B-doped GQD supported cobalt sulfide nanocomposite: A defect engineering approach for superior oxygen electrode performance

Developing an efficient and durable electrocatalysts for oxygen electrolysis is crucial for advancing clean energy technologies. However, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), along with catalyst degradation, remain major obstacles. Here, we optimized the composition of composite nanocatalysts obtained by doping of an electron deficient, B-atoms into graphene quantum dots (GQD) attached with Cobalt Sulfide (CoS) nanostructures. Optimizing the surface structure and investigating the interfacial interactions, the catalyst demonstrated an exceptional oxygen electrode reaction performance. The faster electronic synergism between the defect engineering BGQD and CoS offers more catalytic active sites as well as faster electrical conductivity and higher adsorption/desorption rate of oxygenated intermediates at the electrode surface for the electrolysis processes. Among the optimized composite electrode material CSBGQD-13 (CoS/BGQD (1:3)) exhibited high positive onset (E_onset = 1.04 V vs. RHE) and half-wave potential (E_1/2 = 0.84 V vs. RHE) with high limiting current density of 7.6 mA/cm² at 1600 rpm and a reasonable resistance to the MeOH crossover effect during ORR. In addition, our electrocatalyst demonstrated long-term durability and effective OER activity with the lowest Tafel slope of 82 mV/dec among other CSBGQDs and a lower overpotential of 0.27 V vs. RHE at a current density of 10 mA/cm². Furthermore, the CSBGQD-13 claims excellent dual function electrocatalytic performance towards ORR and OER with a very small ΔE value (only 0.66 V vs. RHE), a higher catalytic current density. Henceforth, for possible fuel cell applications, we believe that this electrode material may provide an understanding of the principles of metal sulfide carbon dots hybrid catalysts.