Tri-Functional Electrocatalysis for Zinc-Air Battery Coupled Water Splitting: A Catalyst-Electrode-Device-System Perspective.

Tri‑functional electrocatalysis is crucial for coupling rechargeable zinc‑air batteries with water splitting (WS), enabling self‑powered hydrogen production and versatile energy conversion. Although numerous catalysts demonstrate excellent half-cell activities toward the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction, their practical application in battery-driven water electrolysis remains challenging. The major bottleneck is multiscale mismatch, which involves conflicting adsorption energetics at atomic sites, unstable gas‑liquid‑solid interfaces at electrodes, device degradation under alternating charge‑discharge and electrolysis modes, and voltage‑power imbalances at the system level. This review goes beyond conventional material summaries by constructing a catalyst-electrode-device-system framework to systematically examine how electronic modulation, defect engineering, heterostructure design, single-atom site tuning, and self-supported electrode construction influence intrinsic activity, mass transport, interfacial durability, and overall cell performance. Importantly, the actual operating point of the coupled system is determined by the intersection of the battery discharge curve and the electrolyzer polarization curve, rather than by isolated half‑cell metrics alone. Finally, we highlight future opportunities including operando characterization techniques, AI‑driven catalyst screening, standardized device evaluation protocols, and system-level co‑design for practical renewable energy devices.