Effect of the OH−/Pt Ratio During Polyol Synthesis on Metal Loading and Particle Size in DMFC Catalysts
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A systematic variation of the molar ratio between hydroxide ions and platinum during polyol synthesis of Pt electrocatalysts supported on carbon nanotubes was conducted. The resulting materials were physically characterized by transmission electron microscopy, thermogravimetric analysis, and X-ray diffraction. It could be shown that precise control of the OH−/Pt ratio is necessary for achieving small-sized uniformly distributed Pt nanoparticles at high chemical yield. Simple adjustment of the pH value is not sufficient to control the reduction conditions since even small pH variations give rise to significant changes of the catalyst properties. The optimal OH−/Pt molar ratio was found to be 5:1 resulting in small particle size (ca. 2.5 nm in diameter) and high platinum loading (ca. 39 wt% at a nominal loading of 40 wt%). Moreover, we have shown that the developed electrocatalyst exhibits a high activity toward the oxygen reduction reaction which is confirmed by half-cell experiments in a rotating disk electrode and in single-cell experiments in direct methanol fuel cells.
KeywordsPlatinum nanoparticles Multi-wall carbon nanotubes (CNT) Direct methanol fuel cell (DMFC) Polyol reduction pH value Particle size control
The authors thank the Energy Research Centre of Niedersachsen (Energie-Forschungszentrum Niedersachsen) for financial support of this work. The authors also would like to express their gratitude to the following persons and institutes at Clausthal University of Technology, Germany: Peggy Knospe at Particle Technology for TEM investigations, Ulrike Köcher at Technical Chemistry for TGA measurements, and Philipp Schlender at Inorganic and Analytical Chemistry for XRD measurements.
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