Nitrogen-doped carbon xerogels catalyst for oxygen reduction reaction: Improved structural and catalytic activity by enhancing nitrogen species and cobalt insertion

Highly active nitrogen-doped carbon xerogel (N-CX) electrocatalysts for the oxygen reduction reaction (ORR) were synthesized through a simple sol-gel method. The N-CX samples are prepared using resorcinol - formaldehyde resin as the carbon precursor and dicyandiamide as the nitrogen precursor. The N-CX samples carbonized at different temperatures are inspected to interpret the effect of the high-temperature conditions towards the structures and ORR activity of the final products. As-prepared N-CX samples with different carbonized temperatures are characterized via X-ray photoelectron spectroscopy (XPS), X-ray diffractometry and Raman spectroscopy. The N-CX sample carbonized at 800 degrees C demonstrated the greatest ORR activity, and the structural properties and catalytic activities of the catalyst are then further improved by insertion of cobalt metal under an ammonia atmosphere. Metal doping evidently promotes the catalytic activity of the N-CX catalyst. Raman and XPS studies show that cobalt increases the creation of pyridinic-N and quaternary-N groups through the formation of more graphitic structures. The ammonia atmosphere is demonstrated to act as an additional N source by increasing the total N content in the carbon structure after high temperature treatment of the N-CX catalyst. Metal-N-like and metal carbide configurations generated play a role in catalyst production with high catalytic activity. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.