Novel Oxygen Evolution Catalysts for Proton Exchange Membrane Water Electrolysis

Proton exchange membrane (PEM) water electrolysis offers significant potential for sustainable production of green hydrogen due to its high current density, superior hydrogen purity, and excellent conversion efficiency. However, widespread industrial implementation remains challenging because state-of-the-art oxygen evolution reaction (OER) catalysts heavily rely on iridium, a precious metal with limited global supply and high costs.1–4 Therefore, considerable research efforts have been dedicated to developing new catalysts requiring lower iridium loadings. Although PEM electrolysis typically operates at elevated temperatures (50-80°C),1 most studies assessing catalyst activity and stability have been performed at room temperature, and the limited available temperature-dependent studies primarily focus on alkaline environments.5,6 In this work, we have systematically investigated the temperature-dependent activity and stability of two representative Ir-based catalysts: a commercial IrO₂ catalyst and a supported core-shell Ir@IrOₓ catalyst. Using a high-temperature rotating-disk electrode (RDE) setup, electrochemical assessments of the activity and stability of the catalysts were performed across a range of operating temperatures from 20°C up to 80°C. We investigated how the increased operating temperature affects the OER activities of these two catalysts, observing not only enhanced kinetics with the increased working temperatures but also altered reaction mechanisms, as indicated by the Tafel analysis of the OER polarization curves. Furthermore, by employing an accelerated stress test protocol, we evaluated the stability of the two catalysts under varied temperatures. Comprehensive in-situ and post-mortem characterization techniques, including in-situ XRD, XPS (Figure 1), TEM, and ICP, were employed to investigate the structural changes of the catalysts during the stability tests, which revealed the accelerated degradation at higher working temperatures, but also the surprisingly high OER stability of the core-shell Ir@IrOx structure under high working temperatures.Figure 1: Comparison the Ir 4f XPS spectra of the sample before and after the stability test at 60 °C.References Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int J Hydrogen Energy 38, 4901–4934 (2013). Wang, C. & Feng, L. Recent advances and perspectives of Ir-based anode catalysts in PEM water electrolysis. Energy Advances 3, 14–29 (2024). Kibsgaard, J. & Chorkendorff, I. Considerations for the scaling-up of water splitting catalysts. Nature Energy 2019 4:6 4, 430–433 (2019). Reier, T., Oezaslan, M. & Strasser, P. Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and pt catalysts: A comparative study of nanoparticles and bulk materials. ACS Catal 2, 1765–1772 (2012). Shi, G. et al. Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni-Co Oxide Catalysts with Amorphous/Crystalline Surfaces. ACS Catal 12, 14209–14219 (2022). Lyu, X., Li, J., Yang, J. & Serov, A. Significance of slight ambient temperature variation on the electrocatalyst performance toward oxygen evolution reaction. J Environ Chem Eng 11, 111492 (2023). Figure 1

Electrolysis – Proton-exchange membrane electrolyzer | Proton exchange membrane water electrolysis: State-of-the-art technique and systems

