalyst layers. Nel Hydrogen’s pathway to meet these DOE goals is through the i) use of 50-75% thinner membranes that operate at 80-90 oC, while controlling mechanical creep and gas crossover; ii) reducing the catalyst loading to 1/10th the current value on both electrodes, while controlling water distribution and the porous transport layer/catalyst layer (PTL/CL) electrochemical interface; iii) incorporation of a less stable but more active Ru containing catalyst managed on the anode side of the cell, which is achievable with lower voltage operation (accomplished via low ohmic drop in the anode catalyst layer, thinner membranes, and higher temperature operation); and iv) fabricating a membrane electrode assembly (MEA) integrating all of these characteristics. In this talk, some of the advancements achieved and how these have impacted the cost of hydrogen will be discussed, as well as the longer-term targets that need to be reached to provide the robustness required for commercial applications. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the PEM electrolysis technology cost, show the critical areas to focus on to provide the largest impact towards meeting cost target goals and what is required to go beyond. Figure 1

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.

Anion Exchange Membrane Fuel Cells (AEMFCs) are a developing alternative to Proton Exchange Fuel Cell (PEMFC) technology. A great advantage of this technology is the possibility of replacing PGM catalysts on both anode and cathode and therefore reducing the costs. For example several PGM-free electrocatalysts have demonstrated superior fuel oxidation performance[1]. In AEM electrolysis both Hydrogen [2] and Oxygen Evolution[3] PGM-free catalysts have been demonstrated. In the present work we present unprecedented performance of a Nickel-based Hydrogen Evolution (HER) catalysts that are bifunctional for the Hydrogen Oxidation (HOR) reaction. These Nickel-based catalysts are multifunctional catalytic systems and rely on g alloying and mixed and low-coverage complementary metal oxides to fine tune surface-electrochemical interactions and reactions. While the goal of the work is to create reversible HER/HOR PGM-free catalysts, the efforts to date were focused on making the most active nickel-based bifunctional HER and HOR catalysts. Next reversible electrodes will be developed and catalyst stability under HER/HOR mode switching will be tested. (ARPA-E OPEN 2015 DE-AR0000688) A series of nickel-based catalysts were synthesized to create mixed Nickel-alloys and oxides that promote the activation of water and hydroxyl groups on the catalysts. A range of wet-chemical routes was used to produce carbon-supported NiMo, NiCu, and NiMoCu supported on a range of standard and novel Interconnected Mesoporous Carbon™ supports. The materials were characterized through physical parameters such as crystal phase, size, and surface chemistry using XRD, XPS, and Raman Spectroscopy. These materials were evaluated in membrane electrode assemblies [MEAs] using a variety of membranes and ionomers. Unprecedented PGM-free HER performance exceeding 1000 mA/cm2 @ 1.9V and HOR performance exceeding 300 mA/cm2 @ 0.65V were achieved. Reversible MEA structures for these catalysts are still being optimized. References [1] U. Martinez, et al Phys. Chem. Chem. Phys. 14 (2012) 5512-5517. [2] Bates, M. et al J Phys Chem C Nanomater Interfaces. 2015 Mar 12; 119(10): 5467–5477. [3] Bates, M. et al ACS Catal., 2016, 6 (1), pp 155–161 Figure 1

Sustainable sources of hydrogen are a key need for reducing environmental impact of chemical processes, with over 95% of hydrogen for industrial applications currently made from fossil fuels through natural gas reforming or coal gasification. Hydrogen is an important industrial gas, representing a 10 million metric tons/year industry worth $100 billion. While proton exchange membrane (PEM)-based water electrolysis has been commercially available for many years, the production scale has been too small until recently to make large impacts. Also, because of the legacy of the technology in life support applications and lower R&D investment relative to PEM fuel cells, there is still significant room for cost and efficiency improvement of PEM electrolysis through materials and manufacturing advancements. This talk will discuss recent work in high efficiency catalysts and membranes and fundamental challenges in translating laboratory tests to manufacturable components. While catalyst composition and structure is important in understanding and increasing activity, integration is also a key part of materials and technology development. Solution data is not sufficient for predicting behavior in solid state electrolytes or interfaces with other cell components. Most laboratory experiments also do not provide sufficient information on durability beyond a screening tool for early stages of testing. A holistic approach is needed in materials, processing, and component interactions to advance the field. Current technology scale for PEM electrolysis and pathways for large scale renewable hydrogen production will also provide a framework for potential impact in the near term.

