Aqueous Biphasic Dye-Sensitized Photosynthesis Cells for TEMPO-Based Oxidation of Glycerol

This work reports an aqueous dye-sensitized photoelectrochemical cell (DSPEC) capable of oxidizing glycerol (an archetypical biobased compound) coupled with H-2 production. We employed a mesoporous TiO2 photoanode sensitized with the high potential thienopyrroledione-based dye AP11, encased in an acetonitrile-based redox-gel that protects the photoanode from degradation by aqueous electrolytes. The use of the gel creates a biphasic system with an interface at the organic (gel) electrode and aqueous anolyte. Embedded in the acetonitrile gel is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), acting as both a redox-mediator and a catalyst for oxidative transformations. Upon oxidation of TEMPO by the photoexcited dye, the in situ generated TEMPO+ shuttles through the gel to the acetonitrile-aqueous interface, where it acts as an oxidant for the selective conversion of glycerol to glyceraldehyde. The introduction of the redox-gel layer affords a 10-fold increase in the conversion of glycerol compared to the purely aqueous system. Our redox-gel protected photoanode yielded a stable photocurrent over 48 hours of continuous operation, demonstrating that this DSPEC is compatible with alkaline aqueous reactions.

Automated summary

This study reports a dye-sensitized photoelectrochemical cell that is capable of oxidizing glycerol and producing hydrogen. The use of a redox-gel layer with a high potential dye-sensitized mesoporous TiO2 photoanode protects the photoanode from degradation and significantly improves the conversion rate of glycerol. The redox-gel protected photoanode also demonstrates stable photocurrent over extended periods of continuous operation.