In a significant breakthrough poised to transform the landscape of hydrogen production, researchers have unveiled a pioneering proton exchange membrane (PEM) electrolyser capable of operating efficiently with impure water sources. This advancement directly addresses a longstanding challenge in PEM electrolyser technology—its stringent requirement for ultrapure water feedstocks due to the detrimental effect of trace contaminants. Such impurities, particularly cationic species, have historically compromised electrolyser longevity and performance, necessitating costly and energy-intensive water pretreatment systems. The newly developed system deftly bypasses this limitation, maintaining stable operation over extensive durations while preserving high efficiency, marking a milestone in sustainable hydrogen production.
PEM electrolysers represent a cornerstone technology in the green hydrogen economy because of their ability to convert electrical energy into hydrogen gas with high purity and efficiency. Nevertheless, their deployment has been hindered by vulnerabilities related to feedwater quality. Even minute levels of ionic contaminants can lead to catalyst poisoning, membrane degradation, and deposition issues within the cell, shortening lifespan and escalating operational expenses. Until now, ensuring water purity through ultrafiltration, deionization, or reverse osmosis has been obligatory, constricting PEM electrolysers’ versatility and scalability, especially for remote or resource-constrained environments.
The research team, led by Wang, Yang, Guo, and colleagues, has overcome these challenges by ingeniously engineering the cathode catalyst layer with a Brønsted acid oxide—specifically, molybdenum oxide (MoO₃₋ₓ). This modification creates a locally acidic microenvironment at the cathode surface, a disruption from conventional neutral or alkaline conditions typical in PEM electrolysers. Their approach integrates detailed, in situ electrochemical analysis to monitor the pH at microscopic scales, offering unprecedented insight into the electrolyser’s operational microenvironment and its influence on performance and durability.
Conventionally, the PEM electrolyser’s susceptibility to fouling and degradation arises because undesirable species accumulate or precipitate at electrode surfaces under near-neutral pH conditions. By introducing MoO₃₋ₓ—a Brønsted acid oxide—onto the platinum/carbon (Pt/C) cathode, the researchers effectively lower the localized pH. This acidification facilitates faster kinetically favorable hydrogen evolution reactions while simultaneously hindering the deposition of contaminants that would otherwise impair the catalytic sites or the ionomer-membrane interface. The acidity also acts to stabilize the polymer electrolyte membrane, protecting it against chemical degradation pathways commonly exacerbated by contaminants.
To unravel these nuanced interfacial phenomena, the team employed a combination of scanning electrochemical microscopy (SECM) alongside ultramicroelectrode-based pH measurements. This sophisticated methodology allowed them to capture the spatial and temporal distributions of pH within the operating cell, a feat rarely achieved in PEM electrolysis research. Their findings revealed that the MoO₃₋ₓ modified cathode sustained an acidic microenvironment robust enough to enhance hydrogen production kinetics even when fed with tap water of typical impurity levels—a remarkable contrast to previous designs requiring ultrapure water.
Performance testing of the modified PEM electrolyser demonstrated over 3,000 hours of continuous operation at a high current density of 1.0 A cm⁻² using impure water. Remarkably, the electrolyser’s efficiency and output maintained parity with state-of-the-art systems fueled by ultrapure water. This longevity under challenging feed conditions signifies a notable step forward in practical electrolyser design, especially considering the economic and environmental costs associated with extensive water purification. The modification thus promises substantial reductions in both infrastructure complexity and operating expenditures.
Beyond the immediate improvements in operational resilience, this discovery paves the way for broader deployment of PEM electrolysers in diverse settings where water purity cannot be guaranteed. Remote areas, industrial sites, and emerging markets stand to benefit tremendously from electrolyser systems that tolerate native water sources without compromising durability or hydrogen yield. Furthermore, by reducing dependence on highly purified inputs, the technology aligns well with global goals for sustainable and decentralized hydrogen production networks.
