Development of photoelectrochemical anodes for solar redox flow batteries (2020)
Type of ContentTheses / Dissertations
Thesis DisciplineChemical and Process Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsSavoie, Maximeshow all
Photoelectrochemical processes have been widely studied for water splitting and dye-sensitized solar cells. Lately, a new concept has emerged, the photoelectrochemical redox flow battery. A photoelectrochemical redox battery is charged by using a semiconducting electrode to convert solar energy into stored chemical energy. Currently, the majority of published photoelectrochemical tests are conducted using two-electrode measurements with V4+/V5+ as redox couple in the anodic electrolyte. Here, the behavior of a TiO2 photoanode is studied using a three-electrode measurement, to gain a greater understanding of the factors which limit photoelectrochemical redox batteries. The recorded linear sweep voltammetry measurements had two different regions. The first region between 0.4 V to 0.7 V vs Ag|AgCl typically shows photo-oxidation of V4+ to V5+, confirmed by UV Vis spectroscopy and oxidation of V3+ to V4+ in the dark. The second region was between 0 V and 0.4 V vs Ag|AgCl, wherein electrochemical reduction of V4+ to V3+ occurred in parallel with the photoxidation of V3+ species to V4+. By changing the deposition process, and the used solvent used, the photoactivity of the TiO2 photoanode has been improved for VOSO4 photo-oxidation. The addition of titanium isopropoxide formed an interconnection between the TiO2 particles and the substrate. Finally, the addition of an underlayer grown directly on the FTO substrate improves the TiO2 performance by creating a proper contact between the TiO2 film and the FTO substrate (350 µA cm-2 mg-1). The TiO2 performance can be increased by doping the TiO2 layer or through the deposition of gold nanoparticles and nanoclusters: The addition of 1.7 wt% Au nanoparticles to a standard photoelectrode leads to the photocurrent enhanced by 30 % and an addition of 8.5 wt% of Au6 nanoclusters leads to a photocurrent increase of 50%, due to the extension of the absorption range.
The effect of different redox couples in hydrochloric acid and an organic solvent was studied. A promising redox couple was a standard dye-sensitised redox couple, I3/I- coupled with Fe3+/Fe2+. The Fe3+/Fe2+ was shown to give a photocurrent of 119 ± 8 µA cm-2 mg-1 at 0.5 V vs. Ag|AgCl. Therefore, by combining the the materials with the best photocurrent of each study, a photocurrent of 82 ± 0.5 µA cm-2 (410.2 ± 0.5µA cm-2 mg-1) could be achieved for VOSO4 electrolyte at 0.5 V vs. Ag|AgCl with the addition of 8.5 Wt% Au6 nanoclusters to the hydrothermal growth film and an additional 85% P-25 15% TTIP film. The triiodide electrolyte gave a photocurrent of 99.3 ± 0.2 µA cm-2 (496.3± 0.2 µA cm-2 mg-1) at 0.5 V vs. Ag|AgCl. The Fe2+ electrolyte allowed a photocurrent of 107 ± 0.4 µA cm-2 (535 ± 0.4 µA cm-2 mg-1) at 0.5 V vs. Ag|AgCl