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Title: Photo-electrochemical engineering of solar water splitting devices
Author: Holmes-Gentle, Isaac
ISNI:       0000 0004 9350 6237
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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In order to scale up photo-electrochemical (PEC) water splitting, there are a number of engineering challenges that must be overcome. In order to logically approach this task, the PEC device was deconstructed into a classification framework comprising of two parts: the fundamental conceptual design and the engineering PEC device design. The first is used to investigate the fundamental limiting efficiencies of permutations of conceptual design, and the second to study the common elements of photo-electrode reactor design and critically compare examples from literature. After identifying the engineering challenges of scaling PEC devices, two specific issues were explored: 1) the optical losses from light scattered by bubbles at the gas-evolving photo-electrode under ‘front side’ illumination 2) the resistive losses in large area low conductivity substrate such as fluorine doped tin oxide (FTO). For both, the realistic losses were quantified and mitigation strategies evaluated. Finally, a new class of photo-electrochemical reactor was proposed: a membrane-less flow cell reactor that employs hydrodynamic separation of dissolved gaseous products. It is theoretically demonstrated that current densities typical of current PEC devices can be supported whilst suppressing bubble formation through operation at high pressure. The general operational design space was assessed with non-dimensional analysis and numerical modelling. Positive preliminary experimental results are displayed and a future work plan outlined. In summary, this thesis defines the role of photo-electrochemical engineering for solar to hydrogen devices, outlines the most pertinent challenges and begins to tackle a number of them, demonstrating that careful engineering design is required in order to realise any photo-electrochemical water splitting process.
Supervisor: Hellgardt, Klaus Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral