New polymer photocatalyst architectures for solar fuel generation

The production of clean energy and access to clean water are two very important contemporary challenges in materials chemistry. Both challenges can be addressed through photocatalytic processes catalysed by semiconductors with water splitting yielding hydrogen which is a storable energy carrier or the reduction of carbon dioxide into solar fuels, and photocatalytic water disinfection being used to inactivate bacteria present in water.

For photocatalytic water splitting to occur a semiconductor is required that absorbs light and creates charge carriers that are then transferred to water resulting in hydrogen and oxygen production. Until recently, the field was dominated by inorganic semiconductors, such as titanium dioxide, often coupled with a precious metal co-catalyst. However, the 2009 Nature Materials report by Antonietti (Nat. Mater. 2009, 8, 76) has provoked a surge of interest in organic materials for water-splitting, the vast majority relating to carbon nitride and its variants. In 2015 it was shown that conjugated polymers can compete with carbon nitrides for photocatalytic hydrogen evolution (J. Am. Chem. Soc. 2015, 137, 3265) and photocatalytic carbon dioxide reduction (J. Mater. Chem. A, 2021, 9, 4291).

Similarly, photocatalytic water disinfection with titanium dioxide has been well studied, but also requires UV light to create as it is a wide band-gap material. Unbranched conjugated polymers have also been found to generate reactive species, such as hydroxyl and superoxide radicals or hydrogen peroxide, under illumination and it has been demonstrated for example by Schanze (Langmuir 2011, 27, 4956) and several follow up studies that this can be used for bacteria inactivation. Conjugated microporous polymers have also been shown to be active for this application (J. Mater. Chem. B 2016, 4, 5112), but are far less explored to date.

Fundamentally, these processes are severely limited in their efficiency due to the high exciton binding energies observed in organic materials which result in fewer charges being generated compared to inorganic photocatalysts (Chem. Soc. Rev. 2020, 49, 3981).
The project will develop new material architectures with energy offsets that will result in significantly enhanced activity for photocatalytic oxidation and reduction reactions. The materials will be used for the generation of hydrogen from water, carbon dioxide reduction and bacteria inactivation. A particular focus will be on processability of the materials allowing for the fabrication of devices at scale going forward.