Hydrogen Crossover Research Articles

Suppression of Chemical Degradation By Gas Barrier Polymer Electrolyte Membranes

[Introduction]Polymer electrolyte fuel cell (PEFC) is one of the promising technologies for decarbonization. Especially, PEFC is suitable to power heavy-duty vehicles (HDV) because of its high efficiency and high fuel capacity. However, there are some serious technical challenges for PEFC application for HDV such as the durability. When we focus on the chemical degradation of polymer electrolyte membranes (PEMs), it happens due to attack by radical species. One of the radical formation mechanisms is the reaction at the anode side by the penetrated oxygen from cathode. Therefore, a promising mitigation strategy against chemical degradation is the suppression of oxygen permeability through the PEM.To verify this concept, we developed high gas barrier PEM. As a model gas barrier PEM, we made a sandwich type PEM with high oxygen barrier property. The sandwich PEM was prepared by depositing a thin interlayer consisting blended poly(vinyl alcohol) (PVA) as a gas barrier material and poly(vinyl sulfonic acid) (PVS) as a proton conductor in between two layers of Nafion 211 membranes. We evaluate chemical durability using the sandwich gas barrier PEM and discuss about the mechanism.[Experimental]To fabricate thin sandwich PEMs (15-20 µm), ethanol diluted Nafion dispersion solution (20 mg/ml) and PVA/PVS solution (10 mg/ml) were sprayed on a polytetrafluoroethylene (PTFE) sheet by a spray gun (Tamiya HG wide airbrush). The thickness of each layer was controlled by controlling the deposited weight. Then, membrane characterization procedures such as surface roughness, proton conductivity, and dimensional stability were performed. To evaluate fuel cell performance, the PEMs were mounted to a JARI cell with 1 cm2 active area. Chemically accelerated stress test was performed by open circuit voltage (OCV) holding test following NEDO protocol.[Results and Discussion]Several areal densities of PVA/PVS interlayer were successfully incorporated into Nafion membrane to make sandwich PEM. The sandwich PEM shows considerable fuel cell performance, and thin sandwich PEMs show higher performance than the 50 µm sandwich PEM, although it is lower than the thin sprayed Nafion. For example, the peak power density of 15 µm sandwich PEM was 0.44 W cm-2 compared to 0.30 W cm-2 and 0.50 W cm-2 for 50 µm sandwich PEM and 15 µm Nafion, respectively. Furthermore, the incorporation of interlayer to thin PEM can suppress the hydrogen crossover current density from 7.8 mA cm-2 to 5.5 mA cm-2 indicating superior gas barrier property. From the higher gas barrier property, it is predicted thin sandwich PEMs will have higher chemical durability than Nafion with similar thickness.

Casting Electrodes on PEEK Reinforced Sulfonated Polyphenylsulfone Membrane

Researchers are exploring the potential of proton exchange membranes made from hydrocarbon polymers that do not contain fluorine. These polymers possess desirable properties that could make them more environmentally friendly and cost-effective compared to current perfluorinated sulfonic acids (PFSA). Hydrocarbon polymers have a unique structure that maintains high proton conductivity while reducing gas crossover, thus presenting a promising alternative to PFSA membranes [1]. Previous studies have demonstrated the potential of hydrocarbon membranes in electrolyzers using sulfonated polyphenylene sulfone (sPPS) [2]. However, sPPS has a high ion exchange capacity (2.17 – 3.57 meq/g), leading to excessive water uptake that causes the membrane to swelling and impedes upscaling, such as casting anodes directly onto the membrane. To overcome this issue, a woven, open-mesh PEEK substrate was incorporated into the membrane. The reinforced membrane exhibited a significant reduction in water uptake of up to 53% at room temperature and 43% at 60°C compared to the initial membrane. This improvement made it possible to cast the anode directly onto the membrane, resulting in a homogeneous surface (Fig. 1 left). In addition, preliminary electrolysis tests showed promising performance with low membrane resistance of 69 mΩcm² for a 74 µm thick membrane (Fig. 1 right). Literature: [1] Miyake, J.; Taki, R.; Mochizuki, T.; Shimizu, R.; Akiyama, R.; Uchida, M.; Miyatake, K. Design of flexible polyphenylene proton-conducting membrane for next-generation fuel cells. Sci. Adv. 2017, 3(10), eaao0476. DOI: 10.1126/sciadv.aao0476[2] Klose, C.; Saatkamp, T.; Münchinger, A.; Bohn, L.; Titvinidze, G.; Breitwieser, M.; Kreuer, K.; Vierrath, S. All‐Hydrocarbon MEA for PEM Water Electrolysis Combining Low Hydrogen Crossover and High Efficiency. Adv. Energy Mater. 2020, 10 (14), 1903995. DOI: 10.1002/aenm.201903995 Figure 1

