The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable, and efficient systems for the conversion and storage of renewable energy sources such as solar energy. The sunlight-driven production of hydrogen or other carbon-based fuels through reduction of water or CO2, with oxygen evolution as a by-product, appears to be a promising and appealing solution, which could be answered by the design of light-driven devices able to achieve light-to-chemical energy conversion. The design of such efficient photo-electrochemical systems remains to be achieved. In order to reach this ambitious goal, PhotoCAT will be undertaken by a consortium gathering teams with complementary expertise in the fields of molecular H2-evolving catalysts and surface chemistry (France CEA/LCBM), molecular CO2-reducing catalysts and homogeneous CO2-reducing photocatalysts (Tokyo Tech) and solid-state material chemistry (Kyoto Univ.). As a first step towards this end, PhotoCAT aims at designing new biomimetic materials for the engineering of photoelectrodes that will be finally implemented within a Photo-Electrochemical Cell (PEC) consisting of a photoanode for water oxidation (O2 evolution), feeding a photocathode with electrons for H2 evolution or CO2 reduction. This process reproduces the Z-scheme found in the photosynthetic machinery of plants and micro-algae. Novel H2-evolving or CO2-reducing photocathodes will be developed through the cografting of bio-inspired H2-evolving catalysts and CO2-reduction catalysts together with metal-organic and fully organic dyes onto transparent p-type semi-conductive substrates such as NiO. These photocathodes will be developed in collaboration between all three partners of PhotoCAT (Kyoto Univ for the fabrication of NiO-based materials, TokyoTech for metal-organic dyes and CO2-reducing catalysts and CEA/LCBM for H2-evolution catalysts, organic dyes and grafting methodologies. Two types of photoanode materials will be used for the construction of the final PEC devices: inorganic metal-oxide-based photoanode materials developed at Kyoto Univ. and molecular photoanode materials obtained from collaboration with a group from Arizona State University (Devens Gust, Ana and Tom Moore).

In the lower atmosphere ozone (O3) is an important anthropogenic greenhouse gas and is an air pollutant responsible for several billion euros in lost plant productivity each year. Surface O3 has doubled since 1850 due to chemical emissions from vehicles, industrial processes, and the burning of forests. While land ecosystems (primarily forests) are currently slowing down global warming by storing about a quarter of human-released carbon dioxide (CO2) emissions, this could be undermined by rising O3 concentrations impacting forest growth. This in turn would result in more CO2 left in the atmosphere adding to global climate change. Tropical rainforests are responsible for nearly half of global plant productivity and it is in these tropical regions that we are likely to see the greatest expansion of human populations this century. For example, Manaus, in the centre of the Amazon rainforest has seen a population boom in the last 25 years, with the number of residents doubling to just over 2 million people. Alongside this growing population, we see the expansion of O3 precursor emissions from urbanization and high-intensity agricultural areas. The global impacts of changing air pollution on tropical forests are potentially profound. In his seminal work in 2007, PI Sitch and colleagues at the Met Office and Centre for Ecology and Hydrology, were the first to identify the large potential risk to tropical forests from O3 pollution, and how that could in turn accelerate global warming. However, their study presented two major challenges for the research community: 1) the scale of this effect is highly uncertain; as their global modelling study was based on extrapolating plant O3 sensitivity data from temperate and boreal species. This project will address this by providing the first comprehensive set of measurements of O3 effects on plant functioning and growth in tropical trees. Also, as both O3, CO2 and H2O are exchanged between the atmosphere and leaves through a plants stoma, higher levels of CO2 provide plants the opportunity to reduce their stomatal opening, which in turn leads to reduced O3 uptake and damage. This project will for the first time investigate the potential synergistic or antagonistic impacts of climate change (CO2 and Temperature) on O3 responses in tropical forest species. 2) a fundamental challenge in all global vegetation modelling is to accurately represent the structure and function of highly biodiverse ecosystems; global models are generally only able to represent a limited set of generalized plant functional types (e.g. evergreen trees, C4-grasses etc). However, recent collection and synthesis of plant functional trait data (e.g. leaf nutrient concentrations, leaf size and shape) have enabled improved representation of ecology and plant function in global models. A group of scientists, including project partner Johan Uddling, have very recently proposed a unifying theory for O3 sensitivity in temperate and boreal tree species based upon leaf-functional traits. We are in a unique position to take this work forward to test the theory in tropical forest species, and to test the implications of this at the regional and global scale. The inclusion of the relationship between O3 sensitivity and basic plant functional traits in our global vegetation model, JULES (Joint UK Land Environmental Simulator), will lead to a step-change in our ability to assess the impact of air quality on tropical forest productivity and consequences for carbon sequestration. The model will be applied at O3 hotspot locations in tropical forests and together with observed plant trait information and O3 concentrations we will be able to extrapolate beyond the single plant functional type (PFT) paradigm. Global runs of JULES will also enable us to investigate the implications of future O3 concentrations, changes in land-use, and climate change scenarios on the tropical forest productivity and the global carbon sink.

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