Electrochemical and Photoelectrochemical Water Oxidation Using α-Fe2O3

There is a global need to reduce the use of fossil fuels due to the negative impacts of anthropogenic greenhouse gas emissions on climate change. An alternative to a carbon-based energy system is therefore necessary, and hydrogen is considered one of the most promising energy carrier replacements. This thesis focuses on the renewable production of hydrogen via photoelectrochemical (PEC) water splitting using Earth-abundant iron oxide (α-Fe2O3, or hematite) as a photoanode. Hematite is considered a promising semiconductor candidate for PEC water oxidation due to its strong absorption of visible light, long-term stability under operating conditions, and low cost. However despite these benefits, rapid recombination of charge carriers and sluggish water oxidation kinetics have hindered its commercial applicability. Here, we have demonstrated that the effective application of three-dimensional nanoscaffolds, composed of a transparent conducting oxide, can significantly enhance the electrochemical surface area of solution-processed iron oxide thin films. The underlying scaffolds were also found to enhance the activity of the surface catalysts due to an electronic “spacer” effect, and light absorption was increased within the disordered structures due to effective trapping of photons and increased catalyst loading. Following this, we demonstrated that the solution-processed films, which were initially PEC-inactive, could be activated via high-temperature treatment under flowing hydrogen gas. The result was the formation of a non-stoichiometric α-Fe2O3-x photocatalyst that suppressed charge recombination and increased photoactivity. This photoactivity was further correlated to the build-up of charged species at the photoanode surface that mediate the water oxidation reaction. Finally, to improve the kinetics of our newly activated material, we functionalized our α-Fe2O3-x thin films with a stable homogeneous iridium co-catalyst. The co-catalyst was found to greatly enhance the activity of the system, and extensive electrochemical testing revealed that this was almost entirely due to improved kinetics at the semiconductor-electrolyte interface.Ph.D.2018-07-08 00:00:0