Vacancy-rich graphene supported electrocatalysts synthesized by radio-frequency plasma for oxygen evolution reaction

Abstract

Transition metals and their compounds supported on graphene are promising electrocatalysts for application. Their catalytic performance benefits from the vacancy defects of these electrolytes. However, the facile and effective generation of vacancy defects is still a challenge, and the role of vacancy defects is also unclear. In this work, an efficient radio-frequency (RF) plasma treatment strategy has been employed to achieve sulfur vacancies and oxygen vacancies in electrocatalysts for the oxygen evolution reaction. H₂, Ar/H₂, and Ar were used for the generation of plasma, respectively. Plasma treatment was found to reduce Co³⁺ to Co²⁺, and create sulfur and oxygen vacancy defects on the surface of cobalt compounds and graphene. The reactive radicals generated by plasma reduce graphene oxide to graphene nanosheets, which provide space for the movement of carriers and nanoparticles. Among the three different plasma systems, the H₂ plasma has the most prominent ability to create vacancy defects in the electrocatalysts. The XRD pattern and Raman spectrum of the catalyst prepared by H₂ plasma show large displacement, indicating that the plasma is responsible for changing the lattice parameters and cell volume, and vacancy defect structure of the sample. The overpotential of H₂-V_S/rGO was 340 mV at 50 mA cm⁻² and the Tafel slope was 84.4 mV dec⁻¹. After 12 hours of amperometric i–t curve test, its OER performance was found to surpass that of IrO₂. DFT calculation results show that the vacancy defects effectively regulate the electronic structure, enhance the electron migration efficiency and promote the adsorption process of OER. The method of plasma treatment for creating vacancy structures is facile and effective, which provides a new route for the preparation of OER catalysts.