Facile synthesis of the NiFe bimetallic alloy wrapped on the porous N-doped graphene aerogel via thermal reduction and electronic structure modulation for boosting oxygen evolution reaction

Electrochemical water splitting is a promising green technique for hydrogen production. However, the scarcity and high cost of noble catalysts for oxygen evolution reaction (OER) have restricted their applications. Traditionally, metal aerogels are synthesized by chemically reducing metal salt precursors. Here, we report for the first time a novel NiFe bimetallic alloy wrapped on porous N-doped graphene aerogel (NiFe/NGA), synthesized by thermal reduction of NiFe₂O₄ spinel aerogel under porous carbon. It displays abundant three-dimensional pore structures with NiFe bimetallic nanoparticles of several tens of nanometers and wrapped N-doped graphene layer, thereby exposing many active sites. Due to the easy oxidation of the binary metal, the NiFe nanoalloy spontaneously transforms into NiFe layered double hydroxide (LDH), while porous carbon enhances electron transfer. The as-prepared NiFe/NGA demonstrates superior OER activity compared to commercial RuO₂/C. It requires only 285 mV overpotential at 10 mA cm⁻ 2 , has a low Tafel slope of 50.1 mV·dec⁻ 1 , showing excellent stability without significant current decay under 40,000 s galvanostatic polarization test. Density Functional Theory (DFT) calculations reveal that the rate-determining step of the OER process is the transformation of ∗OOH to a bare surface, which is largely attributed to the decreased binding strength of ∗OH on the catalyst surface.