Amorphous-crystalline hybrid of Ru/CoRuO x with microcrystalline framework for highly efficient and durable overall water splitting

Abstract

Overall water splitting demands cost-effective electrocatalysts. Compared with benchmark Pt and IrO2, Ru-and RuO₂-based electrocatalysts offer comparable activities for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), while at much lower cost. In particular, amorphous RuO₂ presents greater potential for OER due to its abundant unsaturated active sites, but its further oxidation under highly oxidative conditions compromises long-term stability. To address this challenge, we developed an amorphous Ru/CoRuO_x electrocatalyst with uniformly dispersed microcrystalline domains. In this architecture, amorphous RuO₂ directly formed via controlled Ru oxidation, acts as the OER-active center; partially retained metallic Ru serves as the HER-active center; and highly crystalline spinel Co₃O₄ functions as a robust structural matrix. Benefiting from the uniform integration of Ru, RuO₂, and Co₃O₄, coupled with an optimized electronic structure and open framework, Ru/CoRuO_x shows highly activity and durability for overall water splitting. As a result, the optimized Ru/CoRuO_x-400 achieved low overpotentials of 194 mV for OER and 83 mV for HER at 10 mA cm^-2 , while maintaining excellent long-term electrochemical stability. Density functional theory (DFT) calculations further revealed that Ru/CoRuO_x-400 exhibited favorable adsorption configurations and reduced free energies for key intermediates, supporting the beneficial role of the amorphous RuO₂-containing interfacial environment. Additionally, an assembled Ru/CoRuO_x-400//Ru/CoRuO_x-400 cell delivered 10 mA cm^-2 at 1.52 V, outperforming the benchmark RuO₂//Pt/C cell, while retaining long-term operational durability. Overall, this work presents a universal approach for designing low-cost, high-performance bifunctional electrocatalysts for next-generation water splitting technologies.