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

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.