Development of Reactor Technology for the Photoelectrolysis of Seawater

Abstract

Global industrialisation, population growth and pollution has led to increased strain on the provision of energy, potable water and food. Global warming is now recognised as a significant threat, therefore, attention has shifted to the deployment of low carbon technologies which can reduce emissions and help improve water, energy and food security throughout the world. Photocatalysis and by extension, photoelectrochemistry (PEC), is a process capable of environmental remediation and energy production via water splitting. This research focuses upon the development of novel materials and reactor technology which can be deployed for the purpose of chlorine generation, a powerful disinfectant, from saline solutions similar to that of seawater. Chlorine is currently formed via an energy intensive electrochemical process with high energy inputs and associated emissions. Using photoelectrochemical applications this can be carried out at lower energy requirements and in a more environmentally friendly manner.

TiO2 materials such as sol-gel photoanodes and titania nanotubes have been shown as immobilised photocatalysts capable of chloride oxidation with the latter exhibiting higher faradaic efficiencies of ~ 60 % under UV illumination. A propeller reactor system has been developed for application as a photoanode in a PEC setup within a stacked frame photo reactor design. Firstly, the propeller was designed and optimised for light delivery and effective mass transfer through the use of COMSOL Multiphysics® and also through experimental validation using coumarin as a probe molecule. COMSOL modelling has been successfully demonstrated as a means of evaluating the effective light delivery to an immobilised photocatalyst surface, providing a less biased estimate of the irradiance on the surface than other known methodologies. This reactor demonstrated improved mass transfer with increased coumarin degradation and OH radical formation at increased propeller rotation speeds of 300 RPM.

The propeller was then deployed as a photoanode within a PEC system to generate active chlorine. Titania nanotubes were grown on the surface of the propeller using a concentric anodization process with this being the first report of an anodization process being carried out upon such a challenging anode geometry. Significant improvements in faradaic efficiency (~ 9 %) were observed for chlorine generation by improving the mixing within the reactor at high propeller rotation speeds with mass transfer having a clear impact upon this PEC application, something less discussed within literature. This reactor has been used for a novel material deployed within an engineered setup and capable of improving efficiency of operation for PEC application by providing mixing from the support upon which the photocatalyst surface is immobilised.

Date of Award	Dec 2020
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Peter Robertson (Supervisor) & Andrew Mills (Supervisor)