Reactive Spray Deposition Technology Research Articles

Advanced Porous Transport Electrode for High-Performance Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) hold great potential for supplying green hydrogen to support extensive energy storage and mobility in a future energy landscape centered on renewable energy sources.1,2 However, their contribution to global hydrogen production is currently limited, mainly due to their comparatively high cost.3 To improve the economic competitiveness of green hydrogen and foster broader market penetration, the Department of Energy (DOE) has launched the Hydrogen Earthshots, aiming for a substantial cost reduction to $2 per kilogram by 2025 and $1 per kilogram for green hydrogen by 2030.4 The high efficiency and prolonged durability are pivotal for the overall performance and cost reduction of the PEMWEs. This requires careful consideration of the interfacial contact between the porous transport layer (PTL) and the anode catalyst layer.5 One option for PEMWEs is to directly coat the anode catalyst layer onto the PTL, forming porous transport electrodes (PTEs). Recent literature suggests that it is feasible to manufacture PTEs with low precious metal loading, demonstrating both high performance and durability.6,7 In this study, an innovative reactive spray deposition technology (RSDT) is used to fabricate PTEs with low PGM loading (0.2 - 0.3 mgPGM cm-2) in both catalyst layers. The RSDT is a flame-based method that combines the synthesis and deposition of the catalyst in a single step, significantly reducing the fabrication time and cost of the membrane electrode assembly (MEA).8–11 The RSDT-fabricated PTEs are coupled with various membranes, and their performance has been assessed and compared to the state-of-the-art MEAs for PEMWEs. In addition, the performance loss in each cell has been studied and discussed in detail. Furthermore, a standard accelerated stress test (AST) protocol has been applied to assess the durability of the RSDT-fabricated MEAs, with one order of magnitude lower PGM loading in their catalyst layers in comparison to the commercial MEAs for PEMWEs.Reference1. Pham, C. Van, Escalera-López, D., Mayrhofer, K., Cherevko, S. & Thiele, S. Essentials of High Performance Water Electrolyzers – From Catalyst Layer Materials to Electrode Engineering. Adv. Energy Mater. 11, (2021).2. Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy 38, 4901–4934 (2013).3. Buttler, A. & Spliethoff, H. Current status of water electrolysis for energy storage, grid balancing, and sector coupling via power-to-gas and power-to-liquids: A review. Renew. Sustain. Energy Rev. 82, 2440–2454 (2018).4. Styapal, S. et al. DOE Update on Hydrogen Shot, RFI Results, and Summary of Hydrogen Provisions. (2021).5. Peng, X. et al. Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra-Low Iridium Loadings. Adv. Sci. 8, (2021).6. Xie, Z. et al. Ionomer-free nanoporous iridium nanosheet electrodes with boosted performance and catalyst utilization for high-efficiency water electrolyzers. Appl. Catal. B Environ. 341, 123298 (2024).7. Lee, J. K. et al. Ionomer-free and recyclable porous-transport electrode for high-performing proton-exchange-membrane water electrolysis. Nat. Commun. 14, 1–11 (2023).8. Zeng, Z. et al. Advanced nickel-based catalysts for the hydrogen oxidation reaction in alkaline media synthesized by reactive spray deposition technology: Study of the effect of particle size. Int. J. Hydrogen Energy 1–12 (2023) doi:10.1016/j.ijhydene.2023.03.249.9. Zeng, Z. et al. Degradation Mechanisms in Advanced MEAs for PEM Water Electrolyzers Fabricated by Reactive Spray Deposition Technology. J. Electrochem. Soc. 169, 054536 (2022).10. Xing, J. et al. Long-term durability test of highly efficient membrane electrode assemblies for anion exchange membrane seawater electrolyzers. J. Power Sources 558, 232564 (2023).11. Mirshekari, G. et al. High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment. Int. J. Hydrogen Energy 46, 1526–1539 (2021).

Comparative Study of Anion Exchange Membranes for Application in Advanced AEM Water Electrolysers

The chemical nature of hydrogen combined with its capability to be an energy carrier for energy conversion devices with zero- emission and its higher energy density than any other commercial fossil fuel-based energy source, make it unique [1]. The International Renewable Energy Agency has identified three of the most viable technologies for producing hydrogen in large volume, namely: alkaline water electrolyzers (AWEs), proton exchange membrane water electrolyzers (PEMWEs), and anion exchange membrane water electrolyzers (AEMWEs) [2]. Among the three types of electrochemical devices the AEMWEs are the newest and most promising, because they (i) have the same slim design of the PEMWEs, (ii) can operate at high current densities, and (iii) can use non-precious catalysts [3]. The durability and efficiency of the AEMWEs systems are significantly influenced by the anion exchange membranes (AEMs), which are currently under development. In addition, the used catalysts, as well as the methods for fabrication of the membrane electrode assemblies (MEAs) also impact substantially the electrolyzer’s performance. Catalyst-coated substrate (CCS) is one of the methods for fabrication of MEAs [4], while the other used method is known as catalyst coated membranes (CCMs). The Reactive Spray Deposition Technology (RSDT) is an innovative flame-assisted method that can be used for fabrication MEAs from both types [5].In this work, CCS are fabricated by the ultrasonic spray deposition method and 5 MEAs are assembled with various AEM membranes. This approach involves the application of Platinum Group Metal (PGM) catalysts, Pt/C and as cathode and anode catalyst layers, onto a Gas Diffusion Layer (C-GDL) and a porous transport layer (Ti-PTL). As fabricated CCSs are assembled with the three state-of-the-art commercially available AEMs, namely: FAA-3, Sustainion X-37, and TM1, and their performance is evaluated. In addition, CCSs with ultra-low PGM loadings in their catalyst layers are fabricated with the RSDT method and better performance in comparison to the baseline MEAs with high PGM loadings, is achieved. This comparative study provides valuable insights into the strengths and weaknesses of each membrane type for application in AEM water electrolysers. Reference: [1] M. G. Rasul, M. A. Hazrat, M. A. Sattar, M. I. Jahirul, and M. J. Shearer, “The future of hydrogen: Challenges on production, storage and applications,” Energy Conversion and Management, vol. 272, p. 116326, Nov. 2022, doi: 10.1016/j.enconman.2022.116326.[2] D. Yang et al., “Patent analysis on green hydrogen technology for future promising technologies,” International Journal of Hydrogen Energy, vol. 48, no. 83, pp. 32241–32260, Oct. 2023, doi: 10.1016/j.ijhydene.2023.04.317.[3] D. S. Falcão, “Green Hydrogen Production by Anion Exchange Membrane Water Electrolysis: Status and Future Perspectives,” Energies, vol. 16, no. 2, p. 943, Jan. 2023, doi: 10.3390/en16020943.[4] J. E. Park et al., “High-performance anion-exchange membrane water electrolysis,” Electrochimica Acta, vol. 295, pp. 99–106, Feb. 2019, doi: 10.1016/j.electacta.2018.10.143.[5] Z. Zeng, J. Xing, L. Bonville, D. R. Dekel, R. Maric, and S. Bliznakov, “Advanced nickel-based catalysts for the hydrogen oxidation reaction in alkaline media synthesized by reactive spray deposition technology: Study of the effect of particle size,” International Journal of Hydrogen Energy, p. S0360319923013721, Apr. 2023, doi: 10.1016/j.ijhydene.2023.03.249.

