Synergistic Interfacial Effect of Ru/Co₃O₄ Heterojunctions for Boosting Overall Water Splitting

Low-cost bifunctional electrocatalysts capable of efficiently driving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are needed for the growth of a green hydrogen economy. Herein, a Ru/Co₃O₄ heterojunction catalyst rich in oxygen vacancies (V_O) and supported on carbon cloth (RCO-V_O@CC) is prepared via a solid phase reaction (SPR) strategy. A RuO₂/Co₉S₈@CC precursor (ROC@CC) is first prepared by loading Co₉S₈ nanosheets onto CC, following the addition of RuO₂ nanoparticles (NPs). After the SPR process in an Ar atmosphere, Ru/Co₃O₄ heterojunctions with abundant V_O are formed on the CC. The compositionally optimized RCO-V_O@CC electrocatalyst with a Ru content of 0.55 wt.% exhibits very low overpotential values of 11 and 253 mV at 10 mA cm^-2 for HER and OER, respectively, in 1 m KOH. Further, a low cell voltage of only 1.49 V is required to achieve a current density of 10 mA cm^-2. Density functional theoretical calculations verify that the outstanding bifunctional electrocatalytic performance originates from synergistic charge transfer between Ru metal and V_O-rich Co₃O₄. This work reports a novel approach toward a high-efficiency HER/OER electrocatalyst for energy storage and conversion.