Abstract
This thesis first employed the density functional theory (DFT) to evaluate the effect of different photoanode designs on the electron transport in photoelectrochemical biofuel cells. The electron transfer between different nano structures of the photoanode, various sensitizers, and bio-electrolytes are analyzed via this computational quantum mechanics technique. The photoanode material used zinc oxide semiconductors, which could have a great potential in many ways including cost reduction, higher dye absorption ability and feasibility in the industry. Several molecular models, such as ZnO nanowires, ZnO nanotubes, and some novel biological pigments have been set up using minimum energy principles. Simulation results reveal that ZnO nanotubes possess lower conduction bands which potentially easier to transfer electrons from biopigments (e.g., chlorin, chlorophyll a and cyanidin) to the anode. As the preliminary conclusion, this first-principles technique is able to determine the photoelectrochemical properties of nano designs and screen different novel design ideas. Secondly, it is intended to find out the main factors that affect the power conversion efficiency of chlorin derivatives. By employing the first principles calculation again with density functional theory (DFT) plus hybrid exchange-correlation functional B3LYP, CIS and 6-31G basis set, this research calculated the photoelectronic properties, such as energy gaps, molecular orbital and UV/VIS absorption spectroscopy, of chlorin derivatives. The chlorin was used as a basic structure and the central ring was substituted by different metals. The difference in electronegativity between the central metal ion and the adjacent nitrogen atoms causes changes in distribution of electron clouds, which indirectly affect the molecule absorbance magnitude in ultraviolet and long wavelength range. By alternating the central metals with different electronegativities, the absorption spectra can be controlled. Finally, this research focused on the electron transmitting path and the reaction rate at the perovskite cathode of the photoelectrochemical cell for hydrogen production. The field of electron density, projected density of states (PDOS), electron distribution and electron transfer path between the [Fe-Fe] hydrogenase and the peroskite cathode can be obtained. Simulation results reveal that the perovskite cathode is better than traditional cathodes for hydrogen production. Before transmission to the [Fe-Fe] hydrogenase, electron clouds mainly aggregate at the periphery of NH3 organic molecules. Then, electrons are transmitted to the hydrocarbon structural chain, finally reaching Fe atoms. Rice, Ramsperger, Kassel and Marcus (RRKM) theory was used to predict the reaction rates at different temperatures. It was found that the reaction rates coincide perfectly with the experimental results from other literatures. This research provides more physical insight into the electron transfer mechanism during the hydrogen production process. It also proves that photoelectrochemical biofuel cells can play the role as a dye sensitized solar cell during daytime, work as a biofuel cell in the evening. Also they can be designed as a part of hydrogen production system during day and night.