Metal–Organic-Framework-Derived Hollow CoS_<i>x</i>@MoS₂ Microcubes as Superior Bifunctional\nElectrocatalysts for Hydrogen Evolution and Oxygen Evolution Reactions

Abstract

Electrocatalytic\nwater-splitting catalysts play important roles\nin clean energy conversion systems. Herein, metal–organic framework-derived\n(MOF-derived) hollow CoS_<i>x</i>@MoS₂ microcubes were successfully synthesized by a novel method. Co-MOF\n[(CH₃)₂NH₂]­[Co­(HCOO)₃]\nprepared by a simple liquid precipitation method at room temperature\nreacted with S^2– released from thioacetamide (TAA)\nto generate Co₉S₈ under solvothermal conditions. Through hydrothermal treatment,\nnumerous MoS₂ nanosheets grew on the surface of CoS_<i>x</i> vertically and uniformly after introduction\nof sulfur and molybdenum sources, finally generating CoS_<i>x</i>@MoS₂ heterostructures. As bifunctional\nelectrocatalysts, the heterostructures exhibited remarkable performance\nfor the hydrogen evolution reaction with a low overpotential of 239\nmV when the current density increased up to 10 mA cm^–2 and a small Tafel slope of 103 mV dec^–1 in 0.5\nM H₂SO₄. They also worked effectively for the\noxygen evolution reaction with a low overpotential of 347 mV at 10\nmA cm^–2 in 1 M KOH. The enhanced electrocatalytic\nactivities of CoS_<i>x</i>@MoS₂ can\nbe ascribed to their unique heterostructures and the synergism between\nCoS_<i>x</i> and MoS₂.