The Surface Sensitization Of TiO₂Nanotube Array Electrode And Its Interfacial Property

In order to find clean new energy to solve the increasing shortage of fossilenergy in the world, the photoelectrochemical water splitting hydrogen production,which is called “solar-hydrogen technology”, has been widely paied attention to. TiO₂is considered to be the best photoanode material in reaserch because of its richness,innoxiousness and stableness, Hower, its energy gap limited its photoelectrocatalyticefficiency. In this research we studied the surface sensitized TiO₂nanotube arrays（Dye sensitized TNT, CdS QDs sensitized TNT） with rapid electron transferproperties in order to improve the visible light response performance and enhance thecharge transfer interfacial properties.TiO₂nanotube arrays were fabricated by electrochemical anodic oxidationmethod and surface sensitization was through the immersion method and acousticassist chemical deposition. The morphologies, spectral properties and the QDs’ radiuswere characterized by means of SEM, UV-Vis, DRS and XPS techniques, respectively.The photoelectrical properties of electrodes were analyzed with Current-time curves,voltage-time curve, photon to current conversion efficiency （IPCE） curves,Mott-schottky plots and electrochemical impedance spectroscopy （EIS） techniques.The results are showed as follows:The length of the nanotube arrays fabricated in wt%NH4F+2v%H2O ethanediolsolution and in0.5mol/L H3PO4+0.14mol/L NaF water solution was15μm （TNT-a）and600nm （TNT-b）, respectively. Eosin Y and RuL was used as the sensitizer ofTNT-a and TNT-b, respectively. The tubewall turned thicker after sensitization, thesensitized samples had better visible light （500-700nm） absorption ability. To the CdSQDs surface sensitized TNT-b samples, according to the XPS test results, the radius ofthese QDs was3nm, considering the increased nanotube wall thickness aftersensitization, there were almost one layer of QDs adhered on the inside tube wall. TheUVDRS test results further confirmed the CdS quantum dots sensitization enhancedvisible light absorption ability of TiO₂nanotube arrays.The sunlight simulator （AM1.5,100mW/cm²） was used as the light source,Ag/AgCl as the reference electrode. The photoelectrochemical properties of the dyesensitized TNT and the CdS QDs sensitized TNT are obviously improved. Thephotocurrent density of Eosin-TNT-a、TNT-a are0.46mA/cm²、0.24mA/cm²,respectively. The photocurrent of samples before and after RuL sensitization remains0.065mA/cm²and0.165mA/cm², respectively. The photocurrent density of the QDssensitized nanotube arrays could be increased from0.35mA/cm²to3.75mA/cm².Under500-1100nm light range, the photoelectric conversion efficiency （IPCE） of CdS quantum dots sensitized electrode was up to25%.Basing on the analysis and numerical study of Mott-Schottky plots, wecalculated and analysed the width of the depletion layer of TiO₂nanotube arraysbefore and after sensitization, established the model and theory that sensitizedelectrode’s depletion layer was wider, and thus could enhance the faster separationand transmission of photo generated electron and holl pairs. According to theelectrochemical impedance spectroscopy （EIS） technique, we analysed the interfacialimpedance and capacitance of the TiO₂nanotube arrays before and after sensitization.The sensitized samples’s impedance radius decreased obviously, the capacitanceincreased after sensitization, so they showed better photoelectrochemical interfacialproperties.