Anode Alchemy on Multiscale: Engineering from Intrinsic Activity to Impedance Optimization for Efficient Water...

The past decade has seen significant progress in proton exchange membrane water electrolyzers (PEMWE), but the growing demand for cost-effective electrolytic hydrogen pushes for higher efficiency at lower costs. As a complex system, the performance of PEMWE is governed by a combination of multiscale factors. This review summarizes the latest progress from quantum to macroscopic scales. At the quantum level, electron spin configurations can be optimized to enhance catalytic activity. At the nano and meso scales, advancements in atomic structure optimization, crystal phase engineering, and heterostructure design improve catalytic performance and mass transport. At the macro scale, innovative techniques in gas bubble management and internal resistance reduction drive further efficiency gains under ampere-level operating conditions. These modifications at the quantum level cascade through meso- and macro-scales, affecting charge transfer, reaction kinetics, and gas evolution management. Unlike conventional approaches that focus solely on one scale-either at the catalyst level (e.g., atomic, or crystal modifications) or at the device level (e.g., porous transport layers design)-combining multiscale optimizations unlocks greater performance improvements. Finally, a perspective on future opportunities for multiscale engineering in PEMWE anode design toward commercial viability is offered.