Functional metal oxide coatings from molecular precursors for energy applications

The ability to create and optimise new interfaces is essential to develop and optimise materials for use in sustainable energy storage and conversion technologies. In this thesis, the solution-deposition of coatings from molecular precursors is explored as a promising approach towards this end. First, a facile method for the deposition of electrocatalytically active zirconium-based films for photoelectrochemical water oxidation is developed. The films were derived from three novel alkoxy cage compounds containing Zr and a first-row transition metal (Co, Fe or Cu). The deposition of a Co-doped ZrO₂ coating onto the BiVO₄ photoanode lowers its onset potential by 0.12 V to 0.21 V vs. the reversible hydrogen electrode (RHE) and increases the maximum photocurrent density by ∼50% to 2.41 mA cm⁻² compared to the uncoated BiVO₄. In the next chapter, a new solution deposition method to coat the Li-ion battery cathode LiNi₀.₈Mn₀.₁Co₀.₁O₂ (NMC811) with Al₂O₃ using aluminium isopropoxide (AIP) is developed. High-field solid-state nuclear magnetic resonance spectroscopy (SSNMR) probes the formation of γ-LiAlO₂ at 600 °C and doping of aluminium into NMC811 starting at 500-600 °C. NMC811 coated with amorphous Al₂O₃ (200-400 °C) had a capacity retention comparable to pristine NMC811, while higher annealing temperatures led to more crystalline coatings and surface Al-doping which were found to increase the rate of degradation of NMC811 upon cycling. Finally, LiAlO₂ coatings are deposited onto NMC811 using heterobimetallic alkoxides: LiAl[(OCH₂Ph)₄], LiAl[(OⁱPr)₄] and LiAl[(O^tBu)₄]. The later showing the most promise as a coating precursor due to its high solubility in tetrahydrofuran (THF), low temperature decomposition (283 °C) and reaction with hydroxyl groups present on the surface of NMC811. This coating was tested on polycrystalline NMC811 (PC-NMC811) and Al₂O₃ coated single-crystal NMC811 (Al₂O₃/SC-NMC811). Significant improvements in capacity retention (17.2% more C/2 capacity retained after 107 cycles vs. Al₂O₃/SC-NMC811) were seen in the LiAlO₂/Al₂O₃/SC-NMC811 system. Furthermore, coating PC-NMC811 that was previously degraded by soaking in water improved the capacity retention (50.1% more capacity retention at C/2 after 215 cycles vs. uncoated PC-NMC811 soaked in water and annealed at 400 °C) suggesting that the combination of a LiAlO₂ coating and subsequent annealing step can recover NMC811 surfaces that have been previously degraded by soaking in water.