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Sebastian Johannes Bold

Ultrafast spectroscopic characterization of dye-sensitized H2-evolving photocathodes: Towards optimized devices

Published on 1 December 2021
Thesis presented December 01, 2021

The summary presented here is only the beginning of that in the thesis since it is longer than the 4000 characters permitted.
Dye-sensitized photoelectrochemical cells represent a highly promising technology for the production of solar fuels via light-driven water splitting as an integral part of a carbon-neutral economy. In that context, the design of more performant dye-catalyst assemblies is highly demanded as they should allow to precisely control over the excited state processes, especially ET. However, detailed investigations on the light-induced processes of dyad-sensitized photocathodes under operando conditions are scarce in the literature, and few studies have addressed in depth the degradation processes in those photocathodes. Therefore, this work aimed at providing a comprehensive understanding of the performances of hydrogen-evolving DSPC based on a series of molecular dye-catalyst assemblies varying by the nature of the dye and the catalyst, including the elucidation of the systems’ weak points and bottlenecks for hydrogen production. To this end, a full characterization of the photoelectrochemistry and activity of the photocathodes was combined with the study of the excited state processes both in solution and on films to gain a full understanding of the systems and their performance-limiting factors. Especially important was the determination of the lifetime of the CSS and the kinetics of the ET to the catalyst unit. The mainly studied compounds were a series of four noble-metal free dyads which varied in the nature of the push-pull organic dye (T1 or T2R) and in that of the catalyst for proton reduction (Co or Cat1). Assessing the activity of all four combinations enabled the determination of each part’s contribution to the overall performance and therefore to link the molecular structure to the activity of the system. The elucidation of such a structure-acitivity relationship is important to be able to rationally improve the molecular structure of the dyads. The best-performing system T2R-Cat1 was studied in detail, notably including the excited state processes at applied potential by TA-SEC and post- and in-operando measurements to determine the deactivation pathways and kinetics. In addition, NiO photocathodes sensitized with a Ruthenium-cobalt dyad were studied by TA-SEC for comparison.

H2 production, Ultrafast spectroscopy, Dye-Sensitized photocathodes, Spectroelectrochemistry

On-line thesis.