Direct conversion of solid g-C3N4 into metal-ended N-doped carbon nanotubes for rechargeable Zn-air batteries

Developing low-cost and bifunctional electrocatalysts with activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable for metal-air batteries. Herein, we demonstrate an approach to realize the direct conversion of two-dimensional (2D) graphitic carbon nitride (g-C3N4) into one-dimensional (1D) metal-ended nitrogen doped carbon nanotubes (M-NCNTs). For Co-NCNTs, Co@CoOx nanoblocks were found at the end of the nanotubes. The Co@CoOx nanoparticles in Co-NCNTs can be chemically modulated by acid etching to endow them with catalytic activity towards the ORR and OER. After nitric acid (HNO3) etching, the Co-NCNTs-N shows superior activity both in the ORR with an onset potential of 0.86 V and a half-wave potential of 0.80 V and in the OER with a potential of 1.58 V at 10 mA cm(-2). Assembled in Zn-air batteries, the Co-NCNTs-N electrode also presents an ultrahigh power density of 210 mW cm(-2), a small charge-discharge voltage gap of 0.80 V and a good stability of 130 hours, outperforming the commercial Pt/C-RuO2 electrode.

Automated summary

This study demonstrates a low-cost and bifunctional electrocatalyst for metal-air batteries. By converting two-dimensional graphitic carbon nitride into one-dimensional metal-ended nitrogen doped carbon nanotubes, the catalytic activity for ORR and OER can be achieved. The chemically modulated Co-NCNTs-N exhibited excellent activity in both ORR and OER, and showed superior performance in Zn-air batteries.