Hydrogen production by alkaline water electrolysis using hydroxide anion exchange membranes has seen a renewed interest as an alternative to traditional liquid alkaline water electrolyzers, proton exchange membrane (PEM) electrolyzers, and solid oxide water electrolyzers (1). Anion exchange membrane electrolyzers provide an efficient, modular, and reliable method to produce hydrogen from water and renewable electricity sources. One of the main benefits of anion exchange membrane electrolyzers arises from better oxygen evolution reaction (OER) kinetics in alkaline environments and the possibility of employing non-platinum group catalysts (non-PGM) and PGMs modified with transition metals for enhanced activity without suffering the stability problems common in acid media. However, one challenge is the sluggish kinetics for the HER in alkaline media. During our comprehensive research into active and stable OER catalysts for alkaline operation, pyrochlores emerged as among the most active and stable OER catalysts reported in the literature. Electrically conducting metal oxides (eliminating the need of a conducting support for the catalyst) with the pyrochlore structure (A2B2O7-y, with A=Pb or Bi and B= Ru, Ir or Os) were synthesized via precipitation/crystallization in alkaline medium and/or via solid-state reaction. The electrocatalytic activity for the oxygen evolution reaction (OER) in 0.1M KOH showed that lead and bismuth ruthenate pyrochlores had significantly lower overpotentials for the OER than the state-of-the-art IrO2 catalyst. Specific activities (at 1.5 V vs. RHE) of 3.0±0.2 Am-2, 1.3±0.2 Am-2 and 0.06±0.01 Am-2 were obtained for Pb2Ru2O6.5, Bi2.4Ru1.6O7, and IrO2 respectively. Specific activities for iridate-based pyrochlores (0.3-0.5 Am-2) were 5-10 times lower than those for ruthenate-based pyrochlores. Lead osmate pyrochlore showed the lowest OER activity among all the pyrochlores evaluated, with a specific activity of 0.10±0.07 Am-2. The exceptional OER activity and stability of lead ruthenate pyrochlore catalysts were evaluated in an anion exchange membrane water electrolyzer. The overpotentials obtained were 0.1-0.2 V lower than for IrO2 across the entire current density range and the performance was stable for at least 200 h. Since operation in alkaline media leads to more sluggish HER kinetics, we have evaluated ways to improve the HER catalytic kinetics of Pt electrocatalysts. Bifunctional electrocatalysts containing Pt clusters to combine the protons to form hydrogen gas, and hydrophilic domains able to help in water dissociation are promising candidates to substantially improve HER kinetics under alkaline conditions and to facilitate the introduction of commercial alkaline membrane water electrolyzers. The hydrophilic moieties that help the water splitting are varied. We have investigated nickel hydroxide and ruthenium oxide as co-catalysts together with Pt. Rotating disk electrode (RDE) measurements were performed in 0.1M KOH at temperatures ranging from 273.15 K to 303.15 K, and the HOR/HER kinetic currents, obtained after IR and mass transport corrections, were fitted using the Butler-Volmer equation to estimate the exchange current densities at each temperature. Arrhenius plots showed very similar activation energies for Pt/C (35±6 kJ/mol) and the bi-functional catalysts (38±6 kJ/mol) –Pt/C/X%Ni(OH)2. The maximum exchange current density (2.44±0.07 mA cm-2 Pt at 303.15 K) was obtained with the catalyst containing 10wt% Ni(OH)2, and was 2.4 times higher than for Pt/C (1.03±0.07 mA cm-2 Pt at 303.15 K). The bi-functional catalysts were evaluated in an anion-exchange membrane water electrolyzer operated with ultrapure water, and outperformed Pt/C by about 0.15 V across the entire current density range. Similarly, electrolyzer experiments showed that Pt/C/10%Ni(OH)2 performs as well as Pt/C with only half the Pt loading. Long-term stability experiments in the electrolyzer are ongoing. We have also found enhanced HER activity in a Pt electrocatalyst deposited onto a mixed-metal-oxide support composed of titanium dioxide (TiO2) and ruthenium dioxide (RuO2). The Pt/RuO2-TiO2 (Pt/RTO) electrocatalyst outperformed the benchmark Pt/C over the entire range of temperatures evaluated (275-313K). The exchange current density for Pt/RTO was 2.31±0.06mAcm-2 Pt (at 295 K), which was more than five times the value for Pt/C. In a solid-state alkaline water electrolyzer, MEAs fabricated with Pt/RTO in the cathode and IrO2 as anode catalyst exhibited a 100-200mV reduction in the cell voltage, when compared to MEAs fabricated with Pt/C in the cathode. References A. Brisse, J. Schefold and M. Zahid, Int. J. Hydrogen Energy, 33, 5375 (2008).

