In search for a cheaper anode catalyst for the oxidation of ethanol for development of direct alcohol fuel cells, Pd has been considered here as an interesting substitute for Pt in Pt Ru binary electrodeposite. The binary catalyst when co-deposited on nickel support has been found to increase the current density and decrease the anodic overvoltage significantly with respect to pure Pt, Pd and Ni. Its electrocatalytic capability is also comparable with that of the Pt-Ru binary electrocatalyst on Ni-support, when studied in 1 M EtOH containing 1 M NaOH solution. The effect of loading of Pd Ru electrocatalyst on Ni support has also been tested. The electrocatalytic activity of the electrodes for oxidation of ethanol has been explained by studies of cyclic voltammetry, chronopotentiometry, steady-state polarization, and conjugated scanning electron microscopy-energy dispersion X-ray spectroscopy. It has been found that electrode containing the higher amount of deposit are less affected by carbonaceous poisons.
Spherical nanoparticles of palladium with varying particle diameters have been prepared from PdCl 2 by wet chemical single pot synthesis using citric acid as reducing agent in the presence of PVA. The size of the nanoparticles has been tuned by changing the duration of reflux. The resulting nanoparticles have been dip-coated on Ni-foil, and evaluated as anode catalysts for oxidation of ethanol under alkaline conditions. The morphology and surface characteristics of the Pd nano-catalyst have been investigated by TEM and FE-SEM in conjugation with EDS. Measurements of catalytic activity by electrochemical methods (cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy) reveal that the majority of the nanoparticle-embedded anodes, despite less Pd 0 loading, act as superior electrocatalysts as compared to the nickel-supported Pd electrode constructed electrochemically. In this study, the effects of the different extent of catalyst-loading on the experimental parameters have been rationalized to obtain the size-dependence of the electrocatalytic activity. The experimental results clearly show that there is noticeable development in the intrinsic catalytic activity and poisoning resistance of the anode catalysts. In addition, the intrinsic electrocatalytic activity of the nano-palladium is found to be size-dependent, which increases with decrease in particle size particularly below the diameter of 19 nm.
In order to synthesize stable, catalytically active palladium nanoparticles with low polydispersity, a one-pot synthesis by the facile reduction of palladium chloride with citric acid in an aqueous solution of steric stabilizer polyvinyl alcohol (PVA) has been developed. The resulting nanoparticles are highly water-dispersible, excellent electro-catalysts, and have long shelf life. The palladium nanoparticles have been characterized by physico-chemical, spectroscopic, microscopic, and CV studies. The average size of the nanoparticles can be readily tuned from 8.1 to 53 nm by controlling the extent of reflux for mixtures containing suitable concentrations of metal ion, reducing agent and capping polymer, which also influence the size. Despite the surface-protecting action of PVA, the palladium nanoparticles are electro-catalytically active and exhibit size-dependent electro-catalytic behavior.
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