About me
I currently reside in Zhejiang, China and am looking for a postdoctoral research position in first principles calculations.
I obtained my PhD in Condensed Matter and Materials Physics at University College London, under the supervision of Prof. Jochen Blumberger, and have recently completed a postdoctoral research project at Imperial College London under the supervision of Dr. Clotilde Cucinotta.
PhD Thesis (Official version):
Charge transport in bulk hematite and at the hematite/water interface.
PhD Thesis (Unofficial version with additional corrections):
Charge transport in bulk hematite and at the hematite/water interface.
Abstract:
Transition metal oxide materials have attracted much attention for photoelectrochemical water splitting, but problems remain, e.g. the sluggish transport of excess charge carriers in these materials, which is not well understood. In this thesis I will show how periodic, spin-constrained and gap-optimised hybrid density functional theory can be used to uncover the nature and transport mechanisms of excess electrons and electron holes in a widely used water splitting material, hematite (α-Fe2O3). I will show that upon ionisation the electron hole relaxes from a delocalized band state to a polaron localised on a single iron atom with localisation induced by tetragonal distortion of the 6 surrounding iron-oxygen bonds. This distortion is responsible for the sluggish hopping transport in bulk hematite, characterised by an activation energy of 70 meV and a hole mobility of 0.031 cm2/Vs. By contrast, the excess electron induces a smaller distortion of the iron-oxygen bonds resulting in delocalisation over two neighbouring Fe units. I will show that 2-site delocalisation is advantageous for charge transport due to the larger spatial displacements per transfer step. As a result, the electron mobility is predicted to be a factor of 3 higher than the hole mobility, 0.098 cm2/Vs, in qualitative agreement with experimental observations. Extending this analysis to the hematite/liquid water interface, I will show that both excess electrons and electron holes localise at the interface with qualitatively similar structures to bulk hematite. However, the presence of the interface breaks the symmetry present in the bulk crystal and as a result the hole mobility is expected to be greatly reduced. These calculations provide new fundamental insights essential for a better understanding of rate-limiting transport processes governing photocatalytic water splitting efficiency at the hematite/liquid water interface.