One-step electrodeposition of NixFe3-xO4/Ni hybrid nanosheet arrays as highly active and robust electrocatalysts for oxygen evolution

The non-precious transition metal oxide-based materials have shown a promising prospect as the electrocatalysts for the oxygen evolution reaction (OER). Herein, we report a template-free and annealing-free one-step electrodeposition approach for the in-situ fabrication of composition- and morphology-controllable NixFe3-xO4/Ni hybrid and NixFe3-xO4 nanosheet arrays (NSAs) on different conducting substrates as highly active and robust oxygen-evolving electrocatalysts. The optimal NixFe3-xO4/Ni hybrid NSA electrodeposited on nickel foam requires a low overpotential of only 218 and 262 mV to deliver an OER current density of 10 and 100 mA cm-2, respectively, with a small Tafel slope of 45 mV dec-1, which are the best among the reported Ni-Fe oxide-based OER electrocatalysts. The NixFe3-xO4/Ni hybrid NSA also exhibits robust stability under the OER conditions, showing no decline of the catalytic activity after a continuous oxygen-evolving test conducted at current densities ranging from 10 to 500 mA cm-2 for totally 220 h. The excellent electrocatalytic OER performance of the electrodeposited NixFe3-xO4/Ni hybrid NSA could be attributed to its vertically aligned nanosheet morphology providing a large electrochemically active surface area, better matched Fermi energy of NixFe3-xO4 with the O2 production potential and faster electron transfer due to the proper Ni incorporation, and low interfacial resistance and robust contact between the NixFe3-xO4/Ni hybrid and the substrate due to the in-situ electrodeposition. This work provides a facile (around 3 min of electrodeposition) and low-cost synthesis strategy that could be applicable for the fabrication of nanostructures of various metal oxides or metal oxide/metal hybrids for different applications.