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 Ti C T 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 and 70 mV for OER and HER, respectively, at 10 mA cm 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 H -O fuel cell using the as-prepared catalyst can reach as high as 941 mW cm . Theoretical calculations reveal that isolated Ru-O 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.