1-Butyl-3-methylimidazolium hydrogen sulfate-induced structure modification and reconstruction of nickel foams for oxygen evolution reactions

Abstract

Surface chemical etching for the in situ growth of metal–organic materials and electrochemical reconstruction are expected to efficiently improve the catalytic performance of oxygen evolution reactions (OERs). In this work, 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO₄) was used to chemically etch the surface structure of nickel foams (NFs) and form metal–organic thin films in situ at the surface of the NF ([BMIM]–SO₄–Ni@NF). Anion HSO₄⁻ in [BMIM]HSO₄ chemically etched the NF surface to provide bivalent nickels (Ni²⁺). Ni²⁺ and [BMIM]HSO₄ formed a [BMIM]–SO₄–Ni coating in situ on the surface of the modified NF. During the OER process, nitrogen and sulfur leached out from the surface of [BMIM]–SO₄–Ni@NF, along with the reconstruction of [BMIM]–SO₄–Ni@NF to C–NiOOH@NF. C–NiOOH@NF possessed a hierarchical and defective nanoflower structure and enlarged the electrochemical active surface area and surface-active sites for OER activity. The effect of [BMIM]HSO₄ on the performance of oxygen evolution reactions (OERs) was investigated. The results indicated that [BMIM]HSO₄ modification promoted the formation of γ-NiOOH and significantly improved the OER performance of NFs. The OER performance was obtained at a [BMIM]HSO₄ mass concentration ([BMIM]HSO₄%) of 2.4%. However, high [BMIM]HSO₄% results in the damage of the NF frame structure and a high content of carbon doping, leading to a reduction in OER activity.