Surface plasmon-driven photoelectrochemical water splitting of TiO2 nanowires decorated with Ag nanoparticles under visible light illumination

Abstract

Here, we demonstrate that TiO2 nanowires (NWs) can be significantly driven by visible light through the decoration with Ag nanoparticles (NPs) (Ag-decorated TiO2 NWs). The Ag-decorated TiO2 NWs show remarkably photoelectrochemical (PEC) water splitting performance under illumination with λ>420 visible light due to surface plasmon resonance (SPR) of Ag NPs. In this work, low power of the used light source (100mW/cm2) was not capable of heating the Ag-decorated TiO2 nanowire photoanode enough to directly split water. In addition, under irradiation with λ>420nm visible light, no photocurrent was produced by TiO2 nanowire photoanode indicates that electron transitions between valence band and conduction band do not take place in prepared anatase TiO2 NWs. Meanwhile, the SPR energy (2.95–2.13eV <3.2eV) is insufficient to excite TiO2 NWs to generate electro-hole pairs through SPR-enhanced electromagnetic fields. Thus the remarkably visible-light-responsive PEC water splitting activity of Ag-decorated TiO2 NWs is not attributed to local heating caused by SPR-mediated photothermal process, large enhancement of electromagnetic fields induced by SPR and scattering of resonant photons. We propose that the visible light PEC water splitting performance of Ag-decorated TiO2 NWs is attributed to electron transfer from Ag NPs to the conduction band of TiO2 NWs mediated by SPR. In addition, a Schottky barrier established at the interface of Ag NPs and TiO2 NWs prevents these transferred electrons from returning to the Ag NPs and significantly retarded the recombination of electron-hole pairs in the Ag NPs, also contributing to visible-light-driven PEC water splitting performance. So the remarkably visible-light-driven PEC water splitting performance of Ag-decorated TiO2 NWs is attributed to the synergistic effects of electron transfer mediated by SPR and the Schottky barrier between Ag NPs and TiO2 NWs. The achieved Ag-decorated TiO2 NWs can be added to these previously prepared TiO2 photocatalysts mainly driven by SPR of Au NPs for the development of new visible light photocatalysts.