B,N,S tri-doped reduced graphite oxide–cobalt oxide composite: a bifunctional electrocatalyst for enhanced oxygen reduction and oxygen evolution reactions

Abstract

In the present study, we followed a unique approach to synthesize a nanocomposite of B,N,S tri-doped graphite oxide and cobalt oxide. Initially, B,N,S tri-doped carbon quantum dots were prepared by a hydrothermal method using boric acid and L-cysteine as precursors, and were further immobilized on graphite oxide in the presence of a cobalt precursor to synthesise a nanocomposite of cobalt oxide and B,N,S tri-doped graphite oxide. The crystal structure and morphology of the BNS/rGO–Co nanocomposite were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) imaging, respectively. Electrochemical studies indicated a substantially higher electrocatalytic activity of the catalyst with an onset potential (E_onset) of 0.87 V vs. RHE and a current density (J_L) of 4.4 mA cm⁻² at 1600 rpm in alkaline conditions. Additionally, rotating ring disc electrode (RRDE) measurements confirmed a single step ∼4 electron transfer pathway, similar to that of Pt/C catalyst. Interestingly, the BNS/rGO–Co nanocomposite shows enhanced stability (up to 5000 cycles under similar conditions) and a high tolerance to methanol crossover effects, when compared to the state-of-the-art Pt/C catalyst. Concomitantly, the catalyst also exhibits remarkable oxygen evolution reaction activity. Such a remarkable electrocatalytic activity of the BNS/rGO–Co nanocomposite over its N,S-bi-doped counterpart is due to the importance of boron synergy with the N and S sites in the rGO, and also to the presence of the cobalt oxide interface for better conversion.