Electrochemical water splitting utilizing renewable electricity is a promising technology for the production of clean and sustainable hydrogen. The most active electrocatalyst for the hydrogen evolution reaction (HER) is platinum. However, the high costs and scarcity associated with platinum motivate the search for alternative catalysts.1 Promising HER activities have been reported for many families of materials including transition metal chalcogenides, carbides and in particular, phosphides.2 Specifically, cobalt phosphide (CoP) is an interesting and active non-precious metal HER catalyst in acid media.3 In this work we synthesise active and stable CoP catalysts on carbon supports at the 1 – 5 g batch scale. The CoP catalysts are prepared by wetness impregnation Vulcan carbon followed by a red phosphorous based vapour phase phosphidation. The crystal structure and chemical composition of the CoP catalyst is verified by XPS and XRD. The morphology of the catalyst is shown to consist of -2. Beyond three-electrode laboratory scale electrochemistry screening, the most active and durable HER catalysts were used to fabricate 25 cm2 single cell stack membrane electrode assemblies (MEA). The performance of the CoP MEAs was assessed by polarization curve as well as steady state measurements at various current densities and were found to be stable for >20 h of testing. This work highlights the remarkable stability and promise of transition metal phosphides in an MEA configuration. References (1) Ng, J. W. D.; Hellstern, T. R.; Kibsgaard, J.; Hinckley, A. C.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2015, 8 (20), 3512. (2) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Science 2017, 355 (6321), eaad4998. (3) Hellstern, T. R.; Benck, J. D.; Kibsgaard, J.; Hahn, C.; Jaramillo, T. F. Adv. Energy Mater. 2016, 6 (4), 1501758.

Electrochemistry is becoming increasingly important in transitioning from primarily fossil fuel based energy sources to more renewable options. This challenge will require a combination of solutions, depending on geography, the mix of renewables, and other factors. The intermittent nature of wind, solar, and other forms of renewable energy, as well as demand fluctuations which do not match the generation capacity, drives the need for modular, distributed energy storage solutions, where electrochemistry can be ideal. However, for very long storage times, conversion of energy to a chemical fuel is often the most practical solution. Electrochemical generation of fuels such as hydrogen, ammonia, and CO2-derived hydrocarbons are all related and have similar R&D challenges. In addition, all of these chemicals have different advantages and disadvantages, and have benefits in different scenarios. This talk will focus on some of the considerations in developing a new electrochemical device, and research challenges applicable to low temperature electrochemical fuel generation. While fundamental research in understanding electrocatalytic reactions at the molecular level is valuable from a basic science perspective, understanding the application requirements for each market, and pricing structure vs. scale, can guide application of this research to the next logical stage. There is a large application space for fuels and industrial chemicals with widely varying price points based on scale and requirements. For example, different ground vehicle classes (consumer vehicles, heavy duty trucks, fork trucks, industrial equipment etc.,) may each be best served by different fuels depending on power and range requirements as well as customer preferences. Ships and airborne vehicles may have different optimal solutions. Smaller scale or emerging markets such as unmanned vehicles may also serve as easier market entry points. At the materials discovery stage, all of the above reactions require catalyst design and fundamental understanding in order to achieve high activity and efficiency. Specifically for ammonia and carbon-based fuels, selectivity is a key issue, and structural approaches to control the active site and competition for binding sites are being pursued. Beyond the catalyst, the electrode structure and integration also need to be designed for optimal performance, including effective fluid flow and catalyst access. While the individual catalyst composition and structures will be different, all of these pathways involve hydrogen or oxygen evolution reactions and ion exchange membranes, and can both leverage and inform electrolysis research. Proton’s work in these areas will be discussed, as well as key needs for additional research and collaborations between applied and fundamental science.

Membrane (PEM)-based electrolysis provides an ideal near-term technology to address the growing energy storage demands as intermittent renewable energy becomes more prevalent. While proton exchange membrane (PEM) systems are often viewed as preferred solutions to legacy KOH systems due to the lack of corrosive electrolyte, small footprint, and dynamic operating range due to the ability of the PEM systems to generate hydrogen at differential pressure, they still present capital cost challenges. In particular, the platinum group metal catalysts and valve metals for separator and flow field construction required for stability in the acidic environment become a significant cost driver at scale. Alkaline exchange membrane (AEM)-based electrolysis is therefore viewed as a potential replacement to the current PEM systems as a means of driving down the high capital cost. This cost reduction is accomplished by replacing the typical high cost catalyst and materials of cell construction with lower cost metals that would corrode in the acidic PEM environments, but are stable in the alkaline chemistries. In theory, this approach is highly promising, but testing of the current state-of the art has shown the technology gaps between the two platforms in terms of stability, durability, and operating electrical efficiency. Modeling has shown that savings realized in capital cost are typically off-set by an increase in operating expense resulting from the lower activity of the non-PGM catalysts and poor conductivity of the AEM. Additionally, thermal instability of the AEMs require stacks to be operated at lower temperatures than a typical PEM system, impacting conductivity further and slowing kinetics. The addition of liquid electrolyte to the water feed has been shown by some groups to be effective in reducing cell operating potentials and providing overall voltage stability. However, this solution adds management and additional maintenance of handling the caustics typically used. Efforts at Proton have shown significant improvements in operation under milder conditions, showing some potential to achieve targets required to compete with incumbent technology. In this talk, some of the advancements achieved and how these have impacted the cost of the hydrogen will be discussed. An example of this improvement is shown in the figure below, where collaborative ionomer research and partnering with a commercial entity for scale-up of catalyst synthesis have translated into an immediate improvement over targets previously established. Additionally, cost models will be compared to show the path needed to establish equivalence with current PEM systems and what is required to go beyond. Figure 1

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