Next Generation Fluorine-Free Proton Exchange Membranes for Electrochemical Energy Applications

Most commercially available proton exchange membrane (PEM)-based fuel cell and electrolyser systems currently employ perfluorinated sulfonic acid (PFSA)-based PEMs, e.g., Nafion. The use of these fluorinated polymers presents serious health and environmental concerns as their production, degradation, and disposal results in the release of hazardous perfluorinted compounds that have been shown to accumulate in the environment and are toxic to living organisms.[1] Developing non-toxic, safe-by-design hydrocarbon PEMs is therefore crucial to ensure that renewable technologies that rely on proton exchange membranes remain an environmentally friendly solution. Additional shortcomings of PFSA-based PEMs include their expensive synthetic cost, inherently high hydrogen crossover, and limited operating temperature range due to poor thermo-mechanical properties above 90 °C. Hydrocarbon (HC)-based membranes offer advantages over their perfluorinated counterparts in these specific areas, however, the main drawback of HC-PEMs is that they require a much greater density of sulfonic acid groups to achieve similar proton conductivities as PFSA-based polymers.[2] This leads to greater water uptake and excessive swelling which ultimately leads to reduced mechanical stability of HC membranes.More recently there has been an increasing number of reports exploring the use of block copolymer strategies to limit the water uptake and swelling properties of hydrocarbon PEMs while maintaining good ionic conductivity.[3] As the ion, liquid, and gas transport properties of the membrane are largely attributed to the hydrophilic blocks (i.e., with sulfonic acid groups) and the mechanical, chemical, and thermal stability of the resulting membrane is determined by the hydrophobic blocks (i.e., no sulfonic acid groups), it is postulated that the resulting membrane properties can be tuned by varying the fraction of hydrophilic/hydrophobic blocks.The overall goal of this project is to synthesise hydrocarbon block copolymer PEMs with reduced gas crossover and enhanced the mechanical properties while maintaining sufficiently high ionic conductivity, ultimately leading to higher performance and greater durability inelectrochemical energy conversion and storage systems, e.g., fuel cells and electrolysers. In this project we have compared the ex-situ properties of novel hydrocarbon block copolymers with PFSA-based Nafion membranes, e.g., water uptake and swelling, conductivity measurements, oxidative stability via Fenton's test, etc., as well as in-situ performance tests in single cell fuel cell and electroylzers.[1]Feng, M.; Wang, Z. et al. Sci. Rep. 2015, 5, 9859.[2]Holdcroft, S. Chem. Mater. 2014, 26, 381.[3]Guiver, M. et al. Chem. Rev. 2017, 117, 4759.

Suppression of PEFC Membrane Degradation By Using SnO2 As Electrocatalyst Support

Introduction Long-term durability of polymer electrolyte fuel cells (PEFCs) is required for various applications such as automobiles. It has been suggested that certain ions dissolved from electrocatalyst materials accelerate radical formation and subsequent chemical degradation of polymer electrolyte membrane (PEM) by the Fenton reaction [1]. Membrane degradation increases hydrogen and oxygen permeability and decreases proton conductivity and mechanical strength [2]. These phenomena significantly affect the electrochemical performance and durability of PEFCs. Therefore, in case metal oxides are used as catalyst support, it is necessary to check the dissolution of metal ions and to evaluate their effects on membranes. Our research group has been studying Nb-doped SnO2 (Sn(Nb)O2), showing improved durability of the electrocatalysts [3]. Here in this study, we evaluate the effects of Sn(Nb)O2 on the chemical degradation of PEMs. Experimental A commercial Pt/C catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used as the anode catalyst, while three types of cathode catalysts were applied and compared: 1) the commercial Pt/C; 2) Pt/MC where Pt was directly deposited on mesoporous carbon (MC); and 3) Pt/Sn(Nb)O2/MC where Pt was deposited on the Sn(Nb)O2 decorated on the MC. The durability test at open circuit voltage (OCV) was performed for 100 h. Before and after the durability test, cell performance, hydrogen crossover current density, and electrochemical surface area (ECSA) were characterized. The degree of membrane degradation was evaluated by measuring fluorine emission rate (FER) by ion chromatography, and membrane thickness and elemental distribution by energy-dispersive x-ray spectroscopy (EDS) coupled with field-emission scanning electron microscopy (FESEM). Results and discussion It was found that the use of Pt/Sn(Nb)O2/MC led to better durability in the OCV durability test. The decrease in OCV using Pt/Sn(Nb)O2/MC was smaller than that using Pt/C and Pt/MC, less than half of that Pt/C, as shown in Figure 1. The membrane thickness with Pt/Sn(Nb)O2/MC after the durability test was the same as that before the durability test, indicating that SnO2 actually suppressed the membrane degradation as shown in Figure 2. EDS elemental analysis confirmed no Sn ion dissolution from the cathode side as shown in Figure 3, also suggesting that SnO2 at the cathode suppressed the membrane degradation. In this presentation, we will quantitatively analyze the membrane degradation in using SnO2 and discuss possible mechanisms. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Comparative Studies of Atomically Thin Proton Conductive Films to Reduce Crossover in Hydrogen Fuel Cells.

