Steering structural mesoporosity and working microenvironment of Fe-N-C catalysts for boosting cathodic mass transport of zinc-air batteries

Transition metal-N-C materials have considerably been demonstrated as promising catalysts for cathodic oxygen reduction reaction (ORR) in Zn-air batteries. Current efforts mainly focus on tailoring coordination structure and identifying active sites of metal-N-C materials for ORR, while the mass transport of metal-N-C employed in catalytic layers of working electrodes is seldom engineered. Herein, a Fe-N-C single-atom catalyst featuring high mesoporosity and abundant electrochemically accessible active sites is developed through post-loading Fe species into defective N-doped carbon support. The Fe-N-C single-atom catalyst serving as the air cathode of Zn-air battery delivers a peak power density of 189.9 mW cm−2, significantly larger than 114.2 mW cm−2 of commercial Pt/C and 162.9 mW cm−2 of the Fe-N-C contrast catalyst with low mesoporosity. More importantly, through adding hydrophobic polytetrafluoroethylene (PTFE) nanoparticles in the catalytic layer of air cathode, the peak power density of Fe-N-C single-atom catalyst is further increased to 212.3 mW cm−2. The increased peak power density is attributed to the enhancement of O2 mass transport, as evidenced by a substantially decreased diffusion layer thickness that is obtained from electrochemical impedance spectroscopy.