Radiation-induced synthesis of carbon-supported niobium oxide nanoparticle catalysts and investigation of heat treatment conditions to improve the oxygen reduction reaction activity

Abstract

Carbon-supported niobium oxide nanoparticle catalysts were synthesized for the oxygen reduction reaction (ORR) in acidic media. These catalysts were prepared using a ⁶⁰Co gamma-ray and heat-treated with polyacrylonitrile. Carbon black powder or multi-walled carbon nanotube (CNT) was used as the support for the niobium nanoparticle. Nb₂O₅ nanoparticles with low crystallinity were fine and well dispersed on the carbon support in the as-irradiated samples. The loading amount of niobium increased with the absorbed dose, which indicated that niobium nanoparticles were produced by the irradiation. The as-irradiated composite nanoparticles were heat-treated under an H₂ atmosphere (5 %) or a mixed atmosphere of H₂ (2 %) and O₂ (0.05 %) to introduce active sites. The ORR activities were significantly enhanced by the heat treatment. Furthermore, the ORR activities were improved by using multi-walled CNT as the support.