Preparation And Thermoelectric Performance Of Two-dimension Mo（S，Se）₂ And Its Composite Materials

Rapid development in human civilization and industrialization provided benefits to our daily life and economics as well as environment pollution and energy shortage.Therefore,eco-friendly energy sources are getting increasing attention in worldwide.Thermoelectric materials can generate electricity with waste heat from industrial and daily life raising wide attention.In the past decade,two dimensional transitional metal dichalcogenides（2D TMDCs）catch concern in a wide range in energy storage and conversion,catalysis,photoelectron fields.Besides,2D TMDCs also possess an adjustable electronic energy band structure and low thermal conductivity,which endows them great potential in thermoelectric materials.As typical 2D TMDCs,molybdenum disulfide（MoS₂）and delenide molybdenum（MoSe₂）are semi-conductive materials with controllable band structure.Theoretical calculation predicts the vast potential for future development out of their high carrier mobility and Seebeck coefficient as well as low thermal conductivity.According to current researches,thermoelectric performance of nanostructured materials is higher than that of bulk materials,which was mainly ascribed to quantum confinement effect.Furthermore,electrical conductivity of TMDCs can be further improved compared with electrical conductivity of many inorganic materials or conductive polymers.At present,constructing composite material has been proven to be an efficient way to obtain high performance thermoelectric materials.To achieve elevation in thermoelectric properties,it is of great significance to systematically investigate the synthesis and thermoelectric properties of Mo（S,Se）₂ based composite materials.In this work,liquid-phase exfoliation was employed to obtain single or few layered MoS₂ and MoSe₂nanosheets,which was subsequently composite with different materials and the thermoelectric performance of these composite materials was systematically explored.Main results are as follow:1.Ag-MoS₂ composite thin films was obtained via lithium intercalation–exfoliation accompanied with in situ composite and we studied its thermoelectric performance.It was found that the decoration of Ag nanoparticles achieved the decoupling in electrical conductivity,which was increased for 1.24 and 1.14 times respectively,consequently leading to an optimized power factor as 30.3μW m^-1 K^-2.Besides,Au,Pt and Pd were also employed to decorate the MoS₂ nanosheets,and the thermoelectric performance of Au-MoS₂,Pt-MoS₂ and Pd-MoS₂ were studied.2.The surface charge in solution dispersible 1T-MoS₂ nanosheets was anisotropy.We adapted Cu²⁺as regulator to decorate defects in MoS₂ thin film via colloidal forces in nano-confinement and investigated its effect on thermoelectric performance of MoS₂.It was found that the decoration of Cu²⁺on MoS₂ gel thin film was mainly concentrated on gap defects among edges between MoS₂ nanosheets.Furthermore,the introduction of Cu²⁺bridged the gap between nanosheets,providing a better carrier transportation.The maximum Seebeck coefficient and optimized power factor of Cu-MoS₂ composite gel film was 159.4μV K^-1 and 23.5μW m^-1 K^-2,respectively.Meanwhile,the stability of its thermoelectric performance was also improved.This current work breaks the traditional conception that the decoration of 2D materials can only be deployed in interlayer gap,which would facilitate the fundamental research and potential application of 2D thin film materials.3.Inspiring from the low thermal conductivity of aerogel,we obtained MoS₂/PEDOT:PSS composite aerogel via freeze drying and systematically investigated the effect of ethylene glycol post treatment on thermoelectric performance of this composite hydrogel.Experimental results presented that as-prepared composite hydrogel was light-weighted and had a low density and an optimized power factor was calculated as 6μW m^-1 K^-2.Moreover,thermoelectric performance was stable after immersed with ethylene glycol,illustrating the structure stability of this composite aerogel.High thermoelectric performance can be achieved for aerogel benefiting from its low thermal conductivity,which was proven to be an efficient way to obtain high performance thermoelectric materials.4.MoSe₂ powders were synthesized by hydrothermal method,and then s-MoSe₂and l-MoSe₂ with 1T phase nanosheets were prepared via solvent direct ultrasonic exfoliation and lithium intercalation–exfoliation method.s-MoSe₂/PEDOT:PSS and l-MoSe₂/PEDOT:PSS were obtained and their thermoelectric performance was systematically investigated.The maximum power factor was remarkably enhanced to48.6μW m^-1 K^-2 when weight ratio of MoSe₂ was 7 wt.%.This obvious promotion in thermoelectric performance was mainly ascribed to following two factors:an increasing energy filtering effect induced by the formation of abundant interfaces and partial removal of insulating PSS chains via solution post treatment.Experimental results presented that MoSe₂/PEDOT:PSS composite materials can effectively utilize advantages of both components to achieve a higher thermoelectric performance.