Investigating the bifunctional electrocatalytic activity of nickel oxide/nitrogen-doped reduced graphene oxide nanocomposite for zinc-air battery application

The performance of electrically rechargeable zinc-air batteries (ErZAB) depends on the efficiency of bifunctional electrocatalysts. Herein, four different forms of the nickel oxide/nitrogen-doped reduced graphene oxide (NiO/rGO), with various amounts of the Acacia Ataxacantha leaves extract, were synthesized by a hydrothermal method. The effect of the extract loading on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is reported. The energy dispersive X-ray spectra confirm that the plant extract can act as a dopant for nitrogen and reductant for the graphene oxide, whereas the field emission scanning electron microscopic (FE-SEM) images demonstrate that the NiO nanoparticles were uniformly dispersed onto the surface of the rGO thereby providing greater number of active sites for electrocatalytic activity. The electrochemical characterization reveals that the doping of the N improves the bifunctional electrocatalytic activity of NiO-rGO nanocomposite. Furthermore, the ORR and OER onset potential were found to decrease and increase with an increase in the loading level of the plant extract respectively. It was found that 7.5 mL of the plant extract is the optimum loading level to achieve the highest ORR and OER electrocatalytic activities. Furthermore, battery testing indicated that the bifunctional electrocatalyst showed outstanding charge-discharge cycle performances, with its voltage polarization exhibiting a 0.25% decrease in discharge and a 1.4% increase in charge after 50 charge-discharge cycles.