Activating Lattice Oxygen in a Nanoporous Crystalline/Amorphous NiFe(II, III)OxHy Heterostructure for Electrocatalytic Water Oxidation with Ampere-Level Activity and Durability

Developing oxygen evolution reaction (OER) electrocatalysts with ampere-level activity and durability is an open challenge toward the final industrial application. Here, a nanoporous crystalline/amorphous nickel–iron oxyhydroxide heterostructure with abundant Fe2+ (c/a NiFe(II, III)OxHy) by partially substituting Ni2+ with Fe2+ is reported. Combination of X-ray absorption spectroscopy, in situ Raman, and density functional theory investigation suggested that the crystalline/amorphous structure with abundant cation defects and oxygen vacancy is conducive to lattice oxygen oxidation mechanism (LOM) and enhances OER kinetics. Fe2+ acts as an electron-sacrificing band to protect Fe3+ from overoxidation and promote the chemical stability. Meanwhile, the nanoporous structure can accelerate the detachment of the O2 and minimize structural oscillations to strengthen the mechanical stability. As a result, the c/a NiFe(II, III)OxHy catalyst not only exhibits superior electrocatalytic activity with an ultralow overpotential of 192 mV at 10 mA/cm2 and a Tafel slope of 41.8 mV/dec but also delivers industrial stability over 200 h at a current density of 1000 mA/cm2. This work provides a simple strategy and fundamental understanding for the development of industrial OER electrocatalysts.