Interface engineering of hierarchical flower-like N, P, O-doped NiP self-supported electrodes for highly efficient water-to-hydrogen fuel/oxygen conversion.

Rational construction of efficient bifunctional catalysts with robust catalytic activity and durability is significant for overall water splitting (conversion between water and hydrogen fuel/oxygen) using non-precious metal systems. In this work, the hierarchically porous N, P, O-doped transition metal phosphate in the Ni foam (NF) electrode (hollow flower-like NPO/NiP@NF) was prepared through facile hydrothermal method coupled with phosphorization treatment. The hierarchical hollow flower-like NPO/NiP@NF electrodes exhibited high bifunctional activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solutions. The optimized electrode showed low overpotentials of 76 and 240 mV for HER and OER to reach a current density of 10 mA cm, respectively. Notably, the NPO/NiP@NF electrode only required a low voltage of 1.99 V to reach the current densities of 100 mA cm with long-term stability for overall water splitting using the NPO/NiP@NF|| NPO/NiP@NF cell, surpassing that of the Pt/C-RuO (2.24 V@ 100 mA cm). The good catalytic and battery performance should be attributed to i) the open hierarchical structure that enhanced the mass transfer; ii) a highly conductive substrate that accelerated the electron transfer; iii) the rich heterojunction and strong synergy between NiP and NiP that improved the catalytic kinetic; iv) the proper-thickness amorphous phosphorus oxide nitride (PON) shell that realized the stability. This work demonstrates a promising methodology for designing bifunctional transition metal phosphides with high performance for efficient water splitting.