Photothermally enhanced electrocatalytic water splitting with iron-doped nickel phosphide

Abstract

Although electrocatalytic water splitting holds significant promise for hydrogen production, unfavorable reaction energy barriers and kinetic properties lead to unsatisfactory conversion efficiency. Herein, we provide an innovative strategy to optimize the electrochemical activity of the Fe/Ni₂P catalyst through near-infrared (NIR)-induced photothermal effect. The Fe/Ni₂P-NIR yields a current density of 10 mA cm⁻² at ultralow overpotentials of 16 mV for the hydrogen evolution reaction (HER) and 167 mV for the oxygen evolution reaction (OER), with Tafel slopes of 38.7 and 46.2 mV dec⁻¹, respectively. This bifunctional catalyst also delivers 10 mA cm⁻² at a low voltage of 1.40 V for overall water splitting. The NIR photoinduced local thermal effect activates abundant catalytic sites, accelerates charge and mass transfer, and improves intrinsic reaction kinetics. Guided by density functional theory (DFT) calculations, the photothermal effect reduces the energy barriers of the rate-determining steps (RDS) for *H desorption on Fe/Ni₂P during HER and *O formation on its reconstructed active phase NiFeOOH during OER. We realized photothermal-electrochemical integration with Fe/Ni₂P-NIR in an anion exchange membrane (AEM) electrolyzer, attaining 500 mA cm⁻² at 1.76 V, with excellent stability over 50 h. This strategy may significantly advance energy conversion technology towards economic hydrogen production through water electrolysis.