Rational design of hollow oxygen deficiency-enriched NiFe2O4@N/rGO as bifunctional electrocatalysts for overall water splitting

Bimetallic metal organic framework (MOF) as a precursor to prepare catalysts with bifunctional catalytic activity of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) attracts more and more attention. Herein, hollow oxygen deficiency-enriched NiFe2O4 is synthesized by pyrolytic FeNi bimetallic MOF. The defects of rGO during carbonization can act as nucleation sites for FeNi particles. After nucleation and N doping, the FeNi particles were served as catalysts for the deposition of dissolved carbon in the defects of the N/rGO. These deposited carbon, like a bridge, connect N/rGO and hollow oxygen deficiency-enriched NiFe2O4 together, which giving full play to the advantages of N/rGO in fast electron transfer, thereby improving its catalytic activity. The resultant NiFe2O4@N/rGO-800 exhibits a low overpotential of 252 mV at 20 mA cm−2 for OER and 157 mV at 10 mA cm−2 for HER in 1 M KOH, respectively. When used as bifunctional electrodes for overall water splitting, it also shows low cell voltage of 1.60 V and 1.67 V at 10 and 20 mA cm−2, respectively.