Electrodeposition of metallic and semiconducting nanocentres

Abstract

Nanoparticles, particularly those of noble metals, are of considerable importance for their applications in catalysis and fuel cells. Fundamentally they are interesting for their unusual physical and chemical properties due to their size and shape. Generally, they owe their large catalytic activity per gram to their high surface area to volume ratio but often nanoparticles are facetted and the large proportion of surface atoms located on edges and corners further enhances their reactivity. In the main part of this project the electrodeposition of palladium (from ammonium tetrachloropalladate (II)) on gold and carbon substrates was studied using cyclic voltammetry and chronoamperometry. Pd deposits on vitreous carbon substrates were prepared by electrodeposition from liquid crystal phases (both micellar and hexagonal phases) consisting of self-assembled non-ionic surfactant molecules. The morphology of the deposits varies with the concentration of surfactant but all are made up of aggregated nanoparticles circa 9 nm in diameter. The deposits from the micellar phase of the surfactant offer the largest electroactive area and specific activity for the hydrogen evolution, oxygen evolution and reduction reactions, formic acid and ethanol oxidations. Unexpectedly the deposits yield an increase in catalytic activity far in excess of that expected from an enhancement in electroactive area. The chronoamperometric transients recorded during the deposition were analysed using the nucleation and growth model from Heerman and Tarallo to investigate if and how the surfactant template affected the nucleation and growth parameters, number of nucleation sites and nucleation rate. Nanostructured palladium and platinum films were also produced on gold substrates with the micellar phase mixtures. Interestingly their specific catalyst area was found to be larger than those obtained when the films were prepared without template or with the hexagonal phase.
The second part of the work investigated the electrodeposition and doping of ZnSe particles for the purpose of developing a nano-scale light emitting diode. The ZnSe was electrochemically deposited and several trials were conducted to fabricate a p-n junction between two electrically conductive carbon nonporous materials. ZnSe was successfully deposited on different carbon substrates; the characterization by EDX indicated a good ratio between Zn and Se. XRD confirmed the presence of cubic ZnSe and current voltage curves recorded by contacting two doped ZnSe surfaces showed rectification indicative of a p-n junction.

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ORCID for Guy Denuault: orcid.org/0000-0002-8630-9492

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