Amorphous NiFe layered double hydroxide nanosheets decorated on 3D nickel phosphide nanoarrays: a hierarchical core–shell electrocatalyst for efficient oxygen evolution

Abstract

The rational design of efficient and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) plays a paramount role in hydrogen production by water electrolysis. Here we report a 3D hierarchical core–shell nanostructured OER electrocatalyst, in which amorphous NiFe layered double hydroxide (LDH) nanosheets are decorated on 3D conductive nickel phosphide nanoarrays. The integrated 3D core–shell electrode simultaneously offers excellent electrical conductivity for fast electron transfer, a large surface area with numerous active edge sites, and a hierarchical nanostructure for rapid release of gas bubbles, thus contributing to outstanding catalytic performance: low overpotentials (197, 243, and 283 mV for current densities of 10, 100, and 300 mA cm⁻², respectively), a small Tafel slope (46.6 mV dec⁻¹), and superior stability, which are better than those of almost all reported LDH-based OER catalysts. When this hybrid catalyst is combined with nickel phosphide for overall water splitting, the two-electrode cell achieves current densities of 10 mA cm⁻² at 1.52 V and 100 mA cm⁻² at 1.68 V in alkaline media, which are even superior to those of benchmark IrO₂ and Pt. This work paves an effective approach to design 3D hierarchical hybrid electrocatalysts for energy conversion and storage.