Energy storage challenges exist in both the transportation industry, including electric vehicles, and in developing next-generation consumer electronics, such as flexible devices for communication and healthcare. Meeting these challenges depends on developing low-cost, high-performance rechargeable batteries.
In their recent publication in Advanced Materials, Professor Chen Zhong from Tianjin University, China, Professor Zhongwei Chen and Jing Fu from the University of Waterloo, Canada, and their co-workers, introduce a bifunctional oxygen electrocatalyst that can efficiently recharge zinc–air batteries.
The synthesis involves a solvothermal reaction to yield amorphous, oxidized cobalt sulfide nanoparticles supported on freestanding nitrogen-doped graphene. Treatment with ammonia gas at 700 °C converts the precursor core–shell nanoparticles—composed of a cobalt sulfide core and oxygen shell—to single-solid-phase, oxygen-vacancy-rich cobalt oxysulfide nanoparticles. The N-doped graphene is also converted to porous, nitrogen-doped graphene nanomesh (GN). The catalyst is highly dispersible in water, and after filtering, the freestanding catalyst film can be obtained and used directly in the zinc–air battery.
Compared to nonporous graphene, the GN provides intimate contact with the nanoparticles through covalent bonds between cobalt and nitrogen, along with much more open space and shorter diffusion channels for the reactants and intermediates involved in the oxygen reduction reaction (ORR) and evolution reaction (OER). Compared to benchmark catalysts (i.e., Pt/C for ORR and Ir/C for OER), the novel catalyst retains its activity better over 3000 cycles of cyclic voltammetry.
A binder-free prototype battery was constructed and found to have a more stable charging performance compared to a variant using the binder Nafion, indicated by the lower overpotential in charge and discharge, smaller ohmic and charge-transfer resistances, and higher energy efficiency and power density. The energy efficiency remains unchanged for at least 300 cycles compared to the benchmark device, which deteriorates after 50 cycles.
To learn more about this novel bifunctional oxygen electrocatalyst, please visit the Advanced Materials homepage.