Hydrogen fuel cells based on proton exchange membrane fuel cell (PEMFC) technology are promising as a source of clean energy to power a decarbonized future. However, PEMFCs are limited by a number of major inefficiencies; one of the most significant is hydrogen crossover. In this work, we comprehensively study the effects of two-dimensional (2D) materials applied to the anode side of the membrane as H2 barrier coatings on Nafion to reduce crossover effects on hydrogen fuel cells, while studying adverse effects on conductivity and catalyst performance in the beginning of life testing. The barrier layers studied include graphene, hexagonal boron nitride (hBN), amorphous boron nitride (aBN), and varying thicknesses of molybdenum disulfide (MoS2), all chosen due to their expected stability in a fuel cell environment. Crossover mitigation in the materials studied ranges from 4.4% (1 nm MoS2) to 46.1% (graphene) as compared to Nafion 211. Effects on proton conductivity are also studied, suggesting high areal proton transport in materials previously thought to be effectively nonconductive, such as 2 nm MoS2 and amorphous boron nitride under the conditions studied. The results indicate that a number of 2D materials are able to improve crossover effects, with those coated with 8 nm MoS2 and 1 L graphene able to achieve greater crossover reduction while minimizing conductivity penalty.

Empirical Degradation Models of the Different Indexes of the Proton Exchange Membrane Fuel Cell Based on the Component Degradation

To describe the degradation of proton exchange membrane fuel cells (PEMFCs), empirical degradation models of different indexes of PEMFCs are established. Firstly, the simulation process and assumptions of PEMFC degradation are proposed. Secondly, the degradation simulation results including the performance and distribution indexes under the different degradation levels are conducted by AVL FIRE M. Finally, the empirical degradation models of performance and distribution indexes are established based on the above simulation results and experimental data. The results show that the relationship between the experimental and simulation results is established by the index of current density. The empirical degradation models of current density, average equilibrium potential on the cathode catalyst layer (CL), average membrane water content, average oxygen molar concentration on the cathode CL, and average hydrogen crossover flux are the linear function. The empirical degradation models of average exchange current density on the anode CL, average hydrogen molar concentration on the anode CL, and average oxygen crossover flux are the quadratic function. The empirical degradation model of average activation overpotential on the cathode CL is the quintic function.

Modeling Contact Resistance and Water Transport within a Cathode Liquid-Fed Proton Exchange Membrane Electrolyzer

Conventional proton-exchange membrane (PEM) water electrolyzers use thicker membranes (>175 μm) than their PEM fuel cell counterparts (<25 μm), which reduces hydrogen crossover but also reduces electrolyzer efficiency due to the increased resistance. Reduction of hydrogen crossover is critical in conventional systems to avoid buildup of hydrogen in the anode above the lower flammability limit. New concepts for operating PEM water electrolyzers are emerging, such as the patented concept involving liquid water supply at the cathode while operating the anode with air, which reduces the safety concern related to hydrogen crossover using thin membranes. Experimental work has demonstrated the viability of this approach, but open questions remain regarding the interplay between water transport, water consumption, and cell performance, as well as identifying the components and material properties that enable high performance. In this work, a physics-based computational model of a cathode-fed PEM water electrolyzer was developed. The model highlights the importance of limiting contact resistance and explores the effect of cell compression on non-uniformity of current distributions. Sensitivity studies found that membranes up to 50 μm thick can be used without significant water transport limitations.

