Excellent Overall Water Splitting Catalyst of Single Phase 6H Triple Perovskite Ba₃Co(Co_0.25Ru_0.75)₂O₉ at 1 A cm^-2...

Developing efficient bifunctional electrocatalysts for overall water splitting (OWS) remains a critical challenge due to the divergent reaction mechanisms required for oxygen and hydrogen evolution reactions (OER and HER), especially in a single-phase material. Here, we present a novel self-adaptive 6H triple perovskite oxide, Ba₃Co(Co_0.25Ru_0.75)₂O₉ (BCCRO), as a highly active and durable alkaline OWS catalyst. BCCRO exhibits low overpotentials of 178 and 32 mV for the OER and HER at 10 mA cm^-2 in 1.0 M KOH, respectively. A symmetric electrolyzer maintains stable performance for 1000 h at 1 A cm^-2. Operando X-ray absorption spectroscopy reveals its dynamic surface restructuring processes: under OER conditions, Co³⁺ and Ru⁵⁺ are oxidized to Co⁴⁺ and Ru⁶⁺, while during HER, they transform into metallic CoRu nanoparticles. Density functional theory calculations indicate that its high activity of OWS originates from synergy between high valence Ru⁶⁺ and Co⁴⁺ for OER, and between metallic Co and Ru for HER. This study presents a rare single-phase oxide catalyst that achieves exceptional OWS performance through operando adaptation, providing a transformative framework for developing practical water-splitting technologies.