Surface modification of titanium dioxide and synthesis of non- electroactive coatings by electrochemical polymerization

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Virginia Polytechnic Institute and State University


The objective of this project was the modification of TiO₂ electrodes with various silanes in order to evaluate the stability of modified layers when they are used on photoelectrodes in SEMICONDUCTOR LIQUID-JUNCTION SOLAR CELLS (SLJSC). To determine the nature of the reactivity of surface hydroxyl groups towards different silanes, a surface IR study was carried out on TiO₂ powders. The powder (TiO₂) was pressed into a pellet and subjected to reactions with various silanes under different reaction conditions. All of these reactions were carried out in a vacuum line under very anhydrous conditions in order to prevent polymerization of the silanes. This study provided an understanding of the reactivity of different silanes towards surface hydroxyl groups of TiO₂ and the best reaction conditions for this purpose.

With this information in hand we studied the TiO₂ (rutile) single crystal electrodes. These electrodes were subjected to reaction with silanes under the same conditions as the powders. Then the modified surface was studied using ESCA. These electrodes were subsequently subjected to photoelectrochemical conditions (photocurrent generation) and were reexamined using ESCA in order to evaluate the stability of the modified layer. A reaction scheme which was devised to induce crosslinking in the modified layer was shown to enhance the stability of the surface bound silane during the photocurrent generation.

In order to form more homogeneous modified surfaces electrochemically derived polymer coatings were synthesized from divinylbenzene, 4-vinylpyridine, N-methyl-4-vinylpyridinium salts, and phenol. Except for polymers formed from N-methyl-4-vinyl pyridinium salts, other coatings were shown to be neutral. An anomalous pre-wave, and potential-induced polymer swelling and shrinking phenomena were observed in these coatings.

The photocorrosion of small bandgap n-type semiconductor electrodes is a serious impediment to the development of efficient and durable conversion (photoelectrochemical) devices. Our objective in this investigation was to develop newer modified surfaces that are useful for the inhibition of this photocorrosion, and enhance the performance of n-type small bandgap semiconductors in the photoelectrochemical systems.