Temperature dependence of CO desorption and oxidation from cathodicelectrochemically treated carbon paper supported Pt electrodes

The Proton Exchange Membrane Fuel Cells (PEMFCs) are considered good alternatives as powergeneration systems for different kinds of applications because of their high efficiency in energy conversion and suitability. One of the problems appears when using hydrogen obtained fromreforming, because it contains CO, which can strongly compete with H2 for adsorption on Pt surface .This contamination lead to the metal poisoning and decreases the anode performance[1].Three mechanisms have been suggested to explain improved CO tolerance of Pt based catalyst compared to pure Pt: the bifunctional mechanism, the ligand effect mechanism, and the detoxification mechanism [2].Whereas the bifunctional and ligand effect mechanisms explain theimproved CO tolerance by a favoured electrochemical oxidation of CO, the detoxification mechanism proposes a lower equilibrium CO coverage at the surface, simply via the CO adsorption/desorption process. Therefore, both the electrochemical CO oxidation and the equilibrium attained through the adsorption/desorption process should be considered as physicochemical processes affecting the CO tolerance [3].Studies have shown that particle size,exposed crystal faces and oxidation state of carbon supports are important factors which have influence on specific activity of the Pt electrocatalyst for CO and methanol oxidation [4] Studies show the effect of electrochemical treatment of GC support [5] and oxidation of the HOPG substrate [4] on CO and methanol oxidation, because a large influence on the particle size and better distribution of platinum on the substrate. But, as we know, these supports are not real support for fuel cells. The study of the electrooxidation mechanisms of COad on Pt based catalysts is very important for designing more effective CO-tolerant electrocatalysts for fuel cell.To the best of the authors’ knowledge, there is no study about the effect of temperature on cathodic oxidation of carbon paper as a support for Pt electrodeposition on CO electrooxidation . The goal of this study isto investigate the effect of temperature on CO tolerancefor cathodic electrochemically treated carbon paper supported Pt with considering two approaches: electrochemical CO oxidation and the equilibrium coverage attained through the adsorption/desorption process.0.25 cm2 carbon paper(TGPH-090;Toray) was used as the support for electrochemical catalyst preparation. Oxidation on carbon papers were performed by applying -2 V for cathodic oxidation for 5 min in 0.5M H2SO4 solution. Pt was electrodeposited onto the carbon paper by electrodeposition in an electrolytesolution of 0.2M H2SO4 +2mM H2PtCl6.6H2O . Single-pulse chronoamperometry electrodepsitionby adjusting potential profile of 0V (1 s) and 1.15 V (600 s) (vs.Ag/AgCl(sat)) was done. All chemicals used in this investigation were of analytical grade (Merck

Keywords:

CO oxidation , carbon paper , cathodic oxidation , coverage , desorption , Temperatureeffect