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1

Hydrogen is one of the most efficient energy carriers and can be produced by different methods. Among all the production methods, the proton exchange membrane water electrolyzer (PEMWE) is considered as the most promising technique to produce highly pure hydrogen from renewable energy sources with pure oxygen as by-products with no carbon emissions. The PEMWE technology has reached the early stages of commercial deployment while the mass production is tied to cost reduction. A PEMWE single cell comprises a membrane electrode assembly which considered as a core component where the electrochemical reactions take places in three phase boundaries. It also includes a titanium based porous transport layer (PTL) in anode side and carbon-based gas diffusion layer (GDL) in cathode side for the transportation of water and gas into and out of the cell. Additionally, bipolar plates (BPPs) with grooves provide mechanical support for the cell and distribute the water inside the cell and remove generated gases to the outlet trough flow field distribution channels. PTLs and BPPs, which are metallic components, are designed to endure the corrosive conditions present in the electrolyzer and they both needs protective coatings to stand at high voltage (<2 V), acidic media, temperature (60–80 °C) and oxygen saturated environment (anode).In this research, a modified electroplating process is used to deposit gold thin film as a protective film on both stainless steel (SS) and titanium based BPPs and PTLs, respectively. The electroplating of gold is a mature technology and easy to implement for large scale coating. This process will be impacted by many factors, such as the ingredient of plating solution, arrangement of electrodes, current distribution, and operating parameters. In addition, pre-treating the surface plays an important role to develop the durable thin films with proper adhesion. The gold striking underlayer on the SS substrate passivated the surface oxides and facilitated a dense electroplated chromium layer. Furthermore, a uniform gold protective layer was electroplated on the chromium coated substrate to achieve a promising anti-corrosive property. To evaluate the impact of pre-treatment and the anti-corrosion properties of the developed coating, different physical and electrochemical characterization techniques are conducted. As a result, The Au/Cr/Au coating on the SS substrate showed corrosion current density of 0.84 µA/cm2 and lower degradation as compared to without gold striking underlayer.The surface morphology and the crystallinity and phase analysis are investigated by scanning electron microscopy and X-ray diffraction (XRD), respectively. X-ray photoelectron spectroscopy (XPS) is used to study the surface properties and the bonds between the elements. The contact resistance also is studied under different pressures. In addition, traditional lab-scale durability analysis, using stagnant liquid electrolyte and three-electrode cell setups, might not provide such a precise information for PEM water electrolyzer. The three-electrode setup does not include crucial parameters relating to real cell-operating conditions or contributions to the PTL by other key cell components such as the membrane, catalyst layer, ionomer, and bipolar plates. Flow electrochemical setup is developed in our lab and is used to run the accelerate stress test to check the durability of the coated samples. Potentiodynamic, chronoamperometry and impedance also used to evaluate the samples. Figure 1. (a) Schematic of gold electroplating on the SS substrate, (b) SEM image and EDX analysis of Au/Cr/Au coating.We would like to acknowledge the support of the Natural Sciences and Engineering Research Council of Canada, Canada Research Chair and Mitacs Accelerate program and Intlvac Thin Film for their constant support. Figure 1

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. Membrane and electrode assemblies (MEAs) of PEM electrolyzers typically use iridium (Ir) as an anode catalyst and Pt as a cathode catalyst. The durability of MEAs plays an essential role for the electrolyzers’ lifetime and cost. However, unlike the well-established MEA durability protocols of PEM fuel cells, there have been a lack of effective procedures for PEM electrolyzer MEA durability evaluation. The objective of this work is to establish a series of test protocols that can help to rapidly evaluate PEM electrolyzer MEA durability. Three testing approaches have been used in this work, which include high-voltage hold (>1.8 V), voltage cycling (1.4 to 1.8 V or 2.0 V), and constant low-current operations. The electrochemical surface area (ECSA) and polarization curves of the MEAs will be obtained after each test. Two categories of anode catalysts have been evaluated using the above durability test protocols: one is the commercial Ir black and the other is Ir supported on tungsten-doped titanium oxide (Ir/WxTi1-xO2) developed at Giner. The supported Ir/WxTi1-xO2 catalyst proves to possess 8-10 x higher mass activity than the Ir black. The MEAs made of these two anode catalysts have been evaluated at a variety of loading, low (0.1 mg/cm2), medium (0.4 mg/cm2) and high (1.0 mg/cm2). Figure 1 shows the durability of these two catalysts after voltage cycling from 1.4 V to 1.8 V: (a) 2 mg/cm2 Ir from Ir black; (b) 0.4 mg/cm2 Ir from Ir/WxTi1-xO2. It can be seen that at medium to high Ir loadings, these two catalysts demonstrates minimal performance decay after voltage cycling. The morphology and structure of MEAs after durability tests will be characterized to correlate to their performance and to elucidate their degradation mechanisms. Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471. Figure 1

Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis

One promising way to store and distribute large amounts of renewable energy is water electrolysis, coupled with transport of hydrogen in the gas grid and storage in tanks and caverns. The intermittent availability of renewal energy makes it difficult to integrate it with established alkaline water electrolysis technology. Proton exchange membrane (PEM) water electrolysis (PEMEC) is promising, but limited by the necessity to use expensive platinum and iridium catalysts. The expected solution is anion exchange membrane (AEM) water electrolysis, which combines the use of cheap and abundant catalyst materials with the advantages of PEM water electrolysis, namely, a low foot print, large operational capacity, and fast response to changing operating conditions. The key component for AEM water electrolysis is a cheap, stable, gas tight and highly hydroxide conductive polymeric AEM. Here, we present target values and technical requirements for AEMs, discuss the chemical structures involved and the related degradation pathways, give an overview over the most prominent and promising commercial AEMs (Fumatech Fumasep® FAA3, Tokuyama A201, Ionomr Aemion™, Dioxide materials Sustainion®, and membranes commercialized by Orion Polymer), and review their properties and performances of water electrolyzers using these membranes.

