Engineering of metal Co/Ni-CoO nanoparticles embedded in N-doped unclosed hollow carbon nanoboxes as a highly efficient bifunctional electrocatalyst for overall water splitting

Hollow materials are attracting considerable attention in water electrolysis due to their clear internal space and large surface areas. However, the completely enclosed hollow nanostructures are affected by the large mass-transfer resistance and incompletely exposure of the inner space. Here, an unclosed hollow electrocatalyst consisting of metal Co-loaded Ni-doped CoO multiphase nanoparticles inserted in N-doped hollow carbon shells (Co/Ni-CoO@NC) is designed and constructed by a room-temperature stirring corrosion method and subsequent pyrolysis. The as-prepared Co/Ni-CoO@NC displays outstanding electrocatalytic activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes. And the optimized products show an ultra-small overpotential of only 61 mV at 10 mA cm−2 current density for HER. For OER, the overpotential is 215 mV at the same current density. The excellent catalytic properties of Co/Ni-CoO@NC are mainly due to the high electrical conductivity of nitrogen-doped carbon materials (NC), the great specific surface area of the hollow NC nanoboxes, the exposed internal space and accessible active sites, and the abundant mass transfer channels of the hollow architectures. Moreover, the obtained catalysts exhibit excellent durability and stability in HER and OER applications. This research develops a feasible way to construct bifunctional unclosed hollow electrocatalysts for decomposing water.