The present study aims to produce a nanostructured hierarchical photoanode, made by different materials: TiO2, FeOOH and NiOOH, that can be applied for water splitting applications. The nanostructured TiO2 has the function of light absorber, it is a non-toxic, earth abundant n-type semiconductor, with a large band gap of 3.1 eV. In the first part of the work, it is reported an optimization of the hydrothermal synthesis of the TiO2: starting from a solution containing 0.3 ml of titanium n-butoxide and 10 ml of deionized water and hydrochloric acid, it is maintained at 150 °C and high pressure for 5 hours, as result a nanorods array grow on the surface of the FTO substrate, then are annealed in air at 500 °C for 30 minutes. The photoanodes properties were analyzed through XRD, SEM, Raman, XPS, ICP and LSV analysis, has been found a highly oriented crystalline structure that is able to produce around 0.7 mA/cm2 at 1.23 V vs RHE. In order to improve the efficiency of the photoanode a hydrogenation treatment has been executed maintaining the samples at 350 °C for 30 minutes in a hydrogen rich atmosphere, in this way the photoactivity of the material is increased, obtaining 1 mA/cm2 at 1.23 V vs RHE. The hydrogenation treatment does not modify the morphological structure of the samples, but increase the photoluminescence, as showed by the raman spectra, XPS analysis shows a slight reduction of the bandgap and formation of a valence band tail. Then on the hydrogenated TiO2 nanorods FeOOH and NiOOH has been photodeposited, obtaining a hierarchical structure: H:TiO2/FeOOH/NiOOH. The iron and nickel oxyhydroxides have been photodeposited using 0.005 M solutions of FeSO4 and NiSO4 respectively and applying on the samples +0.250 and +0.300 V vs Ag/AgCl respectively. FeOOH and NiOOH are two materials particularly resistant to photocorrosion that act as catalysts for oxygen evolution. Different improvements were obtained: photoluminescence has been reduced obtaining an increase of the efficiency, photoelectrochemical curve has been shifted toward more negative potentials, almost no degradation during prolonged test.
Il presente studio mira a produrre un fotoanodo nanostrutturato, realizzato con diversi materiali: TiO2, FeOOH e NiOOH, che possa essere utilizzato per applicazioni di scissione dell'acqua. Il TiO2 nanostrutturato ha il compito di assorbire la luce, esso è un semiconduttore di tipo n, non tossico e abbondante sulla terra, con un ampio band gap di 3,1 eV. Nella prima parte del lavoro, è riportata l'ottimizzazione della sintesi idrotermica del TiO2: una soluzione contenente 0,3 ml di n-butossido di titanio e 10 ml di acqua deionizzata e acido cloridrico, viene mantenuta a 150°C e ad alta pressione per 5 ore, di conseguenza avviene la crescita ordinata delle nanobacchette sulla superficie del substrato FTO, quindi viene ricotto in aira a 500 ° C per 30 minuti. Le proprietà del fotoanodo sono state analizzate mediante XRD, SEM, Raman, XPS, ICP e LSV, è stata trovata una struttura cristallina altamente orientata in grado di produrre circa 0,7 mA/cm2 a 1,23 V vs RHE. Per aumentare l'efficienza il fotoanodo è stato eseguito idrogenato mantenendo i campioni a 350 ° C per 30 minuti in un'atmosfera ricca di idrogeno, in questo modo la fotoattività del materiale viene aumentata, ottenendo 1 mA/cm2 a 1,23 V vs RHE. Il trattamento di idrogenazione non ha modificato la struttura morfologica dei campioni, ma ne ha aumentato la fotoluminescenza, come mostrato dagli spettri raman, mentre l'analisi XPS ha mostrato una leggera riduzione del band gap e la formazione di una coda nella banda di valenza. Quindi sulle nanobacchette di TiO2 idrogenata sono stati fotodeposti FeOOH e NiOOH, ottenendo una struttura gerarchica: H:TiO2/FeOOH/NiOOH. Gli ossidrossidi di ferro e nichel sono stati fotodeposti usando rispettivamente una soluzione 0,005 M di FeSO4 e NiSO4 e applicando sui campioni +0,250 e +0,300 V vs Ag/AgCl. FeOOH e NiOOH fungono da catalizzatori per l'evoluzione dell'ossigeno, inoltre sono due materiali particolarmente resistenti alla fotocorrosione. Sono stati ottenuti diversi vantaggi: la fotoluminescenza è stata ridotta aumentando l’efficienza, la curva fotoelettrochimica è stata spostata verso potenziali più negativi, assenza di degradazione in test prolungati.
Titanium dioxide-based photoanode for water splitting application
PANZERI, ALBERTO
2018/2019
Abstract
The present study aims to produce a nanostructured hierarchical photoanode, made by different materials: TiO2, FeOOH and NiOOH, that can be applied for water splitting applications. The nanostructured TiO2 has the function of light absorber, it is a non-toxic, earth abundant n-type semiconductor, with a large band gap of 3.1 eV. In the first part of the work, it is reported an optimization of the hydrothermal synthesis of the TiO2: starting from a solution containing 0.3 ml of titanium n-butoxide and 10 ml of deionized water and hydrochloric acid, it is maintained at 150 °C and high pressure for 5 hours, as result a nanorods array grow on the surface of the FTO substrate, then are annealed in air at 500 °C for 30 minutes. The photoanodes properties were analyzed through XRD, SEM, Raman, XPS, ICP and LSV analysis, has been found a highly oriented crystalline structure that is able to produce around 0.7 mA/cm2 at 1.23 V vs RHE. In order to improve the efficiency of the photoanode a hydrogenation treatment has been executed maintaining the samples at 350 °C for 30 minutes in a hydrogen rich atmosphere, in this way the photoactivity of the material is increased, obtaining 1 mA/cm2 at 1.23 V vs RHE. The hydrogenation treatment does not modify the morphological structure of the samples, but increase the photoluminescence, as showed by the raman spectra, XPS analysis shows a slight reduction of the bandgap and formation of a valence band tail. Then on the hydrogenated TiO2 nanorods FeOOH and NiOOH has been photodeposited, obtaining a hierarchical structure: H:TiO2/FeOOH/NiOOH. The iron and nickel oxyhydroxides have been photodeposited using 0.005 M solutions of FeSO4 and NiSO4 respectively and applying on the samples +0.250 and +0.300 V vs Ag/AgCl respectively. FeOOH and NiOOH are two materials particularly resistant to photocorrosion that act as catalysts for oxygen evolution. Different improvements were obtained: photoluminescence has been reduced obtaining an increase of the efficiency, photoelectrochemical curve has been shifted toward more negative potentials, almost no degradation during prolonged test.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/152029