Manipulating atomic order-disorder in octahedral building blocks ([MO6]/[M2O9]) for advanced hydrogen evolution electrocatalysis

Atomic-scale modulation of crystalline ordering in heterogeneous catalysts offers a critical pathway to enhance reaction kinetics, yet fundamental understanding of how their dynamic structural evolution governs active-site stability remains elusive. Here, we decode these effects by precisely engineering crystallographic gradients from ordered to disordered states, within octahedral building blocks (isolated octahedra [MO 6 ] or dimer [M 2 O 9 ]) of perovskite oxides Ba 3 M x Ru 2-x O 9 (M = Fe, Co). This atomic-level control induces systematic shifts in d / p -band centers and optimizes charge distribution architectures within active regions. Crucially, the highly disordered Ba 3 FeRu 2 O 9 achieves exceptional stability via a self-sacrificial reduction of iron, which generates a built-in electric field (BEF). The BEF promotes optimal adsorption/desorption kinetics of OH*/H* intermediates for the hydrogen evolution reaction (HER). Consequently, Ba 3 FeRu 2 O 9 delivers benchmark alkaline HER performance, achieving an overpotential of just 24 mV at 10 mA cm −2 and demonstrating operational stability exceeding 600 h. Our results reveal that structural reorganization, enabled by atomic-level ordering modulation, is critical for establishing dynamic structure-performance frameworks to guide advanced catalyst design.