Mechanism of CO Tolerance on Molybdenum-Based Electrocatalysts for PEMFC

Abstract

In this work, the mechanism of CO tolerance for the hydrogen oxidation reaction (HOR) was investigated on Mo-based carbon dispersed electrocatalysts (Mo/C and PtMo/C). Gas-diffusion electrodes with a diffusion layer formed by Mo/C and a catalyst layer composed by Pt/C, PtRu/C, or PtMo/C, showed enhanced electrocatalytic activity for the HOR in the presence of CO. This phenomenon was associated to a lowering of the CO concentration in the gas channel of the electrodes promoted by a water gas shift (WGS) reaction taking place in the Mo/C layer. The occurrence of this reaction was confirmed by gas chromatographic analyses of the CO content, conducted at the outlet of a Mo/C reactor operating at 100°C and fed with different <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML1" overflow="scroll"> <mml:msub> <mml:mo>H</mml:mo> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>O</mml:mo> <mml:mo>/</mml:mo> <mml:msub> <mml:mo>H</mml:mo> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:mo>CO</mml:mo> <mml:mo>/</mml:mo> <mml:msub> <mml:mo>CO</mml:mo> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> mixtures. Experiments made in the presence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML2" overflow="scroll"> <mml:msub> <mml:mo>CO</mml:mo> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> indicated an additional CO poisoning effect due to the reversing of the WGS reaction, but the Mo-based electrodes still showed a performance superior to that of the standard state-of-the-art PtRu/C. © 2004 The Electrochemical Society. All rights reserved.