Chaotropic Agents Boosting the Performance of Photo-ionic Cells

Photo-ionic cells are a simple and scalable concept for direct solar energy storage, where the redox fuels produced by the photoreaction are separated in different phases to prevent recombination. The presence of chaotropic agents such as urea, that break the structure of water, was found to drastically enhance the quantum yield; a ten-fold increase of quantum yield to over 13 % was achieved by addition of chaotropes into a system based on the reductive quenching of Azure B by Co(II)-EDTA in water and the extraction of the leuco-dye in 1,2-dichloroethane

Artificial Photosynthesis at Soft Interfaces

The concept of artificial photosynthesis at a polarised liquid membrane is presented. It includes two photosystems, one at each interface for the hydrogen and oxygen evolution respectively. Both reactions involve proton coupled electron transfer reactions, and some ultrafast steps at the photosensitization stage

Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

The self-assembly of the oppositely charged watersoluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP4+) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS4−), at the interface with an organic solvent to form molecular “rafts”, provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV−visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP4+/ CoTPPS4− complex and its capability to bind oxygen

Interfacial Self-Assembly as Catalytic Platform for Multielectron Redox Reactions

In Nature, many vital biological processes take place across the interface formed between two dielectric media. For instance, photosynthesis and aerobic respiration involve a series of redox reactions occurring across energy-transducing membranes, in charge of converting the energy released in the exothermic multielectron redox reactions into an electrical potential difference across the membrane that finally drives the synthesis of ATP. Thus, the interface between two immiscible electrolyte solutions (ITIES) is considered a bio-inspired medium that provides electrochemical control of processes as ion transfer, assisted ion transfer and heterogeneous electron transfer. Moreover, the ITIES is recognized as a catalytic platform providing separation of the reactants and products in two different phases making feasible to perform reactions that are thermodynamically unfavorable in homogeneous systems. Self-assembled metalloporphyrins are fundamental units in the biochemical machineries that carry out vital processes in living organisms. For instance, in photosynthesis, magnesium complexes of porphyrins known as chlorophyll and bacteriochlorophylls self assemble to build the functional units that carry out the fundamental steps, light-harvesting and charge separation. Such supramolecular arrangement significantly enhances the catalytic properties of porphyrins. iiThis thesis represents an important contribution to the development of new biomimetic catalysts based on artificial supramolecular architectures able to resemble Nature’s way to address kinetically challenging multielectron reactions that are fundamental in the development of renewable energy devices. Particularly in the case of the four-electron reduction of oxygen, reaction that determines the efficiency of fuel cells and batteries, the development of selective precious metal-free catalysts would contribute to improve considerably the performance and stability of the devices at a relative low cost. The biomimetic catalysts developed in this thesis consist of self-assembled cobalt porphyrins adsorbed at ITIES, where the self assembled system intend to mimic the function of the multi metal complexes in charge of respiration in mitochondria, and the liquid/liquid interface mimics the function of an energy-transducing membrane by providing a media suitable for proton and electron transfer. The systems were found to be highly selective towards the four-electron reduction, opening new projects on interfacial self-assembled systems to catalyze other challenging multielectron reactions, as photo induced hydrogen evolution and water splitting. Considering that in parallel projects our group have successfully employed ITIES to drive important photo induced reactions as hydrogen evolution and water splitting, we have designed and built up a time resolved surface second harmonic generation (TR-SSHG) and sum frequency generation (SFG) setup in order to selectively characterize the behavior of photoactive molecules adsorbed at ITIES upon photoexcitation. This setup is aimed at studying charge and electron transfer between aqueous soluble photocatalysts and/or photosensitizers, and organic soluble electron donors/acceptors

Visible-Light-Driven Water Oxidation on Self-Assembled Metal-Free Organic@Carbon Junctions at Neutral pH

Sustainable water oxidation requires low-cost, stable, and efficient redox couples, photosensitizers, and catalysts. Here, we introduce the in situ self-assembly of metal-atom-free organic-based semiconductive structures on the surface of carbon supports. The resulting TTF/TTF•+@carbon junction (TTF = tetrathiafulvalene) acts as an all-in-one highly stable redox-shuttle/photosensitizer/molecular-catalyst triad for the visible-light-driven water oxidation reaction (WOR) at neutral pH, eliminating the need for metallic or organometallic catalysts and sacrificial electron acceptors. A water/butyronitrile emulsion was used to physically separate the photoproducts of the WOR, H+ and TTF, allowing the extraction and subsequent reduction of protons in water, and the in situ electrochemical oxidation of TTF to TTF•+ on carbon in butyronitrile by constant anode potential electrolysis. During 100 h, no decomposition of TTF was observed and O2 was generated from the emulsion while H2 was constantly produced in the aqueous phase. This work opens new perspectives for a new generation of metal-atom-free, low-cost, redox-driven water-splitting strategies.Fil: Olaya, Astrid Johana. École Polytechnique Fédérale de Lausanne; SuizaFil: Riva, Jullieta Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. École Polytechnique Fédérale de Lausanne; SuizaFil: Baster, Dominika. École Polytechnique Fédérale de Lausanne; SuizaFil: Silva, Wanderson O.. École Polytechnique Fédérale de Lausanne; SuizaFil: Pichard, François. École Polytechnique Fédérale de Lausanne; SuizaFil: Girault, Hubert. École Polytechnique Fédérale de Lausanne; Suiz