Abstract
Nanotubes of the transition metal oxide, TiO2, prepared by electrochemical anodization have been investigated and utilized in many fields because of their specific physical and chemical properties. However, the usage of bare anodic TiO2 nanotubes in (photo)electrochemical reactions is limited by their higher charge transfer resistance and higher bandgaps than those of semiconductor or metal catalysts. In this review, we describe several techniques for doping TiO2 nanotubes with suitable catalysts or active materials to overcome the insulating properties of TiO2 and enhance its charge transfer reaction, and we suggest anodization parameters for the formation of TiO2 nanotubes. We then focus on the (photo)electrochemistry and photocatalysis-related applications of catalyst-doped anodic TiO2 nanotubes grown on Ti foil, including water electrolysis, photocatalysis, and solar cells. We also discuss key examples of the effects of doping and the resulting improvements in the efficiency of doped TiO2 electrodes for the desired (photo)electrochemical reactions.
Highlights
Anodization is a facile process that allows the physical and chemical properties of an entire metal surface to be modified at a very low cost, and it has long been recognized as a well-established industrial surface treatment technique [1,2]
This paper reviewed the growth of catalyst-doped anodic TiO2 nanotubes and their applications
This paper reviewed the growth of catalyst-doped anodic TiO2 nanotubes and their applications as binder-free electrodes for highly desirableelectrochemical reactions that require a low as binder-free electrodes for highly desirableelectrochemical reactions that require a low overvoltage or bandgap
Summary
Anodization is a facile process that allows the physical and chemical properties of an entire metal surface to be modified at a very low cost, and it has long been recognized as a well-established industrial surface treatment technique [1,2]. Anodization can be carried out in a F− -based electrolyte containing a negatively charged precursor (for example, RuO4− , which is dissociated from KRuO4 ) that can be incorporated into the anodic oxide during the anodization, the growth of anodic TiO2 nanotubes occurs and doping with the foreign catalyst occur simultaneously (so-called single-step anodization for doping). Some novel metal precursors inherently produce Cl− ; for example, H2 PtCl6 is dissociated to 2H+ + PtCl6 2− , which generates Cl− ions In such cases, underpotential shock, in which the potential shock voltage is lower than that used for anodization, has been successfully demonstrated as an alternative doping method. We focus on the use of TiO2 nanotubes as (photo)electrochemical binder-free electrodes in applications that require low overpotential or narrow bandgaps to achieve the desired reactions. Various doping processes to adjust the overpotential and bandgap are comprehensively reviewed
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