Transforming bio-oil into nitrogen-doped hierarchical porous carbons: Excellent oxygen reduction electrocatalysts for Zn-air batteries

Nitrogen-doped hierarchical porous carbons are considered as important substitutes for noble metal electrocatalysts for the oxygen reduction reaction (ORR) in green-energy devices. Herein, bio-oil, the liquid product of biomass pyrolysis, and urea were used as the carbon and nitrogen source based on a simple MgO template approach. The obtained carbons exhibited a micro-/meso-/macroporous structure, considerable specific surface area and abundance of Graphitic and Pyridinic nitrogen species, leading to the excellent ORR catalytic performance with a half-wave potential of 0.84 V. The assembled primary Zn-air battery displayed a maximum power density of 239.36 mW cm−2 and consistent discharging stability. This work verified the great potential of bio-oil as a sustainable and low-cost precursor of advanced functional carbon materials and was conducive to the large-scale production of efficient carbon-based ORR catalysts.