In-situ Formation of Cobalt Nitrides/Graphitic Carbon Composites as Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

Developing cost-effective and highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great interest for overall water splitting, but still remains challenging issue. Herein, a self-template route is employed to fabricate a unique hybrid composite constructed by encapsulating cobalt nitrides (Co5.47N) nanoparticles within three-dimensional (3D) N-doped porous carbon polyhedra (Co5.47N NP@N-PC), which can be served as highly active bifunctional electrocatalyst. To afford a current density of 10 mA cm-2, the as-fabricated Co5.47N NP@N-PC only requires overpotentials as low as 149 mV and 248 mV for HER and OER, respectively. Moreover, an electrolyzer with Co5.47N NP@N-PC electrodes as both the cathode and anode catalyst in alkaline solutions can drive a current density of 10 mA cm-2 at a cell voltage of only 1.62 V, superior to that of the Pt/IrO2 couple.The excellent electrocatalytic activity of Co5.47N NP@N-PC can be mainly ascribed to the high inherent conductivity and rich nitrogen vacancies of Co5.47N lattice, the electronic modulation of N-doped carbon towards Co5.47N as well as the hierarchically porous structure design.