Effect of particle size on the oxygen reduction reaction activity of carbon-supported niobium-oxide-based nanoparticle catalysts

In this study, niobium oxynitride nanoparticles were examined to determine the effect of particle size on oxygen reduction reaction (ORR) activity. To this end, catalyst precursors with niobium oxides dispersed on carbon supports were prepared using the irradiation or impregnation method. Polyacrylonitrile was added to each precursor, followed by heat treatment under an ammonia-containing atmosphere to synthesize niobium oxynitride nanoparticles. The structures of the prepared catalysts were analyzed using transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy. The results indicated that two catalysts with the same crystal phase but different particle sizes were obtained. Comparing their ORR activities revealed that the effect of particle size on ORR activity was limited. Thus, it was inferred that controlling the microelectron conduction paths can help maximize the benefits of particle size reduction. In addition, niobium oxynitride nanoparticles with different structures were obtained by varying the heat-treatment temperatures, and the ORR activity of each prepared catalyst was evaluated. These findings suggest that forming graphitized carbon residues with high electrical conductivity and controlling nitrogen-doping in the oxide nanoparticles are crucial steps for enhancing the ORR activity of oxide-based catalysts. These findings offer valuable insights for developing material design strategies to improve oxide-based catalyst performance.