Electrocatalytic activity of nitrogen-doped holey carbon nanotubes in oxygen reduction and evolution reactions and their application in rechargeable zinc–air batteries

Nitrogen-doped holey carbon nanotubes (N-HCNTs) were fabricated for use as a cathode material of Zn–air batteries. Holes were formed in the carbon nanotube (CNT) by reacting it with hydrogen peroxide, following which the oxidized CNT was pyrolyzed with urea to form N-HCNT. The electrocatalytic activities of N-HCNT in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were compared with those of Pt/C and IrO2; N-HCNT exhibited excellent bifunctional electrocatalytic activity in both, the ORR and OER, while Pt/C and IrO2 exhibited excellent electrocatalytic activity only in the ORR and OER, respectively. Further, the maximum power density of a Zn–air rechargeable battery using the N-HCNT electrode was 17.6% higher than that of a battery using a mixture of Pt/C and IrO2 (1:1) as the electrode. Moreover, after 500 cycles, the change in the charge-discharge voltage gap of the battery using the N-HCNT electrode (18.3%) was much smaller than that of the battery using the mixture of Pt/C and IrO2 (118.1%). The excellent electrocatalytic activity and cycle life of the N-HCNT electrode in Zn–air battery demonstrate its promise in the development of future energy devices.