CoNi nano-alloy anchored on biomass-derived N-doped carbon frameworks for enhanced oxygen reduction and evolution reactions

Bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important for energy conversion systems such as fuel cells, water splitting, and metal-air battery devices. In this work, an earthly abundant and cheap biomass of tobacco-stem was used to prepare a novel porous carbon framework (NiCo@N[sbnd]C) by incorporating transition metal alloy and nitrogen-rich small molecules. The resultant catalyst affords an onset potential of 0.92 V and a half-wave potential of 0.86 V for oxygen reduction reaction in alkaline media, which is better than commercial Pt/C. Besides, the catalyst also exhibits good oxygen evolution reaction performance with a low overpotential of 280 mV @ 10 mA cm⁻², and the potential gap between ORR and OER is only 0.65 V. The incorporation of NiCo alloy and N heteroatom modulates the electronic structure of the prepared carbon frameworks, creates abundant active sites, and improves charge redistribution, thus resulting in faster ORR and OER reaction kinetics. The applicability of the prepared NiCo@N[sbnd]C is fully harnessed for use as an air-cathode in a Zn-air battery. This work creates a platform for developing efficient porous and functionalized biomass-derived oxygen electrocatalysts for energy applications.