Effect of porous structure on doping and the catalytic performance of carbon xerogels towards the oxygen reduction reaction

Abstract

The development of new electrocatalysts based on carbon materials lies in the appropriate design of their physico-chemical properties. The porous structure of the carbon xerogels is expected to have a direct effect on the subsequent processes used to further design the properties. Hence, it is essential to understand how the porous structure can affect the efficiency of the doping method and change the catalytic performance. To this end, carbon xerogels with different micropore volumes and electrical conductivities were prepared by applying different treatments (carbonization, activation and graphitization) to a macroporous organic xerogel synthesized by microwave heating. Nitrogen functionalities and iron nanoparticles were introduced into the carbonaceous structures. Doped and un-doped materials were tested as electrocatalysts for the oxygen reduction reaction. The amount of nitrogen introduced into the carbon structure decreases as the degree of order increases, while the type of nitrogen functional groups depends on the porous structure: higher volume of micropores allows the incorporation of quaternary nitrogen. Catalytic sites are mainly located in the micropores, macroporosity facilitates the access of the reactants, and nitrogen functionalities shift the mechanism of the reaction to the four-electron pathway. The addition of iron particles allows achieving the same performance as that of the platinum-based reference material.