Activating The Basal Plane Of 1T Phase Molybdenum Disulfide For Electrocatalytic Hydrogen Evolution

Hydrogen production from water electrolysis,as a clean energy conversion and storage technology,is highly expected to alleviate the fossil energy crisis and achieve a sustainable and stable supply of clean energy in the future.Currently,the main difficulty in the large-scale application of water electrolysis is the lack of cheap and efficient catalysts.1T-phase molybdenum disulfide（1T-MoS₂）,as a typical two-dimensional layered material,has advantages in reactant diffusion,charge transfer and specific surface area during electrocatalytic reactions.Moreover,its metal-like electrical conductivity and the abundance of active sites in the edge and the basal plane make 1T-MoS₂ more promising for catalytic hydrogen evolution reaction（HER）.However,the poor HER catalytic activity of 1T-MoS₂ resulted from the weak interaction between the basal plane sites and the adsorbed hydrogen,limits the further improvement of the catalytic performance of 1T-MoS₂.In this thesis,we constructed out-of-plane heterostructures to regulate the electronic structure of 1T-MoS₂ basal plane through the interfacial effect between heterogeneous phases,thus optimizing the hydrogen adsorption free energy and enhancing the catalytic hydrogen evolution activity.Further,we delicately constructed in-plane heterostructures based on the interfacial geometry with the heterogeneous phase embedded in the 1T-MoS₂ lattice.Combining experiments and density functional theory calculations,we investigated the factors affecting the in-plane heterostructures on the electronic structure of1T-MoS₂ basal plane and catalytic hydrogen evolution activity.The main research contents and results are as follows:1.For the current scaled-up alkaline water electrolytsis system,we prepared a self-supporting electrode constructed by 1T-MoS₂ nanosheet nanowire arrays modified by Ni（OH）₂ nanoparticles（Ni（OH）₂@1T-MoS₂ NWAs）for alkaline water electrolytsis.Combining the experimental and density functional theory calculations,the heterostructure constructed by Ni（OH）₂ and 1T-MoS₂ integrated the adsorption of H and OH,thus accelerating the dissociation of water molecules in the alkaline HER.Moreover,the interfacial effect of the heterostructure electronically modulateed the Ni（OH）₂ and 1T-MoS₂ basal planes,which in turn enhanced the interaction of the1T-MoS₂ basal site with the adsorbed hydrogen and the OER kinetics of Ni（OH）₂.In addition,the elaborate constructed nanowire array structure exposed a large number of catalytically active sites and facilitated the mass transport.Benefiting from these advantages,the alkaline HER activity of the 1T-MoS₂ basal plane was significantly enhanced and the prepared electrode revealed high activity with only 56.9 m V,265.8m V,and 1.51 V overpotential to drive alkaline HER,OER,and overall water electrolysis at a current density of 10 m A cm^-2.2.We prepared a heterostructure of CoS₂ nanoparticles loaded on 1T-MoS₂nanosheets and served it as a self-supporting electrode（CoS₂@1T-MoS₂/CC）for catalyzing HER in a wider p H range.The prepared electrode reached 10 m A cm^-2current density at overpotentials of 100,352 and 155 m V in the electrolyte system at p H of 0,7 and 14,respectively.Besides,CoS₂@1T-MoS₂/CC were catalytically stable at a current density of 200 m A cm^-2 for 30 h.Combining density functional theory calculations,we investigated the influence of interface effect on 1T-MoS₂basal plane,and established the structure-effect relationship between the electronic structure and catalytic activity of the 1T-MoS₂ basal plane.It revealed that the improved catalytic activity of the interfacial S atoms originated from the enhanced hydrogen adsorption capacity on account of the proper shift of the S 2p orbital center to the Fermi energy level.This work provides insights for the rational tuning of the electronic structure to optimize the HER catalytic activity of 1T-MoS₂ basal plane.3.We developed a synthesis technology for 1T-MoS₂ based in-plane heterostructures.The Mn S@1T-MoS₂/CC self-supported electrode was fabricated by replacing part of the MoS₂ nanodomains with Mn S clusters embedded in 1T-MoS₂nanosheets.With the in-situ transformation from Mn S to Mn O₂,we fabricated the Mn O₂@1T-MoS₂/CC self-supporting electrode and demonstrated the distinct in-plane heterostructure of the prepared electrodes.This in-plane heterostructure retained the advantages of heterostructure with optimized interfacial electronic structure and regulated hydrogen adsorption free energy,while overcoming the drawbacks of out-of-plane heterostructures in which heterogeneous phases were easily overgrowth and the heterointerfaces were exposured incompletly.The prepared Mn S@1T-MoS₂/CC and Mn O₂@1T-MoS₂/CC both exhibit excellent HER catalytic activity and excellent electrochemical stability,with an overpotential of only 225 and161 m V to reach 20 m A cm^-2 and a current density retention of more than 90%after stability tests.4.Based on the synthesis technique of in-plane heterostructures,we prepared TMSs@1T-MoS₂（TM=Fe,Co,Ni）in-plane heterostructure catalysts and explored the structure-effect relationship between TMSs species and the activity enhancement of 1T-MoS₂ basal plane.Experimental and density functional theory results showed that the insertion of TMSs led to the contraction of 1T-MoS₂ nanosheet spacing and the expansion of the in-plane lattice,and it also induced the migration of electrons from TMSs to 1T-MoS₂ at the heterointerface.It revealed that the activity modulation of 1T-MoS₂ basal plane site by TMSs depended on the TMSs-induced lattice tension strength and the amount of electron migration.Among FeS₂,CoS₂,and NiS₂,NiS₂acts most obviously.With NiS₂ insertion,the 1T-MoS₂ lattice had the largest tensile strain and accepts the most electrons.Consequently,the lowest electron content of antibonding orbitals was filled below the Fermi energy level,and the corresponding in-plane heterostructures with the strengthened interactions to H^*,exhibited optimal HER catalytic activity.NiS₂@1T-MoS₂ can drove a current density of 10 m A cm^-2 at low overpotentials of 73 and 71 m V in acidic and basic electrolytes,respectively.This work provides a new insight for the design of advanced two-dimensional layered material electrocatalysts.