Doctor of Philosophy, University of Akron, 2022, Polymer Science

Photoelectrochemical (PEC) conversion of biomass (e.g., lignin) to hydrogen, a carbon-negative emission technology, is characterized by four key processes: (i) photo-generated electron-hole pairs, (ii) electron transport from the anode to the cathode, (iii) hydrogen generation at the cathode and (iv) biomass oxidation by photogenerated holes in the valence band. Overall performance of the photoelectrochemical cell is governed by step (i), electron-hole generation, followed by step (iv), charge transfer at the semiconductor/electrolyte interface. This dissertation will discuss the development of an in situ infrared spectroscopic (IR) approach to study charge dynamics during PEC reactions. Accumulated photogenerated electrons on the semiconductor surface in PEC reactions exhibit a structureless, and featureless spectrum centered around 2000 cm-1. The intensity and rate of the IR profile of photogenerated electrons at this wavenumber correlates to the charge transport in the PEC process, qualitatively characterizing the efficiency of the catalyst. Electron accumulation can also be observed under dark conditions with negative voltage bias. Adsorbed water on the semiconductor surface serves as a hole scavenger and shields the catalyst surface from oxygen, preventing electron-hole recombination, while simultaneously promoting the formation of a double layer of electrons and protons on the semiconductor surface. The effect of voltage on the performance of the PEC cell is investigated through the analysis of the IR profile (i.e., relative concentration) of photogenerated electrons. The results of charge dynamics shed a light on the PEC mechanism and provide a scientific basis for devising novel approaches to enhance the PEC efficiency. The observations of the dynamics of accumulated electrons and water coverage in PEC reactions revealed the applicability of the in situ IR approach to electro-swing CO2 capture in liquid monoethanolamine (MEA). CO2 reacts with amines (open full item for complete abstract)

Committee: Steven S.C. Chuang (Advisor); Toshikazu Miyoshi (Committee Member); Zhenmeng Peng (Committee Member); Mesfin Tsige (Committee Member); Yu Zhu (Committee Member) Subjects: Alternative Energy; Analytical Chemistry; Polymers