Electrochemically self-doped TiO2 nanotube photoanodes decorated with Pt nanoparticles: trade-off between photocatalytic activity and dark electrocatalysis for ethanol oxidation

Abstract

TiO2 nanotube electrodes are commonly used in photoelectrocatalytic applications; however, their poor conductivity limits their electrochemical potential. In this work, we have prepared self-doped TiO2 nanotube electrodes by electrochemical anodization followed by electrochemical cathodic polarization. Electrochemically self-doped TiO2 nanotube (SD-TNT) electrodes were prepared by cathodic polarization and subsequently decorated with Pt nanoparticles (3.3 ± 0.6 nm) via impregnation and electrochemical reduction. SD-TNT supports a complete Pt voltammetric profile and enables ethanol electro-oxidation in the dark. In contrast, Pt-decorated pristine nanotubes (Pt/TNT) exhibit only hydrogen adsorption/desorption features and no anodic currents in acidic media. Under simulated solar irradiation, pristine TNT exhibits the highest photocurrents and product formation. At the same time, both self-doping and Pt decoration decrease the photocurrent density, highlighting a trade-off between enhanced dark conductivity and increased recombination in highly defective TiO2. Nevertheless, Pt/SD-TNT electrodes combine dark electrocatalytic activity with photoresponse, operating in a dual mode that is relevant for devices under intermittent illumination. These results clarify the distinct roles of self-doping and Pt decoration on TiO2 nanotube electrodes, highlighting a trade-off between maximizing photocurrent and enabling Pt-based electrocatalysis on a normally rectifying semiconductor support.