Desarrollo y caracterización de nuevos materiales de cátodo basados en aleaciones de níquel para la reacción de evolución de hidrógeno en medio alcalino
[EN] The current energy system, based basically on the use of fossil fuels is a non-sustainable system and the research for new energy alternatives is necessary. Hydrogen is an ideal energy carrier to become the future fuel, creating a new energy system called "Hydrogen Economy". T...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Universitat Politècnica de València (UPV) |
| Repositorio: | RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia |
| Idioma: | español |
| OAI Identifier: | oai:riunet.upv.es:10251/68494 |
| Acceso en línea: | https://riunet.upv.es/handle/10251/68494 |
| Access Level: | acceso abierto |
| Palabra clave: | Economía del hidrógeno Reacción de evolución de hidrógeno Electrólisis alcalina del agua Cátodos basados en aleaciones de níquel Electrocatálisis INGENIERIA QUIMICA |
| Sumario: | [EN] The current energy system, based basically on the use of fossil fuels is a non-sustainable system and the research for new energy alternatives is necessary. Hydrogen is an ideal energy carrier to become the future fuel, creating a new energy system called "Hydrogen Economy". To achieve this aim a method for producing hydrogen in a clean and renewable way is necessary. Alkaline water electrolysis is a simple and proven technology for hydrogen production in a clean and renewable way. However, its low efficiency is a major disadvantage for its widespread use. One of the aspects which causes this low efficiency is the overpotential required for the hydrogen evolution reaction (HER) at the cathode of an electrolysis cell. This overpotential depends on the electrode material, and although there are materials with high catalytic activity for HER, these are based on the use of noble materials such as platinum, whose high cost and scarcity restrain their use on a large scale. In this context, this Doctoral Thesis aims to contribute to the energy efficiency improvement and the cost reduction of alkaline water electrolysis, as a means of hydrogen production, through the development of cathode materials based on nickel, a material more economic and available than the noble metals. With nickel as base material, increasing the catalytic activity of an electrode can be performed basically in two ways: by alloying nickel with other materials in order to obtain a synergistic effect between their catalytic properties or by using electrodes with a high surface area (porous electrodes). In order to combine both strategies to obtain electrode materials more active towards the HER than those commonly employed in industrial alkaline electrolysis, in this Doctoral Thesis, porous electrodes based on nickel and nickel alloys with cobalt and molybdenum have been developed by using two different techniques of high current density electrodeposition. With the first one, macroporous electrodes are obtained by electrodeposition with a dynamic template formed by hydrogen bubbles generated simultaneously to the electrodeposition process. The second technique uses a template of another material, copper, for the desired deposit structure, a tridimensional foam. The surface characterization of the obtained deposits by scanning electron microscopy and confocal laser microscopy has allowed observing the characteristics of the generated deposits by the two different techniques and studying the influence of certain parameters on the formation of the copper template. The developed electrodes have been preliminarily characterized by means of polarization curves steady state and electrochemical impedance spectroscopy (EIS). The EIS technique has permitted us to determine the roughness factor of the fabricated cathodes, a key parameter in electrocatalysis. From the obtained results from both techniques it has been possible to evaluate the intrinsic and apparent catalytic activities and the reaction mechanism. The HER takes place on all the synthesized materials following the Volmer-Heyrovsky mechanism, being the electrochemical desorption the rate determining step. The best cathode materials have been characterized by hydrogen discharge curves and galvanostatic tests in conditions simulating industrial alkaline electrolysis. The use of any of the developed Ni-based porous electrodes alloys with Co and Mo, reduces the energy consumption of hydrogen production compared to smooth commercial nickel electrodes. |
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