Two-step synthesis of binary Ni–Fe sulfides supported on nickel foam as highly efficient electrocatalysts for the oxygen evolution reaction

Abstract

A facile two-step method has been used to synthesize binary Ni–Fe sulfides supported on nickel foam (NF) as electrocatalysts for the oxygen evolution reaction (OER). Firstly, NiFe hydroxide nanosheets have been electrodeposited on NF (NiFe/NF) as a precursor with a large surface area. Secondly, the as-prepared NiFe/NF has been subjected to a hydrothermal sulfuration process in order to prepare NiFeS/NF as an efficient electrocatalyst for the OER. The as-prepared samples have been characterized by XRD, XPS and SEM. The SEM images show that the NiFeS film was composed of needle-like nanostructures covering the surface of the NF. The corresponding OER performances in alkaline media have been systematically investigated. NiFeS/NF shows a superior overpotential of 65 mV at 10 mA cm⁻², which is much lower than most Ni-based electrocatalysts. The overpotential of 189 mV at 100 mA cm⁻² of NiFeS/NF suggests very promising OER activity for industrial applications. The electrochemically active surface area (251.25 cm²) of NiFeS/NF is obviously larger than that of NiFeS/NF (173.75 cm²) and NiFeS/NF (205.00 cm²). However, the stability of NiFeS/NF is not very good due to the intrinsic nature of metal sulfides in alkaline solution. An approach of electrodeposition of Fe hydroxide film on NiFeS/NF (NiFeS–Fe/NF) has been used to protect NiFeS/NF for better stability for the OER. The OER performances of NiFeS–Fe/NF demonstrate enhanced stability but lower activity with 101.6 mV at 10 mA cm⁻². Therefore, there may be an optimal balance between activity and stability of transition metal sulfides for the OER.