Photoelectrochemical Poperties of Anodic TiO2 Nanosponge Layers

Abstract

In the present work we grow TiO 2 nanosponge structures by anodizing Ti in a glycerol/water/NH 4 F electrolyte to thickness of some m. We evaluate the photoelectrochemical behavior (band gap, photocurrent-voltage characteristics) in presence and absence of methanol. Methanol drastically affects the photoresponse (due to hole capture and current doubling). The optimum thickness for photoelectrochemical applications of these nanostructures is dependent on the excitation wavelength. For applications such as solar light water splitting, anodic sponge structure of ≈ 500 nm thickness can be beneficially used to increase the photoresponse compared to compact TiO 2 layers.

Preparation and optimization of TiO2 photoanodes fabricated by pulsed laser deposition for photoelectrochemical water splitting

“…In the latter case, several nanostructured TiO2 networks (e.g. tubes [15][16][17], rods [18][19][20], wires [21,22], sponges [23,24]) emerged as promising materials that can be used as photoanodes in water photoelectrolysis cells. In particular, as summarized in very recent reviews [25][26][27][28][29][30], extensive research has been performed on TiO2 nanotube arrays (T-NTs) because their unique high surface-to-volume ratios (even though not as high as those obtained with nanoparticle assemblies), ordered geometry and tunable morphologies are claimed for fast charge separation and transport, and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 electrolytes in the case of photoelectrochemical solar cells, pollutants or reagents in the case of photocatalysis), and also (iv) anisotropic morphology (similarly to nanotubes or nanowires) to ensure better electron transport towards the electrical contact [31,32].…”

“…In the latter case, several nanostructured TiO2 networks (e.g. tubes [15][16][17], rods [18][19][20], wires [21,22], sponges 23 [23,24]) emerged as promising materials that can be used as photoanodes in water photoelectrolysis cells. In particular,…”

Effect of Reynolds number and lithium cation insertion on titanium anodization

“…The latter has the advantage of removing the "initiation layer" in the same process of anodization and, therefore, other independent processes in order to remove this layer are not needed. Moreover, the use of hydrodynamic conditions can significantly affect on the final TiO 2 nanotube geometry [22,26,27]. After anodization, an amorphous structure is obtained which implies the presence of a high number of defects.…”

The effect of Reynolds number on TiO2 nanosponges doped with Li+ cations

“…Anodization of titanium in fluoride-based electrolytes is other possible method, in fact it is one of the most promising method to synthesize TiO2 nanotubes because it allows obtaining highly ordered nanotube arrays directly grown into the Ti substrate, and their dimensions (length, diameter, and tube wall) can be precisely controlled [40][41][42]. In previous works, the authors showed that under specific anodization in glycerol/water electrolytes and using hydrodynamic conditions, a transition from a TiO2 nanotube morphology (stagnant conditions) to a nanosponge morphology (hydrodynamic conditions) occurs [34,43,44]. These nanosponges provide better performance for water splitting than the tube morphologies obtained in glycerol/water electrolytes [34].…”

“…As an example,Figure 3shows the top surface of the nanostructure formed at Re=600. This nanostructure is called nanosponge and is characterized by a connected and highly porous TiO2 structure[34,43,44].…”