A six-dimensional framework for water splitting electrocatalysts: from intrinsic activity to practical performance.

Electrocatalytic water splitting using renewable electricity is widely regarded as a promising route to sustainable hydrogen production. However, its practical application is hindered by the sluggish kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). A critical challenge remains: the lack of electrocatalysts that simultaneously achieve high intrinsic activity, long-term durability, and industrially relevant efficiency. Despite advances in catalyst design, current studies are still dominated by static descriptors and single-dimensional optimization, which fail to address the mismatch between material-level activity and device-level performance. In this review, we propose a six-dimensional coupled design framework for water electrolysis electrocatalysts. Specifically, electronic structure regulation (E), atomic-level active site definition (A), bulk-phase framework engineering (B), interfacial coupling (I), hierarchical architecture design (H), and dynamic evolution (D) are discussed as six mutually constraining dimensions. Altogether, these dimensions cover a hierarchical range, extending from microscopic electronic states at the atomic scale to the operational behavior of macroscopic devices. We first introduce the fundamentals of water electrolysis, including HER/OER mechanisms, thermodynamic and kinetic constraints, and evaluation metrics from intrinsic activity to industrially relevant performance. Subsequently, representative catalyst systems and design strategies are systematically discussed within the E-A-B-I-H-D framework, emphasizing structure-activity relationships and cross-dimensional interconnections. Finally, the key challenges and future directions toward predictive, multidimensional, and industrially relevant catalyst design are highlighted. This review aims to provide an integrative multiscale framework and practical design guidelines for developing high-performance electrocatalysts that bridge fundamental research and industrial water electrolysis.