Crystalline phase-function relationship of in situ growth NixSy controlled by sulfuration degree for oxygen evolution reaction

• Effect of sulfurization degree on crystal phase of NixSy has been investigated.
• Altering crystal phase of NixSy can be achieved by changing sulfurization degree.
• NiS phase outperforms better activity for OER than other NixSy phases.

Relationship between crystal structure of NixSy and sulfurization degree has been investigated via in situ growth NixSy on nickel foam (NixSy/NF) by solvothermal process with thiourea as sulfur source. NixSy with different phases are controlled by mass of thiourea from 1 g, 1.5 g, 2 g, 2.5 g–3 g. XRD shows the presence of NiS2, NiS and Ni3S2 in NixSy. Pure Ni3S2 synthesized by 2.5 g thiourea implies easy access to pristine NixSy phase. Notably, only one sample (synthesized by 2 g of thiourea) contains unique NiS phase with special flake accumulation morphology, owning superior performance for oxygen evolution reaction (OER) by electrochemical measurements. It suggests that NiS phase outperforms other NixSy, probably the best phase for OER in NixSy phases. All data confirm the achievement of altering crystal structure of NixSy by tiny changes of sulfurization degree, which may provide a new strategy to prepare enhanced electrocatalysts for OER.

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