Assemblies of Semiconductor and Metal Nanoparticles for Renewable Energy
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Assemblies of Semiconductor and Metal Nanoparticles for Renewable Energy Marie Zabel Markarian, Maysaa El-Harakeh, Rabieh Makki and Lara I. Halaoui* Department of Chemistry, American University of Beirut, Beirut 110236, Lebanon *
Corresponding author: [email protected]
ABSTRACT Nanostructured electrodes were assembled layer-by-layer from polyacrylate-capped Pt nanoparticles (=2.5 ± 0.6 nm) in a cationic polyelectrolyte. Cyclic voltammetry revealed hydrogen adsorption peaks at the modified nanoparticles characteristic of an activated polycrystalline Pt surface, with a negative shift in the peak potentials indicating a less facile electro-adsorption relative to the polycrystalline electrode, possibly due to nanoparticle surface modification. Current-voltage measurements at multilayers of Pt nanoparticles in polyelectrolytes indicated the feasibility of charge hopping between the particles embedded in the insulating matrix. Such feasibility was also evidenced in photoluminescence quenching of Q-CdS dots (=3.6 ± 0.5 nm) assembled in polyelectrolytes upon inserting Pt nanoparticles in the architecture. INTRODUCTION The unique behavior of metals and semiconductors in confined dimensions has been under heavy investigation in the past two decades because of the potential applications of nanomaterials in various technologies including fuel cells, catalysis, and the conversion of light into electrical energy or chemical fuel. The assembly of metal and semiconductor nanocrystallites in two- and three- dimensional architectures and understanding the catalytic and electrochemical properties of the ensembles, including the effect of the embedding environment and architecture, are necessary for nanoparticle incorporation in devices. The nanoscale dimension affords a significant increase in surface-to-volume ratio, thus increasing the catalytic activity per mass and minimizing the cost of structures employing rare materials as catalysts. Pt, the focus of this work, is a catalyst for many technologically important reactions including the hydrogen evolution reaction, hydrogen oxidation, oxygen reduction, hydrogenation reactions, and oxidation of methanol, amongst others. Many of these reactions constitute a backbone in the quest for renewable energy whether in fuel cells, or the production of clean fuel (viz., hydrogen). It is yet to be established whether the surface structure at the nanoscale might provide increased activity for some reactions, as a result of a possible crystallite size effect or exposure of some crystalline faces or surface defects. It is believed that the preparation of capped-nanoparticles in solution provides the advantage of control over the size and shape of crystalline nanoparticles. For instance, cubic, tetrahedral, and polyhedral polyacrylate-capped Pt nanocrystallites have been synthesized by ElSayed et al. by reduction of PtCl62- with hydrogen under kinetic control [1]. We found that polyacrylate, by imparting an appreciable negative charge to the nanoparticles surface, allows for their a
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