(Invited) Novel Design of Low-Loaded Membrane Electrode Assemblies for Advanced Low-Temperature Water Electrolyzers

Development of advanced low-temperature (LT) water electrolyzers (WEs) is of crucial importance for implementation of the Hydrogen Economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. “Green” hydrogen can be produced at large scale by integration of WEs with renewable energy sources. Currently, the low-temperature proton exchange membrane (PEM) and anion exchange membrane (AEM) WEs are considered to be the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for LTWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers; (ii) limited durability caused by the instability of the catalysts and the other cell components, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].This work is aimed on designing of novel MEAs for LTWEs with dramatically reduced catalysts loadings, enhanced durability, and improved H2 crossover capabilities. Reactive Spray Deposition Technology (RSDT) is used as an innovative methodology for designing of advanced catalysts, catalyst and recombination layers, and MEAs for LTWEs. The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs for application in LT fuel cells and water electrolyzers [5, 6]. As fabricated MEAs with ultra-low PGM catalysts loadings are tested at operating conditions typical for industrial PEM hydrogen production systems, and performance of 1.8 V at 3 A/cm2 is achieved. The MEAs of interest are tested for over 1000 hrs at steady-state conditions at 3 A/cm2. Comprehensive post-test characterization is performed by using high-resolution TEM, STEM, EDS, SEM, ICP, XRF, XCT, and digital optical microscopy and the governing degradation mechanisms are identified and discussed in detail. The impact of the design of low-loaded MEAs for LTWEs on their performance and durability is discussed in detail and their potential to meet and surpass the DOE 2030 targets is demonstrated.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdfKlose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

High Efficiency and High Durability Proton Exchange Membrane Water Electrolyzers for Hydrogen Production with Advanced Catalyst Coated Membranes

Water electrolyzers and fuel cells can be used to create a closed loop system for space exploration. Electrolyzers allow for reliable self-sustainable generation of hydrogen and oxygen for energy storage, followed by conversion into electrical energy in a fuel cell. A first-order safety concern for water electrolyzer operation is hydrogen crossover. Transport of hydrogen to the oxygen rich anode in proton exchange membrane (PEM) water electrolyzers poses safety concerns when the hydrogen concentration in the anode flow field approaches the hydrogen lower flammability limit (LFL). Hydrogen storage efficiency relies on high hydrogen pressure, leading to pressure-driven hydrogen crossover. Mitigation of hydrogen crossover through research and development of a platinum metal recombination layer has been demonstrated in high performing, durable PEMWEs.1-4 Ouimet4 explored the use of a novel dual recombination layer configuration to mitigate PEM water electrolyzer hydrogen crossover. In addition, the current state of the art for PEM fuel cells and water electrolyzers rely on perfluoro-sulfonated acid (PSFA) based membranes. There are significant challenges facing the use of PSFA-based membranes; namely, environmental contamination and performance limitations. The use of a hydrocarbon membrane allows for the development of a PSFA-free system that shows higher efficiency and durability. Investigation of hydrocarbon membranes pave way for developing a PEM water electrolyzer that will demonstrate improved gas permeability resistance, mechanical strength, and thermal stability.5-8 There is a need for both hydrogen crossover mitigation strategies and durability testing with hydrocarbon membranes.The research outlined in this work is focused on the development of PSFA-free PEM water electrolyzers with low hydrogen crossover. In this work, the dual recombination layer configuration will be incorporated into a hydrocarbon membrane for PEM water electrolysis. Polarization, electrochemical impedance spectroscopy, electrochemical equivalent circuits, distribution of relaxation times, and materials characterization will be used to investigate the cell performance and durability. References G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Maric, “High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment,” international journal of hydrogen energy, vol. 46, no. 2, pp. 1526–1539, 2021.Z. Zeng, R. Ouimet, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, A. P. Soleymani, J. Jankovic, H. Yu, G. Mirshekari, et al., “Degradation mechanisms in advanced meas for pem water electrolyzers fabricated by reactive spray deposition technology,” Journal of The Electrochemical Society, vol. 169, no. 5, p. 054536, 2022.A. Martin, D. Abbas, P. Trinke, T. Böhm, M. Bierling, B. Bensmann, S. Thiele, and R. Hanke-Rauschenbach, “Communication—proving the importance of ptinterlayer position in pemwe membranes for the effective reduction of the anodic hydrogen content,” Journal of The Electrochemical Society, vol. 168, no. 9, p. 094509, 2021.R. J. Ouimet, “Catalyst development by a novel fabrication process for energy applications,” University of Connecticut Doctoral Dissertation, 2021.P. Trinke, P. Haug, J. Brauns, B. Bensmann, R. Hanke-Rauschenbach, and T. Turek, “Hydrogen crossover in pem and alkaline water electrolysis: mechanisms, direct comparison and mitigation strategies,” Journal of The Electrochemical Society, vol. 165, no. 7, p. F502, 2018.P. Trinke, B. Bensmann, and R. Hanke-Rauschenbach, “Current density effect on hydrogen permeation in pem water electrolyzers,” International Journal of Hydrogen Energy, vol. 42, no. 21, pp. 14355–14366, 2017.H. Q. Nguyen and B. Shabani, “Proton exchange membrane fuel cells heat recovery opportunities for combined heating/cooling and power applications,” Energy Conversion and Management, vol. 204, p. 112328, 2020.C. Klose, T. Saatkamp, A. Münchinger, L. Bohn, G. Titvinidze, M. Breitwieser, K. D. Kreuer, and S. Vierrath, “All-hydrocarbon mea for pem water electrolysis combining low hydrogen crossover and high efficiency,” Advanced Energy Materials, vol. 10, no. 14, p. 1903995, 2020.