Degradation of Pt-Based Cathode Catalysts Upon Voltage Cycling in Single-Cell PEM Fuel Cells Under Air or N2 at Different Relative Humidities

A major degradation mechanism of polymer electrolyte membrane fuel cells (PEMFCs) in transportation applications is the loss of the electrochemically active surface area (ECSA) of platinum cathode catalysts upon dynamic load cycling (resulting in cathode potential cycles). This is commonly investigated by accelerated stress tests (ASTs), cycling the cell voltage under H2/N2 (anode/cathode). Here we examine the degradation of membrane electrode assemblies with Vulcan carbon supported Pt catalysts over extended square-wave voltage cycles between 0.6-1.0 VRHE at 80 °C and 30%-100% RH under either H2/N2 or H2/Air; for the latter case, differential reactant flows were used, and the lower potential limit is controlled to correspond to the high-frequency resistance corrected cell voltage, assuring comparable aging conditions. Over the course of the ASTs, changes of the ECSA, the hydrogen crossover current, the proton conduction resistance and the oxygen transport resistance of the cathode electrode, as well as the differential-flow H2/O2 and H2/Air performance at 80 °C/100% RH were monitored. While the ECSA loss decreases with decreasing RH, it is independent of the gas feeds. Furthermore, the H2/Air performance loss only depends on the ECSA loss. ASTs under H2/N2 versus H2/Air only differ with regards to the chemical/mechanical degradation of the membrane.

New multi-functional catalyst coated membrane structure for improved water electrolysis

The state of proton exchange membrane water electrolysis (PEMWE) technology is largely dependent on conventional iridium catalyst layers with a lack of material and structural alternatives. For the first time, a catalyst coated membrane (CCM) structure is demonstrated to improve iridium catalyst utilization and decrease hydrogen crossover simultaneously. The anode catalyst layer is composed of an electrolessly-deposited Pt layer (<130 μg cm−2) at the membrane surface with a lower loading of iridium oxide catalyst (∼1.2 mg cm−2 IrOx) sprayed on the platinized membrane with variable thicknesses. These samples were subjected to rigorous catalyst characterization and crossover evaluation via a benchtop modified rotating disk electrode (MRDE) and an electrolysis cell (50 cm2), respectively. The MRDE results show that the CCM structure with the electroless Pt layer decreases the potential by as much as 100–200 mV at 1 A cm−2. At the unit cell level, the performance enhancement was in the range of 400–600 mV at 2 A cm−2. The parasitic hydrogen crossover current density is reduced by about 40 % when comparing this novel structure approach to baseline CCMs. This multi-functional CCM structure can potentially reshape the standards for PEM and for alkaline electrolyte membrane water electrolysis.

Effects of mechanical pressure on anion exchange membrane water electrolysis: A non-negligible yet neglected factor

Commercialized implementations of anion exchange membrane water electrolysis (AEMWE) require stable operation at high current density. To achieve this, ohmic, electrochemical and concentration polarizations are supposed to be exceedingly suppressed. Among all crucial materials, porous electrodes with catalyst coatings extensively affect the above polarizations, which are highly sensitive to specific mechanical pressure for cell assembly. However, the imposed mechanical pressure and its effects on cell performance are rarely reported in AEMWE cells. Here, quantitative characterizations of mechanical pressure and its effects on i) physical properties of catalyst coated electrodes and ii) corresponding single-cell performance are comprehensively investigated. First, the imposed mechanical pressure on membrane electrode assembly (MEA) is controlled by different total thickness gaps between anode/cathode and poly-tetra-fluoroethylene (PTFE) gaskets (Δd = 0, 100, 200, 300 μm). Second, the above resulted distributions of mechanical pressure are quantitatively studied by a mechanical pressure tracking method. Third, the influence of the mechanical pressure on the physical properties of the electrodes and cell performance are demonstrated. It is proved that the mechanical pressure of ca. 0.5 MPa is comprehensively beneficial for suppressing internal resistance (RΩ) and charge transfer resistance (Rct), with slightly increased mass diffusion resistance (Rmd) and hydrogen crossover. This study unveils the intrinsic effects of mechanical pressure on cell performance and provides critical insights into baseline benchmarking and single-cell even stack optimization.

