Periodic Reporting for period 2 - SOFT-PHOTOCONVERSION (Solar Energy Conversion without Solid State Architectures: Pushing the Boundaries of Photoconversion Efficiencies at Self-healing Photosensitiser Functionalised Soft Interfaces)
Reporting period: 2018-10-01 to 2020-03-31
The second WP in this project is a series of experimental approaches to dye-sensitizing the liquid-liquid interface with the aim of maximise photoconversion at electrified soft interfaces. The UV/vis in TIR setup has proved particularly valuable to monitor the kinetics of porphyrin self-assembly. Furthermore, the photoelectrochemical setup designed to test traditional solar cells, such as dye-sensitized solar cells (DSSC), in a laboratory environment has proved superb at testing dye-sensitized liquid-liquid interfaces. Indeed, all photoelectrochemical methodologies, such as photocurrent transient or intensity modulated photocurrent spectroscopy (IMPS) measurements, applicable to a DSSCs have been demonstrated to be equally applicable at a dye-sensitized liquid-liquid interface.
Using a multi-technique approach, to date a precise set of experimental conditions has been determined to form ordered porphyrin nanostructures that are highly photoactive. Furthermore, the underlying mechanism giving rise to “dark” electrochemical signals in the presence of the porphyrin nanostructures has been identified. The use of superhydrophobic electron donors that do not partition to the aqueous phase has been particularly useful to eliminate artefacts due to ion transfer that may mask photo-induced electron transfer signals at the electrified liquid-liquid interface. Advanced models to determine the kinetics of each step in the photo-process (electron transfer, photoproduct separation, photoproduct recombination) have been developed and used to successfully model the IMPS data.
Future work remaining in the project will involve enhancing the conductivity of the porphyrin films by incorporation of conducting carbon nanomaterials and enhancing the photocurrents plasmonically by integrating metallic nanoparticles within the porphyrin films. Photoconversion efficiencies far beyond the current state-of-the-art using electrified soft interfaces have already been attained, but scope remains to further improve them and scale-up the self-assembled photoactive biphasic system for real-world deployment.
The interfacial porphyrin nanostructures developed thus far in the project are highly photoactive, as shown in the Figure. Major progress has been achieved to fully elucidate the mechanism of photocurrent generation in terms of the influence of the applied interfacial potential in particular. This has been achieved by firstly developing an understanding of the mechanism underpinning the electrochemical response of the interfacial porphyrin nanostructures in the dark. The latter stems from an adsorption/ion exchange mechanism involving both the interfacial porphyrin nanostructures, aqueous protons and organic cations. By understanding the origin of the dark electrochemical signals, they were suppressed using a careful choice of experimental conditions. This allows the full potential window to be accessed with which to study the influence of the applied electric field on the magnitude and kinetics of the photocurrents generated in the presence of an electron donor specie sin the organic phase.
Future work in the project will involve developing prorphyrin nanocomposites with conductive carbon nanomaterials, including those sources sustainably such as lignin. Also, attempts will be made to enhance the photoconversion efficiencies using plasmons generated at the interface in the presence of metallic nanoparticles. Ultimately, scale-up of the dye-sensitized liquid-liquid interfaces is envisioned to convert solar energy to chemical energy using a biphasic system that self-assembles spontaneously upon contact of the two immiscible phases.