Preparation And Photoelectrochemical Water Splitting Properties Of Surface Modificated Si Doped Titania Nanotubes Photoanodes

Photoelectrochemical water splitting（PEC）based on TiO₂nanomaterials is an effective way to solve the energy crisis.However,the light absorption is mainly concentrated in the ultraviolet light region due to its large forbidden band width,so the utilization rate of sunlight is low.In addition,the photogenerated electrons and holes are easily to recombine,which lead low quantum efficiency.These two problems seriously affect its PEC performance.In order to improve the performance of TiO₂in the production of hydrogen by photolysis of water,Si-doped TiO₂nanotube arrays were first prepared by anodizing Ti-8.5Si alloy,and Ti³⁺/V_Ostates was reduced by NaBH₄reduction,electrochemical hydrogenation reduction,and Sn metal reduction on the surface of the nanotube array.It could improve the light absorption characteristics of Si-doped TiO₂nanotubes,reduce the photo-generated hole and electron recombination rate,and improve the photoelectrochemical water splitting properties of TiO₂nanotubes.The effects of different heat treatment temperatures on the morphology,phase and photocatalytic performance of reduced TiO₂photoanode were studied during the experiment.The main results are as follows:（1）Highly ordered Si-doped TiO₂ nanotube arrays were fabricated by anodiziation of Ti-8.5Si alloy and the photoanode was mainly composed of Ti,Si,and O elements.The surface of TiO₂nanotubes began to crack when the heat treatment temperature was too high.And the increase of temperature also resulted in an increase of the rutile phase content in the crystal structure.（2）Photoelectrochemical measurement results of crystallized Si-doped TiO₂nanotuebs demonstrated that the Si-doped TiO₂nanotubes annealed at600oC possess higher PEC activity,and the photocurrent density reaches to0.72 m A/cm².（3）Ti³⁺/V_O states were introduced into the Ti-Si-O nanotubes by NaBH₄reduction,electrochemical hydrogenation reduction and Sn reduction,respectively.The presence of Ti³⁺/V_Opromoted enhanced optical absorption and reduced band gap.Photoelectrochemical measurements showed that the introduction of Ti³⁺/V_Ocould effectively inhibit the recombination of photo-generated electron-hole,resulting in significant increase of photocurrent density,negative shift of flat band potential and improved PEC properties.After 0.4 M NaBH₄reduction for 3 h,photocurrent density of the Ti-Si-O photoanode reached 1.5 m A/cm²and corresponding solar to hydrogen efficiency could reach 0.7%.When the TiO₂photoanode was electrochemically reduced by 0.5 M Na SO4 for 10 min with 4 V bias voltages,the photocurrent density could reach 2.1 m A/cm²and solar to hydrogen efficiency could reach 0.88%.After Sn reduction,photocurrent density of the Ti-Si-O nanotubes reached 1.8 m A/cm²and efficiency from solar to hydrogen could reach 0.7%.