Metal-organic framework-decorated PTFE reinforced membranes with immobilized caffeic acid radical scavenger towards improved performance and durability of PEMFC

During the continuous operation of fuel cell, the generated free radicals have an irreversible effect on the proton exchange membrane (PEM), and the introduction of free radical scavengers is an effective strategy for improving its durability. In this study, we proposed to prepare thin and highly durable reinforced membranes by immobilizing organic radical scavenger caffeic acid on the fibrous PTFE supporting layer decorated with amino-functionalized metal-organic framework. The electrostatic force between the amino and sulphonic acid groups can induce an orderly aggregation of hydrophilic cationic groups within the Nafion, endowing the reinforced composite PEMs with superior proton conductivity. The mechanical properties and dimensional stability of the reinforced membranes were effectively enhanced by the reinforcement of the PTFE layer decorated with the MOF network, and the hydrogen crossover was mitigated. The thickness of Nafion reinforced membranes was reduced to 25 µm with the PTFE reinforcement. After assembling in a single cell, the Nafion composite membrane (PPUC-Nafion-3) with a 3 wt% doping of caffeic acid achieved a maximum power density (PDmax) of 812.64 mW cm−2 and the open circuit voltage (OCV) decay rate of only 1.11 mV h−1 over 100 h. For comparison under the same conditions, recast Nafion possessed a much lower PDmax of only 486.30 mW cm−2 and a higher OCV decay rate of 1.91 mV h−1. This study demonstrates an effective approach to developing highly durable and thin PEMs for the realization of PEMFC with improved output performance and durability simultaneously.

Impact of an electrode-diaphragm gap on diffusive hydrogen crossover in alkaline water electrolysis

Hydrogen crossover limits the load range of alkaline water electrolyzers, hindering their integration with renewable energy. This study examines the impact of the electrode-diaphragm gap on crossover, focusing on diffusive transport. Both finite-gap and zero-gap designs employing the state-of-the-art Zirfon UTP Perl 500 and UTP 220 diaphragms were investigated at room temperature and with a 12 wt% KOH electrolyte. Experimental results reveal a relatively high crossover for a zero-gap configuration, which corresponds to supersaturation levels at the diaphragm-electrolyte interface of 8–80, with significant fluctuations over time and between experiments due to an imperfect zero-gap design. In contrast, a finite-gap (500 μm) has a significantly smaller crossover, corresponding to supersaturation levels of 2–4. Introducing a cathode gap strongly decreases crossover, unlike an anode gap. Our results suggest that adding a small cathode-gap can significantly decrease gas impurity, potentially increase the operating range of alkaline electrolyzers, while maintaining good efficiency.

Ce-radical Scavenger-Based Perfluorosulfonic Acid Aquivion® Membrane for Pressurised PEM Electrolysers.

A Ce-radical scavenger-based perfluorosulfonic acid (PFSA) Aquivion® membrane (C98 05S-RSP) was developed and assessed for polymer electrolyte membrane (PEM) electrolyser applications. The membrane, produced by Solvay Specialty Polymers, had an equivalent weight (EW) of 980 g/eq and a thickness of 50 μm to reduce ohmic losses at a high current density. The electrochemical properties and gas crossover through the membrane were evaluated upon the formation of a membrane-electrode assembly (MEA) in a range of temperatures between 30 and 90 °C and at various differential pressures (ambient, 10 and 20 bars). Bare extruded (E98 05S) and reinforced (R98 05S) PFSA Aquivion® membranes with similar EWs and thicknesses were assessed for comparison in terms of their performance, stability and hydrogen crossover under the same operating conditions. The method used for the membrane manufacturing significantly influenced the interfacial properties, with the electrodes affecting the polarisation resistance and H2 permeation in the oxygen stream, as well as the degradation rate, as observed in the durability studies.

Advancements in Thin, Reinforced Proton Exchange Membranes for Water Electrolysis

Proton exchange membrane water electrolysis (PEMWE) is emerging as one of the most promising methods to produce clean hydrogen at industrial scale. New PEMWE stack designs require high voltage efficiency and differential pressure operation without sacrificing low hydrogen in oxygen concentrations in the anode stream. Membranes used in current stack designs, such as Chemours Nafion™ N115, are thick to provide strong mechanical stability. However, employing a thinner and mechanically supported membrane can enhance both the electrochemical performance and mechanical properties. With the demand for cheaper hydrogen, these new membrane designs are needed to achieve advanced performance metrics. In this presentation, recent improvements in membrane design at Chemours will be summarized.Novel architectures comprise a thin, reinforced composite membrane approach, utilizing a lower equivalent weight (EW) polymer that can surpass the performance of the current commercial membranes. For example, overpotential is reduced by >150 mV at 3 A/cm2 for novel membranes compared to Nafion™ N115 at 80°C. However, one concern with having a thinner film is the increase in hydrogen crossover, since the lower explosive limit (LEL) for hydrogen in oxygen is only 4 vol %. PEMWE differential pressures of up to 30 bar on the cathode side can exacerbate these hydrogen crossover challenges. To mitigate this hazard, gas recombination catalyst (GRC) additives have been implemented within the membrane where the GRC recombines hydrogen and oxygen to form water. A reduction in anodic hydrogen in oxygen content of >50x has been observed, assuring the safe operation at high differential pressures for these thin membranes. Polarization curves across different membrane constructions were analyzed as well as hydrogen crossover for various GRC designs. Comparisons will be presented demonstrating the improved performance and reduced hydrogen crossover. Figure 1

