Photocatalytic hydrogen production coupled to glucose oxidation using a conjugated polyelectrolyte photocatalyst Rhys Bourhill 1 , Efthalia Chatzisymeon 2 , Reiner Sebastian Sprick 1 1 University of Strathclyde, United Kingdom, 2 University of Edinburgh, United Kingdom Photocatalysts can enable the production of hydrogen from water using solar light through water splitting. However, the water oxidation half reaction is kinetically and thermodynamically challenging and therefore in most cases sacrificial reagents are added to discourage exciton recombination and improve the efficiency of the proton reduction half-reaction. 1 The use of a sacrificial agent also allows for the production of value-added products from the corresponding oxidation reaction instead of the oxygen produced by water splitting. However, commonly used sacrificial agents such as triethylamine are petrochemically derived compounds, are toxic and are typically oxidised into non-useful waste products, making the overall process unsustainable. 2 Utilising abundantly available biomass such as glucose as a sacrificial reagent allows for an overall more sustainable process while also being oxidised more easily than water into potentially useful products. 3 Conjugated organic polymers present themselves as an alternative to traditional inorganic photocatalysts. Their optical and physical properties can be more easily fine-tuned than in inorganic materials due to the wide variety of monomer units that are available to be used in their synthesis. This allows for properties such as band-gap size, band energy levels and polarity to be optimised for photocatalytic applications. In conjugated materials, ionising functional groups present on side chains to generate a conjugated polyelectrolyte (CPE) is another method to customise the properties of conjugated materials. Ionic pendant groups on the side chains of conjugated materials have been shown to influence the packing structure of the polymer and increase the polarity of the material, allowing for greater interactions with sacrificial reagents in aqueous media and increased dispersibility. 4 By utilising a CPE photocatalyst with ionic ammonium side chains alongside glucose, hydrogen was successfully produced at a rate more than double that obtained when using triethylamine as a scavenger and tenfold higher than that observed when an analogous non-ionic conjugated polymer is used. This indicates that there is a significant unique interaction between charged polymer side chains and glucose that does not occur with triethylamine. Furthermore, glucose was successfully oxidised into gluconic acid (88%) and mannitol (12%) which have uses in the construction and medical industries respectively. This work highlights the unique enhancement of photocatalytic hydrogen production when using a conjugated polyelectrolyte photocatalyst with glucose as a more sustainable scavenger over typical tertiary amine scavengers. References 1. Nishioka, S. et al . Photocatalytic water splitting. Nat Rev Methods Primers 3 , 1–15 (2023). 2. Aitchison, C. et al . Structure–activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water. Chemical Science 11 , 8744–8756 (2020). 3. Davis, K. A. et al . Photocatalytic hydrogen evolution from biomass conversion. Nano Convergence 8 , 6 (2021). 4. Dai, C., Panahandeh-Fard, M., Gong, X., Xue, C. & Liu, B. Water-Dispersed Conjugated Polyelectrolyte for Visible-Light Hydrogen Production. Solar RRL 3 , 1800255 (2019).
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