Investigation of Interfacial Charge Transfer Processes in Energy Conversion Devices

The past few decades have witnessed great technological advances in the energy conversion devices impacting our lifestyle. Knowledge of the interfacial charge transfer processes in those electrochemical energy conversion devices (e.g. solar cells, water splitting cells, etc.) is crucial to both the fundamental science development and the practical device optimization. The focus of this dissertation is to elucidate interfacial charge transfer processes related to dye-sensitized photocathodes and heterogeneous hydrogen evolution catalysis electrodes.;A fundamental and systematic investigation of NiO based p-type dye-sensitized solar cells (p-DSCs) using electrochemical impedance spectroscopy (EIS) is presented for the first time. Based on this, the low fill factors ( FFs) of NiO p-DSCs are probed by investigating the charge transfer resistances of the key interfaces of the cells under various bias and illumination conditions. The quantitative analysis demonstrates that the FF value is largely attenuated by the recombination of holes of NiO with the reduced dyes.;The effects of searching alternative and more efficient photocathodes are explored. The dye-controlled interfacial charge transfer is studied at ITO/dye and tin oxide/dye interfaces. The generation of high cathodic photocurrents via sensitizing n-type semiconductors is demonstrated. The study reveals a new perspective toward the selection of electrode materials for sensitized photocathodes.;The photoelectrode and electrocatalyst can be integrated into solar fuel production devices. We also study the heterogeneous hydrogen evolution reaction (HER) electrocatalysis using molecular clusters mimicking the active MoS 2 edge sites. A dimeric molecular analog [Mo2S12] 2- is conceptually designed as the smallest unit possessing both the terminal and bridging disulfide ligands. The electrochemical investigations show that [Mo2S12]2- is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo2S12]2- exhibits a hydrogen adsorption free energy near zero (-0.05 eV). We use this catalyst as a model case to study the charge transfer process in the catalytic cycle. The work helps shed light on the rational design of HER catalysts and biomimetics of hydrogen evolving enzymes.