Influence of Different Operating Conditions on Iridium Dissolution in a Proton Exchange Membrane Water Electrolyzer

Polymer electrolyte membrane (PEM) water electrolysis plays a key role in the global decarbonization scheme by coupling the intermittent renewable energy sources to the production of high-purity hydrogen. Its deployment onto a GW scale, however, is hindered by the cost and availability of the precious metal catalysts utilized in today’s commercial systems, primarily by that of Ir used as the anode catalyst for the oxygen evolution reaction (OER). With the continuous increase in the demand for carbon-free hydrogen, drastic reductions from the current Ir loading of 1 – 2 mgIr cm-2 by at least an order of magnitude, without compromising the overall electrolyzer performance, are of crucial importance.1 In the recent years, significant efforts have been focused on understanding PEM electrolyzer degradation mechanisms and developing the necessary mitigation strategies, with a special focus being placed on the anode catalyst layer (CL).2-4 Recent results from our group showed that there are two main pathways for Ir to be removed from the anode CL: dissolution into the anode water line and transport through the membrane and the cathode CL.5 In the present work, we aim to shed light onto the effects influencing Ir dissolution under intermittent operation by quantitative analysis of the main Ir sinks within an electrolyzer and the determination of the charge of the dissolved Ir species.5, 6 Various accelerated stress tests with square-wave configuration aimed at accelerating Ir-based anode CL degradation were performed and the results were compared to those obtained during steady-state operation of the electrolyzer cell, which was used as a reference point. The influence of electro-diffusion, electroosmotic drag and Ir redeposition back to the ACL onto Ir dissolution were analyzed in detail to obtain deeper understanding on the Ir degradation processes. M. Clapp, C. M. Zalitis, M. Ryan, Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis. Catal Today 420, (2023). S. M. Alia et al., Electrolyzer Performance Loss from Accelerated Stress Tests and Corresponding Changes to Catalyst Layers and Interfaces. J Electrochem Soc 169, (2022). Z. Q. Zeng et al., Degradation Mechanisms in Advanced MEAs for PEM Water Electrolyzers Fabricated by Reactive Spray Deposition Technology. J Electrochem Soc 169, (2022). A. Weiss et al., Impact of Intermittent Operation on Lifetime and Performance of a PEM Water Electrolyzer. J Electrochem Soc 166, F487-F497 (2019). M. Milosevic et al., In Search of Lost Iridium: Quantification of Anode Catalyst Layer Dissolution in Proton Exchange Membrane Water Electrolyzers. Acs Energy Lett 8, 2682-2688 (2023). A. P. Dam, B. Y. A. Abuthaher, G. Papakonstantinou, K. Sundmacher, Insights into the Path-Dependent Charge of Iridium Dissolution Products and Stability of Electrocatalytic Water Splitting. J Electrochem Soc 170, (2023).

Improving the Selectivity of Commercial Membranes in Vanadium Redox Flow Batteries through the Direct Deposition of an Additional Selective Layer

The evolution of both energy demand and energy supply requires large energy storage systems to face the challenges related to the not-programmable nature of renewable energy source. Vanadium Redox Flow Batteries (VRFB) is a promising solution for these challenges due to its decoupled energy and power, high flexibility, fast response time and long cycle life [1]. However, some technological issues limit the competitiveness of the technology by increasing the cost of the system. One of these issues is vanadium cross-over, which is the undesired transport of vanadium ions through the not-ideally selective membrane, causing battery self-discharge, capacity loss and electrolyte imbalance [1]. Relatively thick membranes (>50 µm) are usually employed in the commercial applications to mitigate cross-over losses, leading to increased voltage ohmic losses and high system costs. Indeed, the membrane is one of the main cost items of the technology as it may contribute up to 50% of total stack costs [2]. Therefore, the development of a low-cost and selective separator will improve the technology. As demonstrated by the authors [3], an effective strategy to reduce system costs and cross-over losses is to improve the selectivity of NafionTM membranes with an additional selective layer, allowing to reduce the thickness, thus the costs and the ohmic losses. The additional selective layer, referred as “the barrier”, proposed by the authors is a layer of controlled morphological properties directly deposited on the membrane that introduces a tortuous path for the ion transport, successfully mitigating vanadium fluxes through the separator [3]. In previous works the barrier was deposited by Reactive Spray Deposition Technology (RSDT) [3], but in this work the barrier was manufactured via Ultrasonic Spray Coating (USC), a commercial and easily scalable technique. Exploiting the USC for the manufacturing of the barrier accelerates the scale-up of the barrier to a scale closer to the commercial applications (100 cm2). Moreover, the barrier is composed by only commercially available materials (NafionTM ionomer, Vulcan® XC-72R and silica nanoparticles) and deposited on commercial membranes, thus facilitating a future industrial production.In this work, further developments of the barrier with respect to previous works [4] are discussed. In particular, the deposition process is further investigated by evaluating the influence of the heat-plate temperature and the ink flow rate on the evaporation process of the solvent and its impact on the performance of the barrier. Regarding barrier composition, different commercial polymers (AquivionTM and NafionTM ) were employed both as ionomer in the barrier layer and as supporting membrane to analyse the influence of different equivalent weight and the coupling of different materials on the selectivity of the barrier. Moreover, the barrier was also deposited on thin membranes (<25 µm) to enable their use in commercial applications, reducing system costs and ohmic losses.The barrier layers were characterized combining morphological and electrochemical characterization. SEM analysis was conducted to relate the morphology of the layer with the ink composition and the deposition parameters. Instead, charge-discharge cycles with voltage cut-offs were performed to evaluate the influence of the different barrier layers on the capacity loss and the efficiency of the battery. A commercial electrolyte was used for the cycling test to assess the ability of the barriers in operating conditions closer to the ones of real applications. In these operating conditions the capacity loss due to cross-over was reduced by nearly 20%, as reported in Figure 1, while the net vanadium transport by 30% with respect the bare membrane, as resulted from ICP-OES analysis of electrolytes at the end of the test. The barrier effectiveness is further improved adopting different electrolyte composition.Finally, the combination of ink and deposition parameters that ensured the highest selectivity were used to deposit a barrier with an active area of 100 cm2. The barrier was able to mitigate cross-over losses and reduced the capacity decay due to cross-over, confirming its effectiveness also at higher cell area.Figure 1 – Comparison of the discharged capacity with NafionTM N212 and the barrier during charge-discharge cycles with cut-off voltages at 100 mA cm-2. Cycles at different current densities were performed at beginning and end of test to evaluate battery performance in different conditions.

