Trifunctional Single-Atomic Ru Sites Enable Efficient Overall Water Splitting and Oxygen Reduction in Acidic Media

Development of cost-effective, active trifunctional catalysts for acidic oxygen reduction (ORR) as well as hydrogen- and oxygen-evolution reactions (HER and OER, respectively) is highly desirable, albeit challenging. Herein, single-atomic Ru sites anchored onto Ti₃C₂T_x MXene nanosheets are first reported to serve as trifunctional electrocatalysts for simultaneously catalyzing acidic HER, OER, and ORR. A half-wave potential of 0.80 V for ORR and small overpotentials of 290 mV and 70 mV for OER and HER, respectively, at 10 mA cm⁻² are achieved. Hence, a low cell voltage of 1.56 V is required for the acidic overall water splitting. The maximum power density of an H₂–O₂ fuel cell using the as-prepared catalyst can reach as high as 941 mW cm⁻². Theoretical calculations revealed that isolated Ru–O₂ sites can effectively optimize the adsorption of reactants/intermediates and lower the energy barriers for the potential-determining steps, thereby accelerating the HER, ORR, and OER kinetics.