Palladium-Based Electrocatalysts for Alcohol Oxidation in Half Cells and in Direct Alcohol Fuel Cells

Istituto di Chimica dei Composti OrganoMetallici (ICCOM-CNR), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy.
Chemical Reviews (Impact Factor: 45.66). 08/2009; 109(9):4183-206. DOI: 10.1021/cr9000995
Source: PubMed

ABSTRACT Palladium is emerging as an attractive replacement for platinum in a number of electrochemical applications, including lowtemperature
fuel cells, electrolyzers and sensors. Palladium is more abundant in nature and less expensive than platinum.1 However, cost-associated
issues are not the main driving force behind the increasing interest in palladium as it remains a rare noble metal whose introduction
for a broad technological use would lead to an irreversible increase in its market price.

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    ABSTRACT: The catalytic activity of Pd–CeO 2 /C and non-supported Pd–CeO 2 electrocatalysts for the formic acid (FAOR) and glycerol oxidation reaction (GOR) is evaluated in this work. The materials have been synthesized by pyrolysis in H 2 atmosphere at 300 and 600 °C, with a nominal Pd:CeO 2 ratio of 1:1. X-ray diffraction analysis demonstrates polycrystalline materials with particles sizes ranging from 11 to 14 nm (Pd) and 26 to 48 nm (CeO 2). Electrocatalytic measurements show a positive effect of dispersing the catalysts on Vulcan in the case of the FAOR, in terms of potential-current density profile and onset potential. While unsupported Pd–CeO 2 nanoparticles behave poorly, the Pd–CeO 2 /C anodes show a very high performance towards the FAOR. Particularly, Pd–CeO 2 /C obtained at 600 °C shows a significantly high catalytic activity, with a higher mass current density than a comparable Pd/C electrocatalyst. X-ray photoelectron spectroscopy analysis undoubtedly demonstrates that the carbon support has an important effect on the oxidation states of Pd and CeO 2 , which in turns influences positively the catalytic behavior of Pd–CeO 2 /C catalysts. Furthermore , both supported and unsupported Pt–CeO 2 materials have shown no catalytic activity for the GOR. The results indicate that Pd–CeO 2 /C electrocatalysts can be considered as excellent candidate anodes for direct formic acid fuel cells. Keywords Nanostructured anode materials Á Pd–CeO 2 /C electrocatalysts Á Formic acid oxidation reaction Á Glycerol oxidation reaction Á Direct formic acid fuel cells
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    DESCRIPTION: In this study, catalytic activity and performance of bis (dibenzylidene acetone) palladium (0) catalyst, Pd (DBA)2, was evaluated toward glycerol oxidation reaction (GOR) in alkaline half cell and alkaline direct glycerol fuel cell (DGFC). The electrooxidation of glycerol on Pd (DBA)2 was characterized in half cell by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. Obtained results have highlighted the excellent electrocatalyst activity of Pd (DBA)2 in terms of specific peak current density and onset potential compared to the results obtained by conventional Pd base catalysts. CVs results also demonstrate that Pd (DBA)2 is still active even after 200 cycles. In order to determine the performance of Pd (DBA)2 in alkaline DGFC, membraneelectrode assembly was fabricated by employing the Pd (DBA)2 catalyst in anode electrode, Acta commercial cathode and Tokuyama anion-exchange membrane and successfully evaluated in a single passive DGFC. Cell open circuit voltage and maximum power density of 800 mV and 24 mW cm�2 were achieved, respectively by using static aqueous fuel containing 5 wt% of glycerol. Half and whole cell results exhibit acceptable activity and performance of Pd (DBA)2 in GOR and suggesting it as a new promising anode catalyst for DGFC in alkaline media.
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    ABSTRACT: In this study, we report the synthesis of Co@Pt nanoparticles via a fast and simple method and the fabrication of an anodic electrocatalyst, Co@Pt supported on carbon-ceramic substrate, for fuel cell applications. The present synthesis method is very facile and economical which may be suitable for large-scale production of Co@Pt nanoparticles with high activity. The surface morphology, structure and composition of the as-prepared core–shell nanoparticles were characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. Then, the electrooxidation of ethylene glycol (EG) and glycerol (Gly) was investigated on the Co@Pt nanoparticles supported on carbon-ceramic electrode (Co@Pt/CCE) in 0.5 M H2SO4 solution. Electrocatalytic characteristics were methodically investigated by electrochemical techniques such as cyclic voltammetry and chronoamperometry. The Co@Pt/CCE electrocatalyst demonstrates improved specific activity toward EG and Gly electrooxidation compared to the Pt-alone nanoparticles supported on carbon-ceramic electrode (Pt/CCE) and also shows much high structural stability and tolerance to carbonaceous species poisoning. Therefore, the Co@Pt/CCE can be extended as a promising electrocatalyst for the polyol alcohols electrooxidation reactions in fuel cells.
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