(Invited) Innovative Membrane Electrode Assemblies for the Next Generation Proton Exchange Membrane Water Electrolyzers

The Hydrogen Economy (HE) is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. The HE implementation relies on the development of zero-carbon emission technologies for Hydrogen (H2) production. “Green” hydrogen can be produced at large scale by integration of water electrolyzers (WEs) with renewable energy sources. Currently, the proton exchange membrane water electrolyzers (PEMWEs) are considered to be the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for PEMWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers (2-3 mgPGM/cm2 in each electrode), and time consuming and expensive multi-step fabrication processes associated with their manufacturing; (ii) limited durability caused by the instability of the catalysts and the other cell components, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].In this work, we demonstrate the capabilities of a unique methodology for fabrication of advanced catalysts, catalyst layers, and MEAs for PEMWEs, known as Reactive Spray Deposition Technology (RSDT). The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs for application in PEM fuel cells and water electrolyzers [5, 6]. This technology allows precise control of the composition, morphology, and particle size distribution of a wide range of nanoparticles, supported and unsupported on carbon, and ensures fine tuning of the catalysts’ activity and durability. MEAs with geometric areas of 86 cm2 and 680 cm2, both with one order of magnitude lower PGM loading in their catalyst layers in comparison to the state-of-the-art MEAs for PEM water electrolyzers [6,7], are fabricated by the RSDT and evaluated for up to 5000 hours at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. Diagnostic tests that include polarization curves, electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen crossover measurements are performed periodically in order to evaluate the cell performance change during the long-term durability test. After the test, the MEAs are disassembled and subjected to comprehensive post test analysis. A wide range of techniques, including high-resolution TEM, STEM, EDS, SEM, ICP, XCT, XPS, and digital optical microscopy, have been used to study the degradation mechanisms governing the performance loss in the MEAs during the long-term steady state operation. The results from these tests will be presented and discussed in detail in this talk.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdfKlose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).Ayers, K. Current Opinion in Electrochemistry, 18, 9–15 (2019).

Advanced Porous Transport Layers for PEM Water Electrolyzers: Impact of the Interfacial and Bulk Properties of the PTLs on the Electrolyzers Performance

Proton exchange membrane water electrolyzers (PEMWEs) are widely seen as a crucial technology for integration with renewable energy sources to convert the generated electricity to green hydrogen, which is a clean and sustainable energy carrier.1 However, their high capital cost and operational expenditures increase the production cost of green H2.2 To make the technology economically competitive and boost its market penetration, DOE implemented targets of $2 kg-1 by 2025 and $1 kg-1 hydrogen by 2030.3 The interfacial and bulk properties of the porous transport layer (PTL) are vital to the PEMWEs performance.4–6 The optimal bulk properties of PTL improve cell performance mainly by improving the mass transport, while the reduced interfacial contact resistance between the anode catalyst layer and PTL, also enhances the catalyst utilization, allowing for a reduction of the precious metal loading. Further reduction of the interfacial contact resistance between the PTL and the catalyst layer is of crucial importance for increasing the efficiency of the PEMWEs, as well as for decreasing the production cost of green H2.In this study, an innovative reactive spray deposition technology (RSDT) is used to fabricate catalyst-coated membranes (CCMs) and catalyst-coated electrodes (CCEs) with ultra-low PGM loading (0.2 - 0.3 mgPGM cm-2) in both catalyst layers. The RSDT is a flame-based method that combines the synthesis and deposition of the catalyst in a single step, which results in a significant reduction of the MEA fabrication time and cost, respectively.7–9 A set of commercially available Ti PTLs with various thicknesses and porosities have been used to assemble single cells as fabricated MEAs, and their performance has been assessed and compared to the state-of-the-art MEAs for PEMWEs. In addition, the impact of the thickness and porosity of the PTL, as well as the interfacial contact resistance between the PTL and catalyst layer for both single-cell PEMWE configurations (CCMs and CCEs) have been investigated. The performance loss in each cell configuration has been identified and discussed in detail. Furthermore, a standard accelerated stress test (AST) protocol has been applied to assess the durability of the RSDT-fabricated MEAs, with one order of magnitude lower PGM loading in their catalyst layers in comparison to the best reported in the literature MEAs for PEMWEs.Reference1. Carmo, M. et al. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy 38, 4901–4934 (2013).2. Babic, U. et al. Critical Review — Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development Review — Identifying Critical Gaps for Polymer Electrolyte Water. (2017) doi:10.1149/2.1441704jes.3. https://www.energy.gov/eere/fuelcells/hydrogen-shot4. Peng, X. et al. Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra-Low Iridium Loadings. Adv. Sci. 8, 1–9 (2021).5. Bühler, M. et al. Optimization of anodic porous transport electrodes for proton exchange membrane water electrolyzers. J. Mater. Chem. A 7, 26984–26995 (2019).6. Kulkarni, D. et al. Elucidating effects of catalyst loadings and porous transport layer morphologies on the operation of proton exchange membrane water electrolyzers. Appl. Catal. B Environ. 308, 121213 (2022).7. Zeng, Z. et al. Degradation Mechanisms in Advanced MEAs for PEM Water Electrolyzers Fabricated by Reactive Spray Deposition Technology. J. Electrochem. Soc. 169, 054536 (2022).8. Mirshekari, G. et al. High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment. Int. J. Hydrogen Energy 46, 1526–1539 (2021).9. Yu, H. et al. Nano-size IrOx catalyst of high activity and stability in PEM water electrolyzer with ultra-low iridium loading. Appl. Catal. B Environ. 239, 133–146 (2018).

