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 Ti3C2Tx 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−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 reveal 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. Single‐atomic Ru sites supported on ultrathin Ti3C2Tx MXene nanosheets are synthesized and identified as high‐performance trifunctional electrocatalysts for simultaneously catalyzing overall water splitting and oxygen reduction in acidic media. Experiments and theoretical simulations clearly reveal that isolated Ru–O2 sites can optimize the adsorption of reactants/intermediates, making the three reaction pathways on the designed catalyst along an energetic‐favorable process.