Compressed Ru skin on atomic-ordered hexagonal Ru-Ni enabling rapid Volmer-Tafel kinetics for efficient alkaline hydrogen evolution

Abstract

Ru-based materials are promising electrocatalysts for hydrogen evolution reaction (HER) owing to their low-cost (one twenty-fifth of Pt) and similar Gibbs free energy of H* adsorption (ΔGH*) to that of Pt. However, the inadequate ability for the water dissociation of Ru catalysts is significantly impeding the water splitting efficiency. In this work, we demonstrate an atomically ordered hexagonal Ru-Ni alloy with compressive-strained Ru skin as a high-performance HER catalyst for significantly boosting the water dissociation. The Ordered Ru-Ni achieves an optimized catalytic activity for alkaline HER with a low overpotential of 23 mV at 10 mA cm−2, Tafel slope of 25.9 mV dec−1 and superior mass activity of 4.83 A mg−1Ru, which is 15.1 times higher than Ru/C. According to DFT calculations, the ordered RuNi core imposes homogeneous compressive strain on the Ru skin, resulting in an optimum binding energy towards H*/OH* intermediates on Ru active sites for rapid Tafel step kinetics. Moreover, the decreased H2O dissociation energy barrier of Ordered Ru-Ni suggests a promoted Volmer-Tafel kinetics is achieved, significantly boosting the overall HER efficiency. This work provides a practical avenue for surface strain engineering of Ru-based catalysts to promote the HER activity.