Sequential self-reconstruction of localized Mo species in hierarchical carbon/Co-Mo oxide heterostructures for boosting alkaline hydrogen evolution kinetics and durability

Surface self-reconstruction processes in alkaline hydrogen evolution reaction (HER), especially regarding the explicit structure-activity relationships, remain elusive. Here, we first design a hierarchical Co@NCNT/CoMoOx precatalyst constituted by defective CoMoOx nanosheets grafted with flexible Co@NCNT arrays, followed by a delicate anodic treatment for fast dissolution balance. Benefiting from the multi-level Co@NCNT arrays as a stable micro-environment, the resultant Co@NCNT/CoMoyOx displays excellent electrocatalytic activity with a low overpotential of 195 mV at -100 mA cm-2 and stable 600 h operation for the HER in alkaline media, including natural seawater, which is better than most reported carbon/transition metal-based catalysts. In situ Raman analyses disclose a local high-resolution self-reconstruction evolution of localized Mo species at controllable negative potentials. Density functional theory calculations further demonstrate that the ultimate Mo-Mo surface state accelerates reaction kinetics to promote H2 generation in alkaline media. Our findings provide a unique insight into the mechanism of the structural evolution in the alkaline HER process to pave a new avenue guiding the design of durable and efficient catalysts.