Enhancing the oxygen evolution reaction of cobalt hydroxide by fabricating nanocomposites with fluorine-doped graphene oxide

Abstract

Fluorine and nitrogen codoped cobalt hydroxide–graphene oxide nanocomposites (N,F-Co(OH)₂/GO) were synthesized by a simple hydrothermal method and demonstrated highly enhanced oxygen evolution activity in an alkaline medium. N,F-Co(OH)₂/GO synthesized under optimized reaction conditions required an overpotential of 228 mV to produce the benchmark current density of 10 mA cm⁻² (scan rate 1 mV s⁻¹). In contrast, N,F-Co(OH)₂ without GO and Co(OH)₂/GO without fluorine required higher overpotentials (370 (N,F-Co(OH)₂) and 325 mV (Co(OH)₂/GO)) for producing the current density of 10 mA cm⁻². The low Tafel slope (52.6 mV dec⁻¹) and charge transfer resistance, and high electrochemical double layer capacitance of N,F-Co(OH)₂/GO compared to N,F-Co(OH)₂ indicate faster kinetics at the electrode–catalyst interface. The N,F-Co(OH)₂/GO catalyst showed good stability over 30 h. High-resolution transmission electron microscope (HR-TEM) images showed good dispersion of polycrystalline Co(OH)₂ nanoparticles in the GO matrix. X-ray photoelectron spectroscopic (XPS) analysis revealed the coexistence of Co²⁺/Co³⁺ and the doping of nitrogen and fluorine in N,F-Co(OH)₂/GO. XPS further revealed the presence of F in its ionic state and being covalently attached to GO. The integration of highly electronegative F with GO stabilizes the Co²⁺ active centre along with improving the charge transfer and adsorption process that contributes to improved OER. Thus, the present work reports a facile method for preparing F-doped GO–Co(OH)₂ electrocatalysts with enhanced OER activity under alkaline conditions.