Portland State University. Department of Chemistry
Date of Award
Doctor of Philosophy (Ph.D.) in Chemistry
1 online resource (xviii, 102 pages)
Pyrites, Photoelectrochemistry, Solar energy, Infrared spectroscopy
The recurring theme of this dissertation is the correlation between FeS2 surface chemistry and key electrical and electronic properties of FeS2. Efforts have been made to identify and characterize the FeS2 surface, investigate the photoelectrochemistry of FeS2 photoanodes under anhydrous and anoxic conditions, and investigate the influence of deliberate surface chemistry on FeS2 photoelectrochemistry.
Infrared reflection-absorption spectroscopy (IRRAS) was used to investigate a thin adsorbate layer on pyrite. The results showed that the combination of angle-dependent studies and computational efforts are a powerful tool for characterizing the pyrite surface.
The photoelectrochemistry of FeS2 photoanodes was investigated in an I¯/I3¯ acetonitrile electrolyte acetonitrile electrolyte. The results revealed that the non-aqueous system was suitable for strictly anhydrous and anoxic photoelectrochemical studies. A model was proposed to explain the observed influence of concentration of dissolved I2 on the photovoltage. A central component of the proposed model was that shunting was assumed to take place at physically distinct regions of the electrode and that mass-transport to and from these regions could be treated separately from mass-transport to the regions responsible for the rectifying behavior of the FeS2/liquid junction. The implication of the agreement between experimental and calculated J-E curves is that macroscopic photoelectrochemical investigations may underestimate the quality of FeS2 photoanodes due to the presence of defects.
The influence of surface treatments on FeS2 photoelectrochemistry was further studied using non-coordinating redox species. A statistically significant increase of photovoltage was observed after treating FeS2 surfaces with KCN. X-ray photoelectron spectroscopy was used to study chemical bond formation between the electron donating ligands and iron(II) centers on the pyrite surface. The results were discussed in terms of charge recombination models and surface coordination chemistry.
Unfinished work is also presented. Cathodic polarization in acidic media is a prerequisite for any detectable photoresponse. The exact function of the electrochemical activations was further investigated by electropolishing pyrite electrode under different experimental conditions including etchant identity and applied bias. The results suggested that the electrochemical treatment removes the damaged surface layer caused by mechanical polishing, and might also stabilize the surface states. Further experiments can be focus on anhydrous etching of pyrite photoanode.
The research presented in this dissertation guides future studies of thin film FeS2 photovoltaics.
Tong, Qi, "The Influence of Surface Chemistry on the Photoelectrochemical Properties of FeS(2) Photoanodes" (2015). Dissertations and Theses. Paper 2482.