Comparing the Catalytic Activity of High Entropy Oxides and their Parent Compounds in the Oxygen Evolution Reaction

Open Access
- Author:
- Vincent, William
- Area of Honors:
- Mechanical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Raymond Edward Schaak, Thesis Supervisor
Margaret Louise Byron, Thesis Honors Advisor
Derek M Hall, Faculty Reader - Keywords:
- Electrochemistry
Renewable Energy
OER - Abstract:
- Countries all around the world are facing a very difficult challenge: to rapidly phase out fossil fuels to slow the effects of climate change while also meeting constantly increasing energy demands. In the pursuit of achieving both goals, the development of enhanced energy storage systems that do not rely on hydrocarbons is essential. Hydrogen, considered by many to be a key element in the global transition away from fossil fuels and towards a more sustainable future, shows immense promise to help develop these systems. Its prevalence and versatility allow for wide-ranging applications, including energy generation and storage. Electrochemical water splitting to generate the hydrogen needed to support these sustainable advances is an area of research with continued focus. During electrolysis, the sluggish oxygen evolution reaction (OER) reduces the efficiency of electrochemical cells and remains an obstacle for energy storage efforts. Additionally, the acidic and alkaline environments where OER takes place can cause material degradation and subsequently compromised systems. The best performing catalysts for OER in extreme environments are RuO2 and IrO2, both of which are composed of rare and expensive metals. Current research focuses on identifying more cost-effective catalysts that match the reactivity and stability of RuO2 and IrO2 to speed up the OER. This thesis first explores a variety of tungsten oxide, molybdenum oxide, and antimony oxide compounds, many of which have been theoretically predicted to be strong OER catalysts. These compounds are synthesized via solid-state methods and tested for catalytic activity and stability. The results of the tests show that these compounds do they display catalytic activity at the level of existing OER catalysts, nor are they resistant to degradation in extreme environments. Thus, this thesis concludes that these oxides do not show promise as effective or practical catalysts for the OER. After examining the results of the aforementioned oxides, this thesis then examines a different category of compounds referred to as high entropy oxides (HEO) and their potential for OER catalysts. HEOs are complex compounds made up of five or more unique metal cations. This variety in elements causes distortion of the compound’s lattice structure, in turn leading to unique mechanical and chemical characteristics. In this thesis, two HEOs are discussed: A6WO4 (A = Co, Cu, Fe, Mn, Ni, and Zn in equal proportions) and B25Mo3O8 (B = Mn, Fe, Co, Ni, and Zn in equal proportions). The two HEOs are tested for catalytic activity and stability in corrosive environments and compared to their parent compounds. The results of these tests prove the two HEOs to be both more reactive and more stable than their parent compounds. As electrochemical water splitting to produce elemental hydrogen remains an active area of research, HEOs show promise as an exciting area of opportunity for discovering an efficient, stable, and cost-effective catalyst for the OER.