Platinum/polypyrrole-carbon electrocatalysts for direct borohydride-peroxide fuel cells

Abstract

Polypyrrole-carbon (PPy-C) composites having different amounts of carbon (5–35 wt.%) decorated with platinum nanoparticles (Pt/PPy-C) were prepared and investigated for borohydride oxidation reaction (BOR) in alkaline medium and for hydrogen peroxide reduction reaction (HPRR) in acidic medium. Structural and morphological properties and composition of these electrocatalysts were determined by FTIR, Raman, XPS, SEM/EDS, TEM and ICP-MS analyses. Pt/PPy-C electrocatalysts were evaluated for BOR and HPRR by cyclic voltammetry and chronoamperometry. Faradaic and kinetic parameters, such as the number of exchanged electrons, n, charge transfer coefficient, α, apparent activation energy, Eaapp, and order of reaction, β, were calculated. n for BOR ranged from 6.0 to 7.6, while n for HPRR ranged from 1.0 to 2.0. Eaapp was found to range from 10 to 18 kJ mol−1 for BOR and from 8 to 14 kJ mol−1 for HPRR. The BOR was found to be a 1st order reaction with respect to BH4−. Pt/PPy-C35% electrocatalyst showed the best activity for both reactions. Fuel cell tests were done with Pt/PPy-C electrodes as anode, as cathode and as both anode and cathode in a direct borohydride-peroxide fuel cell (DBPFC). DBPFC with Pt/PPy-C35% as anode electrocatalyst gave the highest peak power density of 1432 W gPt−1 at current density of 2046 A gPt−1 and cell voltage of 0.70 V.