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Page count: 94

Recent scientific efforts aim to blend light harvesting with the fuel forming catalysis, as a novel method to store the energy captured from the Sun. Our approach is to construct an efficient photoelectrochemical cell using earth-abundant materials. The proposed system contains bioinspired metal-free hydride donors suitable for fuel forming reductions and a p-type semiconductor that serve as a light harvester and source of electrons. In this thesis, we investigate fundamental steps that determine the efficiency of the photoelectrochemical cell: photoreduction of NAD+ dyes by p-GaP semiconductor and the hydricity of NADH analogs. First, thermodynamics for photo-induced electron transfer from p-GaP to NAD+ dyes are evaluated using steady-state UV/Vis absorption and cyclic voltammetry experiments. Photoelectrochemical measurement conducted on p-GaP electrodes immersed in aqueous electrolytes and dye show sensitization for only two dyes. Pump-probe measurements reveal that the "inefficient" dyes have short-lived excited states, inhibiting the successful charge transfer into p-GaP surface. This work provides an insight on timescales of hole-injection rates during dye-sensitization processes. Furthermore, we evaluate the hydricity for model NADH analogs using experimental methods and calculations. The obtained hydricity values display a strong dependence on structural and electronic properties of the model compounds. When compared with metal-based analogs, NADH analogs show similar hydride donor ability. However, the high reduction potentials for metal-free hydride donors hinder their applicability in the catalysis. This work offers a reasonable explanation on why NADH analogs have not been utilized in fuel forming catalysis and provides the answers how to overcome these limitations.