Metal-free nitrogen-doped porous carbons derived from pomelo peel treated by hypersaline environments for oxygen reduction reaction

Abstract

Metal-free nitrogen-doped carbon materials with advanced porous structure are considered as one of the most promising next-generation non-platinum catalysts for the oxygen reduction reaction (ORR) applied to fuel cells and metal-air batteries. In this work, we develop nitrogen-doped porous carbons based on pyrolysis of pomelo peel by chemical treatment under hypersaline environments containing saturated NaCl, ZnCl2 and FeCl3. The obtained carbon exhibits outstanding ORR activity with a half-wave potential (0.86V vs RHE) and the kinetics current (10.40 mA·cm−2), which are much higher than those obtained from the Pt/C (0.83V, 5.22 mA·cm−2 respectively). Also, the carbon displays superior stability and methanol tolerance to the Pt/C. The significantly improved performance of the synthesized carbon can be attributed to a synergy of enlarged pore volume, increased pyridinic nitrogen doping level and decreased stacking defects of graphite layers in the carbon, caused by the unique hypersaline treatment on the pomelo peel. Moreover, the effect of the hypersaline treatment on the formation of the advanced porous nitrogen-doped carbons is discussed here. The proposed synthetic strategy may offer a facile and efficient route to prepare cost-effective carbon materials derived from other biomasses for the current energy storage and conversion fields.