ZnO-templated hollow amorphous carbon: oxygen adsorption and doping synergy for enhanced ORR catalysis

Abstract

In pursuit of highly active zinc–air battery (ZAB) catalysts, nitrogen doping has proven key to enhancing carbon-based non-metallic catalysts’ performance in the oxygen reduction reaction (ORR). This study employed a novel method to synthesize variously sized ZnO materials coated with ZIF-8. Notably, smaller particle sizes correlated with reduced activation energy. ZnO-12, the smallest variant, fully carbonized at 800 °C, resulting in zinc ion evaporation and the formation of an amorphous carbon nano-hollow structure, ZIF8/ZnO-12. This material showcased remarkable ORR properties, with an onset potential of 0.9 V (vs. RHE) and a Tafel slope of 71.4 mV dec⁻¹, surpassing the benchmark Pt/C catalyst and exhibiting excellent stability. Moreover, in ZAB tests, ZIF8/ZnO-12 achieved a specific capacity of 816 mA h g⁻¹, outperforming Pt/C. DFT calculations indicate that under alkaline conditions, nitrogen-doped carbon materials containing adsorbed oxygen and doped oxygen exhibit lower catalytic activation energy for the ORR, which is beneficial for accelerating the ORR. This research provides valuable insights into designing more efficient carbon-based non-metallic catalysts for ZABs.