NiFe Layered-Double-Hydroxide-Derived NiO-NiFe2O4/Reduced Graphene Oxide Architectures for Enhanced Electrocatalysis of Alkaline Water Splitting

Electrochemical water splitting is an environmentally friendly technology to store renewable but intermittent energy into hydrogen fuels. Nowadays, exploiting low-costing, high-performance, and robust catalysts for the electrochemical oxygen evolution reaction (OER) is essential to improve the overall efficiency of water splitting. Herein, the synthesis, structural characterization, and electrocatalytic OER performance of NiO-NiFe2O4 nanoparticles anchored on reduced graphite oxide frameworks (NiO-NiFe2O4/rGO) were investigated. Facile thermal annealing of the NiFe layered double hydroxide (NiFe-LDH) precursor led to the formation of highly dispersible NiO-NiFe2O4 nanoparticles (20-30 nm in size) across the rGO substrate with a NiO/NiFe2O4 molar ratio up to 4.42. In contrast to the nanostructured NiFe-LDH/rGO catalyst, the NiO-NiFe2O4/rGO nanohybrid exhibits a lower OER onset potential (E-onset=1.436 V vs. RHE), affords a smaller overpotential of 296 mV, and achieves a current density of 10 mA cm(-2) with a Tafel slope of about 43 mV dec(-1); these values are comparable to those of the benchmark IrO2 catalyst. The synergy between the abundant catalytically active sites through good dispersion of NiO-NiFe2O4 across the rGO substrate and fluent electron transport arising from the rGO and NiFe2O4 components results in the outstanding electrocatalytic activity. The extremely high catalytic activity, facile synthesis, and low-cost of the NiO-NiFe2O4/rGO nanohybrid make it a very promising catalyst for the OER.