Facile preparation of biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reactions

Abstract

The development of inexpensive and efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still remained a challenge in wide range of renewable energy technologies. Herein, biomass-derived nitrogen self-doped porous carbon nanosheets (NPCNS) are produced by a facile and green pyrolysis of Euonymus japonicus leaves at controlled temperature and then the nitric acid pickling was carried out to remove the excess metal ingredients. The obtained NPCNS exhibits a hierarchically porous distribution, high BET surface area and uniform nitrogen doping. Electrochemical measurements show that the NPCNS possess a high electrocatalytic activity for both ORR and OER. Among these NPCNS catalysts, the sample carbonized at 900 °C (NPCNS-900) with the highest concentration of pyridinic nitrogen shows the best ORR and OER activity. According to our DFT calculations, the high content of pyridinic nitrogen with the moderate O and OH adsorption energies among the three types of nitrogen should be the critical factor for the efficient catalytic performance of NPCNS-900 toward ORR and OER. This work demonstrates that the facile prepared NPCNS-900 is a potential candidate material with excellent performance in electrocatalytic applications such as fuel cells or metal-air batteries.