Redox mediation in dye-sensitized photoelectrochemical cells Coupling solar-driven oxidative catalysis to fuel generation

The transition from fossil fuels to sustainable energy sources is a challenging but necessary task to mitigate climate change. Several new technologies are needed to make this mission possible within our generation. This thesis focuses on developing photoreactors that combine solar fuel production with chemical transformations. Dye-sensitized photoelectrochemical cells (DSPECs) feature electrodes that employ molecular dyes, semiconductors, and catalysts working in harmony to absorb light to power catalytic reactions. The limiting performance in water-splitting DSPECs due the oxygen evolution reaction, is circumvented by exploring organic transformations as alternative reactions to provide the electrons for fuel-forming reduction reactions. Inspired by nature’s photosynthesis, we were curious to explore if additional redox steps in our artificial photosynthetic device architecture—by addition of redox mediators—would enhance the desired electron propagation through the system. The redox mediators were carefully selected to efficiently regenerate the photooxidized dye by donating electrons, yielding excellent chemical oxidants to perform organic oxidation reactions. Three different strategies are reported to gain insight into the electron transfer mechanisms and stability issues: 1) a solution-phase redox mediator approach, 2) a covalent attachment design, and 3) a redox-active matrix construct. We have demonstrated that the implementation of redox-active molecules has a beneficial effect on the multi-electron transfer steps between the oxidative reaction and the photoanode. We also managed to enhance cell efficiencies by making an organic photosynthetic cell, which elegantly combines the generation of chemical oxidants with organic redox catalysis in a one-pot manner.