Development of a nanostructured palladium microelectrode for pH monitoring in scanning electrochemical microscopy

Abstract

This work describes the development of a nanostructured palladium microe1ectrode for use in scanning electrochemical microscopy. Once loaded with hydrogen to form the coexistent a + ~ phase palladium hydride the potential of the nanostructured microsensor depends not on the HlPd ratio, but on the activity of the protons in the solution. This thesis is focussed on extending the lifetime of the microsensor such that it can be successfully utilised in scanning electrochemical experiments. The controlled potential· method of loading the palladium film is investigated by application of a novel analytical technique. A measurement of the amount of hydrogen stripped from within the palladium lattice provides useful information on the efficiency of the controlled potential method of loading and on the amount of palhidium remaining on the underlying disc. It has been shown that repeated use of the microsensor can lead to degradation of the palladium film. A controlled current approach to loading the potential is introduced and many loading parameters are investigated including the loading current, loading time and solution pH. Also investigated are the film properties including film thickness, film freshness and the presence of the nanostructure. It is shown that controlled current loading can provide the required HlPd ratio from first loading, even in a plain palladium film. The use of the palladium microsensor in scanning electrochemical microscopy experiments is introduced. The microsensor is shown to be responsive to the changes in pH surrounding a platinum substrate undergoing cyclic voltammetry in a solution of 0.5 M Na2S04. Well defined peaks whiCh coincide with adsorption, evolution and consequent desorption ofhydrogeiJ. on the Pt disc are seen in the potential, and pH measured by the tip. This shows that it is possible to use this nanostructured palladium hydride microsensor in scanning electrochemical microscopy experiments.

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