1: Electrocatalysts toward Tri-iodide reduction for Dye-sensitized solar cells 2: New Approaches to the Synthesis of Carbide and Hydride Compounds

Dye-sensitized solar cells (DSCs) offer easy fabrication, flexibility of substrate material, and a comparable energy payback with respect to the conventional silicon solar cells, and thus are a promising low cost alternative. In DSCs, the iodide (I-)/tri-iodide (I3- ) redox couple is used to shuttle charge between the photoanode and the counter electrode (CE). During my Ph.D. study, I have worked on preparing and investigating the nanostructured materials for the development of CE in DSCs.;To control the Pt particle size and prevent its agglomeration, mesoporous Nb-doped TiO2 film was prepared by the sol-gel method on a transparent conducting fluorine doped tin oxide (FTO) glass. By fabricating Pt/Nb-doped TiO2 electrode, the charge transfer resistance was reduced and the exchange current density was increased as the result of a larger active surface area of Pt in the mesoporous Nb-doped TiO2. This electrode could be used in other systems where there is a need to control the amount of Pt surface area and hamper Pt particle aggregation when operating at high temperatures.;This work reported the fundamental electrocatalytic properties of graphene films towards I-/I3- by cyclic voltammetry (CV) and EIS. The films were prepared from chemical or thermal reduction of graphene oxide. We demonstrated graphene films obtained under different reduction conditions exhibit different electrocatalytic properties. The mechanism was elucidated by the structural differences as confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. We also showed the electrocatalytic activity of graphene films could be tuned by surface modification with polyelectrolytes.;However, graphene-based materials are still in the early stages of development and they require improvement to obtain an acceptable catalytic effect and mechanical stability. In this study, the composites of graphene and transition metal oxide nanoparticles were synthesized by employing graphene oxide as a metal-anchoring site, facilitating the nanoparticle nucleation and growth on graphene sheets. This system was tested for potential use as a highly efficient electrocatalyst for counter electrode in n- or p-DSCs. The present transition metal oxide/graphene composites provide the new electrocatalysts with excellent electrocatalytic activity, which is of great significance in improving the electrocatalytic property of the transition metal oxides.;In the field of catalysis, the amorphous materials are sometimes catalytically more active and selective than the crystalline catalysts. Here we reported the amorphous CoS CEs deposited on flexible Ti substrate obtained by the sulfurization of amorphous CoO prepared by electrochemical milling (ECM) process. Using Co3O4 film as the starting electrode material in Co 3O4/Li cells, Co3O4 can be electrochemically reduced and oxidized to form amorphous CoO in a controllable way.;Besides the above four projects, this work also includes the new approaches to the synthesis of carbide and hydride compounds. Since graphene oxide (GO) contains only one atomic layer of carbon, thus it could be envisioned to facilitate the diffusion of carbon atom. Cobalt(II) carbide (Co2C) was synthesized by the ammonia evaporation induced method between cobalt(II) salt and GO followed by thermal reduction under H2-N2 mixture. Compared to the traditional high-temperature methods of synthesis of metal carbides, the use of GO has provided the lowest reported temperature (200 °C) for a metal carbide synthesis. (Abstract shortened by UMI.)...