Date of Award
2025-08-01
Degree Name
Doctor of Philosophy
Department
Environmental Sciences
Advisor(s)
Geoffrey B. Saupe
Abstract
This work explores strategies for the production of low-cost hydrogen gas, which is a low polluting renewable storable fuel that also can serve as an energy carrier. By lowering the cost of hydrogen, the research presented here can enable its adoption by making it more competitive with fossil fuel and other options. The present work shows that biomass, such as cellulose and starch, can be reformed into hydrogen using water and special metal oxide catalysts in a photocatalytic process. This field of study promises an economically viable solution for sustainable hydrogen production. Natural biomass is energy-rich, widely available, and very low-cost. Photocatalytic water photolysis is based on a redox reaction, that simultaneously oxidizes the oxygen anions in water into molecular oxygen gas, and it reduces hydrogen cations in water to form molecular hydrogen gas. This work takes advantage organic biomass's ability to donate electrons, and in the process become irreversibly oxidized. As such they are called sacrificial electron donors. With the proper catalyst, biomass is easily oxidized to supply electrons for the photocatalytic reduction of water into hydrogen gas. Here, we explore the parameters that optimize the use of cellulosic and starch materials as sacrificial electron donors, and prove that they are viable alternatives compared to expensive molecular organic donors such as alcohols. Comparison of starch and cellulose as sacrificial electron donors reveals that both biopolymers can drive sustained with excellent catalyst stability and reproducibility. However, cellulose markedly outperforms starch when normalized to mass loading. Starch requires 6 mg/mL concentrations to approach its maximum hydrogen-production rate of 0.109 µmol/min. In contrast, cellulose reaches a rate of 0.115 µmol/min at only 1.5 mg/mL, which is one-quarter of the starch concentration. This laboratory has also pioneered a new class of porous, high surface area photocatalysts, derived from potassium triniobate (KNb3O8). With metallic platinum deposited on the surface as a co-catalyst, under UV light these wide-bandgap semiconductor materials exhibit exceptional stability and good photocatalytic activity for hydrogen generation. This new triniobate catalyst was synthesized and used to evaluate both cellulosic and starch electron donors for water photolysis. It is clearly demonstrated that these biomass materials can function effectively as sacrificial electron donors for water photolysis, and reduce the cost of photocatalytic hydrogen by lowering the cost of a major component, the electron donor. This work also shows, for the first time, the feasibility of using alkane oils as electron donors. Due to their hydrophobic nature, oils do not dissolve in water, making them incompatible with water-based photoreactions, since they struggle to mix with other reactants in an aqueous solution. To overcome this challenge, this work presents a method to render these oils chemically accessible in water, by emulsifying them into nano-sized droplets, or oil-in-water emulsions. Various straight-chain alkanes, C6, C7, C10, C13, C16, and C20 are used as models to investigate the effect of oil type on droplet formation in the emulsions and as electron donors. As C20 solidifies at room temperature, these emulsions were made in heated solutions to liquify the wax and were allowed to cool before use. The behavior of the C20 solid nanoparticle emulsions sheds light on the potential future issues, when using solid organic particles as donors. All of the results reported here use UV light to excite wide band gap semiconductor photocatalysts, because this simplifies and provides faster method optimizations, which can then be applied to visible light-activated photocatalytic systems.
Language
en
Provenance
Received from ProQuest
Copyright Date
2025-08
File Size
125 p.
File Format
application/pdf
Rights Holder
Shonima Piramadathottathil Venu
Recommended Citation
Piramadathottathil Venu, Shonima, "Low-Cost Electron Donors For Hydrogen Fuel From Water Photolysis" (2025). Open Access Theses & Dissertations. 4436.
https://scholarworks.utep.edu/open_etd/4436