2 TiO ₂ Growth And Photoelectrochemical Properties Of O And Cu On The Surface Of The Bias Control Cu

Titanium dioxide (TiO2) has good photo-, gas-, and pressure-sensitive properties andchemical stability, high refractive index (anatase2.5, rutile2.7) and high dielectric constant.Besides, it also has excellent solar energy conversion and photocatalytic properties. SoTiO2is one of the widely investigated materials for solar cells, photonic crystals,photocatalysis, gas sensors, electrochromic and self-cleaning devices. The major obstaclesto their effective utilization lie in poor photo-generated charge separation and inefficientuse of sunlight. In this thesis, we improve the photoelectrochemical properties of TiO2filmby developing Cu2O and/or Cu particles and Cu2O and/or Co-Pi particles on its surface. Wealso studied the growth characteristics of the particles and their changes in themicrostructure and morphology.(1) Based on the cyclic voltammogram of TiO2/Ti electrode in Cu2+ions solution, wefabricated the Cu2O and Cu particles on TiO2flat surface separately or simultaneouslythrough adjusting the applied potentials during electrodeposition. Scanning electronmicroscopy, X-ray diffraction and X-ray photoelectron spectroscopy spectra reflect thatCu2O and Cu have different growth modes: Cu2O particles are crystallized on the TiO2surface separately, while Cu particles nucleate on previously grown particles, formingstacked particle structure. Such growth behaviors were explained by the different electrontransfer behaviors on the Cu2O/TiO2and Cu/TiO2interfaces which are determined by theirband-gap alignment. Compared with the pure TiO2photoanode, significant enhancement ofthe photocurrent was observed in both the Cu2O/TiO2and Cu/TiO2heterostructures.Particularly, there existed a potential region where Cu2O and Cu are grown on the TiO2surface simultaneously and the corresponding photocurrent is relatively stable and reachesthe maximum. The UV-vis diffuse reflectance spectroscopy, electrochemical impedancespectroscopy and photocurrent vs. potential characteristics revealed that the visible lightabsorption of the Cu2O and Cu contributes obviously to the photocurrent, while Cu/TiO2 shows more broad band visible light utilization in the photoelectric conversion. In addition,the increased zero-current potential and the effective charge separation and rapid carriertransfer on the electrode/electrolyte interface are also related to the enhanced PECproperties.(2) TiO2film is prepared on Ti substrates by anodic oxidation method, then Co-Pi andCu2O particles are fabricated on TiO2flat surface using a facial electrochemical depositionmethod. Scanning electron microscopy, X-ray diffraction and photoelectrochemicalproperties reflect that: depositing Co-Pi particles in advance on the surface of TiO2thinfilms can prevent Cu2O forming stacked particle structure and increase the photocurrentsignificantly. While depositing Co-Pi after Cu2O will make Cu2O reduction to Cu and themorphology changes a lot. Specifically, when the deposition time of Co-Pi is set to be300s,the structure of TiO2/Co-Pi/Cu2O can get the maximum photocurrent of200μA·cm-2under100mW/cm2illumination and0V versus Ag/AgCl.