Boosting hydrogen and oxygen evolution of porous CoP nanosheet arrays through electronic modulating with oxygen-anion-incorporation

The exploration of earth-abundant single catalyst with high-efficiency bifunctional catalytic active sites for accelerated hydrogen and oxygen evolution reactions (HER and OER) is highly desirable but challenging. Herein, the synthesis of self-supported directional flake oxygen-incorporated cobalt phosphide arrays (O-CoP) with efficient bifunctional catalytic active sites was achieved by in situ oxidation followed by phosphorization of cobalt metal-organic framework nanosheet arrays (Co-MOF). By controlling the phosphating time, the P/O atomic ratio in the oxygen-incorporated cobalt phosphide could be adjusted, leading to the change of Co3+/Co2+ couples, and thus affecting the electronic environment of the cobalt active site. Benefiting from the tunable electronic structure and unique array architecture, the synthesized catalysts exhibited excellent electrocatalytic water decomposition for both HER and OER. Moreover, in the HER and OER couple system (HER||OER), the optimal O-CoP-40 catalyst delivers a low overpotential of only 1.54 V to obtain the 10 mA cm-2 and stably-running for 36 h. Theoretical calculations demonstrated that the electron-rich P-3p and O-2p orbitals could co-modulate the electronic environment of Co sites, which boosted water dissociation in the HER process and balanced the adsorption/desorption of intermediates in the OER pathway, resulting in a good overall water splitting. This research provides an effective strategy for the construction of efficient bifunctional phosphide electrocatalysts, as well as contributes to the understanding of anion incorporating to regulate the electronic structure of phosphides.