Electrodeposition-Solvothermal Access to Ternary Mixed Metal Ni-Co-Fe Sulfides for Highly Efficient Electrocatalytic Water Oxidation in Alkaline Media

Ternary mixed metal Ni-Co-Fe sulfides based on three dimensional (3D) nickel foam (NiCoFeS/NF) have been synthesized via facile electrodeposition-solvothermal process. Firstly, a uniform film of Co-Fe oxides has been electrodeposited on the surface of 3D skeleton of NF (CoFe/NF). Secondly, an ethanol solvothermal sulfurization has been adopted to convert CoFe/NF to ternary mixed metal sulfides (NiCoFeS/NF). XRD confirms that ternary NiCoFeS is composed of mixed phases including NiS, Ni3S2 and Co3S4 phases but no Fe sulfides phase, implying amorphous state of Fe sulfides. SEM images of ternary NiCoFeS films shows uniform film covering on the surface of NF, which is composed of many hill-shaped bulges structures. The OER measurements confirm the excellent performance of ternary NiCoFeS/NF in 1.0 M KOH, providing low overpotential of 40 and 160 mV to drive 10 and 100 mA cm−2 in 1.0 M KOH, respectively. A further enhancement of the stability of NiCoFeS/NF have been conducted via a secondary electrodeposition of Fe on NiCoFeS/NF to obtain NiCoFeS-Fe/NF, with slightly lower overpotential of 230 mV to drive 100 mA cm−2 than that (310 mV) of NiCoFeS/NF after stability test. The role of Fe on OER ability and stability of NiCoFeS/NF have been discussed.