Co-Mn spinel supported self-catalysis induced N-doped carbon nanotubes with high efficiency electron transport channels for zinc-air batteries

Developing cost-effective and stable Pt-free electrocatalysts for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of zinc-air batteries. Here, we present a simple charge modulation strategy to synthesize Co2+-activated spinel CoMn2O4 supported self-catalysis derived nitrogen-doped carbon nanotubes (CoMn2O4/NCNTs@Ni). Associated with the formation of high valence Mn3.4+ over the octahedral site of CoMn2O4, the corresponding oxygen binding energy can be effectively tuned to greatly enhance the activity of ORR, further revealed by the density functional theory calculations. Benefiting from the highly conductive CoMn2O4-NCNTs-Ni electron transport channels and high valence Mn3.4+, the CoMn2O4/NCNTs@Ni catalyst exhibits excellent oxygen electrocatalytic activity (the limiting-current density was 5.51 mA cm(-2)) and stability (the current density remained at 86.80% within 24 h), with much lower ORR overpotentials than Mn3O4/NCNTs@Ni (the limiting-current density was 5.35 mA cm(-2) and the current density remained at 71.63% within 13 h). The as-obtained CoMn2O4/NCNTs@Ni as a cathode can further assemble a zinc-air battery, which delivers an opencircuit potential of 1.46 V, even close to that of Pt/C (1.50 V), and excellent stability (charge-discharge stably for 238 h). This charge modulation strategy provides a new way to design and explore highly active, durable, and cost-effective catalysts for renewable energy conversion and storage.