Redox‐Mediated Alcohol Oxidation Coupled to Hydrogen Gas Formation in a Dye‐Sensitized Photosynthesis Cell

Abstract

This work reports ad ye-sensitized photoelectrochemical cell (DSPEC) that couples redox-mediated lightdriven oxidative organic transformations to reductive hydrogen (H 2)f ormation.T he DSPEC photoanodec onsists of am esoporousa nataseT iO 2 film on FTO (fluorine-doped tin oxide), sensitized with the thienopyrroledione-based dye AP11,w hileH 2 was formeda taFTO-Pt cathode. Irradiation of the dye-sensitizedp hotoanode transforms 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) to the oxidized TEMPO (TEMPO +), whicha cts as ac hemical oxidant for the conversion of benzyla lcohol. The TEMPO 0/ + couple,p reviously used as redoxm ediator in DSSC, mediates efficient electron transfer from the organic substrate to the photo-oxidized dye. AD SPEC photoreactorw as designed that allows in situ monitoring the reaction progress by infrared spectroscopy and gas chromatography.S ustained light-driven oxidation of benzyla lcoholt ob enzaldehydew ithin the DSPEC photoreactor,u sing of TEMPO as mediator,d emonstrated the efficiency of the device, with ap hotocurrent of 0.4 mA cm À2 ,a pproachingq uantitative Faradaic efficiency and exhibiting excellent device stability. Solar energy is an attractive CO 2-neutral energy source, providing % 4200 times the energy consumption estimated for 2035. [1, 2] Beyondw idely deployed silicon-based photovoltaic (PV) technology,d ye-sensitizeds olar cells (DSSCs) [3] present a low-cost alternative with improved performance in low/diffuse light conditions. DSSCs use molecular dyes, wide-bandg ap semiconductors and redox mediators to absorb light and separate charges affording efficienciest hat have surpassed 14 %. [4, 5] While the application of solar-to-electric energy conversion is increasing, long-term energy storageremains ac hallenge. Elec

Photoelectrochemical hybrid cell for unbiased CO2 reduction coupled to alcohol oxidation

“…Employing the mTiO 2 |DPP-CA system in the presence of solubilized TEMPO (1 mM) in the electrolyte led to 4-MBAd production with high FE (99%). However, limited photocurrents of ~20 µA cm −2 with a TON TEMPO < 1 were reached, in line with previous reports on TEMPO-mediated dye-sensitized systems 44 , which highlights the benefits of immobilized molecular catalysts on heterogeneous scaffolds 14,45 .…”

Beyond Water Oxidation: Hybrid, Molecular-Based Photoanodes for the Production of Value-Added Organics

“…Interestingly, similar photoelectrochemical performances were also obtained by adding the TEMPO catalyst in a homogenous solution, avoiding the synthetic effort to bind it to the porphyrin chromophore. The aspect of heterogenizing the TEMPO catalyst for alcohol oxidation was also discussed by Reek et al ( Bruggeman et al, 2021a ; Bruggeman et al, 2021b ), in the development of photoanodes sensitized with thienopyrroledione-based organic dye (AP11, Figure 2B ). The AP11 dye can be efficiently chemisorbed onto TiO 2, and electron injection from the excited state is energetically favorable by 0.3 eV.…”

Comparison of homogeneous and heterogeneous catalysts in dye-sensitised photoelectrochemical cells for alcohol oxidation coupled to dihydrogen formation

“…Having established the requirement of unimpeded dye regeneration, we utilised homogeneous TEMPO in photosynthetic experiments to oxidise PhCH 2 OH to PhCHO. 44 Here, TEMPO acts as a redox mediator akin to the oxidised dye and the CE in DSSCs. TEMPO is oxidised to TEMPO+ by the photooxidised AP11 , after which TEMPO+ is converted back to TEMPO by oxidation of the substrate.…”

“…The increased stability of the photoanode thanks to the presence of the homogeneous redox mediator demonstrates the importance of fast regeneration of the oxidised photosensitiser in DSPEC design. 44 Here, TEMPO acts as a redox mediator akin to the oxidised dye and the CE in DSSCs. TEMPO is oxidised to TEMPO + by the photooxidized AP11, after which TEMPO + is converted back to TEMPO by oxidation of the substrate.…”

“…‡ ‡ As published in our previous communication. 44 This paper provides new insights and design considerations for optimising DSPECs by focusing on the trade-off between the importance of preorganisation, electron harvesting properties of the photoanode, long-term device stability, and post-reaction product purification.…”