| Since Fujishma and Honda first discovered the photocatalytic water splitting for hydrogen production in the 1970s,the use of hydrogen energy as an ideal green energy to replace fossil fuels has attracted wide attention.The conversion of renewable solar energy into hydrogen energy storage can be achieved by photoelectrochemical water splitting technology.Since then,the search for stable and efficient and non-toxic semiconductor photoelectrode materials has been the focus of photocatalytic research.The introduction of electrocatalysts on the surface of photoanode is an effective way to promote the oxidation reaction of photoanode surface.It is traditionally considered that good conductivity is a typical reference inselection for the electrolytic water catalyst.The higher the conductivity of the catalyst,the better the performance of the catalyst.Ni-based and co-based catalysts are widely used in electrolysis of water because of their high catalytic activity,good chemical stability and low toxicity.Bi based oxide material has a low optical band gap,which is conducive to the absorption of visible light,and is widely used in photocatalysis.In this paper,rutile phase TiO2 is mainly modified by electrocatalysts of Ni(OH)2,Co(OH)2 and perovskite materials BiFeO3 with ferroelectricity respectively.Composite semiconductor materials showed obvious improvement in terms of light absorption and photogenerated carrier separation rate.The main working contents are summarized as follows:1.TiO2 film was prepared by sol-gel spin coating method,and the number and speed of the spinning coating were controlled to obtain uniform and smooth nano film.We synthesized Ni(OH)2 electrocatalysts by electrodeposition on the surface of TiO2 film and studied the effects of different Ni(OH)2 thicknesses on the electrochemical properties of the light.As the number of Ni(OH)2 increases,the current density increases but not in infinite enhancement.There is an optimal deposition time,and an over accumulation of Ni(OH)2 weakens the optical response of photoanode.The photoelectrochemical properties of TiO2/Ni(OH)2 composite photoanode were compared with those of pure TiO2 film.The results indicated that composite photoanode modified with electrocatalyst exhibited higher photocurrent density and more negative initial voltage,which reduced the overpotential value.The reason is that the electrical catalytic properties of Ni(OH)2 and the modification of composite materials have improved the electron separation and transportation on the interface.2.On the basis of above section,another electrocatalyst Co(OH)2 with self-assembled nano sheet was synthesized by electrodeposition.This morphology not only increases the specific surface area but also increases the scattering capacity of light.In addition to controlling deposition time,we further studied the effect of electrolyte concentration on photoelectrochemical properties.TiO2/Co(OH)2 photoanode achieved higher current density in visible light due to the active site provided by electrocatalyst,which reduced the activation energy at the surface reaction and effectively inhibited the recombination of photogenerated electron-hole pairs.3.The homogeneous and dense BFO film was prepared by sol-gel spin coating on TiO2 film.The experimental results showed that the visible light absorption of TiO2/BFO composite film greatly broadened,and more photogenerated carriers were obtained under visible radiation.BFO nanoplates grown on TiO2 yielded the highest photocurrent density of 11mA/cm2,corresponding to over 20 times enhancements compared with bare TiO2 at 1.5v vs.SCE.This is mainly ascribed to the ferroelectric polarization of BFO,which induced electric band bending of TiO2 upward,effectively promoting the separation and transmission of carriers.On this basis,we applied different voltage to polarize the BFO,and explored the influence of polarization on the internal electric field of BFO and the band bending of the contact semiconductor interface. |
PDF Full Text Request