Highly Efficient Solar Water Splitting from Transferred TiO₂ Nanotube Arrays

Abstract

We report a synergistic effect of flame and chemical reduction methods to maximize the efficiency of solar water splitting in transferred TiO2 nanotube (TNT) arrays on a transparent conducting oxide (TCO) substrate. The flame reduction method (>1000 °C) leads to few oxygen vacancies in the anatase TNT arrays, but it exhibits unique advantages for excellent interfacial characteristics between transferred TNT arrays and TCO substrates, which subsequently induce a cathodic on-set potential shift and sharp photocurrent evolution. By contrast, the employed chemical reduction method for TNT arrays/TCO gives rise to an abrupt increase in photocurrent density, which results from the efficient formation of oxygen vacancies in the anatase TiO2 phase, but a decrease in charge transport efficiency with increasing chemical reduction time. We show that flame reduction followed by chemical reduction could significantly improve the saturation photocurrent density and interfacial property of TNT arrays/TCO photoanodes simultaneously without mechanical fracture via the synergistic effects of coreducing methods.

Emission Properties Related to Distinct Phases of Sol-Gel Dip-Coating Titanium Dioxide, and Carrier Photo-Excitation in Different Energy Ranges

“…TiO 2 thin films also are frequently obtained by chemical vapor deposition (CVD) 16 and spray pyrolysis deposition (SPD) 17 . More recently, TiO 2 have been produced in the form of nanotubes 18 , and there have been reports on the growth of nanotube films ordered by anodization 19 , because with this highly ordered arrangement the electron mobility can be improved 20 . Electrical properties such as resistivity, are changed considerably due to the thermal oxidation or reduction of the films, which shows that the concentration of charge carriers in the thin film is dependent on non-stoichiometry 21 .…”

Multi-Scale-Porosity TiO2 scaffolds grown by innovative sputtering methods for high throughput hybrid photovoltaics

“…TiO 2 –based 1D nanostructures are especially appealing to combine the advantages of exposing large active facets12 with good mechanical performances and high electrical conductivity3. All those properties enrich 1D-TiO 2 architectures with a transversal empowering for energy, health, and environment applications, since they can be efficiently used as scaffold for Dye4 and Perovskites Solar Cells5, anodes for Li batteries6, electrodes for water splitting devices7, materials for biosensors detecting DNA8 or glucose3, scaffold for gas sensing910, and scaffold for photo-catalysis1112.…”

Directly Photoexcited Oxides for Photoelectrochemical Water Splitting

“…The most studied examples are TiO 2 , [133,135,136] ZnO, [137][138][139][140] SrTiO 3 , [141,142] andT a 2 O 5 , [143,144] which have E G values between 3.0 and 3.9 eV.I nt he case of TiO 2 ,d ue to the large E G ,t he theoretical STH efficiency is about 1%,a ccording to the Shockley-Queisserl imit. The most studied examples are TiO 2 , [133,135,136] ZnO, [137][138][139][140] SrTiO 3 , [141,142] andT a 2 O 5 , [143,144] which have E G values between 3.0 and 3.9 eV.I nt he case of TiO 2 ,d ue to the large E G ,t he theoretical STH efficiency is about 1%,a ccording to the Shockley-Queisserl imit.…”

“…As the main focus of older water photocatalysis and PEC research,w ide E G metal oxidesh ave provided researchers with an important and accessible platform for studying preparation methods, devices,a nd the electrochemical properties of semiconductors. The most studied examples are TiO 2 , [133,135,136] ZnO, [137][138][139][140] SrTiO 3 , [141,142] andT a 2 O 5 , [143,144] which have E G values between 3.0 and 3.9 eV.I nt he case of TiO 2 ,d ue to the large E G ,t he theoretical STH efficiency is about 1%,a ccording to the Shockley-Queisserl imit. [145,146] (Figure 6a).…”