RuO2-loaded TiO2 nanotube array electrodes for efficient electrocatalytic gas evolution

Abstract

Ruthenium dioxide (RuO2) has an advantage of various chemical reactions like dehydrogenation, gas phase oxidation of HCl, and chloro-alkali process. In order to enhance stability of RuO2-based catalysts, the use of TiO2 is successful in recent years. In general, nanostructured scaffolds with the large relative surface area are adopted in the catalytic reactions for maximizing the number of active sites. For the electrocatalytic reactions, however, the scaffold should be conducting enough so that the charges required for the redox reaction can be transported to the surface of the loaded RuO2 catalysis. In the same context, TiO2 nanotube arrays (NTAs) can be a promising scaffold for the CER reaction, because it can transport charges (as evidenced in the solar cell or PEC applications) and it can be a good combination with RuO2 (as evidenced by DSA®). In addition, the nanoscale morphologies (e.g. tube length, pore diameter, and wall thickness), crystalline structure (e.g. crystalline phase and preferred orientation), and the electrical properties (e.g. conductivity) can be precisely controlled by the processing parameters.

In this study, we firstly report the RuO2-loaded TiO2 NTAs as an efficient nanostructure electrode for the electrocatalytic CER process. Nanostructruring is well-known for enhancing the catalysts activity, we design TiO2 based nanostructure to investigate more active catalysts. The samples have been prepared electrochemically (i.e. electrochemical anodization for preparing TiO2 NTAs and electrochemical deposition for loading RuO2) and the dependence of the CER performance on the materials properties of the composite electrodes such as the crystallinity and electrical conductivity have been investigated. It has been found that the conductivity of the electrode under the anodic polarization is essential for achieving good CER performance, and the black TiO2 prepared by annealing as-anodized NTAs under an Ar atmosphere has been found to be the best scaffold for the RuO2 catalysis.