Carrier Transport Path Of Transition Metal Sulfide And Photocatalytic Hydrogen Evolution Performance

The development of high-efficiency and low-cost photocatalysts for hydrogen evolution reaction is very important to solve the problem of energy shortage and environmental pollution.However,in the field of photocatalytic hydrogen evolution,the recombination of photogenerated carriers is still an urgent problem to be solved.Among many measures,the construction of heterojunction is an effective way to regulate the carrier transport path,inhibit carrier recombination and improve the photocatalytic hydrogen evolution activity.In this paper,a method of coupling different semiconductor materials and transition metal sulfides to form heterojunctions was used to construct photocatalysts with I-type,p-n type,Z-type and S-type heterojunctions in turn,and used for efficient photocatalytic hydrogen evolution reaction.The main research contents are as follows:（1）The Fe₂O₃/NiS p-n heterojunction photocatalyst was synthesized by solvothermal method.Through XRD,SEM and XPS characterization and analysis,it was found that the composite catalyst was composed of NiS nanoparticles and hexagonal Fe₂O₃nanosheets.By adjusting the mass ratio of Fe₂O₃and NiS,the hydrogen production rate of the composite catalyst reached 5.82 mmol·g^-1·h^-1,which was 2.7 times that of NiS and 58.2times that of Fe₂O₃,respectively.The formation of p-n heterojunction effectively promoted the transfer and separation of photogenerated carriers.This result was also confirmed by a series of characterizations such as photoluminescence spectroscopy and photoelectrochemical experiments.（2）The hydrogen evolution activity of CeO₂/CoS₂I-type heterojunction catalyst under visible light was prepared and studied.A series of characterizations such as XRD and XPS proved the successful synthesis of the composite catalyst.The COCS-3 sample with a mass ratio of CeO₂and CoS₂of 1:20 had the best hydrogen evolution activity,with a hydrogen evolution rate of 5.17 mmol·g^-1·h^-1.BET analysis results showed that the introduction of CeO₂could increase the specific surface area of the photocatalyst and exposed more active sites.At the same time,the results of fluorescence and electrochemical experiments showed that the photogenerated carriers of the CeO₂/CoS₂catalyst could be quickly separated and transferred,thereby accelerating the kinetics of the hydrogen evolution reaction.（3）The WO₃/CoS₂Z-type heterojunction photocatalyst was synthesized by a simple hydrothermal method.According to the hydrogen evolution test,the hydrogen production rate of WO₃/CoS₂catalyst reached 4.42 mmol·g^-1·h^-1,which was 80.41 times that of WO₃and 2.17 times that of CoS₂,respectively,and the catalyst had good stability.The characterization results of XRD,SEM,TEM and XPS proved that the WO₃/CoS₂catalyst was successfully synthesized,and the fluorescence and electrochemical experiment results showed that the WO₃/CoS₂catalyst had a high photo-generated carrier separation efficiency.（4）The S-type heterojunction photocatalyst of Zn_0.5Cd_0.5S modified with CoS₂ nanospheres was prepared and studied.The hydrogen production rate of the composite catalyst reaches 25.15 mmol·g^-1·h^-1,which is 3.26 times that of pure Zn_0.5Cd_0.5S.In addition,photoluminescence spectroscopy and electrochemical experiments have effectively demonstrated that the photogenerated carrier separation rate of CoS₂/Zn_0.5Cd_0.5S is better than that of a single CoS₂and Zn_0.5Cd_0.5S.In this study,CoS₂and Zn_0.5Cd_0.5S are both n-type semiconductors.After close contact,they follow the S-type heterojunction electron transfer mechanism,which not only inhibits the recombination of carriers,but also retains a stronger reduction potential,thus promoting the reduction of H⁺in photocatalytic experiments.