Fabrication Of Bismuth Sulfide Based Photocatalyst And Study On Polarization Effect Enhancement Hydrogen Evolution Performance

In September 2020,China explicitly proposed the"double carbon"target.With the implementation of the"double carbon"strategy,the development of the hydrogen energy industry will be further improved.Semiconductor photocatalytic technology has shown great potential in green hydrogen production,which has attracted extensive attention from scientific researchers and become one of the hottest research directions in recent years.The design of efficient photocatalysts and the development of related modification methods have become the key issues in hydrogen production reaction.At present,the common methods of photocatalyst modification mainly include morphology control,semiconductor recombination,ion doping,noble metal loading,etc.However,these traditional modification methods have some limitations on carrier separation,such as low interfacial electric field intensity,limited action range,weak driving force,and easy generation of recombination centers,etc.Under the action of an external field,the crystal of semiconductor photocatalyst is polarized,resulting in a polarized electric field.This field can provide a driving force with wide range and high intensity for carrier separation,thus significantly improving photocatalytic activity.In this paper,Bi₂S₃ is taken as the research object,and the polarized electric field inside the crystal is excited by applying piezoelectric,thermal and magnetic fields,which provides an effective driving force for the separation of carriers.ZnS/Bi₂S₃-PVDF（ZnS-V_S/Bi₂S₃-PVDF,PVDF:polyvinylidene fluoride）piezoelectric thin film photocatalyst containing sulfur vacancies were designed and synthesized by solvothermal method combined with spin coating process.The built-in electric field formed between ZnS-V_S/Bi₂S₃ heterojunction structures can effectively separate electrons and holes.Furthermore,As a kind of polymer piezoelectric material,PVDF is deformed under the action of ultrasonic wave,which effectively converts external force into electric energy and releases surface charge,thus generating polarized electric field.The polarized electric field formed at the interface of ZnS-V_S/Bi₂S₃-PVDF provides the driving force for directional carrier migration.The introduction of sulfur vacancy makes F^-exposed on PVDF surface form Zn-F bond with Zn²⁺,which makes the built-in electric field closely combine with polarized electric field.The hydrogen evolution rate of ZnS-V_S/Bi₂S₃-PVDF reached 10.07 mmol h^-1g^-1 under the synergistic effect of double electric fields.CdS/Bi₂S₃ magnetic composite photocatalyst containing bismuth vacancy(CdS/Bi₂S₃-V_Bi)was synthesized by solvothermal method.The introduction of bismuth vacancies induces the spin polarization of p electrons in sulfur atoms,which makes Bi₂S₃-V_Bi ferromagnetic.Under the action of external magnetic field,spin-polarized electron tunneling in Bi₂S₃-V_Bi makes it have negative magnetoresistance effect,which is beneficial to improve the effective transfer of carriers.In addition,when the photocatalyst moves in the magnetic field,Lorentz force drives the electrons and holes to move in opposite directions,so that the recombination of photogenerated carriers is suppressed and more electrons can participate in the photocatalytic reaction.The hydrogen evolution efficiency of CdS/Bi₂S₃-V_Bi is 9.93 mmol h^-1 g^-1under the synergistic effect of negative magnetoresistance effect and Lorentz force.FeS₂/Bi₂S₃ pyroelectric composite photocatalyst with hollow structure was constructed based on the Kirkendall effect.The FeS₂ serves as a photothermal agent,and provides a hot end for the pyroelectric effect of Bi₂S₃.Its hollow structure is conducive to improving the utilization rate of incident light,thus enhancing the photothermal conversion efficiency.The temperature difference between the heat generated by the photothermal effect and the cold photocatalytic system makes Bi₂S₃generate spontaneous polarization and release surface charge,thus controlling the direction and rate of carrier migration.The results of DFT theoretical calculation and COMSOL numerical simulation show that the improvement of photocatalytic efficiency is due to lower surface work function and higher pyroelectric effect.CdS/Bi₂S₃@C composite photocatalyst with three-dimensional porous honeycomb structure was prepared by high-temperature calcination.Bi₂S₃ absorbs near-infrared light and converts it into heat,three-dimensional porous honeycomb carbon acts as an"incubator"to reduce heat loss and optimize photothermal effect,so that the temperature difference of the system increases from 16.4oC to 57.5oC.This provides a larger temperature difference for the pyroelectric effect of Bi₂S₃,which is conducive to the release of surface polarized charges.COMSOL simulation results show that the larger the temperature difference,the higher the thermoelectric potential,which is more conducive to controlling the migration direction and separation efficiency of photogenerated carriers.Therefore,the photocatalyst with three-dimensional porous honeycomb carbon structure protection has higher hydrogen evolution efficiency.