Efficient utilization of crude bio-oil: the synthesis of nitrogen-doped hierarchically porous carbon as electrocatalysts for the oxygen reduction reaction

Bio-oil, the unavoidable liquid product of the thermal conversion of biomass, shows high contents of carbon and aromatic compounds and is a promising carbon precursor. Herein, nitrogen-doped hierarchically porous carbons (NHPCs) as effective catalysts for the electrochemical reduction of oxygen are successfully synthesized from crude bio-oil through a one-step ZnCl2-based template method. The optimized obtained carbon exhibits favorable electrochemical catalytic activity for the oxygen reduction reaction, with a halfwave potential (E-1/2) of -0.158 V (vs. Ag/AgCl) in 0.1 M KOH electrolyte. It not only shows comparable activity to a commercial Pt/C catalyst (E-1/2 = -0.148 V), but also better long-term stability and methanol resistance ability. The relationship between the structure and chemical properties of carbons and their catalytic performance is comprehensively analyzed. The results show that the high contents of pyridinic and graphitic nitrogen species are responsible for the high activity, while the large specific surface area (up to 920.58 m(2) g(-1)) and rational micro/meso/macroporous structure guarantee the sufficient exposure of active sites and mass transport efficiency. This work provides a facile and low-cost approach to efficient utilization of crude bio-oil as a renewable carbon precursor for NHPCs for electrochemical catalysis.