Synergistic Ru/RuO₂ heterojunctions stabilized by carbon coating as efficient and stable bifunctional electrocatalysts for acidic overall water splitting

The development of highly active and stable acidic water oxidation electrocatalysts is of great significant for promoting the industrial application of proton exchange membrane electrolyzers. Ru-based catalysts have broad application prospects in acidic water oxidation, but their limitations in stability and activity hinder their further application. Herein, a nitrogen-doped carbon coated porous Ru/RuO₂ heterojunctional hollow sphere (Ru/RuO₂/NC) is designed as high-active and stable bifunctional electrocatalyst for acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In synthesis, the key is to use mesoporous polydopamine spheres as a template for forming hollow spheres, a source of NC coating and a reducing agent for forming Ru/RuO₂ heterojunction. The Ru/RuO₂ heterojunction adjusts the electronic structure of Ru active sites, optimizing the adsorption of intermediate species. Furthermore, the NC coating and the interaction between NC and Ru/RuO₂ effectively prevent Ru from over-oxidation and dissolution. The porous hollow structure provides more exposed active sites and promotes mass transfer. Impressively, Ru/RuO₂/NC exhibits outstanding OER and HER performance with low overpotentials of 211 and 32 mV at 10 mA cm^-2, respectively, and shows excellent stability. The acid water splitting electrolyzer, based on the bifunctional Ru/RuO₂/NC, requires low cell voltages of 1.46 and 1.76 V at 10 and 100 mA cm^-2, respectively, with good stability for over 100 h operation, surpassing Pt/C || RuO₂ and most of the reported catalysts.