Effect of preparation conditions of sol-gel-derived Co-N-C-based catalysts on ORR activity in acidic solutions

Using a Co oxide ethanol-based sol as a precursor solution, nitrogen (N)- and carbon (C)-containing ligands [1,2 phenylene diamine (phen) and ethylene diamine (en)] were added to produce an oxygen reduction reaction (ORR) catalyst precursor. After adsorption on carbon powder, heat-treatment in an inert atmosphere at 500-900 degrees C, and the addition of Nafion as a binder, the powdered mixture was coated on a glassy carbon electrode and evaluated for its ORR activity in 0.5 M H2SO4. The catalyst-carbon powder ratio, heat-treatment temperature, ligand type, and ligand:Co ratio were optimized, and the effect of increased catalyst layer thickness, particle size, and C support was also determined. It was concluded that a phen-based catalyst with a metal to ligand ratio of 1:2, a heat-treatment at 900 degrees C, and a concentration of 4 wt % Co was the most active, selective, and stable ORR catalyst material of the materials developed in the present work. X-ray photoelectron spectroscopy and X-ray diffraction analysis showed the formation of both Co metal and CoN4 units upon heat-treatment, with the most active catalyst having a 5.3:1 overall N-Co ratio. (C) 2008 The Electrochemical Society.