Synthesis and characterization of Pt-HxMoO3 catalysts for CO-tolerant PEMFCs

Abstract

Two relatively simple synthetic procedures were developed for the synthesis of Pt–HxMoO3 composites. The obtained materials may be of interest as CO-tolerant catalysts for hydrogen-air fuel cells with proton-exchange membranes (PEMFCs). The first step of both syntheses was to prepare hydrogen molybdenum bronzes (HxMoO3) through the addition of Zn powder to acidic solutions containing Mo(VI) species. Two types of hydrogen-containing molybdenum bronzes were synthesized, namely, red bronze (x≈1.55) and green bronze (x≈2.0). The next step was the Pt deposition in a redox reaction between HxMoO3 and potassium tetrachloroplatinate (K2PtCl4) under open-circuit conditions that resulted in composite materials defined by aPt⋅b(HxMoO3).Numerous physical methods, including XRD, STEM, SEM, and XPS, were used to determine both the composition and structure of the catalysts. Platinum clusters were distributed over the surface of catalytically active support (HxMoO3) in both cases; however, the type of molybdenum bronze used for synthesis affects the size of Pt particles.Linear sweep voltammetry (LSV) was used to determine the regularities of both adsorbed carbon monoxide electrodesorption and dissolved CO electrooxidation. CO-tolerance of prepared composites was estimated using H2/100 ppm CO mixture under conditions of both an electrochemical cell and a membrane electrode assembly (MEA).The results of this work are promising, as they provide a relatively simple method for the synthesis of CO-tolerant catalysts. The understanding of the origin of the CO-tolerance is essential for the development of electrode materials that could be used in the real fuel cells.