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

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 cm(2)) of NiFeS/NF is obviously larger than that of NiFeS/NF (173.75 cm(2)) and NiFeS/NF (205.00 cm(2)). 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.