In situ promoting water dissociation kinetic of Co based electrocatalyst for unprecedentedly enhanced hydrogen evolution reaction in alkaline media

Carbon-encapsulated 3d-transition metal (TM) hybrid structure (denoted as M@C) have been considered as a promising candidate for HER. In recent years, the Co@C composites have exhibited effective HER catalytic performance in acidic media. However, the catalytic performance of Co@C in alkaline media is still unsatisfactory because of the sluggish water dissociation in Volmer step. In this work, by using carbon encapsulated metal Co nanoparticles hybrid structure (CoNP@C) as precatalyst, we firstly demonstrate that the HER activity of Co-based precatalysts could be unprecedentedly promoted through a simple in situ electrochemical activation process. Compared with initial CoNPs@C precatalyst, the activated catalyst realizes about 3.5-fold improved activity and the overpotential greatly decreases from 191 mV to 58 mV at 10 mA cm(-2). Specially, the remarkable reduced Tafel slope (from 113 mV dec(-1) to 51 mV dec(-1)) indicates that the sluggish kinetics of the water dissociation step (Volmer step) is effectively speeded up by in situ electrochemical activation. Such a highly enhanced catalytic performance is mainly due to the in situ introduction of cobalt hydroxides NPs as water dissociation promoter and the synergetic effects among core Co NPs, middle layered carbon structure and outer cobalt hydroxides NPs. Our study offers a generic strategy for development of high-performance 3d-transition metal hybrid based HER catalysts in alkaline media.