Highly Active Three-Dimensional NiFe/Cu₂ O Nanowires/Cu Foam Electrode for Water Oxidation

Water splitting is of paramount importance for exploiting renewable energy-conversion and -storage systems, but is greatly hindered by the kinetically sluggish oxygen evolution reaction (OER). In this work, a three-dimensional, highly efficient, and durable NiFe/Cu₂ O nanowires/Cu foam anode (NiFe/Cu₂ O NWs/CF) for water oxidation in 1.0 m KOH was developed. The obtained electrode exhibited a current density of 10 mA cm^-2 at a uniquely low overpotential of η=215 mV. The average specific current density (j_s ) was estimated, on the basis of the electrocatalytically active surface area, to be 0.163 mA cm^-2 at η=310 mV. The electrode also displayed a low Tafel slope of 42 mV decade^-1 . Moreover, the NiFe/Cu₂ O NWs/CF electrode could maintain a steady current density of 100 mA cm^-2 for 50 h at an overpotential of η=260 mV. The outstanding electrochemical performance of the electrode for the OER was attributed to the high conductivity of the Cu foam and the specific structure of the electrode with a large interfacial area.