Sunlight, water, and specially designed plastic nanoparticles could soon produce hydrogen fuel without any added chemicals to drive the reaction. This matters because most current methods for making green hydrogen rely on metal-based photocatalysts that absorb only a sliver of sunlight, or require sacrificial chemicals that get consumed during the reaction. The researchers aim to build organic semiconductor nanoparticles that capture visible and near-infrared light—the bulk of the solar spectrum—and pair them with bismuth vanadate particles in a tandem system that splits water into hydrogen and oxygen using only sunlight. No sacrificial agents needed. If successful, the project could unlock a low-cost, scalable route to green hydrogen for energy storage, industrial feedstocks, and fuel cells. The work is fundamental science: it combines novel materials synthesis with ultrafast spectroscopy to understand exactly how charges move and recombine inside these nanoparticles. That mechanistic insight will guide iterative design, not just for this system but for future organic photocatalysts. A solar-to-hydrogen efficiency above 1 percent is the target—modest by lab standards, but a critical proof of principle for a truly sustainable process.
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The sustainable generation of green hydrogen is a critical challenge in our transition towards net zero. Artificial photosynthetic systems based on photocatalytic particles in suspension offer one of the potentially lowest cost routes to green hydrogen production using sunlight. However the limited visible light absorption of most photocatalytic systems to date, typically based on metal oxides, has to date limited achievable conversion efficiencies. Recently, substantial breakthroughs have been achieved in the performance of photocatalyst particles based on organic semiconductors, harnessing solar light across the visible and near infrared. However to date efficient hydrogen generation has only been achieved in the presence of sacrificial electron donors. In this project, we will focus on the development of organic heterojunction photocatalysts with controlled nanomorphology and their integration into a hybrid organic / inorganic tandem system for green hydrogen synthesis from water without any sacrificial species. The project brings together the expertise of the Durrant group at Imperial in the spectroscopy and photochemical function of photocatalytic systems with the McCulloch group's expertise in the design and synthesis of organic semiconductors. It further benefits from the participation of two talented researcher / co-investigators, Dr Soranyel Gonzalez Carrera (Imperial) with expertise in nanoparticle processing and photocatalytic characterisation and Dr Catherine Aitchison at Oxford with expertise in templating strategies for organic photocatalysts. The project will focus on the synthesis, characterisation and optimisation of visible / near IR absorbing organic heterojunction photocatalyst nanoparticles. Optimised nanoparticles will be tested in a tandem Z-scheme configuration with facet engineered Bismuth Vanadate particles supplied by our project partner, Prof Can Li from the University of Dalian, in order to achieve overall water splitting. Two strategies will be explored to fabricate heterojunction nanoparticles: i) blended organic heterojunction nanoparticles of selected donor polymers matched with molecular acceptors, using our established nanoemulsion solution processing technique and ii) templated covalent organic framework heterojunctions formed through our novel templating technique of D/A polymer sheets. Both systems will be functionalised with a molecular proton reduction catalyst to maximise selective proton reduction to H2, with nanomorphology and surfactant control used to optimise selective oxidation of a reversible FeII/FeIII redox couple. A core element of this project will be in-depth photophysical characterisation on timescales from fs to seconds, allowing us to determine the timescales of charge separation, recombination, and transfer to the proton reduction catalyst and FeII/FeIII, enabling iterative optimisation of each of these steps and thereby overall photocatalytic performance. Optimised photocatalysts will be selected on the basis of their efficiency for hydrogen generation and their stability, and then integrated into an overall water-splitting Z-scheme system with the BiVO4 water oxidation photocatalysts. The project has thus three specific objectives: -Development of organic semiconductor heterojunction photocatalysts with optimised (nano)morphology, high (photo)stability and selective proton reduction / FeII oxidation -In-depth mechanistic studies using advanced transient optical spectroscopies to identify the key performance descriptors and iterative materials design guidelines. -Optimisation in a Z-Scheme tandem system by integrating organic heterojunction photocatalyst for hydrogen evolution with BiVO4 oxygen evolution photocatalysts using a redox couple to achieve overall water splitting with STH efficiency of >1 %.
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