Development of a Selective Layer Via Ultrasonic Spray Coating for Vanadium Redox Flow Batteries: Analysis of Ink Composition and Component Scale-up

Vanadium Redox Flow Battery (VRFB) is a promising technology for stationary energy storage because of its long cycle life and independent energy to power ratio. However, the competitiveness of the technology is hindered by some technological issues, such as vanadium cross-over. Vanadium cross-over is the undesired transport of vanadium ions trough the ion-exchange membrane, causing capacity loss and electrolyte imbalance. Usually, to mitigate cross-over fluxes between the two half-cells, relatively thick membranes (>50 µm) are employed in the commercial applications, meaning increased ohmic losses, reduced energy efficiency and higher system capital cost: indeed, the membrane can contribute up to 50% the cost of the stack [1]. The state-of-the-art membranes for VRFB are made of NafionTM because of its high conductivity, but its not-ideal selectivity towards vanadium ions prevents the use of thin membranes. Alternative cation exchange membranes like SPEEK or SPI are promising because of their reduced permeability, but the low conductivity limits system power density. Instead, anion exchange membranes are still limited by the poor chemical stability and low conductivity [2].The authors in a recent work [3] successfully demonstrated the possibility of mitigating vanadium cross-over though an innovative additional selective layer directly deposited on the membrane. The selective layer, termed as barrier, is a porous component whose pores size tortuous path, thickness and composition are designed to improve ion/proton selectivity. As reported in Cecchetti et al., the barrier layer, manufactured through Reactive Spray Deposition Technology (RSDT) significantly reduced battery self-discharge without hindering the efficiency of the battery [3].In this work, the possibility of manufacturing the barrier via Ultrasonic Spray Coating (USC) is investigated. USC is a commercial and easily scalable technique that exploits the ultrasonic vibration of the nozzle tip to uniformly atomize and spray an ink on a substrate [4]. In particular, the influence of the process parameters and ink composition on the selectivity of the barrier layer and efficiency of the battery were investigated through both morphological and electrochemical characterization in batteries of 4 cm2 and 25 cm2 active area. The deposited barrier layers were directly deposited on NafionTM 212 to form thin layers of 10 µm thickness (Figure 1). The barriers were composed of commercial silica and Vulcan® XC-72R nanoparticles, that introduce a tortuous path for the vanadium ions through the separators, and NafionTM ionomer, acting as a binder and ensuring proton conductivity.After identifying the combination of process parameters and ink composition that ensures the lowest self-discharge of the battery, the scale-up of the barrier at commercial scale was investigated by directly deposition the barrier on NafionTM 212 to obtain an active area of 100 cm2. The 100 cm2 barrier was tested in a VRFB in cycles of charge-discharge cycles with cut-off voltages of 1.65 V and 1 V showing a capacity decay rate of 0.11 % cycle-1 at 50 mA cm-2: four time lower than the reference value (0.44 % cycle-1) reported by Rodby et al. for VRFB in the same range of current density [5].

Investigation of the Performance and Durability of Reactive Spray Deposition Fabricated Electrodes on a Bifunctional Membrane for Alkaline Water Electrolysis and CO2 Reduction Reaction

Alkaline water electrolysis (AWE) is a promising technology for carbon capture [1]. Anion exchange membrane water electrolyzers (AEMWEs) utilize low-cost, non-precious metal materials, providing an economically viable alternative to more expensive proton exchange membrane water electrolyzers (PEMWEs). While PEMWEs can operate at much higher current densities, they require noble metal catalysts and titanium components for the high potential environment anode [1]. The implementation of a bipolar membrane (BPM) will allow both HER and OER to occur under kinetically favorable conditions [2, 3] by combining both thin AEM and thin PEM layers within a single membrane. AEMs, PEMs, and BPMs have been tested in CO2RR electrolyzers [4]. The BPM may provide a pathway to combine the advantages of both AEMs and PEMs for CO2 reduction. Altering both the membrane and CCM is a focus in the research and development in CO2RR electrolyzers. Lee et al. [5] explored the use of a porous membrane for CO2 reduction. While work can be done to improve performance and crossover, the porous membrane provided excellent mechanical properties and good economic potential.There has been some work done on developing bifunctional membranes for water electrolysis and CO2 reduction [3, 6, 7]. Two key issues with operation of a CO2RR electrolyzer with a BPM is the reactant CO2 that is lost to the AEM and PEM membrane layer interface and the instability of the cell. Both issues contribute to a significant decrease in performance and faradaic efficiency in product conversion. Development of the BPM, both on the membrane’s fabrication and configuration, and electrode layers, needs to be explored to reach higher performances and longer lifespans.In this work, reactive spray deposition technology (RSDT) was used to fabricate electrodes on a UConn fabricated bipolar membrane. Testing of each configuration was conducted as both an AEM water electrolyzer and CO2RR electrolyzer. Polarization, electrochemical impedance spectroscopy, electrochemical equivalent circuits, and distribution of relaxation times were used to investigate cell performance and durability.

Advanced nickel-based catalysts for the hydrogen oxidation reaction in alkaline media synthesized by reactive spray deposition technology: Study of the effect of particle size

Anion exchange membrane fuel cells (AEMFCs) have been regarded as a promising low-cost alternative to proton exchange membrane fuel cells (PEMFCs) due to their potential to utilize platinum group metal (PGM) free catalysts and their recently demonstrated improvement in power density. However, the development of highly active and stable PGM-free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline solutions remains a significant challenge. In this study, reactive spray deposition technology (RSDT) is used to fabricate a set of Ni/CeO2/C catalysts, and their activity toward the HOR is investigated as a function of the nanoparticle size. The structural and morphological characterization of as synthesized Ni/CeO2/C catalysts confirms that the RSDT is capable of precise control of the nanoparticle size by adjusting the deposition parameters. The electrochemical rotating disk electrode study shows that the Ni/CeO2/C catalyst with an average particle size distribution of 3 nm has the highest mass activity of 14.8 A gNi−1, which is among the highest values reported in the literature for Ni-based catalysts. Moreover, the post-test characterization, performed after the accelerated stress test (AST) measurements, reveals that both the catalyst's corrosion and particle size increase are the main contributors to the mass activity loss. The measured electrocatalytic performance confirms the feasibility of the RSDT fabricated Ni/CeO2/C nanoparticles as an efficient PGM-free HOR catalyst for application in AMEFCs, with additional development required to improve their durability.

