Preparation And Properties Of Molybdenum-based Promoter-modified MAPbI₃ Composite Photocatalysts

Energy shortage and environmental pollution are two major problems facing human society today.The main energy sources in today’s society come from coal,oil,natural gas,etc.,which are not only non-renewable fossil energy sources,but also the waste water and waste gas produced by the combustion process will cause serious environmental pollution.Therefore,the development of clean new energy is particularly important.Hydrogen is an ideal clean energy with high energy density and no pollution to the environment.It is a potential alternative to clean energy.As another inexhaustible new energy source,using sunlight to produce clean and renewable hydrogen fuel through semiconductor photocatalysis technology,known as"artificial photosynthesis",can fundamentally solve the energy crisis.In the process of photocatalysis,the choice of photocatalyst is particularly important.Metal halide perovskite materials represented by lead-halide perovskites have a wide absorption range,excellent absorption coefficient,long carrier diffusion distance,long carrier lifetime,etc.,and are widely used in the field of photocatalysis.with broadly application foreground.However,its photocatalytic efficiency is relatively low due to the severe recombination of photogenerated electrons and holes due to its narrow band gap.The supported cocatalyst promotes the separation of electrons and holes to enhance the photocatalytic ability of the catalyst.The comprehensive performance of photocatalysis is improved by supporting cocatalysts,which is due to the fact that the addition of cocatalysts can capture photogenerated electrons from the conduction band of photocatalysts,provide abundant active sites,and reduce the activation energy of hydrogen production reaction.In this paper,different molybdenum-based cocatalysts were synthesized,combined with MAPbI₃ and applied to photocatalytic HI hydrogen production,and their microstructure and hydrogen production mechanism were explored.The specific research results are as follows:（1）MoC/MAPbI₃ Hybrid Composites for Efficient Photocatalytic Hydrogen EvolutionMoC particles were prepared by high temperature calcination method,and MoC/MAPbI₃composite photocatalyst was synthesized by simple electrostatic coupling method.The loading of MoC on the surface of MAPbI₃ can not only reduce the hydrogen evolution potential of the perovskite surface;in addition,MoC as a cocatalyst can promote the separation of electrons and holes at the MoC/MAPbI₃ interface.MoC/MAPbI₃ composite exhibited excellent photocatalytic activity and stability in the HI saturated with MAPbI₃ under visible irradiation（λ≥420 nm）.Among them,the 15%MoC/MAPbI₃ composite exhibited the highest visible light hydrogen evolution activity,which was 38.4μmol h^-1,24 times higher than the monomeric MAPbI₃(1.61μmol h^-1).Furthermore,in multiple consecutive four-hour loop tests,the cyclic stability of MoC/MAPbI₃ did not decrease.More importantly,MoC/MAPbI₃ exhibited a much better catalysis performance than MAPbI₃ modified by tradition noble metal Pt under the same experimental condition.The high catalytic activity may be benefited from the effective charge separation and transfer between MoC and MAPbI₃.（2）Preparation and Photocatalytic Properties of Hollow MoS₂-Supported MAPbI₃CompositesHollow MoS₂ microspheres（donated as H-MoS₂）were prepared by hydrothermal and further acidification using the template method.The H-MoS₂/MAPbI₃ composite material was successfully prepared by combining with MAPbI₃ crystallites by electrostatic coupling method,and carried out photocatalytic HI test.The introduction of H-MoS₂ reduced the hydrogen evolution potential on the surface of MAPbI₃.Meanwhile,as an electron acceptor,it can effectively promote the separation of electrons and holes at the H-MoS₂/MAPbI₃ interface.The H-MoS₂/MAPbI₃composite exhibited good photocatalytic activity and stability under visible light irradiation（λ≥420 nm）.Among them,the hydrogen evolution rate of the 15%H-MoS₂/MAPbI₃ composite was as high as 399μmol h^-1,which was 260 times that of pure MAPbI₃(1.53μmol h^-1)and far superior to that of Pt/MAPbI₃(15.1μmol h^-1).The long-term cyclic stability test results also showed that the H-MoS₂/MAPbI₃ composite has good stability.