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

Abstract

Amorphous-crystalline heterostructures are one of most promising electrocatalysts for enhanced oxygen evolution reaction (OER) as interfacial borders provide excess and tuneable catalytic sites. Here, we report a highly efficient OER catalyst, FeNiPx/FeNiOx/NF, with dense crystalline-amorphous interfacial sites synthesized by coupling crystalline ultrasmall FeNiPx nanoparticles with amorphous FeNiOx nanosheets grown on nickel foam (NF) using a controlled hydrothermal-phosphidation process. FeNiPx/FeNiOx/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 FeNiPx/FeNiOx/NF is used as anode in an electrolyzer, a current density of 1 A cm-2 is achieved at a low cell voltage of 1.9 V, making it among most efficient earth-abundant anode for OER. Crystalline-amorphous interfaces may effectively fine-tune the electronic structure of active sites and suppress the OER overpotential. Theoretical studies reveal a strong synergy between crystalline FeNiPx nanoparticles and amorphous FeNiOx nanosheets via modulation of d-band centres. Studies also find that during OER FeNiPx/FeNiOx/NF produces high valence Ni3+/Fe4+ phases while the embedded crystalline FeNiPx nanoparticles remain stable for longer duration. The suggested synthetic strategy provides directions for designing and developing robust oxygen electrodes for large-scale alkaline water electrolysis.