Oxygen Vacancies-Rich Amorphous Porous NiFe(OH)x Derived from Ni(OH)x/Prussian Blue as Highly Efficient Oxygen Evolution Electrocatalysts

Oxygen vacancies or defects play a significant role in improving the intrinsic activities of bimetallic hydroxides towards oxygen evolution reaction (OER), however, the rational design and preparation remain a great challenge. In this study, oxygen vacancies-rich amorphous porous nickel iron hydroxide nanolayers supported on carbon paper (NiFe(OH)x/CP) is rationally prepared through a facile approach involving sequent electrochemical deposition of Prussian blue (PB) nanocrystal layer and Ni(OH)x layer on carbon paper followed by an alkaline etching process, where PB nanocrystals act as Fe source and template for the formation of amorphous porous NiFe(OH)x layer. The 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 small Tafel slope of 33.8 mV dec-1 in alkaline electrolyte, which is superior to the state-of-art IrO2, and among the best results compared to the reported bimetallic compounds. Moreover, the NiFe(OH)x/CP exhibits excellent long-term stability with negligible degradation after water splitting for 50 h. The 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 optimized Ni/Fe ratio, and the efficient electron and mass transfer of the carbon paper. This work paves a new avenue for rational design and preparation of amorphous porous structures with abundant oxygen vacancies to improve the intrinsc activities for energy storage and conversion applications.