In situ space-confined growth of Co 3 O 4 nanoparticles inside N-doped hollow porous carbon nanospheres as bifunctional oxygen electrocatalysts for high-performance rechargeable zinc–air batteries

Co 3 O 4 -10%@N-HPCNs with high surface area, hollow porous structure and strong interaction between nanoparticles and carbon nanospheres provide sufficient reactive sites and charge/mass transport environment, resulting in improved performance of RZABs.