UC Santa Cruz
Impacts of oxygen vacancies in titanium dioxide-supported metal nanoparticles in the oxygen reduction reaction and the carbon electrooxidation reaction
- Author(s): Sweeney, Samantha
- Advisor(s): Chen, Shaowei
- et al.
With the current energy demands, the burning of fossil fuels is causing many issues, such as global warming, therefore many researchers are looking into replacing the current methods with electrical energy storage devices. One such device is the fuel cell, where the oxidized fuel provides energy to power things, such as cars. However, the reaction in the cathode compartment, the oxygen reduction reaction (ORR), has driven up the price of the fuel cell due to the high catalyst loading needed to achieve efficiencies suitable for industry. In addition, the most common commercial catalyst is platinum nanoparticles deposited on activated carbon nanoparticles. Platinum is rare and expensive and the major contributor to the high cost. The platinum nanoparticles can also detach, move, or change size dependent on reaction conditions. Finally, platinum is easily poisoned by carbon monoxide. Improving platinum’s tolerance for CO will be discussed in chapter 5. The activated carbon nanoparticles are not stable at the operation voltage of fuel cells and therefore constant catalyst replacement lowers their recyclability and shelf-life. Therefore, an alternative to this system is needed.
Transition-metal oxides offer an interesting alternative to the activated carbon because of their stability. TiO2 in particular is abundant and relatively inexpensive. However, due to its semiconducting properties, it has poor activity for electrochemical reactions. The activity can be enhanced with the deposition of nanoparticles, specifically gold due to the strong metal support interactions. However, this is still not sufficient to replace platinum. The creation of oxygen vacancies in titanium dioxide can influence the binding energy of oxygen and the activity of the overall nanocomposite. Their impact is discussed in chapters 2 and 3. Finally, the activity can be altered by doping the TiO2 and in chapter 4 nitrogen doping will be discussed. Overall, these defects will be explored throughout this dissertation and how the kinetics of electrochemical reactions will be affected.