Iridium-based electrocatalysts remain the only practical anode catalysts for proton exchange membrane (PEM) water electrolysis, due to their excellent stability under acidic oxygen evolution reaction (OER), but are greatly limited by their high cost and low reserves. Here, we report a nickel-stabilized, ruthenium dioxide (Ni-RuO2) catalyst, a promising alternative to iridium, with high activity and durability in acidic OER for PEM water electrolysis. While pristine RuO2 showed poor acidic OER stability and degraded within a short period of continuous operation, the incorporation of Ni greatly stabilized the RuO2 lattice and extended its durability by more than one order of magnitude. When applied to the anode of a PEM water electrolyser, our Ni-RuO2 catalyst demonstrated >1,000 h stability under a water-splitting current of 200 mA cm-2, suggesting potential for practical applications. Density functional theory studies, coupled with operando differential electrochemical mass spectroscopy analysis, confirmed the adsorbate-evolving mechanism on Ni-RuO2, as well as the critical role of Ni dopants in stabilization of surface Ru and subsurface oxygen for improved OER durability.

Proton exchange membrane (PEM) water electrolysis (WE) and fuel cells (FCs) stand out as promising technologies for hydrogen generation and utilization, leveraging renewable and sustainable energy sources. A pivotal element in both PEMFC and PEMWE is the membrane-electrode assembly (MEA), comprising catalyst layers (CLs) and a membrane. These CLs facilitate electrochemical reactions at the anode and cathode, crucial for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in PEMWE and PEMFC. The catalyst ink for CLs consists of electrocatalyst, ionomer dispersion, and additional solvents. Among these components, the choice of solvent significantly influences PEMFC and PEMWE performance, shaping the catalyst ink's properties. In this investigation, we formulated ionomer dispersions for CLs to enhance performance in PEMWE and PEMFC. We scrutinized the effects of solvents in terms of solvation energy, thermogravimetric analysis (TGA), particle size distribution (PSD), and electrochemical assessment. Acknowledgments This research was supported in part by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Gas/liquid two-phase transport is the key fundamental scientific issue in the proton exchange membrane (PEM) water electrolysis cell, which has important effects on the overall performance of water electrolysis and microstructure optimization. In this study, a combination of the lattice Boltzmann two-phase model and the QSGS numerical method was used to numerically model the porous diffusion layer and the micro-channel structure, and investigate the effects of porosity and wettability properties on the gas/liquid two-phase transport process. Simulation results show that the value of porosity will obviously affect the association and distribution pattern of solid particles inside the porous diffusion layer, and the reduction of porosity will cause the association part of solid particles to be narrower and longer, resulting in complex and variable pore channels. Some closed pore channels will appear inside the diffusion layer, which is not conducive to the smooth transmission of gas bubbles. In addition, the increase of contact angle will enhance the interaction force between the bubble and the solid wall, making it difficult for the bubble to fall off from the solid surface. Moreover, the increased interaction force will slow down the sliding speed of gas bubbles, which will result in the fusion of more gas bubbles and increase the risk of blocking the flow micro-channel. This study has initially grasped the mechanisms of micro/meso scale gas bubble transport in the PEM water electrolysis cell, which will provide theoretical basis for the optimized development of high-performance water electrolysis system for hydrogen production.

