Proton exchange membrane (PEM) electrolysis has advanced significantly in the last 10 years, scaling from units in the sub 100 kW range to installed systems at 10 megawatts and greater. This technology, among others, is likely to play a major role in decarbonizing the industry, transportation, and energy sectors, as both the cost of electrolyzer technology and the renewable energy to power it have decreased. Still, the capital cost of electrolysis needs to be further reduced to economically replace hydrogen from steam methane reforming in very large applications, especially as capacity factor goes down to take advantage of the lowest cost electricity. There is also significant potential to decrease cost, as electrolyzer manufacturing is still relatively undeveloped.PEM electrolysis has been developed for many decades and is proven as a reliable, scalable technology. However, electrodes are overdesigned due to the manual methods used to produce them, as well as the aerospace legacy of these systems. Many advancements such as reductions in catalyst loadings, use of thinner membranes, novel porous transport layers, and alternate cell configurations have been shown to be feasible in the lab, but have been slow to transition to commercial products.There are many factors in this lag, including the need to often change manufacturing methods when moving from the lab to a product environment. While this effort is sometimes viewed as “just engineering”, there is significant fundamental understanding required to translate a slow, manual process where finished parts can be individually scrutinized, to a fast, automated process that has to include automated inspection as well. For example, a catalyst ink that is hand painted onto a substrate will need different properties and formulation to deposit the catalyst by spray printing, or yet different properties for other methods such as slot die or gravure printing. Determining acceptability of the resulting parts can no longer rely on human judgment but must be well enough understood that the most important properties can be quickly measured and analyzed in real time. In addition, the scale over which high quality needs to be achieved increases by orders of magnitude when moving from lab scale to product scale. This talk will discuss these types of challenges and approaches to solve them.

Water electrolyzers are today of worldwide strategic importance for the deployment of green hydrogen as an energy carrier, and the ultimate integration of stochastic renewable energies into the electrical grid at scale. Targets for the total cost of ownership of hydrogen have been constantly revised, but values around $1 to $2 per kilogram of H2 are generally accepted to reach parity with other energy conversion and storage strategies. However, further advancement of electrolyzers while maintaining durability and robustness of its cell/stack components is still needed. This can only be accomplished through focused research and development efforts that address efficiency, degradation, and cost aspects of the technology.A growing number of research groups are starting to participate in this development with key contributions in the form of fundamental and material advances. However, the high deviation of reported results as well as the complex history the tests performed, and components used have shown that this growth creates challenges that hinder the development of trust in the test results generated. Moreover, such lack of trust ends up hampering the overall progress and leads to wasted allocated resources. Contributors to the HydroGEN Advanced water splitting Materials, Energy Materials Network; and H2-New programs funded by the Department of Energy in the USA; aligned with efforts by the International Energy Agency (IEA) within the Electrolysis Annex 30 are conducting a benchmarking effort: 1) to develop methods to identify reference hardware, cell components, and materials; and 2) to harmonize testing protocols and enable the meaningful comparison of performance across the community.In this presentation, the latest results of this effort will be presented. The talk will also include updates on current strategies among the different teams, round robin testing results, protocol development and fine tuning of test parameters and material specifications. This effort should finally lead to the creation, validation, dissemination, and adoption of accelerated test protocols that can ultimately contribute to conducting collaborative studies on cell and stack degradation.

Significant decreases in the price of electricity from solar photovoltaics and wind are enabling concurrent decreases in the cost of clean hydrogen production by water electrolysis. However, to meet the US Department of Energy’s Hydrogen Shot Initiative target for levelized cost of hydrogen production of < $1 per kg of hydrogen by the year 2030,[1] it will also be necessary to drive down the capital costs of water electrolyzers. Reducing capital costs is especially important for scenarios where close to 100% of the electricity is provided by variable renewable energy generators, which greatly limits the capacity factor of the electrolyzer.[2] Towards this end, our team is exploring a proton exchange membrane (PEM) electrolyzer architecture based on ultrathin (< 1 micron) membranes. Modeling is used to show that defect-free membranes possessing appropriate proton and hydrogen transport properties present opportunities to decrease membrane resistances < 80% relative to conventional Nafion membranes, which can subsequently allow for operation at > 4 A cm-2 while maintaining the same efficiencies achieved by today’s commercialized PEM electrolyzers operated at < 2 A cm-2. Additionally, this talk will describe modeling and experimental efforts that address the viability of using sub-micron thick membranes that can operate with H2 crossover rates < 1%.

The transport of protons and molecular hydrogen (H2) are of relevance to a wide range of electrochemical applications ranging from fuel cells and electrolyzers to sensors and photoelectrochemical cells. One way to modulate the flux of these species to improve device performance such as selectivity and efficiency is to encapsulate electrodes with semi-permeable oxide coatings. [1-3] Thus, knowing the permeabilities of these species within thin oxide layers is of great importance for guiding the design of electrodes and devices. Towards this end, we have employed a modified rotating disk electrode (RDE) set-up to quantify proton and hydrogen permeabilities through sub- 20 nm thick silicon oxide coatings and understand how these transport properties change as a function of the structural and compositional characteristics of the coatings. Oxide coatings were fabricated by both atomic layer deposition (ALD) and photochemical deposition, and their physical and chemical properties characterized by X-Ray Photoelectron spectroscopy and ellipsometry. Based on measurements of the mass transfer limited current density for the hydrogen evolution and hydrogen oxidation reactions, permeabilities were computed. Species permeabilities are furthermore correlated with membrane density and composition, revealing structure-property-performance relationships that can be used to guide the selection of oxide thickness and processing conditions that will optimize performance for an application of interest.

