The world need for energy is growing with its population and technological improvement. The expected future developments are of an even larger energy intake. Even if the non-renewable sources are, up to now, the larger energy source, a lot of research has been performed in the direction of the so called “clean fuels”. One of the best candidates in this direction is hydrogen. Hydrogen is massively present on earth in the form of water and other organic compounds. Even if hydrogen itself is not a sustainable energy source, it can be produced using renewable ones, therefore it can be considered an effective way of storing clean energy. Nowadays, solar energy generation and processes where solar energy is involved are the most widespread. The process of generating hydrogen using a photo-current is called photo-electrochemical water-splitting. In this process, water and light, two renewable sources, are the only reactants and, thus, it can be defined a clean process. Since 1972, TiO2, an n-type semiconductor, was used as photo-catalyst. TiO2, however, is characterized by a band-gap which restricts its use only to part of UV solar spectrum, and a lot of researches are ongoing, nowadays, to improve its photocatalytic efficiency. In this thesis work, the production of a photoanode consisting of metal Ti slabs coated with a thin layer of TiO2 (Degussa P25) is assessed. A cheap and simple deposition technique for the oxide layers, i.e. dip-coating, was studied and experienced. Since the thickness of layer deposited via dip-coating is related to the viscosity of the starting slurry, a qualitative and quantitative study on the slurry composition was performed. Accordingly, TiO2 slurry was properly formulated to obtain homogeneous and thin layers. Moreover, thermal treatment was also considered and tailored to reduce the unavoidable cracking phenomenon during layer consolidation. Final layer morphology was analyzed by SEM and/or optical microscopy to evaluate the quality of the coating. Specimens of photoanodes with oxide layers of different thickness were tested in a photo-electrochemical cell. It was proved that current densities and efficiencies are related to the layer thickness. Namely, thinner TiO2 oxide layers, highly homogeneous and lowly cracked, are best performing, presenting higher current densities and efficiencies comparable with reported literature data for samples prepared via more complex and expensive routes.
Il fabbisogno energetico mondiale sta crescendo in funzione dell’aumento demografico e dell’avanzamento tecnologico. Nonostante i combustibili fossili siano, ad oggi, la fonte principale di approvvigionamento energetico, i cosiddetti “clean fuels” sono oggetto di ricerche approfondite. Uno dei più importanti componenti della suddetta categoria è l’idrogeno. Sebbene l’idrogeno non sia, di per sé, una fonte di energia rinnovabile, può essere prodotto utilizzando energia pulita, immagazzinandola in maniera efficace. L’energia solare è la principale sorgente di energia pulita e il processo di produzione di idrogeno, mediante l’utilizzo di una foto-corrente, viene chiamato “water-splitting fotoelettrochimico”. Dal 1972, il biossido di titanio (TiO2), un semiconduttore di tipo n, è conosciuto per il suo utilizzo come foto-catalizzatore. Esso, tuttavia, è caratterizzato da un band-gap che ne limita l’assorbimento ad una frazione dello spettro solare, e, per questo motivo, molte ricerche sono in corso per migliorarne l'efficienza foto-catalitica. L’obiettivo di questa tesi è stato la produzione di un foto-anodo costituito da una lamina di titanio rivestita da un sottile strato di TiO2 (Degussa P25). Per depositare lo strato foto-attivo è stata scelta una tecnica di deposizione semplice ed economica, il dip-coating. Essendo lo spessore dello strato depositato mediante dip-coating legato alla viscosità della sospensione di partenza, è stato eseguito uno studio qualitativo e quantitativo sulla composizione sospensione, in modo di ottenere strati omogenei e sottili. Inoltre, il trattamento termico è stato analizzato e studiato in modo da ridurre lo shock termico e i fenomeni di criccatura durante il consolidamento dello strato. La morfologia del coating è stata analizzata mediante SEM e/o la microscopia ottica per valutare la qualità dello stesso. Foto-anodi con strati di ossido di diverso spessore sono stati testati in una cella foto-elettrochimica. È stato dimostrato che le densità di corrente e le efficienze ottenute sono collegate allo spessore dello strato. In sostanza, strati più sottili, omogenei e poco criccati, presentano elevate densità di corrente ed efficienze maggiori, paragonabili con dati di letteratura riportati per i campioni preparati con tecniche di deposizione più complesse e costose.
TiO2 deposition by dip-coating for photo-electrochemical applications
SCANDOLA, LUCIO
2015/2016
Abstract
The world need for energy is growing with its population and technological improvement. The expected future developments are of an even larger energy intake. Even if the non-renewable sources are, up to now, the larger energy source, a lot of research has been performed in the direction of the so called “clean fuels”. One of the best candidates in this direction is hydrogen. Hydrogen is massively present on earth in the form of water and other organic compounds. Even if hydrogen itself is not a sustainable energy source, it can be produced using renewable ones, therefore it can be considered an effective way of storing clean energy. Nowadays, solar energy generation and processes where solar energy is involved are the most widespread. The process of generating hydrogen using a photo-current is called photo-electrochemical water-splitting. In this process, water and light, two renewable sources, are the only reactants and, thus, it can be defined a clean process. Since 1972, TiO2, an n-type semiconductor, was used as photo-catalyst. TiO2, however, is characterized by a band-gap which restricts its use only to part of UV solar spectrum, and a lot of researches are ongoing, nowadays, to improve its photocatalytic efficiency. In this thesis work, the production of a photoanode consisting of metal Ti slabs coated with a thin layer of TiO2 (Degussa P25) is assessed. A cheap and simple deposition technique for the oxide layers, i.e. dip-coating, was studied and experienced. Since the thickness of layer deposited via dip-coating is related to the viscosity of the starting slurry, a qualitative and quantitative study on the slurry composition was performed. Accordingly, TiO2 slurry was properly formulated to obtain homogeneous and thin layers. Moreover, thermal treatment was also considered and tailored to reduce the unavoidable cracking phenomenon during layer consolidation. Final layer morphology was analyzed by SEM and/or optical microscopy to evaluate the quality of the coating. Specimens of photoanodes with oxide layers of different thickness were tested in a photo-electrochemical cell. It was proved that current densities and efficiencies are related to the layer thickness. Namely, thinner TiO2 oxide layers, highly homogeneous and lowly cracked, are best performing, presenting higher current densities and efficiencies comparable with reported literature data for samples prepared via more complex and expensive routes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/133473