ESTUDO DA REAÇÃO DE REDUÇÃO DE OXIGÊNIO SOBRE ELETRODOS À BASE DE TETRAMETÓXIFENILPORFIRINAS PARA APLICAÇÕES EM CÉLULAS A COMBUSTÍVEL DE BOROIDRETO DIRETO / STUDY OF THE OXYGEN REDUCTION REACTION ON ELECTRODES BASED OF TETRAMETÓXIFENILPORFIRINAS FOR APPLICATIONS IN CELLS FUEL BOROHYDRIDE DIRECT

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

10/06/2012

RESUMO

The oxygen reduction reaction (ORR) in 1.0 mol/L KOH solutions catalyzed by FeTMPP/C and CoTMPP/C was investigated in absence and presence of BH4- anions with concentrations varying from 10-7 to 1.0 mol/L. Similar cyclic voltammetry and rotating disk electrode experiments have been also performed the commercial E-TEK Pt/C electrocatalysts. In absence of BH4- anions, the ORR proceeds via a direct 4 electron pathway on FeTMPP/C and Pt/C and via a peroxide pathway involving (2-electron process) on CoTMPP/C and Au/C catalysts. In addition, Pt/C presented the most positive onset potential for the reaction. In presence of BH4- anions, a drastic loss in the catalytic activity of the Pt/C electrode was observed, even for concentrations as low as 10-7 mol/L. The effect of temperature on the ORR was studied and from 20C up to 60C the diffusion limited current densities remained nearly constants. At 80C, a decrease in the current of density was observed, probably due to a decrease in the oxygen concentration and viscosity of the solution. Arrhenius plots [ln (k) vs. T-1] were used to evaluate the activations energy (Ea) of the ORR in absence of borohydride and resulted in 47.6 kJ/mol and 50.3 kJ/mol for Pt/C and FeTMPP/C, respectively. In presence of borohydride in solution, the Ea value for Pt/C showed a pronounced decrease to 38.7 kJ/mol, due to borohydride oxidation as a parallel reaction, while for FeTMPP/C the value calculate was 52.7 kJ/mol, i.e., remained practically constant. Such results indicates that FeTMPP is an efficient catalyst for ORR in alkaline solutions and tolerant to BH4 anions.

ASSUNTO(S)

redução de oxigênio eletrocatalisadores oxidação de boroidreto medidas de eletrodo de disco rotatório quimica analitica oxygen reduction electrocatalysts borohydride oxidation rde measurements

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