Modelling of a Proton-Exchange Membrane Electrolysis Cell with Liquid-Fed Cathode

Conventional proton-exchange membrane (PEM) water electrolysers use much thicker membranes (>175 µm) than their PEM fuel cell counterparts (<25 µm), which reduces hydrogen crossover but also reduces electrolyzer efficiency due to the increased Ohmic resistance1. Reduction of hydrogen crossover is critical in conventional systems to avoid buildup of hydrogen in the anode above the lower explosive limit. Due to the use of liquid water at the anode in conventional systems, the anode cannot be flushed with air or an inert gas to reduce the hydrogen concentration.If the liquid water supply is moved to the cathode, the anode can be easily purged with air, reducing the safety concern related to hydrogen crossover. Proof-of-concept experiments2 have demonstrated the viability of this approach, but many open questions remain regarding the interplay between water transport, water consumption, membrane hydration, and cell performance, as well as understanding what components and properties are most important in improving the efficiency of such a device.In this work, a framework for modelling of PEM electrolysis cells will be outlined, with special attention to wet and dry anode conditions. The model will be used to provide guidance for optimizing system performance while contributing to understanding of local processes inside an electrolysis cell such as water transport, heat generation, reaction distribution, and bubble formation. We study the impact of various design and operational choices, such as membrane thicknesses, PTL structure, air feed humidity, and differential pressure operation, on the rate of water transport from cathode to anode and on overall cell polarization performance. Using these results, we provide design recommendations for PEM electrolysers with liquid-fed cathodes. Finally, progress towards an open-source implementation of this model will be discussed.This work has been performed within the HOPE (Revolutionizing Green Hydrogen Production with Next Generation PEM Water Electrolyser Electrodes) and HYSTACK (Low cost, high efficiency PEM electrolyser stack) projects financially supported by the Research Council of Norway under project numbers 325873 and 321466, respectively. Ayers, K. et al. Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale. Annu. Rev. Chem. Biomol. Eng. 10, 219–239 (2019).Barnett, A. O. & Thomassen, M. S. Method for producing hydrogen in a PEM water electrolyser system, PEM water electrolyser cell, stack and system. Patent No.: WO 2019/009732. EP3649276B1. US11408081B2.

The Impact of Cation Contamination on Proton Exchange Membrane Water Electrolyzer (PEMWE)

Hydrogen has emerged as a promising clean energy carrier and source alternative to fossil fuels(1). Mass production of cost-effective hydrogen without pollution is essential for the so-called hydrogen economy and the hydrogen produced in this process is called green hydrogen(2). It uses renewable energy such as wind energy and solar energy to generate electricity and produce hydrogen via water electrolysis, with net-zero carbon emissions. The proton exchange membrane water electrolyzer (PEMWE) is one of the most commercially available devices for water electrolysis. A membrane electrode assembly (MEA), which is laminated from an anode, cathode, and proton exchange membrane, is prone to poor performance and low lifetime if exposed to cation contamination due to the chemical properties of the materials, such as the negatively charged polymer side chain and low potential on the cathode. Therefore, it requires ultra-pure water in the operation condition.Different cations may bring different challenges to the PEMWE. For example, some transition metals, such as Fe2+, once introduced into the membrane, may catalyze the chain formation of radicals (×OH, ×OOH, etc.) due to the Fenton reaction(3), which will cause the decomposition of the membrane. In addition, some common cations that exist in drinking water, such as Ca2+, Na+, and Mg2+, will migrate onto the cathode through the membrane and block the active sites of the catalyst(4). Moreover, typical radical scavengers such as Ce, may migrate through the membrane during the operation process(5) and become a source of contamination due to their mobility in the MEA.In this study, we will investigate the impact of different concentrations of contamination, such as Ca2+ on the polarization curve of PEMWC and discuss the possible influence on its hydrogen crossover. To further clarify the contamination impact on the cathode, the performance of MEAs with different catalyst loadings on the cathode when subjected to cations, will be presented and discussed. In addition, several analytical instruments, such as ion chromatography (IC), inductive coupled plasma mass spectroscopy (ICP-MS), and thermo-gravimetric analysis (TGA) will be utilized to gain deeper insight into the degradation process of these contaminated MEAs. Figure 1

