Ultrasmall FeNiPx nanoparticles embedded into amorphous FeNiOx nanosheets for industrial-level high current density water oxidation

Abstract

Amorphous–crystalline heterostructures are among the most promising electrocatalysts for enhanced oxygen evolution reaction (OER) as interfacial borders provide excess and tuneable catalytic sites. Herein, we report a highly efficient OER catalyst, FeNiP_x/FeNiO_x/NF, with dense crystalline–amorphous interfacial sites synthesized by coupling crystalline ultrasmall FeNiP_x nanoparticles with amorphous FeNiO_x nanosheets grown on nickel foam (NF) using a controlled hydrothermal-phosphidation process. FeNiP_x/FeNiO_x/NF exhibits excellent OER activity with a low overpotential of 220 mV to deliver a current density of 1 A cm⁻² with a Tafel slope of only 42 mV dec⁻¹. When FeNiP_x/FeNiO_x/NF is used as an anode in an electrolyzer, a current density of 1 A cm⁻² is achieved at a low cell voltage of 1.9 V, placing it among the most efficient earth-abundant anodes for the OER. Theoretical studies reveal a strong synergy between crystalline FeNiP_x nanoparticles and amorphous FeNiO_x nanosheets via modulation of d-band centres. Studies also find that during the OER, FeNiP_x/FeNiO_x/NF produces high valence Ni³⁺/Fe⁴⁺ phases, which facilitate the OER process. The suggested new synthetic strategy provides directions for designing and developing robust oxygen electrodes for large-scale alkaline water electrolysis.