UV-assisted anchoring of gold nanoparticles into TiO2 nanotubes for oxygen electroreduction

Abstract

• Au nanoparticles are deposited on TiO 2 nanotubular layers via photocatalytic reduction. • ORR overvoltage of photodeposited AuNPs is lower than AuNPs loaded from colloids. • ORR overvoltage of AuNPs-TNT depends on size, concentration and structure of AuNPs. Gold nanoparticles (AuNPs) have been deposited on titania nanotubular layers (TNT) via photocatalytic deposition, and the activity of the obtained AuNPs-TNT systems toward oxygen electroreduction reaction (ORR) in an alkaline medium has been studied and compared with the activity of AuNPs-TNT composites prepared from Au colloidal solutions. Two photodeposition methods were utilized for anchoring of AuNPs: direct UV-irradiation of a TNT electrode immersed into a HAuCl 4 containing solution (TNT-Au1 composites) and initial adsorption of AuCl 4 − ions on TNT followed by UV-irradiation (TNT-Au2 composites). The size, spatial distribution, structure and surface of AuNPs deposited on TNT layers were studied via scanning and transmission electron microscopy, optical spectroscopy and underpotential deposition of lead ad-atoms on gold. It was found that these parameters depend on the photodeposition method. The TNT-Au2 composites have smaller size, higher surface concentration and more uniform distribution of AuNPs in the TNT layers as compared with the TNT-Au1 systems. The electrocatalytic efficiency of Au-TNT electrodes in ORR was found to depend on various factors such as doping level of TNT support (governed by annealing temperature), AuNPs size and their loading amount. The electroreduction of oxygen was observed at less negative potentials when Au nanoparticles were grown on the TNT surface by photoreduction in comparison with the TNT electrodes modified with AuNPs from sols. The enhanced activity of the photocatalytically prepared AuNPs-TNT composites can be explained by the consolidation of the interface between gold nanoparticles and TiO 2 support and the absence of ligands on the AuNPs surface.