Electrocatalysis of CO tolerance by carbon-supported PtMo electrocatalysts in PEMFCs

This paper is a full version of an earlier short communication, where significantly higher (up to threefold) CO tolerance was reported for PtMo/C (atomic ratio, Pt:Mo, 3:1) relative to the current state-of-the-art PtRu/C (1: 1) in a proton exchange membrane fuel cell (PEMFC) under standard operating conditions (85degreesC, 100% humidification, with H-2 + 100 pm CO//O-2). We report significantly different behavior for PtMo/C in contrast to PtRu/C, wherein there is negligible variation in CO tolerance (100 ppm CO in H-2) with variations in alloying compositions (Pt:Mo, 1: 1 to 5: 1). Further, in contrast to Pt/C and PtRu/C, significantly lower variations in overpotential losses is observed for PtMo/C as a function of temperature (55-115degreesC) and CO concentrations (5-100 ppm, balance H-2). In addition, excellent long-term stability is reported for PtMo/C (1:1) under steady-state conditions (constant potential conditions at 0.6 V) for a total duration of 1500 h, with anode gas composition varied between pure H-2 and those with 100 ppm CO, with or without the presence of other reformate gases (primarily CO2 and N-2). These are discussed in the context of detailed physicochemical characterization of the nanoparticles using a combination of X-ray diffraction, transmission electron microscopy, and in situ synchrotron X-ray absorption spectroscopy. (C) 2004 The Electrochemical Society.