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- Aerogel cathodes for electrochemical CO2 reduction [Comunicação oral]Publication . Messias, Sofia; Fialho, Maria T.; Paninho, A. B.; Branco, Luis C; Nunes, A. V. M.; Martins, Rodrigo; Mendes, Manuel Joao; Nunes, D.; Rangel, C. M.; Machado, AnaABSTRACT: Electrochemical reduction of carbon dioxide powered by renewable energy to produce fuels and chemicals is a technology with potential to contribute to an economy based on a carbon neutral cycle. The development of cost effective, highly active and stable catalysts for CO2 electroreduction is being intensively researched. This work addresses the development of aerogel supported copper-zinc bimetallic catalysts[1]. Aerogels are substances with exceptional properties with many current and potential applications [2-3]. Due to their high surface area, stability in corresponding gaseous or liquid phases, transport through large meso and macropores they are especially suited as catalysts and carrier materials for catalysis and, when electric conductive for electro-catalysis. Aerogels prepared by the sol gel method and impregnated with metallic particles will be tested as cathodes for the co-electrolysis of CO2 and water to produce syngas at temperatures near room temperature and high-pressure. In this way this process can be directly coupled to other high pressure processes, such as Fischer-Tropsch that use high pressure syngas as raw material. Productivities and faradaic efficiencies will be evaluated. The characterization of the aerogel-based cathodes will be undertaken by surface analysis techniques. BET surface areas will be determined. The catalytic cathodes will be tested in an ionic liquid-based electrolyte as a way to increase current densities, due to the high CO2 solubilities exhibited by some ionic liquid families.
- Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for PhotovoltaicsPublication . Centeno, Pedro; Alexandre, Miguel; Neves, Filipe; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel JoaoABSTRACT: he inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 m ohm center dot cm to 17.4 ohm center dot cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.
- Tuning cathode porosity for electrochemical reduction of CO2 at high pressure [Resumo]Publication . Messias, Sofia; Fialho, Maria T.; Paninho, A. B.; Nunes, A. V. M.; Branco, Luis C; Nunes, D.; Martins, Rodrigo; Mendes, Manuel Joao; Rangel, C. M.; Machado, AnaABSTRACT: The development of active and stable catalytic cathodes is critical for advancing electrochemical carbon dioxide reduction into fuels and chemicals from Lab to market. This is a technology with a high potential to contribute to combat climate changes by using captured CO2, water and renewable energy [1]. The use of pressures higher than atmospheric pressure to carry out the co-electrolysis of CO2 and water has been recognized as an important process intensification parameter to increase productivities and energy efficiency [2]. Ongoing work addresses the preparation of aerogels by the sol gel method and impregnation with zinc and copper metallic particles to be used as cathodes for the co-electrolysis of CO2 and water to produce syngas at temperatures near room temperature and high-pressure. Ionic liquid-based electrolytes are used to increase CO2 concentration at the surface of the electrode and consequently productivities, as some ionic liquid families are known to solubilize high amounts of CO2. Aerogels have been investigated for many different applications including as catalyst supports, due to their high surface area, stability in gaseous or liquid phases, and efficient transport through large meso and macropores. The present work reports a strategy to tune the pore sizes of the catalytic electrodes by the use of reticulating agents and supercritical CO2 drying. Productivities and faradaic efficiencies of the porous materials with the different reticulating agents are compared and interpreted in respect to their surface characterization e.g. BET surface areas and morphologies determined by SEM. The potential of new aerogel-based catalytic cathodes on the efficiency of the electrochemical CO2 reduction will be discussed and its impact in fostering supercritical fluids technology through its use in processes for the mitigation of climate changes.
- Estratégias fotónicas para fotovoltaico : novos avanços para além da óticaPublication . Mendes, Manuel Joao; Sanchez-Sobrado, O.; Haque, S.; Centeno, Pedro; Alexandre, Miguel; Ribeiro, Guilherme; Boane, J.; Mateus, T.; Mouquinho, Ana; Menda, U.D.; Águas, H.; Fortunato, Elvira; Martins, RodrigoRESUMO: Estruturas fotónicas com tamanhos comparáveis aos comprimentos de onda da luz solar são as soluções preferenciais para melhorar a eficiência de dispositivos fotovoltaicos através de aprisionamento de luz. As micro-estruturas fotónicas aqui desenvolvidas operam no regime de ótica de ondas, pelo que foram construídos modelos eletromagnéticos que permitiram encontrar os parâmetros ótimos para aplicação no contacto frontal de diferentes tipos de tecnologias, nomeadamente em células de filme fino baseadas em silício ou perovskite. Desta forma, foram obtidas diferentes arquiteturas fotónicas de células, demonstrando melhoras de até 50% na eficiência relativamente a células de referência planas. Os resultados mostram que as vantagens da aplicação de estruturas fotónicas não estão só limitadas a ganhos óticos de melhora da absorção, mas também possibilitam outros benefícios importantes tais como: ganhos elétricos devido à melhora dos contactos transparentes, e melhor desempenho em condições ambientais devido a um encapsulamento avançado dos dispositivos que confere até propriedades de auto-limpeza dos mesmos.
- LocalEnergy: Local Resources for Multifunctional Tetrahedrite-based Energy: Harvesting ApplicationsPublication . Neves, Filipe; Correia, J.B.; Esperto, Luís; Mascarenhas, João; Figueira, Isabel; de Oliveira, Daniel Pipa Soares; Salgueiro, Rute; Silva, Teresa; Santos, Beatriz; Lopes, E.B.; Gonçalves, António Pereira; Centeno, Pedro; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel Joao