Evaluation of Stability and Catalytic Activity Of direct Methanol Fuel Cell nano-catalysts by Cyclic Voltammetry

Abstract

Cyclic voltammetry (CV)is a very useful technique for theevaluation of fuel cell catalysts.CV is commonly employed to determinenot only the electrocatalytic activity and durabilitybut also to investigate reaction kinetics on the catalyst surface. Nanoparticles of platinum, Pt–Ni alloy and Ni@Pt core-shell as catalysts supported on multi-walled carbon nanotubes (MWCNTs)have beeninvestigated in 0.5M LiClO (neutral medium) using the CV technique. This has been 4 employed for the electro-oxidation of methanol on catalysts surfaces.In the anodic sweepwell-defined peaks have been obtained around 0.75Vversus saturated calomel electrode (SCE), while in cathodic sweep alsosharp reverse anodic peaksaround 0.45 V havebeenobserved for the methanol oxidation reaction. In evaluation of peak currents, specific activities and mass activities Ni@Pt/MWCNTs has shown the highest values and Pt is at the lowest. Anodic polarization curves have been plotted using Tafel equation for all the catalysts and exchange current densities o o (i) arecalculated from the curves for comparison yielding higher values ofi for better catalysts.Specific activity 1/2 showed a linear increase with square root of scan rate(ν ) suggeststhe reaction is diffusion controlled. Plots of peak potentials vs. lnν indicate that the electro-oxidation of methanol is an irreversible process. Heterogeneous rate constants for methanol oxidationhave been calculated and are described.Durability studies of the catalysts up to fifty cycles have also been estimated. All the above features suggest that Ni@Pt/MWCNTs can be a promising catalystfor the direct methanol fuel cells.