This review highlights recent advances in low/nonnoble metal catalysts for acidic oxygen evolution reaction, crucial for proton exchange membrane water electrolyzers. It discusses mechanistic insights, noble metal reduction strategies, and nonnoble alternatives, aiming to enhance activity, stability, and cost-efficiency for green hydrogen production. Future research directions are also outlined.

Water electrolysis technology is a core pathway for green hydrogen production and plays a crucial role in enabling efficient storage and conversion of clean energy. Among electrolysis systems, proton exchange membrane water electrolyzers (PEMWEs) are ideal for large-scale hydrogen production due to their high current density, rapid response characteristics, and high-purity hydrogen output. However, the acidic oxygen evolution reaction (OER) at the anode remains a key bottleneck in PEMWEs cost and lifetime due to its sluggish kinetics, high overpotential, and heavy reliance on noble metal-based catalysts (Ir and Ru). Developing highly active, low-cost, and durable acidic OER electrocatalysts is essential for reducing electrolyzer energy consumption and advancing the green hydrogen economy. This review systematically examines advancements in acidic OER catalysts over the past five years, focusing on fundamental mechanistic insights, advanced low-loading noble metal-based catalysts, and progress in nonnoble metal-based catalyst design. An outlook on future directions for acidic OER research, emphasizes mechanistic studies and electrocatalyst design strategies to overcome current challenges.