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 %.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The famous cereal 'green revolution' of the 1960s/1970s increased crop yields, averted famine and fed a growing world population. Green Revolution Varieties (GRVs) of rice and wheat were the genetic foundation of the green revolution. GRVs carry mutant growth regulatory genes that confer dwarfism, and this dwarfism increases yield because it reduces loss due to 'lodging' (flattening of plants by wind and rain), hence causing the yield increases of the green revolution. However, the mutant growth regulatory genes also cause GRVs to be less efficient in assimilating the nitrogen (N) supplied to them in the form of fertilizer. As a result, N that is not assimilated by GRVs is dissipated into the wider environment, where it causes severe damage to terrestrial and aquatic ecosystems, together with atmospheric greenhouse-gas pollution that precipitates climate change. Because today's high-yielding crop varieties still depend upon the mutant dwarfing genes for their high yields, it is necessary to find ways of developing new crop varieties that retain the benefits of GRV dwarfism but that are more efficient in their use of N fertilizers (have improved N use efficiency, NUE). Here we propose to exploit the rapid genetics and molecular biology of the genetic model Arabidopsis to make discoveries that will enable future enhancement of GRV NUE. The GRV dwarfing genes cause accumulation of a class of growth inhibitory proteins called DELLAs, and DELLAs also accumulate in the dwarf Arabidopsis GRV mutant model gai. Accumulated DELLAs inhibit the action of another class of regulatory proteins, the PIFs (or Phytochrome Interacting Factors). Our recent preliminary evidence from studies of Arabidopsis suggest that the inhibitory effect of DELLAs on PIFs may explain the reduced NUE of GRVs, and it is this novel and exciting finding that we exploit in this proposal. We will therefore first further test our working hypothesis that interactions between DELLAs and PIFs affect the assimilation of N: that the DELLAs accumulated in GRVs and gai oppose PIF function, thus reducing N assimilation. If this hypothesis is correct, modulation of the DELLA-PIF relationship may provide a novel route towards improving GRV NUE. We have the following objectives: A. Obtain an in-depth understanding of PIF-regulation of Arabidopsis and rice N assimilation - essentially performing genetic tests of the role of PIFs in regulation of N metabolism and assimilation in Arabidopsis and rice. B. Determine how the DELLA-PIF interaction regulates the abundance of mRNA encoding nitrate reductase (NR), a key enzyme in N assimilation - this an exploration of how the DELLA-PIF interaction controls the expression of the gene encoding that enzyme. C. Determine if the DELLA-PIF interaction also directly affects the abundance and/or specific enzymatic activity of the NR enzyme itself. D. Determine if NUE can be increased despite retaining yield-enhancing dwarfism. This is important because it could lead to the development of crops which retain the high yields of current GRVs, but at reduced environmental cost. First, we will determine if increasing PIF activity might confer such benefits. However, because increasing the activity of PIFs themselves in GRVs might have additional unwanted consequences, we will additionally explore other routes (downstream of PIFs) to improving GRV NUE whilst retaining yield-enhancing dwarfism. Inherent in our strategy is initial translation of findings from Arabidopsis model to crop (rice), exploiting our long-standing combined expertise in DELLA biology, model-crop translations, and whole genome sequence analysis. Our long-term aim (future proposals) is to use the fundamental understanding gained here in the development of rice and wheat GRVs having enhanced NUE, thus enhancing global food security and reducing agricultural environmental degradation.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

China