Non-noble metal-based electro-catalyst for the oxygen evolution reaction (OER): Towards an active & stable electro-catalyst for PEM water electrolysis

Among water electrolysis methods, proton exchange membrane electrolyzers (PEMWEs) stand out for their potential to generate high-purity hydrogen with remarkable efficiency and dynamic response, making them a cornerstone technology for the sustainable hydrogen economy. However, a key bottleneck lies in the slow reaction rate of the oxygen evolution reaction (OER) at the anode, a four-electron transfer process that significantly throttles the system's full potential. This significantly impacts overall efficiency and calls for unfolding stable, durable, and highly active electrocatalysts that are cost-effective. However, the inherent acidity generated by the OER itself complicates this task. Noble metal catalysts like iridium (Ir) and ruthenium (Rh), pure or combined with other elements, exhibit excellent activity in the acidic OER environment. However, their high cost hinders large-scale PEMWE deployment. Therefore, extensive research has concentrated on non-noble metal alternatives, particularly transition metal oxides (monometallic and polymetallic) and carbon-based materials. This comprehensive review meticulously examines the emerging progress in non-noble metal electrocatalysts designed for low-pH OER conditions within PEMWEs. Following an introductory classification of water electrolyzer technologies, it explores how factors such as structure and synthesis route modulate the crucial performance parameters across diverse catalyst groups. Drawing upon these insights, the review also evaluates the current challenges and outlines promising avenues for future research.