In Tio < Sub > 2 < / Sub > Surface Intermittent Pulse Deposition Cu < Sub > 2 < / Sub > O Particles And Photoelectrochemical Properties

Cuprous oxide （Cu₂O）, a direct band gap semiconductor, shows many importantcharacteristics useful for photocatalytic, electrochromic, solar energy cells andphotoelectrochemical applications, including abundant availability, narrow band-gap, andnontoxicity. In addition, Cu₂O is usually a p-type semiconductor with band gap around1.9².2eV, and thus can be used to form heterojunctions with other n-type semiconductorshaving wide band-gap. The heterostructure of titanium oxide （TiO₂） combined with Cu₂Oparticles has been studied and significant enhancement of photo-current conversion and/orphotocatalytic efficiency has been observed by various research groups. However, thestudy as to the controllable growth of the Cu₂O particles is missing when they areelectrodeposited onto TiO₂surface. In addition, the study on the stability of the Cu₂Oparticle during photoelectrochemical （PEC） reaction is also lack. In this study, weelectrodeposited Cu₂O particles on TiO₂flat surface using a special interruptedpulse-electrodeposition method to get modulated particle size and density. The flat Tisubstrate with thermal oxidized TiO₂layer is used in this study, so that we canconveniently observe the microstructural and morphological evolution of the Cu₂Oparticles during the growth or after the PEC reactions.The effect of the growth parameters, including the times of interruptions （periods） andpulse number and height within one period on the morphology, microstructure and PECproperties of the Cu₂O particles is investigated in detail. The photocurrent of theCu₂O/TiO₂heterostructure under zero bias increases significantly compared to that of thepure TiO₂layer. We get the highest photocurrent when6-period interrupted deposition isused, corresponding to the highest density for the single Cu₂O particles on the TiO₂surface.However, more deposition periods than6have negative effects on the photocurrent of theCu₂O/TiO₂heterostructure. Above6-period, Cu₂O particles cover fully the TiO₂surfacealong with the stacked Cu₂O particle structure. Such stacked structure makes the lightabsorption less efficient on the Cu₂O/TiO₂contact region and leads to the decreased photocurrent. We also find that the photocurrent of the Cu₂O/TiO₂heterostructure underzero bias decreases obviously during the PEC measurement, and then the stability of theCu₂O particles during the PEC reaction is studied. The transformation of Cu₂O to Cu isobserved, along with the stabilized photocurrent. Compared with the pure TiO₂layer on Tisubstrate, large enhancement of the PEC activity is presented after Cu₂O or Cu particlesare covered on TiO₂surface and different mechanisms behind the enhancement areproposed in this thesis.The stability of the electrodeposited Cu₂O particles on TiO₂is further studied. We gettwo cathodic peaks from the cyclic voltammogram （CV） of a bare TiO₂/Ti electrode inCu（NO3）2solution, which correspond to Cu²⁺to Cu⁺and Cu⁺to Cu transitions, respectively.Cu₂O and Cu nanoparticles is deposited via electroreduction of Cu₂+to Cu+and Cu+to Cuat proper negative potentials, separately. We find that the Cu₂O nanoparticles deposited at aelectroreduction potential on TiO₂possess a excellent PEC performance due to a large areaof （111） facets. The photocurrent of Cu₂O/TiO₂heterojunctions is more stable anddecreasing slowly during the PEC test. Compared with Cu particles transformed fromCu₂O particles by applied negative voltage, large enhancement of the PEC activity ispresented for the Cu particles deposited on the TiO₂surface using a electroreductionpotential directly and the short-circuit photocurrent density of Cu/TiO₂film is more than21times that of the pure TiO₂film.