Study On The Structure Design And Thermoelectric Properties Of Low Thermal Conductivity Composites

Most countries now are seeking for new energy conversion materials,and one promising candidate is thermoelectric?TE?materials which can convert waste heat into electricity.Because of the problems of energy crisis and environment pollution are becoming more and more seriously.TE materials mainly apply to the temperature difference fields include power generation and refrigeration technology,which is considered to be one of the most development prospects of energy material.For TE materials,the ability of energy conversion between heat and electricity depends on the figure of merit,ZT= S2?T/?.In addition to the temperature T,the three thermoelectric parameters include of Seebeck coefficient?S?,electrical conductivity???and and thermal conductivity?k?play important roles for the improvement of thermoelectric properties.It is an avaluable way that decreasing thermal conductivity to improve the ZT value.So it is valuable that designing a low thermal conductivity material to improve the performance of thermoelectric materials.In order to reduce the thermal conductivity,this article design and preparat the low thermal conductivity composite materials by using of special materials,constructing special structure and doping methods.The specific research contents and conclusions are as follows:?1?In the first part,we report a new nanocomposite aerogel based on Poly?3,4-2 oxygen ethylene thiophene?: poly styrene sulfonic acid?PEDOT: PSS?,MWCNTs and Ag?PCA?.The choice of these two components is motivated by that MWCNTs are expected to construct a three dimensional solid skeleton,and the excellent bulk electrical conductivity of Ag is introduced into PEDOT: PSS system to enhance the electrical conductivity.The SEM results show that PCA aerogels have three-dimensional network structures,and PCA aerogels possess large specific surface areas?228 m2/g?.What's more,the electrical conductivity and Seebeck coefficient of PCA aerogels improves simultaneously with doping Ag nanoflakes while the thermal conductivity keeps a level which is 0.06 W/mK to 0.11 W/mK at room temperature.Compared with pure PEDOT:PSS material which the thermal conductivity is about 0.348±0.01 W/mK,the vualesis of PCA aerogels are much lower.Combinating of three factors,the influence of the preparation of thermoelectric materials ZT value up to 7.56 ×10-3 at room temperature upon addition of Ag contents of 33.32 wt %.?2?In this work,we report a new nanocomposite aerogel based on PEDOT:PSS and Bi₂Te₃,the choice of Bi₂Te₃ is expected to provide excellent bulk electrical conductivity And thermoelectric performance of PEDOT:PSS/ Bi₂Te₃?PB?aerogels were tested and analyzed.Through SEM found that pure PEDOT:PSS aerogel has hole structure obviously,and Bi₂Te₃ powders dispersed in polymer matrix homogenously while the network structure is not damaged.The thermal conductivity of PB aerogels were from 0.15 W/mK to 0.24 W/mK at room temperature and increased with the increase of Bi₂Te₃ contents.At room temperature,with the increasing of Bi₂Te₃ contents,the electric conductivity of PB aerogels significantly,and the Seebeck coefficient increaed to 92.61 ?VK.?3?Thirdly,the PEDOT: PSS/MWCNTs filter?PMF?composite films were perapared successfully with different qualities of MWCNTs were mixed in PEDOT:PSS solution by ultrasonic and casting on the filter paper that has low thermal conductivity.This experiment studies on the influence of different proportion,different layer numbers and different temperature on the properties of composite materials.Results show that MWCNTs were uniformly dispersed in the PEDOT: PSS composite and composited well together with PEDOT: PSS.What is exciting to us is that the thermal conductivity at room temperature of PMF composite is very low,the highest value is about 0.2 W/mK.When the raw materials proportion is 1:1,the electric conductivity of all PMF composites were best;With the increase of coating layer numbers,the electric conductivity increased first and then decreaed,when the raw materials proportion is 1:1 and the number of layer is 3,the electric conductivity increaed into 3530.47 S/m.And the Seebeck coefficient is in the range of feom 15 ?V/K to19 ?V/K.?4?Bismuth telluride?Bi₂Te₃?powder was successfully synthesized by hydrothermal reaction,which was composited with Carbon black?CB?,and then the TE performance of Bi₂Te₃/CB composite materials was investigated.At the same time,TGA,SEM and XRD analysis methods were used to characterize the structure of TE materials and the relationship between microscopic structures.Thermoelectric properties were researched intensively.It was showed that the thermal conductivity of TE materials reduced sharply?from 0.59 W/mK to 0.09 W/mK at room temperature?because of doped with CB under the special structure design.However,the electrical and thermal conductivities increased with the increase of the contents of Bi₂Te₃,and Seebeck coefficients increased first and then decreased.After composite material sintered under 558 ? for 10 min,the ZT value of composites with 88.9 wt% Bi₂Te₃ was the best?ZT=0.21?at room temperature.This topic investigation may provide a new idea for the further study of the thermoelectric materials.