Towards Artificial Photosynthesis: Photoelectrochemical CO2 Reduction to Solar Fuels
This thesis is devoted to prove the concept of the CO(2) reduction to CH(4) with a decreasing in the voltage requirements using a photocatalytic mechanism. Subsequently, part of the solar energy is transferred to the reaction, obtaining an improvement in the total energy balance. The work developed...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2015 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/347965 |
| Acceso en línea: | http://hdl.handle.net/10803/347965 |
| Access Level: | acceso abierto |
| Palabra clave: | Electroquímica Electrochemistry Fotocatàlisi Fotocatálisis Photocatalysis Diòxid de carboni Dióxido de carbono Carbon dioxide Fotosíntesi Fotosíntesis Photosynthesis Ciències Experimentals i Matemàtiques 546 |
| Sumario: | This thesis is devoted to prove the concept of the CO(2) reduction to CH(4) with a decreasing in the voltage requirements using a photocatalytic mechanism. Subsequently, part of the solar energy is transferred to the reaction, obtaining an improvement in the total energy balance. The work developed intends first, to take advantage of the know features of the photoactive nanostructured materials obtained by anodization and hydrothermal synthesis (allowing to obtain better surface areas and improving the photon collection, light photosynthetic reactions). Second investigate the copper and copper oxide cathodes for the CO(2) electroreduction activity to CH(4) (dark photosynthetic reactions) using a complete cell to understand the parameters involved in the process and the products selectivity for each cathodes. And third the implementation of the photoanode and cathode in a photoelectrochemical complete cell. Respect the photoactive materials we are going to talk about TiO(2) based nanostructured materials for water splitting. The first TiO(2) nanostructuration under study are nanotubes obtained by anodization of a Titanium foil using organic electrolytes. The TiO(2) crystal phase obtained by this technique was anatase. The next step in this material was the surface modification to improve the efficiency. To obtain this improvement the anodization process was done using two electrolytes in different steps. As sequence a porous surface with an increment in the surface area was obtained. After, the photoelectrochemical measurements were done in 1 M of sodium hydroxide (NaOH) under AM 1.5G illumination source to observe the photoactivity of these samples. The second nanostructured materials under study were TiO(2) nanorods obtained by hydrothermal synthesis over a conductive glass substrate, Fluorine Tin Oxide (FTO). The nanorods using this technique have rutile structure. An optimization of two parameters involved in the hydrothermal synthesis was studied: (1) initial titanium precursor concentration and (2) increasing the chlorine concentration to obtain larger and thinner rods. To enhance the photoactivity of TiO(2) we try to incorporate other materials inside the structure. The materials selected were: tin which improves the charge carriers, vanadium which allows the absorption in the visible range and nitrogen doping to enhance the efficiency in the photoactivity of the material. Concerning to methane production study, a discussion about the electrochemical CO(2) reduction activity over a copper based electrode using a hydrogen carbonate as supporting electrolyte was done, where the positive ions used are sodium and potassium. The first electrode selected is a pristine copper due to the interest of the methane production. The samples were characterized by scanning electronic microscopy (SEM) and X-Ray diffraction (XRD) to visualize the surface morphology and the crystal structure of the electrode. Afterwards, the electrochemical process is studied to understand the activity of these electrodes. Chronopotentiostatic (CP) experiments were done at different current densities to observe the activity as a function of the reached potential. The second electrode under study was a copper oxide cathode. In the electrochemical experiments an effect was studied related to the electrochemical reduction of the different copper oxide layers generated during the thermal synthesis, leading to a catalytically active copper that enables carbon dioxide reduction. With this type of electrodes a time- dependence test was done to carefully study these crystallographic changes. Finally, another important variable for CO(2) conversion was studied, the humidification of the CO(2) gas stream before the introduction in the electrochemical cell with the impact on the faradaic efficiency of the process. In the implementation in the PEC cell an evaluation of the photoanode and cathode was done. In this evaluation, the external potential requirements were studied concerning about the energy consumption and the benefit from the photoactivated process. |
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