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.