Development of High Durable Pore-Filling Anion Exchange Membranes for Water Electrolysis Application

Water electrolyzer is a device that converts renewable electrical energy into environmentally friendly chemical energy, hydrogen. Water electrolysis is mainly categorized into proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE). Non-precious electrocatalysts and hydrocarbon-based polymeric membranes are used for two different systems. It is advantageous for AEMWE in terms of cost. However, low current density and chemical stability for current anion exchange membrane technology (AEM) restricts early market penetration. Thus, thedevelopment of low resistance and high durable AEMs is of importance. In this study, superior ion conductivity and high durable pore-filling AEMs were developed for AEMWE. Pore-filling AMEs with different contents of crosslinking monomers were prepared by the monomers using chemically stable anion exchangeable functional groups in a porous polyethylene(PE) substrate. Properties of the AEMs were characterized through areal resistance, ionic conductivity, ion exchange capacity, water uptake, swelling ratio, mechanical strength and hydrogen crossover. In addition, AEMWE performance and durability tests were also conducted. Acknowledgments This research was supported in part by Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253), Rural Development Administration, Republic of Korea and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

(Invited) Aemion+® AEM Water Electrolysis with Excellent Iridium-Free Performance and Industrially Relevant Stability in Hot, Caustic Electrolyte

Hydrogen has a unique ability to maximize the utility of and enable new business models for intermittent renewable deployment. It can be stored cost-effectively in geological storage, transported between regions to suit geographic needs and bridge Dunkelflautes. Global electrolysis capacity must increase from the current <2 GW to 850 GW in 2030 (IEA Net Zero 2050) and in excess of 3500 GW in 2050 to enable this transition.Both traditional Alkaline (AWE) and proton-exchange membrane electrolyzers (PEMWE) are mature technologies that are anticipated to split the overall market share. However, each of these technologies face fundamental challenges:AWE operate at low current density, requiring large and difficult to transport systems, require high concentration electrolytes (e.g. 30 wt% KOH) to conduct hydroxides and ensure low gas solubilities for safety, which necessitates the use of expensive and difficult to machine high-nickel steels, especially in advanced, pressurized designs. Additionally, the porous nature of the electrode separator (e.g. Zirfon) compromises the desired dynamic load for pairing with intermittent renewables.PEMWE use a proton-conductive membrane to enable high current densities, dynamic loads, and differential hydrogen pressures, however, the most efficient operation requires iridium catalyst, which presents a near-term challenges with scalability, together with Ti and PGM structural elements that further impede cost-effectiveness.Alkaline anion-exchange water electrolyzers (AEMWE) address both of these challenges by operating with a cohesive, hydroxide-transporting membrane together with alkaline electrolyte to enable high efficiency, high current density operation, without iridium electrocatalysts or other scarce or expensive components. The realization of capital cost-effectiveness, dynamic load, and compact systems in one technology enables the most cost-effective green hydrogen and represents a step-change in the trajectory towards the DOE Hydrogen Shot target of $1/kg.The instability of alkaline anion exchange membrane chemistries based on quaternary amines or pendant imidazolium groups in relevant temperatures and alkalinities to industrial operations have historically resulted in untenable compromises and too-short lifetimes for industrial-scale deployment. Ionomr's Aemion+® AF2-AWP8-75-X and AF3-HWK9-75-X membranes are based on a sterically-protected imidazolium chemistries that are chemically robust (e.g. 6 months, 1 M, 80 °C without alteration to chemical or mechanical properties), and additionally exhibit low swelling to provide mechanical integrity to electrodes and enable operation in low concentration electrolytes. These membranes are an enabling technology for long-duration AEM water electrolysis.This talk highlights how Ionomr's Aemion+® membranes demonstrate target performances (e.g. >2 A/cm² at 2 V) with non-PGM OER catalysts with no apparent losses to 1000 hours operation across several configurations at ≥70 °C and 1 M KOH operation, and several longer lifetime demonstrations including 1 year durability using AWE electrodes and >6 months including hydrogen crossover measurement. This talk further highlights the potential for the three-dimensionality of electrodes in alkaline AEMWE and the necessary processing and operational requirements to create reproducible and stable GDEs with catalyst ink-based deposition techniques. Figure 1

