Ru Single Atoms Tailoring the Acidity of Metallic Tungsten Dioxide for a Boosted Alkaline Hydrogen Evolution Reaction

Currently, the construction of an acid-like catalyst surface in a high-pH electrolyte is advocated as one of the most pioneering strategies for significantly improving the catalytic activity of the alkaline hydrogen evolution reaction. However, the proton transfer kinetics that significantly determines the activity of the proton-coupled electron reaction is largely dependent on the usage of an extensive noble-metal bulk phase. Herein, a well-designed dynamic acid-like catalyst system constructed by the metallic WO2 matrix and supported Ru single atoms (0.89 wt %) is grown on nickel foam (Ru SAC@WO2/NF). The as-prepared Ru SAC@WO2/NF free-standing catalyst exhibits superior activities of hydrogen evolution reaction with delivering current densities of 10, 50, and 200 mA/cm2 only requiring overpotentials of ∼0, 40, and 84 mV, respectively, and an ultralow Tafel slope (38 mV/dec) in 1.0 M KOH electrolyte. Moreover, our deliberately prepared composite catalyst also shows long-term stability with negligible activity decay after continuous hydrogen generation at current densities of 10, 50, and 200 mA/cm2 for more than 50 h. Comprehensive spectroscopy characterizations combined with density function theory calculations reveal that the significantly improved activity of alkaline hydrogen evolution reaction on the Ru SAC@WO2/NF free-standing catalyst can be understood by two reasons: (i) the metallic WO2 matrix contributes to the construction of an acid-like catalytic environment through the formation of weak-acid hydrogen tungsten bronze (HxWOy) intermediates on the solid–liquid interface in an alkaline electrolyte; (ii) unlike the weak electronic interaction between Ru nanoparticles and hydrogen atoms of weak-acid HxWOy intermediates, Ru single atoms are evidenced to efficiently tailor the acidity of HxWOy intermediates for accelerated deprotonation kinetics, thus resulting in the regeneration of active sites for next catalytic cycle. Such an interesting concept of catalyst design driven by basic chemical theories will benefit the exploration of noble-metal single atoms with ultralow usage but higher added-values in water electrolysis and beyond.