Role of surface defects in catalytic properties of CeO2 nanoparticles towards oxygen reduction reaction

•Nanoparticles of ceria are prepared using gel combustion method.•Catalytic activity of the nano ceria towards electrochemical ORR has been studied.•Higher concentration of surface defects in samples with better catalytic activity.•Higher oxygen vacancy concentrations in samples with better catalytic activity.•Oxygen vacancies/surface defects are aiding oxygen adsorption and reduction.

CeO2 nanoparticles have been prepared by gel combustion method. The as-prepared nanoparticles were calcined at 500, 550 and 600 °C. The crystallite size of the nanoparticles has been determined using X-ray diffraction. Catalytic activity has been studied by measuring the Tafel slope in oxygen reduction reaction in cyclic voltammetery. The nanoparticles samples showed higher catalytic activity than bulk ceria sample. Surprisingly, smaller size nanoparticles with large surface area showed less catalytic activity than larger size nanoparticles. Positron annihilation, X-ray photo electron spectroscopy and photoluminescence studies indicated the presence of oxygen vacancies as well as larger surface defects. It has been found that surface defect concentration increased with the increase in calcination temperature and the catalytic activity of the nanoparticles is directly correlated to the surface defect concentrations.