As PEM and similar electrochemical devices get further scaled to meet the growing demand for renewable hydrogen solutions, the real-world design elements of electrochemical cell to balance of plant integration are key factors in the timeline for product development and manufacturing volume increases, for the system performance, and for the overall cost of hydrogen. The optimization of both cell components such as porous transport layers and bipolar plates, as well as system components such as AC-DC rectifiers for real devices need to consider and incorporate the existing volume and size constraints within the supply chain. Form factors of cells, number of cells per stack, number of stacks per plant and the corresponding layout of rectifiers, fluid pipes, and phase separators are considerations for optimization in product stack and system design. As the scale of product manufacturing and the scale of individual building blocks increases, the balance of these trades will evolve over time, requiring flexibility in design approaches to meet near term plants in the 10-MW class and medium-term plants in the 100-MW class. The discussion of these inter-relationships will explain how this evolution has proceeded to date and evaluate the impact of decisions made today on future product roll-out.

A Unitized Reversible Fuel Cell (URFC) system provides many benefits for energy storage by combining a fuel cell and an electrolyzer into a single stack, thus simplifying the system while decreasing weight, footprint, and material costs. URFC systems usually have low overall efficiency due to conflicting optimal operating conditions required for electrolyzer and fuel cell. This study optimized the membrane electrode assembly of the proton exchange membrane cell components to achieve 50% round trip efficiency and reliable performance under relevant duty cycles.Several components have been studied in this project including membranes, bifunctional catalysts for oxygen reduction and evolution reactions and porous transport layers (PTL). Different strategies have been applied to increase the overall performance of the stack while maintaining a low degradation rate. In particular, we looked at reducing the thickness of membranes as well as increasing the operating temperature. A comprehensive study of bifunctional catalyst has been carried out by varying the ratio of catalysts suitable for OER and catalysts suitable for ORR. Variation of the hydrophilicity of the PTL has been done to identify the optimum amount in terms of water and gas transport in the layers for both modes of operation.

Anion exchange membrane (AEM) electrolyzers promise to combine the benefits from proton exchange membrane (PEM) electrolyzers and liquid alkaline electrolyzers. They offer both the compact stack design and high current densities that PEM electrolyzers provide, while also taking advantage of using non-platinum-group-metals (non-PGM) and titanium-free components similar to traditional alkaline electrolyzers. However, AEM stacks and systems must demonstrate competitive performance and durability to allow widespread commercial adoption.As part of AEM development efforts, a comprehensive study has been conducted on the morphology of different porous plates and their impact on the cell performance. The key results demonstrate comparable performance of AEM electrolyzers to PEM electrolyzers under optimized conditions. Different ink formulation and processes have also been evaluated for a series of non-PGM catalysts, while testing their impact on performance and durability. In addition, commercially available AEMs have been evaluated for long term durability in short cell stacks, demonstrating comparable degradation rates to PEM electrolyzer technology.

Porous transport layers (PTLs) serve many important functions for proton exchange membrane water electrolyzers. PTLs facilitate fluid transport towards and away from the anode catalyst layer, act as a mechanical support for the membrane, and provide electrical contact with the anode catalyst layer [1]. As a result, PTLs can greatly impact cell performance. However, while there has been an effort to improve similar gas diffusion layers in PEM fuel cells, there has not been a significant effort to optimize the overall form factor and design of PTLs for PEM water electrolyzers.One of the primary concerns about the current design of PEM water electrolyzer PTLs is how they interact with the anode catalyst layer. In order to ensure proper fluid transport through the PTL, there is significant porosity throughout the PTL including at the anode interface. The large porosity and particle sizes of the PTL can cause heterogeneous contact of the PTL and catalyst layer thus reducing the catalyst utilization. Therefore, high catalyst loadings are required to obtain acceptable performance and durability. One method to address this concern would be to develop a metal microporous layer (MPL) that can be integrated onto a PTL at the anode interface that can withstand the high potentials at the anode while maintaining sufficient fluid transport. The MPL is fabricated using smaller metal particle sizes compared to the bulk PTL, which results in smaller pores creating a more uniform surface. The uniform surface and small pore sizes of the MPL provide a much higher interfacial contact area at the anode interface compared to a traditional PTL and would allow for a more uniform contact pressure across the anode interface. Higher interfacial contact will improve catalyst utilization and facilitate the reduction in anode catalyst loading, leading to reductions in overall electrolyzer capital cost [2].In this work, prototype PTLs with metal MPLs are developed and tuned for optimal PEM water electrolyzer cell performance. The prototype PTLs with MPLs are characterized to understand how specific properties (thickness, porosity, tortuosity, etc.) influence cell performance. Electrochemical testing shows that adding an MPL at the anode/PTL interface can allow for acceptable cell performance with 90% lower anode catalyst loading compared to when using a baseline PTL.

Electrolyzers are a key component in transitioning the world’s reliance on fossil fuels for energy. Accordingly, a substantial influence on electrolyzer costs is operational efficiency. The means of quantifying this efficiency is necessary for sustaining the continuous improvement of this technology.Polarization curves are a critical tool in understanding the behavior and mechanisms of electrochemical devices such as electrolyzers and fuel cells. In this work, a semi-empirical voltage-breakdown method is used to model and identify a series of resistance levels and voltage losses. This model presents the modes of change in electrolyzer performance. Polarization curves are taken at several temperature and time intervals throughout steady state operation. The unique benefit of this method is that no potentiostat is required and that key parameters, such as the Tafel slope and ohmic resistance, are compared to more direct measurements.Presented here, is a user-friendly technique of evaluating the degradation of an electrolyzer over the course of its lifetime. More specifically, it provides insight on the durability of cell components such as membrane, gas diffusion layers, and catalyst layers.

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).