Mesoporous carbon nanospheres with improved conductivity for electro-catalytic reduction of O2 and CO2

Abstract Isolated mesoporous carbon nanospheres doped with carbon nanotubes or nanohorns were obtained for the first time by a sol-gel synthesis. The presence of nanomaterials improves the electrical conductivity of the catalysts increasing the current storage capacity and the electrocatalytic performance. Ni-catalysts were also prepared by impregnation of the supports and by doping during the synthesis. Better Ni-dispersion was obtained in impregnated samples regarding doped ones where Ni-particles are mainly embedded in the carbonaceous matrix and affects the textural properties, especially the mesopores volume which increases with the spheres size. The presence of mesopores shown a positive effect in both electro-reduction reactions. All materials, present electro-catalytic activity in both O2 and CO2 electro-reduction but in very different extension. The presence of carbon nanomaterials clearly improves the electro-activity in ORR even being good free-metal electro-catalysts, however, these nanomaterials does not improve the electro-activity in CO2 reduction. Ni addition improves the electro-activity in both reactions, however in the case of CO2 reduction, a good accessibility of Ni particles to the electrolyte is necessary. Finally, despite the very low contents of carbon nanomaterials and Ni the electro-catalytic results obtained are good enough and similar that those available in the literature based in carbon materials.