P vacancy-induced electron redistribution and phase reconstruction of CoFeP for overall water splitting at industrial-level current density

Hydrogen production through water splitting using transition metal-based phosphide electrocatalysts represents a highly promising and sustainable energy conversion strategy. In this study, phosphating and vacancy engineering are achieved via a single-step Ar plasma-assisted process. CoFePv with phosphorus vacancies (Pv) as a bifunctional electrocatalyst effectively promotes both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), thereby significantly facilitating overall water splitting (OWS) in alkaline media. In the OER and HER processes, the driving overpotentials needed to attain a current density of 1 A cm-2 are only 382 and 367 mV, respectively. Furthermore, the CoFePv (+, -) OWS electrolyzer is capable of maintaining a current density of 2 A cm-2 at 1.98 V under simulated industrial settings (6 M KOH and 80 degrees C). It also demonstrates stable performance at a current density of 0.5 A cm-2 for a duration of 100 hours. In situ Raman spectroscopy observations show that Pv induce rapid catalyst phase reconstruction, thereby significantly enhancing the OER performance of CoFePv. Density functional theory (DFT) calculations demonstrate that phosphorus vacancies can modulate the electronic configuration of Co-Fe-P, facilitate electron transfer, and optimize the adsorption and desorption of reaction intermediates.