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European School on Artificial Leaf : Electrodes Devices

Periodic Reporting for period 1 - eSCALED (European School on Artificial Leaf : Electrodes Devices)

Reporting period: 2018-04-01 to 2020-03-31

Climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. Artificial photosynthesis appears to be an appealing approach for a sustainable energy generation as it produces “solar fuels” or commodities for chemistry in a stable and storable chemical form, from solar energy, H2O & CO2.
The eSCALED project is a contribution to structure early-stage research training at the European level and strengthen European innovation capacity to elaborate an artificial leaf. The ESR will be in charge of combining in a unique device a solar cell and a bioinspired electrochemical stack where H2O oxidation and H+ or CO2 reduction are performed in microreactors.
The novelties in this project are at two levels: (1) Developing sustainable joint doctoral degree structure based on inter/multidisciplinary aspects of biological/biochemical, condensed, inorganic & soft matter to device engineering and innovation development. (2) Scientifically using, cheap and easy processes tandem organic solar cells, earth-abundant materials for water splitting, new generation of catalysts and natural/artificial hydrogenase enzymes for hydrogen production, formate dehydrogenases for catalytic carbon dioxide reduction, new proton-exchange fluorinated membranes and finally, electrode micro porosity to mimic the chloroplasts of a plant. The eSCALED collaborative project brings together for the first time, 12 internationally recognized academic and industrial research groups. The project has an interdisciplinary scientific approach integrating the latest knowledge on catalysis, photovoltaic and polymer chemistry for self-structuration. Major outcomes will include breakthroughs in the development of artificial photosynthetic leaf as a photoelectrochemical device, highly trained researchers & new partners collaborations.
The scientific progress of the project is advancing in the expected timing

Water Oxidation catalysts: a number of synthetic strategies have been developed for the preparation of MOFs based on Ru-tda water oxidation catalyst complexes, properly functionalized with axial pyridyl ligands containing carboxylic groups and ZrOx. In addition, a thorough spectroscopic characterization of reactive intermediates related to the WO catalyst based on Cu and tetra-amidate ligands has been carried out using fast transient absorption spectroscopy methods.

Reductive Catalysis: preparation of derivatized molecular catalysts with proper anchoring groups and their immobilization on porous electrode supports. Catalysts for H2 evolution include cobalt macrocycles and diiron mimics of FeFe hydrogenases and CO2-reducing catalyst are organometallic Rhenium and rhodium complexes as well as Ni(cyclam) complexes. In parallel semi-artificial hydrogenases have been developed and chracterized.

Synthesis of novel materials:
*light harvesting material, synthesis of perovskites nanocrystals (NCs) has been developed following two different methods to make solution processable CsPbBr3 nanocrystals, obtaining good quality CsPbBr3 nanocrystals able to disperse in common organic solvents.
*electrode: materials have been developed thinking of three different strategies, depending on the position of the electrodes relative to the membrane. Different polymers have been synthetized for every strategy, and they have been modified in order to include reactive groups that can anchore the catalysts.
*membranes: For the polyelectrolytes, sulfonation of poly(pentafluorostyrene) has been optimized to obtain control on the degree of sulfonation and suppress crosslinking side reactions. Related new statistical copolymers have been successfully obtained via emulsion polymerization and fully characterized.

Deposition of systems: single junction solar cells have been developed; through the optimization of the processing of p-i-n photovoltaic cells based on solution processed CsPbBr3 nanocrystals. The cells have been evaluated by measuring current density – voltage characteristics under simulated solar light and external quantum efficiency. For the electrodes, novel formulations of the new synthesized polymers have been screen printed and honeycomb structures have been induced, obtaining porous electrodes. The printed porous materials present sufficient electric conductivity to work as electrodes. These have been tested by cyclic voltammetry.

The specifications of all systems have been updated. For the novel device, an evaluation of the materials deposition process for the up-scaling of the device has been performed. Different printing techniques such as Dr. Blade,screen and inkjet printing have been used for the deposition of the structure electrodes/membrane using commercial materials. For the electrodes the MBM/graphite blend has been used and Nafion solution for the membrane. The characterization of the rheological properties of the materials has been also done during this period, including the PPFS copolymer characterization. Moreover, the integration of alternative membranes on the Gas diffusion layer has been performed, developing an innovative integration process. Furthermore, first LCA and LCC studies have started on water oxidation catalysts, membranes and the whole system.
To answer the general objectives the eSCALED project is envisioned as 4 years project in which each partner will use their skills and knowledge to get to the following specific objectives:
• Synthesis and characterization (chemical, structural and electrochemical) of ordered mesoporous electrodes that must: 1) be easily processable and up scalable 2) present a high stability under oxidative conditions 3) reach a high proton conductivity and 4) present surface functional groups able to bind the catalyst
• Synthesis and characterization of efficient heterogeneous catalysts as nanoparticles
• Synthesis and characterization of efficient homogeneous catalysts with improved stability under turnover and intrinsic activity in terms of overpotential requirement and turnover frequency under technologically relevant conditions. Functionalization of these catalysts with groups that allow anchoring them on electrode surfaces.
• Processing of the catalyst onto the electrodes. Characterization and optimization of electro-catalytic properties
• Development of organic and perovskite solar cells to drive reduction/oxidation reactions using the catalytic electrodes. The solar cells will be designed specifically to have its maximum power point at the voltage that is defined by the standard and overpotentials of the catalysts and the surface area. For this purpose new tailored semiconductor materials will be developed.
• Proof-of-concept. Water splitting under applied bias using the catalytic electrodes.
• Fabrication of integrated light driven and self-sustained water oxidation/CO2 reduction devices using materials and conversion concepts from eSCALED. Determine efficiency and stability.
• Life cycle analysis of catalysts, electrodes and membranes upscaled production leading to their final assembly.

Moreover, to better face the challenges of the Renewable Energies field, eSCALED training network will give the ESRs a multi/transdisciplinary cross-national preparation broadening their frontiers for the working environment.
Artificial photosynthesis device schema