Rudge, Andrew John (1991) The photoelectrochemistry of platinum. University of Southampton, Doctoral Thesis.
Abstract
An experimental study of in-situ photoemission from platinum into different electrolytes is presented. Photoemission currents were obtained in acid solution, but the adsorbed hydrogen equilibrium partially quenched this photocurrent. Adsorption of a layer of iodide on the platinum surface was found to inhibit hydrogen adsorption and the photocurrent efficiency increased considerably. Adsorbed iodide was also used to allow photoemission currents to be recorded from neutral and alkaline solutions where nitrate was added as electron scavenger. Photoemission currents were obtained from platinum in neutral solutions in the absence of apparent electron scavenger and this is attributed to water acting as scavenger. Anodic photocurrents from platinum, in the absence of a surface oxide, have also been characterised, and these are attributed to a photohole emission process. It was found that photoemission currents from small 20 A* platinum particles supported on glassy carbon appeared not to differ in magnitude or spectral response from those obtained from smooth platinum. This experiment was complicated, however, by the interference of photo-effects from the glassy carbon substrate, which were also investigated. Photoemission of electrons was observed at glassy carbon, but when nitrate was employed as electron scavenger, a second photo-effect was observed, due to reduction of photoexcited nitrate ions. It is shown that water can act as electron scavenger at glassy carbon. Anodic photocurrent data at glassy carbon are also presented and these are discussed in terms of their spectral and voltammetric behaviour. Anodic photocurrents observed from an oxide film, grown on platinum at 1.6 V vs. RHE, confirm that this oxide is amorphous and not described adequately by a semiconductor model. Cathodic photocurrents were obtained from thicker films when two types of oxide are present. The presence of an outer hydrated oxide is shown to enhance the photocurrent obtained from the inner oxide phase and a further cathodic photocurrent was observed from the outer oxide, after the inner oxide had been reduced.
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