Accelerating PEM-based hydrogen production via acidic hybrid water electrolysis: From molecular catalyst design to industrial system integration

Proton exchange membrane (PEM) water electrolysis is a leading platform for sustainable hydrogen production, yet its efficiency is limited by the sluggish and energy-intensive oxygen evolution reaction (OER) under acidic conditions. Replacing the OER with thermodynamically favorable anodic oxidation reactions offers a promising strategy to reduce cell voltage while enabling the co-production of value-added chemicals. Although most hybrid electrolysis systems have been developed in alkaline media, their incompatibility with PEM technology restricts practical implementation. Acidic hybrid water electrolysis (AHWE) provides distinct advantages, including high proton conductivity, reduced ohmic losses, and operation at industrially relevant current densities. However, its development remains in its infancy due to challenges such as catalyst instability, complex proton-coupled electron transfer mechanisms, limited selectivity, and membrane compatibility. This review presents a cross-scale review and perspective on AHWE, linking molecular catalyst design to PEM device integration, and identifies key principles governing the translation of fundamental insights into practical hydrogen production.