Material Progress in Water Splitting: A Comprehensive Review of Electrocatalyst Advances

Abstract

Electrochemical water splitting is central to green hydrogen production, offering a carbon-neutral way to store and deliver renewable energy. Over the past three years (2023-2025), the field has seen an unprecedented pace of materials development, profoundly shaping the design principles of electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this review, we critically assess key material breakthroughs across five disruptive categories: (i) MXene composites and heterostructure engineering; (ii) single-atom catalysts (SACs) with atomically coordinated active centers; (iii) high-entropy alloys and oxyhydroxides with multi-element synergies; (iv) transition metal phosphides, chalcogenides, and carbides with adjustable electronic states; and (v) novel materials and strategies for direct seawater electrolysis. For each category, we review synthetic approaches, structure-activity correlations, mechanistic insights from density functional theory (DFT) studies, and state-of-the-art electrochemical performance metrics, including overpotential, Tafel slope, turnover frequency (TOF), and stability. Particular attention is paid to advances that have enabled non-precious metal catalysts to match the performance of Pt and IrO2 standards, as well as new challenges in high-current-density operation, membrane electrode assembly (MEA) integration, and selectivity in direct seawater splitting. The review culminates with an outlook on the most pressing challenges and the most promising materials design strategies to achieve scalable, practical green hydrogen production by 2030.