The implications of this breakthrough reverberate into the fundamental understanding of electrochemical interfaces. The concept of deliberately tailoring the proton concentration at the nanoscale within catalyst layers could inspire new design paradigms across fuel cells and electrolytic devices. The deployment of Brønsted acid oxides opens avenues for customizing microenvironment properties to optimize reaction pathways and suppress deleterious side reactions that have long plagued catalyst stability.
Moreover, this study challenges the convention that PEM electrolysers must operate strictly at neutral or mildly acidic bulk conditions. By capitalizing on localized acidification, it is possible to engineer reaction zones that are chemically optimized without compromising the overall system integrity. This duality between micro- and macro-environment control heralds a nuanced approach to catalyst architecture, where the focus shifts from simply enhancing bulk electrolyte properties to fine-tuning the immediate surroundings of active sites.
The team’s methodology also highlights the value of advanced characterization tools in advancing electrochemical technologies. Real-time, spatially resolved pH monitoring within operating cells can reveal complex interactions often overlooked in traditional macroscale studies. Such insights empower researchers to identify mechanistic bottlenecks and engineer solutions precisely at the sites where degradation or performance losses initiate, thereby accelerating the development cycle.
Sustainability considerations further underscore this achievement’s significance. By facilitating extended electrolyser lifespan and eliminating the need for prohibitive feedwater pretreatment, the modified PEM system contributes to lowering the overall carbon footprint associated with green hydrogen production. Reduced maintenance frequency and energy savings from purification processes enhance the technology’s attractiveness for integration with renewable energy sources, including solar and wind generation, where grid flexibility and cost-effectiveness are paramount.
Looking ahead, scaling this technology from laboratory prototypes to commercial-scale systems will test its robustness under real-world load variations and complex impurity profiles. Further optimization of the Brønsted acid oxide deposition techniques and exploration of alternative acid oxides with tailored properties may unlock even greater performance and durability enhancements. Collaborative efforts involving material scientists, electrochemists, and system engineers will be critical in translating these seminal findings into scalable, market-ready solutions.
Importantly, the principles established by this study resonate beyond PEM electrolyser applications, with potential crossover benefits for other electrochemical energy conversion and storage technologies. Fuel cells, redox flow batteries, and CO₂ reduction devices could derive advantages from controlled microenvironment acidity to boost efficiency and stability. The holistic approach championed here—integrating materials innovation with in situ diagnostics—could therefore catalyze breakthroughs across the broader clean energy sector.
This landmark achievement reported by Wang et al. exemplifies how strategic material modifications at the nanoscale can overcome entrenched technological barriers, redefining operational paradigms in hydrogen evolution. As the global energy transition accelerates, such innovations will be instrumental in realizing cost-effective, scalable, and environmentally benign hydrogen production pathways crucial for decarbonizing multiple industries.
In summary, the development of a microenvironment pH-regulated PEM electrolyser with MoO₃₋ₓ-modified cathode catalyst layers represents a paradigm shift in electrolyser technology. By harnessing the acidifying properties of Brønsted acid oxides to optimize the cathode microenvironment, the system achieves stable, high-performance hydrogen generation using impure water. This breakthrough holds immense promise for reducing the complexity and costs of PEM electrolyser deployment worldwide while expanding their applicability to a wider range of water qualities.
The combination of nanoscale materials engineering, in situ electrochemical analysis, and targeted chemical environment control demonstrated here sets a new standard for innovation in electrolysis research. As the hydrogen economy scales globally, innovations like this will be key enablers of sustainable, resilient, and economically viable green energy infrastructures.
Subject of Research: Proton exchange membrane (PEM) electrolysers with enhanced tolerance to impure water via cathode catalyst layer modification
Article Title: Cathode catalyst layers modified with Brønsted acid oxides to improve proton exchange membrane electrolysers for impure water splitting
Article References:
Wang, R., Yang, Y., Guo, J. et al. Cathode catalyst layers modified with Brønsted acid oxides to improve proton exchange membrane electrolysers for impure water splitting. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01787-9
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