Proton exchange membrane (PEM) water electrolysis is a technology designed to produce H2 using only water and electricity as inputs; it has gained increased attention in industry and academia due to its advantages over incumbent H2 generation processes (of which the most widely used are steam reforming and coal gasification) namely, low temperature, carbon-neutral and intermittent operation. PEM electrolysis can be instrumental for creating a hydrogen economy, although still much research needs to be carried out before widespread industrial adoption is achieved. PEM water electrolyzers suffer energy losses associated with the chemical reactions and the transport of charge and mass; of these phenomena, mass transport in PEM electrolyzers is the least understood subject, given the complex nature of the interaction of multiphase flows (mainly consisting of liquid water and evolved gases) through micrometric pores. The subject of multiphase flow in water electrolysis and its relationship with the mass transport phenomena in PEM water electrolysis has been a prevalent subject in the literature. Despite numerous attempts at pinpointing the relationship between mass transport overpotential and the operating parameters, there is no clear consensus about which transport mechanisms dominate, nor about how the component design of PEM electrolyzers affects the mass transport. While the effect of temperature and current density on mass transport losses has been extensively studied and is well understood, there are significantly fewer studies that focus on the effect of water flow and pressure. Both water flow and pressure have a direct effect on mechanisms such as bubble nucleation and two-phase flows that occur in the porous structures within a PEM electrolyzer (electrodes and porous transport layers, PTLs). In this work, I studied the effect of water flow and pressure on the mass transport phenomena in PEM electrolyzers. Chapters 1 and 2 provide an introduction to the topic as well as a description of the materials and experimental setups used. Chapter 3 of this thesis depicts the visualization and modeling of bubble nucleation in an operating PEM electrolyzer. I discovered that bubble detachment radii are largely independent of water flow and I identified two types of bubbles: bubbles that detach after reaching a critical size, and bubbles that fill up the pores of a PTL before detaching. Chapter 3 consists of the measurements I carried out regarding the transport of evolved gas through the water-filled pores of a PTL, where I observed that water flow severely impedes the gas transport through the pores and that such impediment is related to a shear stress exerted by the water flow on the pores. Chapter 5 shows the measuring of mass transport losses using electrochemical impedance spectroscopy (EIS) on an operating PEM electrolyzer; the results indicate that pressure and water flow affect the diffusion of gas in the electrode and that the mass transport overpotential depends on design parameters of the PEM electrolyzer, such as electrode thickness and hydrophobicity. Overall, I derived a theoretical framework based on the assumption that the evolved gas in a PEM electrolyzer permeates through the PTL after diffusing from the active sites to the bubble nucleation sites. Such framework, constructed on the basis of the models regarding gas transport in porous media, can be used to explain the mass transport loses in a PEM electrolyzer that arise from operating with increased water flows and pressures. The model I derived can be used in future work as a guideline to optimize the components of a PEM electrolyzer, in particular regarding the hydrophobicity and pore size distribution of PTLs as well as the composition of the catalyst ink to produce the electrodes. Moreover, this work can also be used to further understand the mass transport losses and optimize the operation of PEM electrolyzers to decrease the energy consumption of H2 generation.

The production of inexpensive, clean hydrogen will be vital for supporting wide decarbonization efforts across the sectors of industrial chemicals, transportation, and the electric grid. Proton exchange membrane water electrolysis (PEMWE) has great potential as a low-temperature, high current density option for low-carbon hydrogen production; however, at present one of its most significant barriers to widespread commercial adoption is the high cost associated with the iridium (Ir) anode catalyst1.Unfortunately, many problems arise when lower Ir loadings are attempted. When considering catalyst layers (CLs) comprised only of IrO2, decreasing Ir loadings directly correlates to diminished mechanical robustness and electrode thickness. In this case, low Ir loading anodes can suffer large performance limitations caused by reduced in-plane electrical conductivity and poor interfacial contact with the porous transport layer (PTL), both of which are known to be crucial for good electrolyzer performance2,3. Some success in reaching sufficient activity with lower loadings has been achieved by synthesizing IrO2 particles on a supporting material4, but these anodes are often limited by high insulating characteristics of viable supports as well as additional chemical processing steps. Towards this end, the next decade’s targets for low Ir loadings and high Ir-specific performance urgently necessitate new designs and methods for fabrication of the PEMWE anode.Herein, we present the successful implementation of a composite anode structure using a conductive additive to enable low Ir loadings for PEMWE while maintaining robust, high-performance operation. As an initial demonstration, we simply use platinum (Pt) black as the conductive additive given its high known electrical conductivity, acid-stability, and a price that is current one-fifth that of Ir5. Results are compared across various loadings of pure-IrO2 anodes, a composite anode with Pt black, and a pure-Pt-black anode. We show physical characterization results from SEM images and four-point probe measurements for sheet resistance, finding that the addition of Pt black reduced electrode sheet resistance by four orders of magnitude. We also present electrochemical characterization results, which revealed that when compared to a high Ir loading anode, the composite anode facilitated a 95% reduction in Ir loading and 80% cost reduction of the anode catalyst materials while maintaining equal current density performance @Ecell = 1.8 V. With this method, we show promising results towards lowering Ir loadings and material costs, addressing a major barrier to the widespread adoption of PEMWE for clean hydrogen production.References K. Ayers, Curr Opin Chem Eng, 33, 100719 (2021).Z. Taie et al., ACS Appl Mater Interfaces, 12, 52701–52712 (2020).E. Leonard et al., Sustain Energy Fuels, 4 (2020).L. Moriau, M. Smiljanić, A. Lončar, and N. Hodnik, ChemCatChem, 14 (2022).“PGM Management,” Johnson Matthey, https://matthey.com/products-and-markets/pgms-and-circularity/pgm-management (accessed 2024-02-15).

