Abstract
Complex perovskites of the structural formula LaIrxNi1xO3 were investigated for their electrochemical behaviour towards the oxygen evolution reaction. The novel compositional space was thoroughly characterised through x-ray and electron diffraction, electron microscopy and x-ray absorption spectroscopic techniques. Density functional theory calculations were used to rationalise the observed activity trends, whereby both electronic structure and surface thermodynamic descriptors compared to experimental data. Intermediate iridium content leads to optimisation of the binding energetics of adsorbates on nickel sites, whereas further iridium substitution lowers activity due to iridium sites having lower intrinsic activity and dominating the surface.Model perovskite catalysts of the structural formula LaxSr1-xBO3, where x =1, 0.83 and 0.66 and B = Mn, Co, Ni, were prepared and thoroughly structurally characterised. The pH dependent electrochemical oxygen evolution activity was measured and studied further with electrochemical impedance spectroscopy and cyclic voltammetry. Higher surface hydroxide at high pH levels was found to lead to a decrease in the resistance to charge transfer at the interface, facilitating the electron transfer of the rate limiting step, decoupling the mechanism leading to the pH dependent kinetics. The electronic structures of the model compounds were calculated using density functional theory and used to estimate the metal-oxygen hybridisation which was found to highly correlated to the pH dependence. The surface acid-base properties were studied using x-ray photoelectron spectroscopy and surface DFT calculations. The acid-base properties were found to have a complex relationship between the materials and no clear correlation to the pH dependence was found, suggesting the change in electron transfer rate dominated.
| Date of Award | 9 May 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David J Fermin (Supervisor) & Andrew Logsdail (Supervisor) |