Application of nitrogen-rich amino acids to active site generation in oxygen reduction catalyst

Noble-metal-free catalysts are demanded for widespread use of polymer electrolyte fuel cells (PEFCs) and the activity enhancement is required for practical use in the PEFC. We showed previously that a heat treatment of a mixture of iron lactate, glucose, and glycine generated a carbon material with Fe–N4 moiety as the active site for cathodic oxygen reduction; although the activity was still lower than conventional Pt-based PEFC cathode catalysts. In this study, the carbon-based noble-metal-free PEFC cathode catalyst was formed using amino acids containing more than one nitrogen atom in the molecule as the nitrogen source in order to obtain fundamental information on the efficient formation of the active site and the activity enhancement. We found that the oxygen reduction currents measured using rotating disk electrodes with the catalyst fixed on the surface were dependent on the amino acid molecular structure. The activity of the catalyst increased with an increase in the number of nitrogen atoms contained in the amino acid. The activity increase was attributed to the improved efficiency of the active site generation, based on the Fe contents, X-ray photoelectron spectra, and the extended X-ray adsorption fine structures at the Fe K-edge of the carbon material.