Photo-electrochemical water-splitting is one of the most promising technologies for the sustainable production of hydrogen by solar energy. In this thesis, a wide literature overview on the photo-anodes electronic properties is given and, in particular, the existing methodologies to improve their performance are investigated. The study is focused on high hierarchical nanostructured TiO2, which is the most used material for this application, synthetized with two different techniques. First of all, a “treelike” nanostructured samples, synthetized with the Pulsed Laser Deposition technique by the Laboratory of Micro and Nanostructured Materials, has been examined. At a later stage, a different type, with a nanotubular structure, has been created via the anodic oxidation process. These nanostructures have been studied as innovative systems in photo-electrochemical water-splitting applications. All the samples, after an annealing essential process for the crystalline transition, have been first characterized with SEM, Raman and UV/VIS/NIR analysis and later tested as photo-anode in a Photo-Electrochemical Cell (PEC). The goals of this thesis are: - the evaluation of the nanostructured photo-anode activity in the water-splitting reaction when irradiated with all the solar spectrum; - the evaluation of the stability and reproducibly of those samples; - the analysis, for the “treelike’ samples, of the atmosphere and pressure deposition effect and the influence of the annealing process atmosphere and period on both the morphological-structural properties and the photo-catalytic performances; - the analysis, for the nanotubular samples, of the operative conditions consequence (anodization time, electrolyte, voltage and magnetic stirring) on both the morphological-structural properties and the photo-catalytic performances. The nanostructured systems investigated were found to be active in water-splitting application, with conversion efficiencies in the range of 0.05÷1%. These values are comparable with the results reported in literature and they also confirm the ability of these systems to absorb the UV range more.
Il water-splitting foto-elettrochimico è una delle tecnologie più promettenti per la produzione sostenibile di idrogeno mediante energia solare. Nel seguente lavoro di tesi è riportata, in primo luogo, un’ampia panoramica della letteratura relativa alle proprietà elettroniche dei foto-anodi e alle metodologie per incrementarne le prestazioni. Lo studio ha quindi riguardato sistemi nanostrutturati a base di TiO2, il materiale più utilizzato in applicazioni foto-catalitiche, preparati mediante due diverse tecniche. In primo luogo si sono indagati i campioni aventi una struttura di tipo gerarchico “ad albero” preparati tramite Pulsed Laser Deposition (PLD) in collaborazione con il Laboratorio di Materiali Micro e Nanostrutturati. Successivamente, si è deciso di sintetizzare una diversa classe di campioni aventi una struttura nanotubolare, mediante un processo di ossidazione anodica. Tali nanostrutture sono state quindi studiate come sistemi innovativi per il water-splitting foto-elettrochimico. Tutti i campioni, a seguito del processo di calcinazione necessario per ottenere la fase cristallina, sono stati prima caratterizzati tramite analisi SEM, Raman, UV/VIS/NIR e poi testati come foto-anodi in una cella foto-elettrochimica (PEC). Gli obiettivi del seguente lavoro di tesi sono stati: - valutare l’attività dei sistemi nanostrutturati preparati come foto-anodi nella reazione di water-splitting quando irradiati con l’intero spettro solare; - valutare la stabilità e riproducibilità nel tempo di tali campioni; - analizzare, per i campioni preparati tramite PLD, l’effetto dell’atmosfera e della pressione di deposizione e successivamente l’influenza della durata e dell’atmosfera di calcinazione sulle prestazioni dei sistemi e sulle loro proprietà morfologico-strutturali; - analizzare, per i campioni preparati tramite ossidazione anodica, l’effetto delle variabili operative di sintesi (tempo di anodizzazione, elettrolita, voltaggio di cella e omogeneità di soluzione) sulle proprietà morfologico-strutturali e sulle performance foto-catalitiche. I sistemi nanostrutturati studiati sono risultati attivi per la reazione di water-splitting con efficienze di conversione comprese nel range di 0.05÷1%. Tali valori sono confrontabili con i risultati di letteratura e confermano la capacità di tali sistemi di assorbire preferenzialmente nel campo di luce ultravioletta.
Sistemi nanostrutturati a base di biossido di titanio per il water splitting foto-elettrochimico
OSIO, ARIANNA FRANCESCA;GROSSETTI, GAIA
2014/2015
Abstract
Photo-electrochemical water-splitting is one of the most promising technologies for the sustainable production of hydrogen by solar energy. In this thesis, a wide literature overview on the photo-anodes electronic properties is given and, in particular, the existing methodologies to improve their performance are investigated. The study is focused on high hierarchical nanostructured TiO2, which is the most used material for this application, synthetized with two different techniques. First of all, a “treelike” nanostructured samples, synthetized with the Pulsed Laser Deposition technique by the Laboratory of Micro and Nanostructured Materials, has been examined. At a later stage, a different type, with a nanotubular structure, has been created via the anodic oxidation process. These nanostructures have been studied as innovative systems in photo-electrochemical water-splitting applications. All the samples, after an annealing essential process for the crystalline transition, have been first characterized with SEM, Raman and UV/VIS/NIR analysis and later tested as photo-anode in a Photo-Electrochemical Cell (PEC). The goals of this thesis are: - the evaluation of the nanostructured photo-anode activity in the water-splitting reaction when irradiated with all the solar spectrum; - the evaluation of the stability and reproducibly of those samples; - the analysis, for the “treelike’ samples, of the atmosphere and pressure deposition effect and the influence of the annealing process atmosphere and period on both the morphological-structural properties and the photo-catalytic performances; - the analysis, for the nanotubular samples, of the operative conditions consequence (anodization time, electrolyte, voltage and magnetic stirring) on both the morphological-structural properties and the photo-catalytic performances. The nanostructured systems investigated were found to be active in water-splitting application, with conversion efficiencies in the range of 0.05÷1%. These values are comparable with the results reported in literature and they also confirm the ability of these systems to absorb the UV range more.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/112554