Proton Exchange Membrane Water Electrolysis (PEMWE) is considered one of the most promising form of green hydrogen production that could lead to a successful decarbonization of industrial processes, with a potential of at least 10% reduction of CO2 emissions of the total abatement needed by 2050 [1]. Since the oxygen evolution reaction (OER) catalyst on the anode side is dominated by Iridium (Ir)-based materials, scarce and expensive, reducing the loading to 0.1 - 0.2 mgIr/cm2 is critical to ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production. As outlined by the U.S. Department of Energy (DOE), the target Ir content in electrodes should be reduced to less than 0.5 mg/cm2 by 2026 [2].To achieve low Ir loadings, Smoltek Hydrogen’s aim is to significantly increase the available surface area of the Porous Transport Layers (PTLs) by growing vertically its patented Carbon NanoFiber (CNFs) structure [3], protected with a corrosion-resistant and conductive layer and electrodeposited with OER catalyst (Fig. 1a), creating a unique Porous Transport Electrode (PTE). With this electrodeposition method, we obtain a thin continuous Ir layer with a strong adhesion along the nanostructures, a high electrical conductivity [4] reducing contact resistance between the catalyst layer and PTL substrates, and a maximum utilization of the catalyst.This work will concentrate on the successful reduction of Ir loading to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in Half-Cell tests (Fig. 1c). The polarization curves of electrodes with low Ir loading obtained in Full-Cell exhibited superior performance compared to cells with significantly higher Ir loading. The aim is now to reach constant current durability tests (Fig. 1d) for 2000 hours or more on PEMWE operation using 0.1 mg/cm2 Ir loaded PTEs, with minimum degradation and overcoming mass transport limitations, particularly at higher current densities. References IEA (2021), Net Zero by 2050, IEA, Paris, https:/www.iea.org/reports/net-zero-by-2050https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysisXin Wen. Enhancing Efficiency and Durability of PEM Water Electrolysis with Low Iridium Loading through Nanofiber-Modified Porous Transport Electrodes, 2024, ECS Meeting s. MA2024-01Krivina et al. Adv.Mater., 2022, 34, 2203033. Figure 1

Corrosion behavior of metallic coatings on titanium bipolar plates of proton exchange membrane water electrolysis

Proton‐exchange membrane water electrolysis (PEMWE) powered by renewable energy sources is an eco‐friendly technology for the mass production of hydrogen. One of the major obstacles in the commercialization of PEMWE is the necessity of using precious metal catalysts under corrosive operating conditions, which can be partially mitigated by using nonprecious metal catalysts for the cathode, where the conditions are less harsh than those for the anode. However, the use of nonprecious transition metal catalysts limits both performance and durability. To overcome this limitation, a wide range of NiMoMn ternary alloy catalyst compositions were fabricated by electrodeposition, and their performances were evaluated. The best‐performing Ni 82.1 Mo 11.6 Mn 6.3 alloy catalyst exhibited an outstanding hydrogen evolution performance with an overpotential of 16 mV at −10 mA cm −2 , and with an increase of only 8 mV after 10,000 potential cycles for durability testing. The application of this material in a PEMWE single cell gave a favorable performance of 1.936 A cm −2 at 2.0 V cell , and an excellent degradation rate of 2.2 mV h −1 in a durability test performed at 1 A cm −2 . This high performance and excellent durability of the Ni 82.1 Mo 11.6 Mn 6.3 catalyst was attributed to the modulation of its electronic structure, in addition to a large electrochemical surface area, and stable Mn oxide formation on the surface. These results indicate the potential of this catalyst for use in lowering the hydrogen production costs associated with PEMWE.