Preparation Of Titanium Dioxide Based Nanomaterials And Study Of Their Water Splitting Performance

Titanium dioxide（TiO₂）is the earliest n-type semiconductor material that was used as photoanode to drive photoelectrochemical（PEC）water splitting.TiO₂ possesses a lot of merits including high chemical stability,high hydrophilicity,high photocorrosion resistance and strong redox ability of the photogenerated carriers.However,TiO₂ has poor visible light response capability and poor electrical conductivity,which limits its PEC water oxidation efficiency.In this thesis,we employed two stretagies including surface modification and ion doping to overcome the drawbacks of TiO₂ and thus to improve its PEC water splitting performance.The specific work is as follows:（1）Doping TiO₂ nanorod arrays with Al.Aluminum doped titanium（Al:TiO₂）photoanode materials were directly synthesized on the fluorine-doped tin oxide（FTO）conductive substrates by hydrothermal synthesis.The PEC properties,crystal structure and morphology of the Al:TiO₂ photoanode materials were studied.The mechanism of the improvement of PEC performance of TiO₂ materials due to aluminum doping was also studied.The results indicate that Al doping decreses the charge transport resistance the contact resistance between the nanorods and the FTO substrates,which significantly improves the PEC performance of Al:TiO₂ photoanodes.For example,the photocurrent density of8%-Al:TiO₂ photoanode material is 0.80 mA/cm² at 1.23 V vs.RHE,which is 5.6 times that of the pure TiO₂ photoanode.（2）The TiO₂ photoanode materials were prepared on the FTO conductive substrate by hydrothermal synthesis.Effects of reactant concentration,reaction time and annealing temperature on the structure and PEC performances of the TiO₂ were studied.Based on above investigations,optimum TiO₂ is synthesized.Then the TiO₂ were modified by CdS and FeOOH quantum dots.The structure and PEC properties of the TiO₂ nanorod anode materials before and after modification were studied.The reasons for PEC improvement of TiO₂ by FeOOH and CdS modification were revealed,which showed that the photocurrent density value of TiO₂ anode material is⁰.50 mA/cm²,however,the TiO₂ photoanode modified with FeOOH and CdS（TiO₂/CdS/FeOOH）showed much enhanced photocurrent density,which was 0.82 mA/cm² at 1.23 V vs.RHE,being 1.29 and 1.61 times more than those of the TiO₂/CdS and pure TiO₂ photoanodes,respectively.（3）Surface modification of TiO₂ nanorod arrays with tungsten oxides through direct and indirect methods,respectively.The effects of temperature,electrodeposition potential,electrodeposition time and annealing temperature and the concentration of copper tungstate sol on the prepared materials were studyed.The studies indicated that after modification with amorphous WO₃,which was prepared by electrodeposition at conditions including-0.6 V of potential,5 s of deposition time,70°C of deposition temperature and heat treatment at 300°C in air,the TiO₂ nanorod arrays acquired 1 time increase in PEC photocurrent density in comparison with the pure TiO₂ nanorod arrays.