Laser diagnostics to characterize the in-flame growth of platinum nanoparticles manufactured by the reactive spray deposition technology

Reactive Spray Deposition Technology (RSDT) is an atmospheric pressure, flame-based advanced manufacturing method used to fabricate Membrane Electrode Assemblies (MEAs) for proton exchange fuel cells and water electrolyzers. RSDT combines the flame synthesis of catalyst nanoparticles and their deposition onto the membrane in one step. The properties of the synthesized nanoparticles, such as their Size Distribution Function (SDF), determine the manufactured electrodes’ performance, which can be evaluated when the deposition is complete via ex-situ characterization of the products. Efforts to improve RSDT for manufacturing state-of-the-art MEAs can be significantly enhanced with integrated laser diagnostics that enable in situ measurement of the synthesized catalyst nanoparticles. This paper reports the implementation of laser diagnostics in an RSDT facility and evaluates their potential to assist the manufacturing process. Laser Light Scattering (LS) and Laser-Induced Incandescence (LII) measurements are performed in the oxygen-rich zone of the flame at various distances from the flame fuel jet nozzle downstream of its luminous region. The measurements quantitatively track the evolution in size and volume fraction of platinum-based nanoparticles in two flames that yield different catalytic properties in the manufactured electrodes. The profiles of the measured nanoparticles’ volume fraction along the flame axis can be estimated a priori so that the average nanoparticle sizes can be measured in quasi-real time via LS. Nanoparticles experience an extremely slow growth rate while being convected at distances from 150 nm to 300 nm from the fuel nozzle. Complementary characterizations of the synthesized nanoparticles are performed ex-situ via High-Angle Annular Darkfield Scanning Transmission Electron Microscopy (HAADF-STEM) image analyses of samples collected on grids at a fixed distance from the fuel jet nozzle. Comparing the results from laser and microscopy techniques not only cross-validates the findings but also provides the parameters to infer the bimodal SDF in-situ and yields evidence that the coagulation efficiency of the synthesized nanoparticles has extremely low values in the investigated zone of the flames.

Effective and Durable Recombination Layers for Hydrogen Crossover Mitigation in Proton Exchange Membrane Water Electrolyzers

The Hydrogen Economy (HE) is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. The HE implementation relies on the development of zero-carbon emission technologies for Hydrogen (H2) production. “Green” hydrogen can be produced in large scale by integration of water electrolyzers (WEs) with renewable energy sources. Currently, the proton exchange membrane water electrolyzers (PEMWEs) are considered as the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for PEMWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers (2-3 mgPGM/cm2 in each electrode) and time consuming and expensive multi-step fabrication processes associated with their manufacturing; (ii) limited durability caused by the instability of the catalysts and the materials, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively mitigate and keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].In this paper, we demonstrate the capabilities of the reactive spray deposition technology (RSDT) to fabricate MEAs with one order of magnitude lower PGM catalyst loadings in their electrodes, and catalytic recombination layers integrated in the volume of the MEAs that effectively suppress the H2 crossover. The RSDT is a flame assisted method that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale MEAs [4, 5, 6]. RSDT-fabricated recombination layers (RLs) demonstrated effective reduction of H2 crossover from 30-50% of the LFL to less than 10% of the LFL when operating at current densities between 0.58 A/cm2 and 1.86 A/cm2. These recombination layers are with Pt loading of only 0.02 mgPt/cm2 and are incorporated in the volume of the membrane of the RSDT-fabricated MEAs. The MEAs with an active area of 86 cm2 and low catalyst loadings (0.3 mgIr/cm2 in the anode and 0.2 mgPt/cm2 in the cathode) have been tested for over 5000 hrs, and it was found that the H2 crossover increased to about 20 % of the LFL after 2000 hrs of operation. In order to improve the durability of the RLs, a new design comprised from two RLs separated with thin (10 um) Nafion membrane has been fabricated by the RSDT, and the results from the stability test of 3000 hrs will be presented and discussed in detail at the 242th ECS meeting. https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Klose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Roller, J., Maric, R., 24(8) December 2015 pp. 1529-1541 (2015).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

Large–Scale, High-Performance, Durable and Low-Cost Membrane Electrode Assemblies for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane (PEM) water electrolyzers, designed to produce hydrogen from intermittent renewable energy, will play a key role in future sustainable energy systems.1 However, the widespread commercialization of PEM water electrolyzers is obstructed by their high cost, low durability, and safety concerns related to the hydrogen crossover. Currently, the production cost of green H2 is in the range of $3-8 kg-1. In order to boost the commercialization of this clean energy devices and lower the production cost of green H2, DOE implemented targets of $2 kg-1 by 2025 and $1 kg-1 hydrogen by 2030.2 In addition, the durability of all electrolyzer components has to be improved in order to increase the lifetime of a PEM water electrolyzer stack to the targeted 80,000 hours. These challenging targets inspired the researchers all over the world to work on development of novel catalyst and catalyst layers with decreased platinum group metal (PGM) loadings, invent new cost-effective methods for fabrication of membrane electrode assemblies (MEAs), develop innovative designs for the MEAs capable of decreasing the hydrogen crossover, and improve the corrosion resistance of the cell hardware and the other stack components to enhance their durability.In this work, the unique Reactive Spray Deposition Technology (RSDT) is used to fabricate a high-performance, durable, and low-cost MEAs with geometric area of 680 cm2. These large scale MEAs have one order of magnitude lower PGM loadings in their catalyst layers in comparison to the state-of-the-art (SOA) commercial MEAs. The RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition in one step and thus substantially reduces the time and cost for MEAs fabrication.3–5 As fabricated large-scale MEAs with 680 cm2 geometric area of their electrodes, have loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode, which are 10 times lower than the loadings in the SOA MEAs. The MEAs of interest have been tested at steady-state conditions that are typical for an industrial hydrogen production system for over 1000 hours. The cell voltage transients, as well as the periodically measured polarization curves during the test, clearly show that as fabricated MEAs have excellent activity and durability performance. Furthermore, the RSDT fabricated MEAs have integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 % LFL at all measured current densities (from 0.58 to 1.8 A/cm2). In addition, the MEA was subjected to comprehensive post-test analysis to study the degradation mechanisms governing the performance loss during the long-term durability test, and the results obtained will be presented and discussed in this presentation.Reference1. C. Van Pham, D. Escalera-López, K. Mayrhofer, S. Cherevko, and S. Thiele, Adv. Energy Mater., 11 (2021).2. https://www.energy.gov/eere/fuelcells/hydrogen-shot-summit-proceedings-panel-session-1-electrolysis3. H. Yu, N. Danilovic, Y. Wang, W. Willis, A. Poozhikunnath, L. Bonville, C. Capuano, K. Ayers, and R. Maric, Appl. Catal. B Environ., 239, 133–146 (2018).4. G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Mari, Int. J. Hydrogen Energy, 46, 1526–1539 (2021).5. H. Yu, L. Bonville, J. Jankovic, and R. Maric, Appl. Catal. B Environ., 260, 118194 (2020).