Gas Crossover and Supersaturation in Advanced Alkaline Water Electrolysis

Conventional alkaline water electrolyzers operate with a finite-gap between the cathode and anode [1]. The ohmic resistance induced by this finite-gap results in energy losses. Therefore, the zero-gap assembly is considered an attractive configuration to perform advanced alkaline water electrolysis. However, gas crossover is enhanced in the zero-gap configuration by supersaturated hydrogen concentrations in the vicinity of the electrode. To avoid excessive gas crossover there is a limiting minimal operational current density.Different transport mechanisms can contribute to gas crossover through the porous separator, namely diffusion, convection, and electrolyte mixing. For well-balanced pressures and industrial flow rates, diffusion is the main contributor to gas crossover [2].Local supersaturation at the diaphragm interface significantly contributes to gas crossover [2]. To confirm this hypothesis, in-situ gas analysis experiments were conducted in an electrolysis setup equipped with in-line gas chromatography that could be operated with negligible influence of convective transport mechanisms to evaluate the diffusive transport in both zero- and finite-gap configurations.There is a clear distinction in gas crossover between zero- and finite-gap designs. In Figure 1 is shown that for the zero-gap assembly, hydrogen crossover rates were found to increase with current density, evidencing that supersaturation at the diaphragm interface plays an important role on gas crossover. In contrast, using a finite-gap configuration, gas crossover was significantly reduced and approached equilibrium diffusion rates, proving that gas crossover is mainly driven by diffusive hydrogen transport. Therefore, advanced alkaline electrolysis could be operated at higher current densities by applying a zero-gap configuration and reducing diaphragm thickness, but gas crossover leads to higher hydrogen in oxygen levels at low power load.[1] J. Brauns, T. Turek. “Alkaline water electrolysis powered by renewable energy: A review”. Processes, vol. 8, no. 2 (2020).[2] M. T. de Groot, J. Kraakman, R. Lira Garcia Barros. “Optimal operating parameters for advanced alkaline water electrolysis”. International Journal of Hydrogen Energy, vol. 47, no. 82 (2022) 34773-34783. Figure 1

(Invited) Recent Polymer Electrolyte Membrane (PEM) Electrolysis Research Advances in the Hydrogen from Next-Generation Electrolyzers of Water (H2NEW) Consortium

The H2NEW consortium is a Department of Energy (DOE)-Hydrogen and Fuel Cell Technology Office (HFTO) funded effort with a vision to enable $2/kg hydrogen production by 2025 through large-scale production of hydrogen by either low-temperature electrolysis (LTE) or high-temperature electrolysis (HTE). The H2NEW consortia was established in October 2020 and has seen a recent increase in emphasis and expansion of scope with the passage of the Bipartisan Infrastructure Law (BIL) and the focus on a Clean Hydrogen Electrolysis Program, a $1B commitment over 5 years from the US government. This has resulted in a series of workshops, supported by members of H2NEW, on topics relevant to electrolysis including liquid alkaline electrolysis,[1] high temperature electrolysis,[2] and manufacturing and advanced materials for polymer electrolyte membrane electrolyzers.[3]H2NEW focuses on better understanding the cost, performance, and durability tradeoffs of electrolysis systems through an increased understanding of the factors that contribute to these metrics. This includes the impact of operating conditions, materials selection, and component design and integration. Techno-economic and system analysis help provide guidance for the primary components of interest based on cost and trade-offs associated with electricity prices as they relate to hydrogen levelized costs. The consortium has a focus on durability without compromising efficiency while dramatically reducing costs.While the efforts of H2NEW have historically covered polymer electrolyte membrane (PEM) and oxide ion conducting solid oxide electrolysis (SOEC), recently these efforts have expanded to also include liquid alkaline electrolysis. An overview of the scope of H2NEW and analysis efforts that relate to all electrolysis technologies will be highlighted in this talk, but a focus will be placed on scientific advances made in PEM technology. For example, H2NEW has made significant progress in the areas of anode stability including investigations of operating strategies and Ir stability under various operating conditions; quantification of performance metrics including hydrogen crossover under operation; processing of inks and electrodes; and development and characterization of porous transport layers. These topics and highlights of research advances will be presented.AcknowledgementsThis presentation is a summary of the research efforts of numerous H2NEW researchers. See h2new.energy.gov for a comprehensive list of the researchers contributing to this work. This research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.References energy.gov/eere/fuelcells/advanced-liquid-alkaline-electrolysis-experts-meetingenergy.gov/eere/fuelcells/us-department-energy-high-temperature-electrolysis-hte-manufacturing-workshopenergy.gov/eere/fuelcells/h2-amp-hydrogen-shot-workshop-advanced-materials-pem-electrolyzers