Optimizing band structure of CoP nanoparticles via rich‐defect carbon shell toward bifunctional electrocatalysts for overall water splitting

Abstract Transition‐metal phosphides (TMPs) with high catalytic activity are widely used in the design of electrodes for water splitting. However, a major challenge is how to achieve the trade‐off between activity and stability of TMPs. Herein, a novel method for synthesizing CoP nanoparticles encapsulated in a rich‐defect carbon shell (CoP/DCS) is developed through the self‐assembly of modified polycyclic aromatic molecules. The graft and removal of high‐activity C–N bonds of aromatic molecules render the controllable design of crystallite defects of carbon shell. The density functional theory calculation indicates that the carbon defects with unpaired electrons could effectively tailor the band structure of CoP. Benefiting from the improved activity and corrosion resistance, the CoP/DCS delivers outstanding difunctional hydrogen evolution reaction (88 mV) and oxygen evolution reaction (251 mV) performances at 10 mA cm⁻² current density. Furthermore, the coupled water electrolyzer with CoP/DCS as both the cathode and anode presents ultralow cell voltages of 1.49 V to achieve 10 mA cm⁻² with long‐time stability. This strategy to improve TMPs electrocatalyst with rich‐DCS and heterogeneous structure will inspire the design of other transition metal compound electrocatalysts for water splitting.