Cobalt Nanoparticles Dispersed Nitrogen-Doped Graphitic Nanospheres-Based Rechargeable High Performance Zinc-Air Batteries

The zinc-air battery (ZAB) is an emerging rechargeable energy storage system having high energy density (1084 Wh/kg) with safe operation and low operation cost (similar to$10 kW/h). Development of a durable and efficient bifunctional catalyst is the bottleneck of rechargeable ZAB technology, and here we demonstrate a hybrid catalyst system having cobalt (Co) nanoparticles dispersed graphitic spheres as an efficient catalyst at the air electrode-performing better than the benchmarked ones while constructing the ZAB cells. Co nanoparticles dispersed nitrogendoped graphitic nanospheres (Co@NGC-NSs) were developed using a unique synthesis strategy, and it showed excellent bifunctional catalytic activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. The potential difference calculated with Co@NGC-NSs, considering the potential for the current density of 10 mAcm(-2) for OER and current density corresponding to the half wave potential for ORR, is found to be (0.78 V) lower than that of Pt/C and IrO2 (0.87 V) system. The zinc-air cell constructed using Co@NGC-NSs shows an open circuit voltage of 1.36 V having a maximum power density of similar to 52 mW cm(-2) and an energy density of 876 Wh/kg, and these values are on par with the Pt/C system while much better in terms of long-term stable performance where Pt/C is found to be failing. A detailed comparison with the reported performance of other catalyst-based ZABs indicates that the Co@NGC-NSs-based ZABs has high potential as a practically viable system, where the catalyst development is also found to be simple and nonexpensive in nature.