Conductive Cu-Doped TiO 2 Nanotubes for Enhanced Photoelectrochemical Methanol Oxidation and Concomitant Hydrogen Generation

Abstract

Cu doping in titania is usually detrimental to the material's photoconductivity, which prevents the use of this combination in photoanodes. In this work, we produce TiO 2 nanotube arrays intrinsically doped with copper and establish sufficient conductivity to use them as efficient photoanodes for methanol oxidation in a photoelectrochemical hydrogen generation setting. Firstly, Cu-doped TiO 2 nanotubes were produced by anodizing a Ti−Cu binary alloy. By subsequent thermal reduction of the structure in an Ar/H 2 environment, conductive copper-doped TiO 2 nanotubes (TiCuTN−Ar/H 2 ) can be achieved with an approximately 10 3 times higher conductivity than the non-reduced material. When these reduced Cu-doped TiO 2 nanotubes are used as photoanode, copper species embedded in the TiO 2 wall catalyze the methanol oxidation reaction. As a result of the combined effect of conductivity and catalytic effect of Cu, such reduced Cu:TiO 2 nanotubes can generate a photocurrent of 0.76 mA cm −2 at 1 V vs. RHE, under AM1.5 (100 mW/Cm 2 ) irradiation – in a 50 : 50 MeOH/water solution – this is 33 times higher than for pristine Cu:TiO 2 nanotubes.