Co/CoNx decorated nitrogen-doped porous carbon derived from melamine sponge as highly active oxygen electrocatalysts for zinc-air batteries

Developing stable and efficient ORR/OER cathode catalysts is crucial to achieve large-scale practical applications for zinc-air battery. Herein, Co/CoNx decorated N-doped porous carbon hybrids with two different morphologies were prepared using commercially available melamine sponge as the precursor. Direct two steps of pyrolysis produced N-doped porous carbon covered with Co/CoNx decorated CNTs (Co@CNT/MSC) with highly dispersed Co2N moiety, while the chemical activation of KOH and the followed high-temperature pyrolysis obtained N,Co co-doped hierarchically porous carbon (Co/HMSC) with CoN, Co2N and CoC8 moieties. Co/HMSC exhibits more excellent bifunctional ORR/OER electrocatalytic activity with an ORR onset potential of 0.95 V, an ORR half-wave potential of 0.84 V, an OER overpotential of 396 mV and an ultralow potential gap of 0.78 V, superior to most previous reports. The assembled Co/HMSC-based Zn-air battery shows excellent rechargeability with a small 0.2 V drop in its continuous charge-discharge cycles for 51.6 h at 10 mA cm−2. The superiority of Co/HMSC is ascribed to the high specific surface area, the affluent active sites and the synergistic effect between the CoNx/CoCx active moieties and the nitrogen-doped carbon support.