Determination of selectivity and specific area related to oxygen reduction reaction as a function of catalyst loading on non-noble metal based electrocatalyst porous electrodes: an example on nitrogen doped carbon nanotube

In a recent paper, model porous electrodes based on carbon nanotube and platinum organically grafted electrocatalysts were used to establish the determination of a specific surface area related to oxygen reduction reaction (ORR) in HClO4 1M, using cyclic voltammetry as a function of scan speed. Identical behavior was found for the trends of this parameter called S-AO2 and the selectivity of the ORR as a function of catalyst loading, for different model porous electrode structures. In the present paper, we report such a study on porous electrodes based on non-noble metal electrocatalysts built from nitrogen doped carbon nanotubes (N-CNT). The trends observed for S-AO2 and the selectivity of the ORR as a function of N-CNT loading are exactly the same as those observed for model porous electrodes. This suggests the interest of these approaches and in particular the determination of the S-AO2 parameter for the comparison of potentialities of different non-noble electrocatalysts, for example based on nitrogen doped carbon structures towards the ORR. Indeed, although the amount of chemical species supposed to be responsible for the ORR can be estimated using various methods, their accessibility at the level of the nano-object itself and more globally in the porous structure of an active layer is essentially unknown. The S-AO2 parameter value is presumably directly related to the active sites which are accessible to the oxygen reduction in a porous structure.