In situ electrochemical dehydrogenation of ultrathin Co(OH)2 nanosheets for enhanced hydrogen evolution

Transition metal hydroxides/oxyhydroxides have recently emerged as highly active electrocatalysts for oxygen evolution reaction in alkaline water electrolysis, while have not yet been widely investigated for hydrogen evolution electrocatalysts owing to their unfavorable H*-adsorption, making it difficult to construct an overall-water-splitting cell for hydrogen production. In this work, we proposed a straightforward and effective approach to develop an efficient in-plane heterostructured CoOOH/Co(OH)2 catalyst via in-situ electrochemical dehydrogenation method, in which the dehydrogenated –CoOOH and Co(OH)2 at the surface synergistically boost the hydrogen evolution reaction (HER) kinetics in base as confirmed by high-resolution transmission electron microscope, synchrotron X-ray absorption spectroscopy, and electron energy loss spectroscopy. Due to the in-situ dehydrogenation of ultrathin Co(OH)2 nanosheets, the catalytic activity of the CoOOH/Co(OH)2 heterostructures is progressively improved, which exhibit outstanding hydrogen-evolving activity in base requiring a low overpotential of 132 mV to afford 10 mA/cm2 with very fast reaction kinetics after 60 h dehydrogenation. The gradually improved catalytic performance for the CoOOH/Co(OH)2 is probably due to the enhanced H*-adsorption induced by the synergistic effect of heterostructures and better conductivity of CoOOH relative to electrically insulating Co(OH)2. This work will open the opportunity for a new family of transition metal hydroxides/oxyhydroxides as active HER catalysts, and also highlight the importance of using in situ techniques to construct precious metal-free efficient catalysts for alkaline hydrogen evolution.