| Hydrogen energy stands out among many clean energy sources,because of its good calorific value,green and sustainable characteristics.The hydrogen production technique of photoelectrochemical water splitting combines the advantages of electrolyzing water and photocatalytic water splitting,which is considered to be an ideal and promising method for hydrogen production.During photoelectrochemical water splitting,the rate of oxygen evolution reaction on the surface of photoanode restricts the overall efficiency of photoelectrochemical water splitting.Moreover,in the photoanode,the migration process of photogenerated carriers restricts the rate of oxygen evolution reaction.Therefore,it is an effective way to improve the oxidation reaction rate and water splitting efficiency to regulate the transport process of photogenerated carriers in photoanode.BiVO4 is a kind of good photoanode material due to its unique optical and electrical properties.However,its application is limited by the low electron mobility and poor surface oxidation kinetics.In this study,aiming at the above problems,the photogenerated carrier migration process on the surface and bulk of the BiVO4 photoanode were regulated by constructing the BiVO4/Rh-SrTiO3 system.And then through the gradual optimization of the photogenerated carrier migration process in the system,the photoanode system with excellent photoelectrochemical properties was finally obtained.The main research results are as follows:1.Aiming at the problem of poor surface oxidation kinetics of BiVO4 photoanode,BiVO4/Rh-SrTiO3 system was constructed by surface modification with oxygen evolution co-catalyst.Among them,BiVO4 is used as a light absorbing layer,and Rh-SrTiO3 acts as an oxygen evolution co-catalyst.For the first time,it is confirmed that Rh-SrTiO3 can not only be used as the hydrogen evolution catalyst in the Z-scheme system,but also possess the ability for oxygen evolution co-catalysis.The results indicate that when the added amount of Rh is 5 mol%,the photoelectrochemical performance of the photoanode is optimal.It is found that Rh provides an oxidation active site during the process of PEC water oxidation.The transfer capacity of photogenerated carriers at the photoanode-electrolyte interface is promoted.At the same time,the theoretical calculation confirms that the OER tended to occur on the（110）crystal plane of Rh-SrTiO3,and Rh doping reduced the oxygen evolution overpotential on this plane significantly.This study provides a new idea for the application of stable and trace amounts of noble metals in the field of oxygen evolution co-catalysis in the future.2.The carriers transfer process of oxygen evolution co-catalyst layer Rh-SrTiO3in the BiVO4/Rh-SrTiO3 photoanode system was regulated.SrTiO3 is a semiconductor material with low electron mobility,which will restrict the migration of photogenerated carriers from the bulk of photoanode to the surface,thus affect the photoelectrochemical properties of the photoanode.Therefore,Rh-SrTiO3 oxygen evolution co-catalyst layer was regulated firstly in this part.Rh-SrTiO3was doped with Fe、Ni、Co,respectively.It is expected to improve the electron mobility and oxygen evolution co-catalytic performance of Rh-SrTiO3 at the same time.The results show that Fe-doping can improve the electron mobility of Rh-SrTiO3,but the improvement of oxygen evolution co-catalytic performance is not obvious.The doping of Ni enhances the oxygen evolution co-catalytic performance of Rh-SrTiO3,but there is not obvious effect on the improvement of electron mobility.Cobalt-doping can not only improve the electron mobility of Rh-SrTiO3,but also enhance the oxygen evolution co-catalytic performance.Moreover,only Co and Rh co-doped SrTiO3 can effectively improve the photoelectrochemical properties of the photoanode.Therefore,by constructing BiVO4/Co Rh-SrTiO3 photoanode system,the photogenerated current density was increased from 0.8 m A/cm2 to 1.1 m A/cm2 at 1.23 V vs RHE bias.3.The photogenerated carriers transfer process of light-absorbing layer BiVO4 in the BiVO4/Co Rh-SrTiO3 photoanode system was regulated.BiVO4 is the main material in this system,and the migration process of photogenerated carriers in it also restricts the photoelectrochemical properties of this system.On the basis of the BiVO4/Co Rh-SrTiO3photoanode system,through one step process of In-doping and controlled anoxic annealing,the migration channel and mobility of photogenerated carriers in BiVO4 photoanode are synergistically optimized.When the addition amount of In element is 5 mol%,the photoelectrochemical performance of photoanode is optimal.Under the condition of anoxic annealing,the introduction of In is conducive to the formation of quasi-oxygen vacancies in the BiVO4 photoanode,which increases the free carrier concentration in it.Moreover,under the synergistic effect of In doping and anoxic annealing,the photoanode BiVO4 presents a nanonet array structure,which can optimize the transfer path of photogenerated carriers,greatly increases the specific surface area of the photoanode,and provides more support sites for the oxygen evolution co-catalyst.Under the synergistic effect of quasi-oxygen vacancies and special nano morphology,the migration ability of photogenerated carriers in BiVO4photoanode is greatly enhanced,the separation efficiency of photogenerated electrons and holes is greatly improved.Therefore,by constructing InBiVO4/Co Rh-SrTiO3 photoanode system,the migration process of photogenerated carriers in photoanode is well regulated and the photogenerated current density increases from 1.1 m A/cm2 to 2.6 m A/cm2 at 1.23 V vs RHE bias.4.The photoanode InBiVO4/CoRh-SrTiO3 was prepared by high-energy laser treatment instead of thermal annealing process.When the laser intensity is 1.0 W,the photoelectrochemical properties of the photoanode obtained by high-energy laser are better than that of the photoanode obtained by thermal annealing,which proves the feasibility of laser treatment.Laser treatment plays an important role in regulating the transfer process of photogenerated carriers in the photoanode.With the increase of free carrier concentration,the migration ability and the lifetime of photogenerated carriers are enhanced,and the separation efficiency of photogenerated electrons and holes is significantly improved.However,the laser with higher intensity will seriously damage the micromorphology,crystal structure and oxygen evolution active sites of the photoanode,which instead limits photogenerated carrier transport capacity in photoanode.Therefore,the laser with appropriate intensity can replace the thermal annealing treatment,which not only saves the energy and time cost,but also can obtain a photoanode with better performance.Finally,through the optimization of the preparation process,the photogenerated current density is increased from 2.6 m A/cm2 to 3.2 m A/cm2 at 1.23 V vs RHE bias. |
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