Free Standing Nitrogen Deficient Carbon Nitride Oxygen Electrodes for Metal-Air Batteries

Designing highly active, long-life durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently required for bringing future renewable energy conversion and storage devices. However, poor conductivity and resulting serious irreversible capacity loss were pronounced for carbon nitride due to its high nitrogen content. Herein, one-dimensional (1D) nitrogen deficient g-C3N4 microtubes based electrocatalysts were fabricated using thermal polymerization of melamine-cyanuric acid complex precursors, followed by denitriding technology to reduce the nitrogen. The resultant ND-g-C3N4 exhibited outstanding bifunctional ORR/OER performances with overpotential of ~ 0.9 V comparable to the commercial noble metal catalysts (such as Pt/C & RuO2). This excellent catalytic performance was attributed to unique one-dimensional tubular structure having abundant active sites, high electrical conductivity, and efficient mass transport in the frameworks. The obtained bifunctional catalysts displayed the outstanding Zn-air battery performance for 400 h stability at 10 mA cm-2 with fast rate capability, open circuit potential of 1.48 V, and high power density of 230 mW cm-2. The outstanding electrochemical performances evidently stimulate the application of g-C3N4 materials in the energy storage devices.