Controllable Synthesis Of Metallic MoS₂/MoSe₂ Co-catalyst And The Mechanism Of Improving Its Photocatalic Hydrogen Production Performance

Photocatalytic hydrogen production can make full use of solar energy to convert it into hydrogen energy with higher energy density.Photocatalysis avoids the high energy consumption and high pollution which are the disadvantages of traditional hydrogen production technology.Therefore,it is considered as the most ideal way to produce hydrogen and has received widespread attention.At present,the key restriction on large-scale application of semiconductor photocatalysis is the rapid recombination of photogenerated carriers,which leads to low photocatalytic efficiency.Co-catalysts can improve the efficiency of photocatalytic hydrogen production by increasing the effective photogenerated electrons which migrate to the surface of the catalyst for the reduction reaction with electron acceptor.Thus,co-catalysts can effectively realize electronic regulation and greatly improve the separation efficiency of photogenerated carriers.However,its application is limited by the low storage and high cost of noble-metals.Therefore,it is of great significance to develop new inexpensive cocatalysts based on earth-abundant-elements to improve photocatalytic efficiency.Mo S₂,Mo Se₂（Mo X₂）has graphene-like two-dimensional structure which gives it unique physical and chemical properties.The instability and excellent electrical conductivity of metallic phase Mo X₂ bring challenges and opportunities According to these,excellent photocatalytic co-catalyst was prepared in this paper,which was combined with semiconductor materials to obtain efficiency photocatalytic composites to produce hydrogen.The detailed work is as follows:（1）The controllable synthesis of metallic phase Mo Se₂（1T-Mo Se₂）is particularly important for its co-catalytic performance.1T-Mo Se₂ in-situ grew on the surface of Ti O₂ particles to prepare the Ti O₂/Mo Se₂ composite photocatalysts with tight contact interface.The synergy of maximized cocatalytic effect of 1T-Mo Se₂ via phase engineering and the optimized contact interface with suitable interfacial barrier between the 1T-Mo Se₂ and Ti O₂ can accelerate the charge carrier separation to promote photocatalysis efficiency.The H₂ yield of the optimal Ti O₂/1T-Mo Se₂hybrid under 5 h simulated sunlight illumination was 17.0 mmol·g^-1,which was 77.6 times higher than that of pure Ti O₂.The H2 yield from seawater of the optimal Ti O₂/1T-rich Mo Se₂ also can reach 1.05mmol g^-1 h^-1.（2）Novel Se-rich 1T’-Mo Se_2.3 uniform grew in Cd S nanosheets surface and formed special2D/2D structure.The 2D/2D structure increased the strong electron coupling interface between Cd S and Mo Se_2.3,also shortened the distance of photoproduction electronic migrated to the activity sites.In addition,the absorption edge was expanded from about 515 nm to about 780 nm after loading Se-rich Mo Se_2.3,shows excellent hydrogen production performance under 550 nm light with AQE of 7%.The Cd S/M-Mo S₂ photocatalytic composites improve the utilization of visible light and photocatalytic efficiency.（3）A monolayer pure metallic Mo S₂（M-Mo S₂）aqueous solution was prepared aim at solve the problem of metallic phase Mo X₂ is not easy to disperse.The prepared monolithic metallic Mo S₂（M-Mo S₂）has good dispersibility in aqueous solution,so as to further composite semiconductor to prepare photocatalytic composite materials.The Cd S particles were grown on the surface of the M-Mo S₂ monolayers and the interface between Cd S and M-Mo S₂ is close and has a strong electron coupling.The M-Mo S₂ co-catalyst can effectively reduce the recombination of charge,thus maximizing the separation of photogenerated carriers,and greatly improving the life of photogenerated charge to generate hydrogen reaction.Therefore,the efficient photocatalyst was obtained,and the rate of photocatalytic hydrogen production under visible light irradiation could reach 27.437 mmol g^-1 h^-1.