The reporting period of the project has been focussed on the benchmarking of semiconducting particles, their corresponding charge transport layers and co-catalysts, for both the hydrogen evolution reaction and glycerol oxidation reaction to 1,3 dihydroxyacetone (DHA). For the hydrogen evolving particle, WSe2 and organic semiconductors were studied and the organic semiconductors were found to generate promising photocurrents (> 4 mA cm-2) under sacrificial conditions, which was found to be highly dependent on the charge transport layers used. In parallel, various MoSx-based co-catalysts are under development, with a focus on performance and transmittance, and these are being combined with the organic semiconductors as a next step. For the glycerol oxidation reaction, BiVO4, BiW2O6, MoS2 and organic semiconductors were tested. So far, BiVO4 has been found to be the most promising semiconductor for glycerol oxidation in terms of photocurrent (3.4 mA cm-2) and onset potential. Selectivity to DHA was found to be > 50%, getting close to our final target of 70%. In order to improve the selectivity we are modifying BiVO4 with dopants and optimising the surface.
The semiconducting particles will be deposited on a transparent conducting porous support (TPCS) based on a fluorine-doped tin oxide coated quartz felt that has been developed in a previous EU-funded project, Sun-To-X. The porosity of the substrate allows us to deposit thin layers to maximise light absorption by the semiconductor. Work has focussed on improving the conductivity, transparency and mechanical stability. The maximum weight that can be borne by the substrate has been increased from 25 to 135 grams through optimising loading, density, and annealing temperature. The process methods have been scaled so the TPCS can now be produced on a 100 cm2 scale.
To support the optimisation of the device design, a zero-dimensional model of various reactor configurations has been prepared. This will later be developed in a multi-scale model that will provide information on how to optimise parameters to maximise light transfer, heat transport, charge transport, mass transport and fluid-flow dynamics. The first photoreactor prototypes have been built on a small scale to allow testing of reactor material compatibility with the electrolytes and identification of any flow problems e.g. gas collection pockets. The design has been refined and a piping and instrumentation diagram (P&ID) has been prepared for the final demonstrator.
Finally, an inventory of materials has been prepared for use in TEA and LCA studies. These studies have shown that, out of the candidate materials, the organic semiconductors result in the lowest manufacturing costs of the photocatalytic sheets. The results of these studies will be complementary to performance and stability data in choosing the most promising materials for eventual integration into the reactor. A market study is also on-going and we have found that the co-production of DHA strongly contributes to economic feasibility, however, due to the limited market size of DHA, it would be interesting to expand PH2OTOGEN technology to other glycerol oxidation products to expand the applicability of the device.
