Polymer Photocatalysts with Side Chain Induced Planarity for Increased Activity for Sacrificial Hydrogen Production from Water

Conjugated polymers are promising materials for photocatalytic hydrogen evolution. However, most reported materials are not solution‐processible, limiting their potential for large‐scale application, for example as solution cast films. Flexible side‐chains are commonly introduced to provide solubility, but these often impart unfavorable properties, such as hydrophobicity, which lowers photocatalytic activity. Here, computational predictions are employed to aid in the design of chloroform soluble polymer photocatalysts that show increased planarity through favorable intramolecular interactions. Using this approach, three conjugated polymer photocatalysts with identical poly(benzene‐dibenzo[b,d]thiophene sulfone) backbones but different solubilizing side‐chains on the benzene‐ring are explored, i.e., tri(ethylene glycol), n‐decyloxy, and n‐dodecyl. These side‐chain variations significantly alterr the properties of the polymers, specifically energy levels, optical gap, and wettability. The hydrophobic n‐decyloxy functionalized polymer has a sacrificial hydrogen evolution rate of 17.0 µmol h−1 in suspension, while the hydrophilic tri(ethylene glycol) functionalized polymer is almost three times more active (45.4 µmol h−1). Conversely, no hydrogen evolution is observed for the purely alkyl side‐chain (n‐dodecyl) containing polymer due to the side‐chain induced torsion of the backbone. A thin‐film of the most active polymer exhibits a promising area‐normalized sacrificial hydrogen evolution rate of 7.4 ± 0.3 mmol h−1 m−2 under visible light irradiation

Visible-light-responsive hybrid photocatalysts for quantitative conversion of CO 2 to highly concentrated formate solutions

Photocatalysts can use visible light to convert CO2 into useful products. However, to date photocatalysts for CO2 conversion are limited by insufficient long-term stability and low CO2 conversion rates. Here we report hybrid photocatalysts consisting of conjugated polymers and a ruthenium(ii)–ruthenium(ii) supramolecular photocatalyst which overcome these challenges. The use of conjugated polymers allows for easy fine-tuning of structural and optoelectronic properties through the choice of monomers, and after loading with silver nanoparticles and the ruthenium-based binuclear metal complex, the resulting hybrid systems displayed remarkably enhanced activity for visible light-driven CO2 conversion to formate. In particular, the hybrid photocatalyst system based on poly(dibenzo[b, d]thiophene sulfone) drove the very active, durable and selective photocatalytic CO2 conversion to formate under visible light irradiation. The turnover number was found to be very high (TON = 349 000) with a similarly high turnover frequency (TOF) of 6.5 s−1, exceeding the CO2 fixation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in natural photosynthesis (TOF = 3.3 s−1), and an apparent quantum yield of 11.2% at 440 nm. Remarkably, quantitative conversion of CO2 (737 μmol, 16.5 mL) to formate was achieved using only 8 mg of the hybrid photocatalyst containing 80 nmol of the supramolecular photocatalyst at standard temperature and pressure. The system sustained photocatalytic activity even after further replenishment of CO2, yielding a very high concentration of formate in the reaction solution up to 0.40 M without significant photocatalyst degradation within the timeframe studied. A range of experiments together with density functional theory calculations allowed us to understand the activity in more detail

Impact of Interfaces, and Nanostructure on the Performance of Conjugated Polymer Photocatalysts for Hydrogen Production from Water

The direct conversion of sunlight into hydrogen through water splitting, and by converting carbon dioxide into useful chemical building blocks and fuels, has been an active area of research since early reports in the 1970s. Most of the semiconductors that drive these photocatalytic processes have been inorganic semiconductors, but since the first report of carbon nitride organic semiconductors have also been considered. Conjugated materials have been relatively extensively studied as photocatalysts for solar fuels generation over the last 5 years due to the synthetic control over composition and properties. The understanding of materials’ properties, its impact on performance and underlying factors is still in its infancy. Here, we focus on the impact of interfaces, and nanostructure on fundamental processes which significantly contribute to performance in these organic photocatalysts. In particular, we focus on presenting explicit examples in understanding the interface of polymer photocatalysts with water and how it affects performance. Wetting has been shown to be a clear factor and we present strategies for increased wettability in conjugated polymer photocatalysts through modifications of the material. Furthermore, the limited exciton diffusion length in organic polymers has also been identified to affect the performance of these materials. Addressing this, we also discuss how increased internal and external surface areas increase the activity of organic polymer photocatalysts for hydrogen production from water

Impact of interfaces, and nanostructure on the performance of conjugated polymer photocatalysts for hydrogen production from water

The direct conversion of sunlight into hydrogen through water splitting and by converting carbon dioxide into useful chemical building blocks and fuels has been an active area of research since early reports in the 1970s. Most of the semiconductors that drive these photocatalytic processes have been inorganic semiconductors but since the first report of carbon nitride organic semiconductors have also been considered. Conjugated materials have been relatively extensively studied as photocatalysts for solar fuels generation over the last 5 years due to the synthetic control over composition and properties. The understanding of materials' properties, its impact on performance and underlying factors is still in its infancy. Here, we focus on the impact of interfaces, and nanostructure on fundamental processes which significantly contribute to performance in these organic photocatalysts. In particular, we focus on presenting explicit examples in understanding the interface of polymer photocatalysts with water and how it affects performance. Wetting has been shown to be a clear factor and we present strategies for increased wettability in conjugated polymer photocatalysts through modifications of the material. Furthermore, the limited exciton diffusion length in organic polymers has also been identified to affect the performance of these materials. Addressing this, we also discuss how increased internal and external surface areas increase the activity of organic polymer photocatalysts for hydrogen production from water

