Tuning crystal phase of NiSx through electro-oxidized nickel foam: A novel route for preparing efficient electrocatalysts for oxygen evolution reaction

A facile solvothermal sulfurization using electro-oxidized nickel foam (NF(Ox)) as support has been applied to prepare NiSx/NF(Ox) electrocatalyst with highly efficient activity for oxygen evolution reaction (OER). XRD patterns confirm the composition of NiSx/NF(Ox): two kinds of crystal phase including beta-NiS and Ni3S2. While using bare NF as support under identical conditions, only Ni3S2 phase can be detected. SEM images reveal two kinds of morphologies of NiSx/NF(Ox) including pyramids structure of beta-NiS and nanorod-like structure of Ni3S2, which implies the tuning effect of electro-pretreatment of NF on the selective preparation of NiSx crystal phase. It can be speculated that Ni(OH)(2) layer derived from electro-oxidized NF is responsible for the growth of beta-NiS while metallic Ni is transformed into Ni2S3 during sulfurization. Electrochemical measurements for OER indicate the enhanced electrocatalytic activity of NiSx/NF(Ox) with a small overpotential of 72 mV to reach 10 mA cm(-2) compared with Ni3S2/NF, which may be ascribed to the improved electron-transfer kinetics relating to the unique atomic configurations and crystalline structures of beta-NiS. The electro-oxidation pretreatment of nickel foam provides a simple and convenient method by tuning different NiSx crystal phases for preparing excellent OER eletrocatalysts. (C) 2016 Elsevier B. V. All rights reserved.