Electrochemical and spectroscopic studies of bodipy dyes and nanostructured electrodes for solar energy harvesting and conversion
The use of fossil fuel-based technologies has contributed to the increase in the concentration of greenhouse gases, especially CO2, causing global climate change. To achieve the global energy demand, advanced energy technologies for renewable and sustainability applications have been gaining much attention. Among several promising approaches, stable organic chromophores and nanostructured materials have provided new opportunities in their application in solar energy harvesting and conversion and storage. This dissertation explores the emerging technologies to harvest solar energy to generate (1) electricity using boron dipyrromethene (BODIPY)-thiophene- triphenylamine (TPA) dye-sensitized solar cells, (2) hydrogen fuel using an unbiased Z-scheme tandem cell, and (3) carbon-free fuels by reducing atmospheric CO2 in the presence of water. Nanostructured electrode materials are used for all these three major projects described in this dissertation because of their surface to volume ratios, tunable light absorption, and enhanced charge transport and transfer. By engineering the structural properties of the proposed functional nanomaterials with respect to increasing solar energy conversion and at a low cost, earth abundant and environmental friendly, metal oxide nanomaterials were synthesized and characterized using different analytical techniques. Firstly, this study investigated a series of BODIPY-based dye-sensitized solar cells (DSSCs). Due to their promising potential as efficient photosensitizers, the synthesized BODIPY-based dyes (Dyes 1-5) containing thiophene and/or triphenylamine as electron donors were studied using optical and electrochemical techniques. Although the highest power efficiency achieved was low, correlation between the BODIPY dye structure and properties were established. Secondly, inspired by nature’s photosynthesis, a Z-scheme solar water splitting system comprised of carbon-modified cuprous oxide (C /Cu2O) nanoneedles and oxygen-deficient titanium dioxide (TiO2-x) nanorods in tandem cell was established to enhance charge carrier-separation for unassisted solar water splitting. Although the overall tandem performance is still limited by the C/Cu2O NNs performance, the proposed tandem cell exhibited a photo-induced catalytic activity of 64.7 µA cm-2 that unfortunately gradually decreases over time. Lastly, a photocatalytic anode material, cobalt-doped WO3/BiVO4, was combined with CuO-based nanoneedles to demonstrate a low cost approach to reduce CO2 selectively and water oxidation under sunlight. In addition to highlighting the optical, electrochemical, and spectroscopic advantages of the proposed nanostructured materials, their limitations and challenges were also addressed.