UC Santa Cruz

Humans are becoming more connected through world trade, aviation, the internet, and social media. Through this connection we are beginning to identify shared problems facing humanity that have the potential to threaten human existence including climate change and infectious disease. There remains time and hope that humans have the potential to understand these threats and find collaborative solutions through innovation. Electric and fuel cell vehicles can reduce human dependency on fossil fuels and reduce global CO2 emissions. Renewable electricity is on the horizon with innovations in electricity generation by wind and solar devices. Water electrolysis devices can complete the renewable energy economy by using renewable electricity to produce hydrogen fuel for fuel cell vehicles. Additional innovations are necessary to improve economics and performance of such devices for large scale adoption. On the front of infectious disease, alternative antibiotics are necessary to combat the rise of antibiotic resistant microorganisms. Generation of reactive species through electrocatalysis or photocatalysis for microbial inactivation are promising solutions to reduce human dependence on traditional β-lactam antibiotics. Additional study is necessary to understand the catalytic generation of these species and their resulting interactions with microorganisms. My thesis has focused on the design and synthesis of nanomaterial catalysts with applications in renewable fuel and microbial inactivation technologies.More specifically, chapter 1 provides background on hydrogen as an alternative and renewable fuel, a mechanistic understanding of hydrogen electrocatalysis, catalyst synthesis methods, methods of material characterization. Furthermore, background on reactive species generation by electrocatalysis and photocatalysis is provided with additional understanding of reactive oxygen species interactions with microorganisms. Chapters 2 and chapter 3 cover two pieces of work focused on the optimization of platinum based electrocatalysts for the hydrogen evolution reaction. Comparison to a commercially available platinum on carbon electrocatalyst is provided. In chapter 2, platinum oxide nanoparticles are deposited on a carbon nitride support material. The influence of platinum valence state is systematically studied revealing the preferential hydrogen generation on platinum oxide in a higher valence state. Utilizing this principle, further studies are carried out to demonstrate electrochemical generation of active Pt4+ species and electrocatalyst recyclability. Chapter 3 manipulates the synthetic parameters from chapter 2 to prevent platinum oxide nanoparticle deposition and promote platinum chelation on pyridinic nitrogen groups within the carbon nitride support material. Phosphorous doping is utilized to improve conductivity of the support material and decrease charge transfer resistance during hydrogen evolution. The mass activity of the material is found to nearly triple compared to platinum nanoparticles on carbon suggesting three times less platinum can be used to generate an equivalent amount of hydrogen gas. Chapter 4, chapter 5, and chapter 6 explore routes toward microbial inactivation through the design of nanomaterials capable of catalyzing reactive species. Specifically, chapter 4 summarizes research utilizing electrocatalysis for the generation of reactive species. Details are provided on targeted reactive species generation including reactive oxygen, chlorine, sulfur, phosphorous, and nitrogen containing species. Interactions of these species with microorganism components including proteins, lipids, and DNA are discussed. The state of the field and requirements to move the field forward are discussed. Chapter 5 summarizes the use of graphene-based nanomaterials for microbial inactivation through physical and photocatalytic mechanisms. Top-down and bottom-up approaches are considered and the transformation of optical properties due to quantum confinement are discussed as a route to generate reactive oxygen species by photocatalysis. Copper doped carbon quantum dots are developed in chapter 6 and are shown to photo catalyze hydroxyl radicals from water. The material is demonstrated to have broad spectrum activity for both gram-positive and gram-negative bacteria strains. Such a material could be implemented in wound care or medical devices to prevent microbial growth. Chapter 7 summarizes the work completed and its possible impact on the future of renewable energy devices and antimicrobial control.