Spinel oxides for photocatalytic water splitting: a computational and experimental study

Hall, C. (2025) Spinel oxides for photocatalytic water splitting: a computational and experimental study. PhD thesis, University of Reading. doi: 10.48683/1926.00128089

Abstract/Summary

Spinel oxides, AB2O4, exhibit significant promise in photocatalysis due to their favourable electronic properties, stability, compositional diversity, and tuneable cation distribution. Their photocatalytic activity can be modified through A and B cation substitution or by altering the cation distribution. The work in this thesis combines advanced quantum-chemical and synchrotron-based experimental methods to characterise various spinel materials and investigate their photocatalytic performance. Considering Co2+, Cu2+ or Zn2+ as A cations in spinel ferrite (AFe2O4) nanoparticles revealed significant differences in their structures and photocatalytic abilities. ZnFe2O4 showed the highest activity for the oxygen evolution reaction, and this was further enhanced by substituting Ga3+ into the B sites: ZnFeGaO4 produced almost double the amount of oxygen compared to ZnFe2O4. The activity of these samples was attributed to their suitable band gaps (3.35 eV and 2.84 eV, respectively) and alignments, as calculated by density functional theory. Exploring the structures of the spinel ferrites by X-ray diffraction and X-ray spectroscopy showed clear differences between bulk and surface cation distribution. Both CoFe2O4 and CuFe2O4 exhibited lower inversion degrees at the surface compared to the bulk, while ZnFe2O4 showed the opposite trend and with a more significant difference: DFT simulations showed that cation inversion in ZnFe2O4 is energetically favourable at the surface. To further understand the surface effects, a ZnFe2O4 (111) single-crystal surface with a well-defined bulk structure was studied. The surface preparation method was shown to have a significant effect on the surface structure. Annealing the sample under ultra-high vacuum resulted in zinc sublimation, leaving an iron-rich magnetite-like surface, whereas annealing under O2 maintained the bulk-like ZnFe2O4 structure. The results highlight the distinct and important behaviour of the surfaces compared to the bulk in spinel ferrite catalysts.

Item Type	Thesis (PhD)
URI	https://centaur.reading.ac.uk/id/eprint/128089
Identification Number/DOI	10.48683/1926.00128089
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
Download/View statistics	View download statistics for this item