Oxygen vacancy-rich amorphous porous NiFe(OH)x derived from Ni(OH)x/Prussian blue as highly efficient oxygen evolution electrocatalysts

Abstract

Oxygen vacancies or defects play a significant role in improving the intrinsic activities of bimetallic hydroxides towards the oxygen evolution reaction (OER); however, their rational design and preparation remain a great challenge. In this study, oxygen vacancy-rich amorphous porous nickel iron hydroxide nanolayers supported on carbon paper (NiFe(OH)_x/CP) are rationally prepared through a facile approach involving the sequential electrochemical deposition of a Prussian blue (PB) nanocrystal layer and Ni(OH)_x layer on carbon paper followed by an alkaline etching process, where PB nanocrystals act as an Fe source and template for the formation of an amorphous porous NiFe(OH)_x layer. NiFe(OH)_x/CP with an ultralow loading of 0.8 mg cm⁻² exhibits outstanding OER activities, showing a low overpotential of 303 mV at 100 mA cm⁻² and a small Tafel slope of 33.8 mV dec⁻¹ in an alkaline electrolyte, which are superior to the state-of-the-art IrO₂ catalysts, and among the best results compared to the reported bimetallic compounds. Moreover, NiFe(OH)_x/CP exhibits excellent long-term stability with negligible degradation after water splitting for 50 h. Its superior electrocatalytic OER performance benefits from the massive oxygen vacancies derived from the amorphous and distorted structures, the synergistic effect between Ni and Fe species with an optimized Ni/Fe ratio, and the efficient electron and mass transfer of carbon paper. This work paves a new avenue for the rational design and preparation of amorphous porous structures with abundant oxygen vacancies to improve the intrinsic activities for energy storage and conversion applications.