Hollow carbon sphere and polyhedral carbon composites supported iron nanoparticles as excellent bifunctional electrocatalysts of Zn‐air battery

Herein, we synthesize Fe-based nanocatalysts supported on the composites composed of hollow carbon spheres (HCSs) and metal–organic frameworks (MOFs) by a facile pyrolysis method. The composites with different ratios of HCSs and MOFs present an interesting phenomenon: the oxygen reduction reaction (ORR) limiting current increases along with the HCSs content, while the onset potential and half-wave potential show the highest values when the ratio between HCSs and MOFs is optimized. The composite catalysts exhibit superior ORR electrocatalytic performance than Pt/C in alkaline and neutral media. Even in the acidic media, these composite catalysts still present a close catalytic activity to Pt/C. For the oxygen evolution reaction (OER) test, the prepared Fe-NC@NHCS-600 shows a reduced overpotential to that of the benchmark IrO2. The rechargeable Zn-air battery using Fe-NC@NHCS-600 as the catalyst of air electrode exhibits superior discharge capability with an open-circuit voltage of 1.620 V and a maximum power density of 278.97 mW cm−2 in alkaline electrolyte, as well as an open-circuit voltage of 1.457 V and a maximum power density of 114.96 mW cm−2 in neutral electrolyte. The battery also exhibits steady cycling stability for more than 90 and 70 h at 5 and 10 mA cm−2, respectively.