Model porous electrodes based and carbon nanotubes and organically grafted platinum electrocatalysts allows development of new approaches for the characterization of porous electrodes devoted to fuel cells

摘要

This paper reports on the characterization of model porous electrodes based on the combination of organically grafted platinum electrocatalysts and carbon nanotubes. Both, the difficulty to make homogeneous and well controlled deposition of porous electrocatalyts structures on rotating electrodes, and the use of unconventional Platinum Organically Grafted Electrocatalysts (Pt-OGE) lead us to contemplate the development of new approaches for the characterization of the Oxygen Reduction Reaction (ORR) in porous electrode structures. Such developments concern the evaluation of the selectivity of the ORR and the determination of a specific surface area related to the ORR using cyclic voltammetry. For the latter, simple equations established for flat electrodes and planar diffusion are used that describe the peak potential and peak current established as a function of scan speed. The easy manipulation of the organically grafted electrocatalysts allows a controlled combination with carbon nanotubes (CNT) in liquid media. In particular, the coverage density of Pt cores at the carbon nanotube surface can be precisely tuned. The overall process leads to the formation of various porous electrodes structures which consists in the active layer based on Pt-OGE/CNT combinations deposited on a carbon felt. The different electrodes structures are characterized as a function of Platinum loading regarding selectivity and the determination of so the called S-AO2 parameter which the specific surface area of the porous electrodes related to the ORR, expressed in m2/g Pt. The recorded trends exhibit a remarkable consistency for the different porous electrode structures leading to the determination of a feature S-AO2 and catalyst critical loading below which the selectivity is lower than 4. Although additional experimental studies are required to get more insights on these results, the high consistency recorded as a function of catalyst loading suggest that these new approaches might be of particular interest for the determination of feature parameters for a given porous electrode structure devoted to Oxygen Reduction, including non-noble metal electrocatalysts porous based structures.