Ag/polydopamine-modified Ti/TiO2 nanotube arrays: A platform for enhanced CO2 photoelectroreduction to methanol

Abstract TiO2 nanotube (NT) arrays were modified with thin films of polydopamine (PDA) and Ag nanoparticles (NP) and were used as electron storage centers on a photoelectrode surface, in order to drive the reduction of CO2 to methanol. Silver nanoparticles were obtained by means of chemical deposition using the catechol groups present in PDA. The Ti/TiO2NT@PDA-AgNP photocathode presented higher photocurrents when irradiated using either UV–vis irradiation or a solar simulator, compared to bare Ti/TiO2NT, indicating improvement of charge carrier separation, while the band gap of the material decreased from 3.12 to 2.3 eV. Under optimized conditions, methanol production of 59.5 μM cm−2 was achieved and under the solar simulator, 19.25 μM cm−2 of methanol was generated, indicating that the PDA-AgNP coating improved the activation by visible light. The Ag present in the modified Ti/TiO2NT electrodes was quantified during photoelectrocatalysis, with the amount of Ag nanoparticles released from the electrodes being negligible. A schematic representation of the charge transfer mechanism at the Ti/TiO2NT@PDA-AgNP electrode is provided.