Bifunctional nitrogen-doped hybrid catalyst based on onion-like carbon and graphitic carbon encapsulated transition metal alloy nanostructure for rechargeable zinc-air battery

We demonstrate a facile approach for the synthesis of bifunctionally active nitrogen-doped mesoporous hybrid material based on onion-like carbon (OLC) and graphitic carbon encapsulated CoFe alloy for the fabrication of rechargeable zinc-air battery (ZAB). The synthetic approach involves controlled temperature annealing of a homogenous mixture of cobalt and iron complexes of hydrolyzed collagen and the subsequent surface engineering by acid treatment. In situ generated CoFe alloy nanoparticle (12.5 nm) catalyzes the growth of OLC. CoFe nanoparticle is encapsulated with multi-layer graphitic carbon shell. The surface-engineered mesopomus catalyst has large surface area (659 m(2) g(-1)) with interconnected mesopores. It is bifunctionally active towards oxygen reduction and oxygen evolution reactions with a potential gap of 0.8 V. It catalyzes oxygen reduction reaction in acidic and alkaline pHs and the kinetics of oxygen reduction in alkaline pH is highly facile with high electron transfer coefficient of 0.95. The Fe-Nx sites of the catalyst actively participate in the oxygen reduction in acidic pH. Rechargeable ZAB is fabricated using the hybrid material based air cathode. It has high open-circuit voltage (1.58 V), peak power density (102 mW/cm(2)) and remarkable charge-discharge cycling stability. The overall performance is superior to that of the traditional catalyst based ZAB.