Reactive Spray Deposition Technology As an Alternative Method for Precious Metals Deposition on Sintered Titanium Porous Transport Layers for Application in Advanced Proton Exchange Membrane Water Electrolyzers

The metal layer deposition technologies have been revolutionized throughout the years. One of the most common forms of thin metal film deposition techniques is Physical Vapor Deposition (PVD). Within the category of PVD, there are many modifications based on the source of deposition. Among all PVD variations, the Electron Beam Physical Vapor Deposition (EB-PVD) has the advantages of higher deposition rates, the ability to deposit a wide range of high purity metals for high purity films, and the creation of continuous film layers. [1,3]. EB-PVD is better known as a thermal vaporization technique. Thermal Vaporization focuses on a source, in this case an Electron Beam (EB), which bombards the desired source material with electrons. The electron beam increases the temperature of the porous metal source until it reaches its vapor phase. The metal vapor is then condensed onto the surface of the substrate holder perpendicular to the source material. While EB-PVD is known for its advantages of higher material utilization efficiency, higher deposition rates, and better step coverage [1], it lacks in its ability to penetrate into the volume of Porous Transport Layer (PTL) or coat surfaces that are not perpendicular to the source. This is important as the PTL is in contact with a corrosive environment, which causes metal corrosion and degradation of the PTL at the surfaces that are not protected by the coating.A key aspect plaguing the thin film deposition techniques is the ability to penetrate deep into the volume of a PTL and provide full coating of the porous material, including surfaces not perpendicular to the source. In an attempt to find a solution to this challenging task, we explored the capability of the Reactive Spray Deposition Technology (RSDT) to deposit precious metal nanoclusters directly onto all surfaces in the volume of the sintered titanium material [2]. The studied metal coating of interest is Gold (Au). In this work, we have deposited Au coatings of various thicknesses onto the Ti-PTLs by using both EB-PVD and RSDT techniques. The Au thin film deposits are characterized by scanning electron microscopy (SEM), digital optical microscopy, inductively coupled plasma (ICP), and focused ion beam scanning electron microscopy (FIB-SEM) [2]. The optimal deposition parameters for thin and continuous Au films with precisely controlled thicknesses have been identified. In addition, the depth of penetration of the deposits in the volume of the PTL as a function of the deposition parameters have been studied in detail, and the results will be reported at the ECS 242 meeting.

Advanced Catalysts for PEM Water Electrolyzers, Fabricated By Reactive Spray Deposition Technology: Study of the Degradation Mechanisms in the Catalysts’ Layers By in-Situ and Ex-Situ Synchrotron X-Ray Absorption Spectroscopy

Development of novel and improved catalysts and membrane electrode assemblies (MEAs) for proton exchange membrane (PEM) based energy conversion devices is of crucial importance for widespread application of the PEM fuel cells (FCs) and water electrolyzers (WEs). These PEM based devices are critical for the Hydrogen Economy (HE) implementation. The HE is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. Currently, the main challenges that the state-of-the-art MEAs for PEMWEs are facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers and time consuming and expensive multi-step fabrication processes; and (ii) poor durability caused by the instability of the catalysts and the materials [1, 2].The reactive spray deposition technology (RSDT), developed at UConn, is a novel methodology for fabrication of advanced MEAs for PEMFCs and PEMWEs [3-5]. The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs [4, 5]. In addition, this technology allows precise control of the composition, morphology, and particle size distribution of wide range of nanoparticles supported and unsupported on carbon, and thus ensures fine tuning of the catalysts’ activity and durability. The RSDT fabricated MEAs have improved activity and durability performance with one order of magnitude lower catalyst loadings in their electrodes in comparison to the state‐of‐the‐art commercial MEAs for PEM water electrolyzers [6]. In this work we report the results from the in‐situ and ex‐situ synchrotron X-ray Absorption Spectroscopy (XAS) studies of the Ir/IrOx (anode) and Pt/C (cathode) catalysts, fabricated by the RSDT. The experiments were performed at beamline 7-BM at NSLS II at Brookhaven National Laboratory. The electronic and atomic structures of the Ir and Pt in the catalyst layers after their fabrication, during operation at different cell voltages, and after long term steady‐state operation were studied by XANES and XAFS, respectively. The results obtained, provide better understanding of the improved activity of the catalysts, as well as of the degradation mechanisms that govern the MEAs’ failure. References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Roller, J., Maric, R., 24(8) December 2015 pp. 1529-1541 (2015).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

(Digital Presentation) Boosting Hydrogen Oxidation Reaction Activity of Nickel Based Catalyst By Reactive Spray Deposition Technology: Effects of Particle Size

Ni-Based materials are one of the most promising candidates for hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells (AEMFC). However, the performance for pure Ni is limited. In this work, Ni mixed CeO2 nanoparticles supported on carbon black were synthesized for the first time by Reactive Spray Deposition Technology (RSDT) and followed by an oxygen reduction process in a furnace. By controlling the reaction parameters during the RSDT fabrication process, the particle size of Ni/CeO2/C is set at 3 nm. The resultant 3 nm catalyst Ni/CeO2/C catalyst exhibits excellent mass activity (14.92 mA mg-1 Ni) compared to the catalyst without the addition of CeO2 (which is Ni/C 4.39mA mg-1 Ni) as well as the activity of most of the other non-precious metal-based materials for HOR. The excellent electrocatalytic performance indicates that Ni/CeO2/C can be considered as a potential non-precious metal at the anodes for AMEFCs.

