Please cite this article in press as: R. Passalacqua, et al., Use of modified anodization procedures to prepare advanced TiO 2 nanostructured catalytic electrodes and thin film materials, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.11.003 ARTICLE IN PRESS G Model CATTOD-9335; No. of Pages 11 Catalysis Today xxx (2014) xxx–xxx Contents lists available at ScienceDirect Catalysis Today j our na l ho me page: www.elsevier.com/locate/cattod Use of modified anodization procedures to prepare advanced TiO 2 nanostructured catalytic electrodes and thin film materials Rosalba Passalacqua ∗ , Siglinda Perathoner, Gabriele Centi Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina and INSTM/CASPE, V.le F. Stagno d’Alcontres 31, 98166 Messina, Italy a r t i c l e i n f o Article history: Available online xxx Keywords: Nanostructured photoelectrode Titanium dioxide TiO2 nanotubes Photocatalytic devices a b s t r a c t The preparation and characteristics of (i) thin films based on an ordered array of TiO 2 nanotubes (NT) supported on flexible Ti metallic substrate, (ii) free-standing TiO 2 NT thin films and (iii) hedgehog-type TiO 2 thin films are investigated. It is evidenced the possibility of a fine tuning of the nano-architecture in relation to applications going from advanced catalytic (photo)electrodes to nanomembranes requiring different nanostructure for an optimized behavior. In the first type of materials, a key issue determining the resistance to electron transfer and performances is the interface between the TiO 2 NT layer and the metallic substrate. Some aspects of the preparation in controlling nanomorphology and photocurrent generation properties are discussed. In free-standing TiO 2 NT thin films the mechanism of formation of flow-through nanomembranes is analyzed. The possibility of generation of hedgehog-type TiO 2 thin films by etching with HF is also shown, evidencing some of the potential advantage of these catalytic materials, particularly for self-cleaning properties. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Creating and mastering nano-objects to design advanced cat- alytic materials [1–3] is one of the key elements to move to a new sustainable use of energy and to cleaner production processes, because the control of the nano-structure and -architecture is a crit- ical item to improve the performances in catalytic electrodes and materials. The ability to design and synthesize nano-engineered structures as functional building blocks with unusual and valuable properties has opened new perspectives in the construction of electrochemical devices for sustainable production of energy [4–6]. A recent example is the preparation of nanostructured electrodes, based on palladium nanoparticles deposited on a three-dimensional (3D) architecture of titania nanotube [7–9], which give exceptionally high performances in the electro- oxidation of ethanol. The use of the specific TiO 2 nanotube array structure is critical to obtain high performances in this reaction [10,11]. The synthesis of tubular one-dimensional (1D) nanostructures grown onto the surface of metals (such as Al, Ti, W) by electro- chemical anodization has attracted growing scientific interest ∗ Corresponding author. Tel.: +39 090 6765610; fax: +39 090 391518. E-mail addresses: rpassalacqua@unime.it, rosalbapassalacqua@yahoo.it (R. Passalacqua). due to their unique size and shape dependent properties that can be exploited in a wide range of applications [12–20]. TiO 2 is the most utilized and studied material for its suitable semiconduct- ing and optical properties, photocatalytic activity, low cost and toxicity. Among the other, nanostructured TiO 2 was successfully applied as water-splitting photocatalyst for hydrogen production in photoelectrochemical (PEC) reactors [21–24], as photo-anode in dye-sensitized solar cells [24–27], as gas sensing material in fuel-cell technology [28,29], and for safety and control purposes in fermentation processes [30]. In each of these applications, aspects such as particle size and shape, crystallinity, surface morphology and chemistry of the titania-based materials are the key parameters to be settled for the process optimization [31–33]. A precise control of the nanotube morphology, length, pore size, wall thickness and packing degree may strongly enhance performances, but the optimal nanostructure depends on the type of application [34]. Fox example, by varying the fluoride concentration and passing from aqueous to organic electrolytes, smooth surface and high aspect ratio TiO 2 nanotube arrays can be fabricated by controlled anodic oxidation techniques [23,35]. It is known how the anodization parameters influence the characteristics and morphology of the obtained samples [36], but more limited indications are available on how these parameters determine the material performances. A better knowledge of how the synthesis procedure allows to control the characteristics of the electrodes and thin film catalytic materials based on titania it useful. The aim of this contribution is http://dx.doi.org/10.1016/j.cattod.2014.11.003 0920-5861/© 2014 Elsevier B.V. All rights reserved.