Microphase Photo-Electrochemistry: Light Driven Liquid-Liquid Ion Transfer Processes and Two-Phase Micro-Photovoltaic Systems

Lead Research Organisation: University of Bath
Department Name: Chemistry


Photoelectrochemical processes are ubiquitous in nature and are a fundamental component in light harvesting processes. These processes occur in biological membranes with complex liquid | liquid reaction zones that have evolved to maximise the benefit to the host organism. Recent work on microphase liquid | liquid interfaces has broadened the range of experiments available for the study of electrochemical ion transfer at similarly complex liquid | liquid interfaces. In this proposal we focus on the next step: studying photo-electrochemical processes and tools at microphase liquid | liquid interfaces and within triple phase boundary reaction zones. This reaction zone offers a unique environment where photo-excited intermediates are in close proximity to both the electrode surface and the liquid | liquid interface.The project is exploratory but ambitious in nature and divided into four main, interconnected parts: (A) the study of electrochemically or photo-electrochemically driven ion transfer processes using fluorescent probe anions, (B) the study and screening of simultaneous electron and ion transfer at microphase liquid | liquid interfaces with novel triple phase boundary-based photochemical and photo-electrochemical methods, (C) the investigation of two-phase processes involving electron and ion transfer on TiO2 substrates or within TiO2 hosts, and (D) characterizing the local environment at the liquid | liquid interfaces using fluorescent probe molecules, and understanding how the potential of the interface and flux of ions across the interface affect the local environment.The primary intellectual merit of this project can be identified in (i) the development of new quantitative mechanistic tools for the study of complex electron/ion transfer at liquid | liquid interfaces, (ii) the exploration of the triple phase boundary domain for photo-electrochemical reactivity (the study of microdroplet size effects and reaction zones within microphase systems), and (iii) gaining an understanding of how the molecular scale organization and dynamics of a liquid interface is influenced by electron and/or ion transport across that interface. All of these aspects of the proposal serve to provide a broad understanding of how photoelectrochemical processes operating within microscopic liquid systems can be used to advantage in applications ranging from energy conversion to chemical sensing.The broader impact of the project lies primarily in providing a multinational cohort of globally competitive scientists to the workforce of both the United States and the United Kingdom. This project will facilitate the creation of a bilateral think tank and will foster the free exchange of ideas in a field of research and development that has direct impact on science at the interface between biosystems and energy conversion. We anticipate that the ideas and experiments developed in this collaborative study will help screen and identify new light harvesting processes, possibly mimicking natural processes, and therefore contribute to new energy harvesting/storage/management systems. It is important to note that both PIs have unique and difficult to replicate capabilities. The success of this work hinges on the collaboration between the Marken and Blanchard groups. If either PI were to undertake the proposed work by themselves, the study would be ineffective because neither lab has either the resources or expertise to perform all of the work proposed here.
Description This project focussed on light-induced reactions at oil-water interfaces with particular emphasis on oil-droplets on electrodes that are surrounded by aqueous electrolyte. In this collaboration with Michigan State University, we were able to demonstrate light energy harvesting at microdroplet surfaces for the first time. We selected and tested different dyes with redox activity in the oil droplet and developed mechanistic schemes to explain coupled electron-transfer and ion-transfer. We found one dye in particular that allowed direct electron transfer into the aqueous phase (a liquid version of the Graetzel cell) and we have shown the effect of anion adsorption on the electron transfer process. In collaboration with the Michigan State Research Group we also developed a new microscope system that allowed mapping of the triple phase boundary. New interfacial phenomena were discovered such as a water in oil emulsion with droplet sizes that change as a function of distance from the triple phase interface.
Exploitation Route Our studies are fundamental in nature and the topic liquid-liquid photo-electrochemistry is linked to natural photosynthesis. Our perspectives review is well cited and the concepts are entirely new. However, solar energy harvesting efficiencies remain low and therefore further development is hampered.

The project has resulted in new ideas in liquid-liquid photo-electrochemistry and the research has now moved on into membrane system with photo-excitable molecular components (Leverhulme funded). This development allows experimental systems to be compared more closely to natural photosynthesis. The link of photo-excitation to interfacial ion flow is under further study.
Sectors Energy,Environment