(Digital Presentation) Large–Scale High-Performance Low Catalyst Loaded Membrane Electrode Assemblies for Advanced Proton Exchange Membrane Water Electrolyzers

Hydrogen is regarded as the next-generation energy carriers for the future hydrogen economy.1 Among the hydrogen production technologies, proton exchange membrane (PEM) water electrolyzers is considered the favored approach for the implementation of the global hydrogen energy transformation due to its several benefits including high power density operation, low ohmic losses and differential pressure operation. However, (i) high cost mainly from the high platinum group metals (PGM) loading in the catalysts layers; (ii) low durability due to instability of the catalysts layers and membrane; and (iii) poor safety because of hydrogen crossover of PEM water electrolyzers have jeopardized their widespread commercialization. Currently, a new Department of Energy Consortium (H2NEW) has targeted hydrogen production from electrolysis, especially PEM water electrolysis, for use as a clean, sustainable fuel, which can achieve $2/kg hydrogen production cost by 2025.2 This requires a balance between the performance, durability and scale-up cost of membrane electrode assemblies (MEAs) for PEM water electrolyzers.In this work, we demonstrate the capability to fabricate large scale MEAs by the unique Reactive Spray Deposition Technology (RSDT), that have one order of magnitude lower PGM loadings in the catalyst layer than the state-of-the-art (SOA) designs, and activity and durability performance comparable to the SOA commercial MEAs. RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition processes into one step and thus substantially reduces the time and cost for their fabrication.3–5 The RSDT fabricated MEA with 680 cm2 geometric area electrodes, and loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode has been tested at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. The initial steady-state test for over 250 hours, clearly shows excellent activity and stability. In addition, the RSDT fabricated MEA has integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 %LFL at all current densities from 0.58 to 1.8 A/cm2.Reference1. M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy, 38, 4901–4934 (2013).2. https://www.energy.gov/sites/default/files/2021-09/h2-shot-summit-panel1-lte-status.pdf3. H. Yu et al., Appl. Catal. B Environ., 239, 133–146 (2018) https://doi.org/10.1016/j.apcatb.2018.07.064.4. H. Yu et al., Electrochim. Acta, 247, 1155–1168 (2017) http://dx.doi.org/10.1016/j.electacta.2017.07.093.5. G. Mirshekari et al., Int. J. Hydrogen Energy, 46, 1526–1539 (2021) https://doi.org/10.1016/j.ijhydene.2020.10.112.

Development of an Additional Selective Layer to Mitigate Crossover in Vanadium Redox Flow Batteries: Influence of Composition on Efficiency and Capacity Decay

Vanadium redox flow battery (VRFB) is a promising technology for energy storage because of its independent energy to power ratio and long cycle life. However, VRFB commercialization is still hindered by some technological issues, among which the capacity loss induced by the undesired transport of ions across the ion-exchange membrane. Depending on the nominal operating condition, the choice of a suitable membrane for VRFB application results from the trade-off between low vanadium ions permeability and high proton conductivity. Usually, in order to reduce undesired ion fluxes between the two half-cell electrolytes, the membrane thickness is relatively high, implying increased ohmic losses (i.e., reduced energy efficiency) and system capital cost. In fact, state of the art membranes can represent up to 50% of stack capital cost [1]. Nafion® is widely used due to its high conductivity, but it is not ideally selective towards vanadium ions, leading to the adoption of thicker membrane to limit capacity loss. Alternative cation exchange membranes like SPEEK or SPI are promising because of their reduced permeability, but the low conductivity limits system power density. Instead, anion exchange membranes are still limited by the poor chemical stability and low conductivity [2].In a recent work [3], the authors demonstrated the proof of concept of an additional selective layer to mitigate vanadium crossover. The selective layer, termed as barrier, is a porous component in which pores size, tortuous path, thickness and composition are designed to improve ion/proton selectivity. The proof of concept was manufactured with reactive spray deposition technology (RSDT), which is a flame-based synthesis process unique to Dr. Radenka Maric’s research group. For the fabrication of the proof of concept, carbon-rich particles ∼4-10 nm in diameter were formed in the RSDT flame and were deposited directly onto Nafion® 212 (50 μm thick) simultaneously with a mixture of 1100EW Nafion® and Vulcan® XC-72R (∼40 nm diameter) that was sprayed from air-assisted secondary nozzles. The presence of the barrier layer significantly reduced battery self-discharge, as reported in [3].In this work, different compositions and morphologies of the barrier layers were analysed in order to improve ion/proton selectivity. In particular, the influence of ionomer to carbon ratio (I/C), the amount of carbon-rich particles and the introduction of silica were investigated. Moreover, the effect of Nafion® 211 (25 μm thick) as a support for barrier deposition was also evaluated. The barrier layers were characterized in a 25 cm2 cell [4] equipped with reference electrodes at both positive and negative electrode in order to monitor the corresponding electrolyte potential and get an insight into battery state of charge (SoC). In addition to electrochemical testing, the structure of the barrier layer was characterized using TEM and SEM.The most suitable I/C ratio was found to be included between 1 and 2, while the presence of carbon-rich particles significantly contributed to crossover reduction, with a minor impact on proton conductivity. Also the introduction of silica nanoparticles from primary nozzle was effective for vanadium ion selectivity, in particular when the amount of carbon from the secondary nozzle is reduced. In fact, the most promising barrier layer resulted the one composed by only silica and ionomer. This layer was also deposited on Nafion® 211 (Figure 1), exhibiting an excellent trade-off between ion selectivity and proton conductivity. This barrier was proved to be stable over 1,000 cycles, presenting a stable coulombic efficiency of 99.5%, with an average capacity decay of 0.08%/cycle at 100 mA cm-2. Figure 1 – SEM image of only Silica barrier deposited on Nafion® 211.

Understanding Proton Exchange Membrane Water Electrolyzer Hydrogen Crossover Mitigation in Reactive Spray Deposition Technology Fabricated Dual Recombination Layers through Distribution of Relaxation Times Analysis

Proton exchange membrane water electrolyzers (PEMWEs) are a promising technology to produce zero-carbon emission, renewable, high-purity hydrogen. [1] There is a need to reduce capital cost while improving performance for the progression of widespread development. The crossover of hydrogen from the cathode into the anode not only restricts cell performance, but also poses a safety hazard, as the crossover reaches the lower explosive limit of hydrogen in oxygen. [2] Previous work has been conducted on the fabrication and testing of Pt recombination layers in PEMWEs. The addition of the Pt recombination layer has proven to be an effective mitigation strategy for hydrogen crossover while improving performance. [3, 4] Further investigation is needed to understand the mechanisms of the Pt recombination layer.In this work, reactive spray deposition technology (RSDT) was used to deposit two Pt recombination layers separated by a membrane. Testing of a single cell 25 cm2 PEMWE was conducted. Polarization analysis, electrochemical impedance spectroscopy, and distribution of relaxation times were used to investigate the cell performance. Results show good cell performance and hydrogen crossover reduction, as well as insight to the mechanisms of the chemical reactions that occur on the dual recombination layer.