Non-conventional bulk heterojunction nanoparticle photocatalysts for sacrificial hydrogen evolution from water

Photocatalyst systems combining donor polymers with acceptor molecules have shown the highest evolution rates for sacrificial hydrogen production from water for organic systems to date. Here, new donor molecules have been designed and synthesised taking inspiration from the structure-performance relationships which have been established in the development of non-fullerene acceptors. While a conventional bulk heterojunction (BHJ) pairing consists of a donor polymer and acceptor small molecules, here we have successfully reversed this approach by using our new p-type small molecules in combination with a n-type conjugated polymer to produce non-conventional BHJ (ncBHJ) nanoparticles. We have applied these ncBHJs as photocatalysts in the sacrificial hydrogen evolution from water, and the best performing heterojunction displayed high activity for sacrificial hydrogen production from water with a hydrogen evolution rate of 22,321 μmol h−1 g−1 which compares well with the state-of-the-art for conventional BHJ photocatalyst systems

Non-Conventional Bulk Heterojunction Nanoparticle Photocatalysts for Sacrificial Hydrogen Evolution from Water

Photocatalyst systems combining donor polymers with acceptor molecules have shown the highest evolution rates for sacrificial hydrogen production from water for organic systems to date. Here, new donor molecules have been designed and synthesised taking inspiration from the structure-performance relationships which have been established in the development of non-fullerene acceptors. While a conventional bulk heterojunction (BHJ) pairing consists of a donor polymer and acceptor small molecules, here we have successfully reversed this approach by using our new molecules in combination with a n-type conjugated polymer to produce non-conventional BHJ nanoparticles and applied these blends to the sacrificial hydrogen evolution from water. The best performing heterojunction displayed high activity for sacrificial hydrogen production from water with a hydrogen evolution rate of 22,321 µmol h−1 g−1 which compares well with the state-of-the-art for conventional BHJ photocatalyst systems

Polymer Photocatalysts with Side Chain Induced Planarity for Increased Activity for Sacrificial Hydrogen Production from Water

AbstractConjugated polymers are promising materials for photocatalytic hydrogen evolution. However, most reported materials are not solution‐processible, limiting their potential for large‐scale application, for example as solution cast films. Flexible side‐chains are commonly introduced to provide solubility, but these often impart unfavorable properties, such as hydrophobicity, which lowers photocatalytic activity. Here, computational predictions are employed to aid in the design of chloroform soluble polymer photocatalysts that show increased planarity through favorable intramolecular interactions. Using this approach, three conjugated polymer photocatalysts with identical poly(benzene‐dibenzo[b,d]thiophene sulfone) backbones but different solubilizing side‐chains on the benzene‐ring are explored, i.e., tri(ethylene glycol), n‐decyloxy, and n‐dodecyl. These side‐chain variations significantly alterr the properties of the polymers, specifically energy levels, optical gap, and wettability. The hydrophobic n‐decyloxy functionalized polymer has a sacrificial hydrogen evolution rate of 17.0 µmol h−1 in suspension, while the hydrophilic tri(ethylene glycol) functionalized polymer is almost three times more active (45.4 µmol h−1). Conversely, no hydrogen evolution is observed for the purely alkyl side‐chain (n‐dodecyl) containing polymer due to the side‐chain induced torsion of the backbone. A thin‐film of the most active polymer exhibits a promising area‐normalized sacrificial hydrogen evolution rate of 7.4 ± 0.3 mmol h−1 m−2 under visible light irradiation.</jats:p

Polymer photocatalysts with side-chain induced planarity for increased activity for sacrificial hydrogen production from water

Conjugated polymers are promising materials for photocatalytic hydrogen evolution. However, most reported materials are not solution processible, which limits their potential for large-scale application, for example as solution cast films. Solution processable conjugated polymers can be prepared through the introduction of flexible side-chains, but these side-chains often impart unfavorable properties, such as hydrophobicity, which lowers photocatalytic activity. Here, we use computational predictions to aid in the design of solution processable polymer photocatalysts that are chloroform soluble. The polymers also show increased planarity through favorable intramolecular interactions. Using this approach, three conjugated polymer photocatalysts with identical poly(benzenedibenzo[b,d]thiophene sulfone) backbones but different solubilizing side-chains on the benzene-ring were explored, i.e., tri(ethylene glycol), n-decyloxy, and n-dodecyl. These side-chain variations altered the opto-electronic properties significantly through changes in charge carrier energy levels, optical gap, and wettability of the materials. The sacrificial hydrogen evolution rate under visible light irradiation for the polymer containing n-decyloxy side-chains was found to be 17.0 µmol h-1 in suspension. When n-decyloxy was substituted for the hydrophilic tri(ethylene glycol) side-chains, the rate increased by almost three times to 45.4 µmol h-1. However, the substitution of alkoxy for purely alkyl side-chains (n-dodecyl) resulted in no activity for sacrificial hydrogen evolution due to the side-chain induced torsion of the conjugated backbone. We then applied the most active of these polymers as a thin-film for photocatalysis, which exhibited a promising area-normalized sacrificial hydrogen evolution rate of 7.4 ± 0.3 mmol h-1 m-2 under visible light irradiation