Photoelectrochemical Fuel Production on Delafossite AgRhO2 and AgFeO2 and Electrochemical Oxidative Etching of Sn-doped Bi2Te2Se

Abstract

Correlating electrochemical and photoelectrochemical behaviors to the materials properties is an important aspect to provide basic understanding in diverse scientific fields that employ (photo)electrochemistry. Among different fields, solar fuel generation is a fascinating method to utilize solar energy to produce fuels, thus alleviating potential energy shortage and concerns on climate change. However, there is still a lack of knowledge on the detailed mechanisms for heterogeneous charge transfer processes (CO2 and H2O reduction) and the effect of the catalysts’ chemical and physical properties.

Inspired by previously reported CuRhO2 and CuFeO2 from the Bocarsly and Cava groups, AgRhO2 and AgFeO2 were prepared and examined for their photocatalytic activities. AgRhO2 photocathode was shown to be photocatalytically active for H2 generation with great photostability. However, AgFeO2 did not possess a suitable conduction band edge position, only providing ~130 mV of overpotential for H2 generation and not sufficient for CO2 reduction to formic acid.

The correlation between chemical compositions and photocatalytic activities was examined by comparing AgFeO2, AgRhO2, CuFeO2, and CuRhO2. It was rationalized that Ag+ (instead of Cu+) in the A-site of the delafossite structure (ABO2) reduces the kinetic barrier for H2 generation, and Fe3+ (instead of Rh3+) in the B-site provides a better catalytic surface for both H2 generation and CO2 reduction.

In this thesis, the effect on bulk properties and topological surface states of topological insulators against electrochemical oxidation was also investigated. With potential usage in spintronics and quantum computing, this should be well-understood for future device applications. The electrochemical treatment resulted in triangular etch pits on the surface, but the bulk properties and topological surface states were unaffected. This proved that electrochemical oxidation is a potential method for altering the surface morphology while maintaining the bulk properties and topological surface states.