| Polypyrrole?PPy?is a kind of potential organic thermoelectric material which has attracted extensive attention in recent years because of its non-toxic environmental protection,low cost,abundant resources,low thermal conductivity and good air stability and so on.However,its application is mainly limited by the relatively low intrinsic electrical conductivity and Seebeck coefficient,and its poor thermal stability.In view of the above problems,this work adopts doping and combining with other materials to improve the electrical transport properties and the thermoelectric properties of PPy via chemical oxidative polymerization method.The effects of different organic acids??-NSA,TsOH?,anionic surfactants?SDS,SDBS?and inorganic carbon materials?MWCNT,rGO?on the morphology,electrical transport properties,thermoelectric properties and thermal stability of PPy have studied systematically.The main research work and the results are as follows:The thermoelectric properties of PPy can be improved effectively when TsOH and?-NSA as dopants.Because the two kinds of organic acids can not only as dopant introduce to the PPy chain,but can as templates induce PPy to form a more orderly chain structure.When TsOH as dopant,the optimal thermoelectric properties of PPy was obtained as the molar ratio of monomer py and TsOH is 1.0:1.25,and the maximum value of ZT is 0.37×10-33 at 300 K.The best thermoelectric figure of merit ZT is 0.62×10-33 at 300 K when the molar ratio of monomer py to?-NSA is 1.0:0.45.It can be seen that?-NSA as dopant,PPy thermoelectric properties have been greatly improved,mainly because the?-NSA has a large conjugate structure which can enhance the conjugation degree of PPy to improve the carrier mobility,so that the thermoelectric performance of PPy can be developed.At the same time,the thermal stability of PPy also can be promoted after doping TsOH and?-NSA.The preparation of PPy by changing the concentration of sodium dodecylsulfonate?SDS?and sodium dodecylbenzene sulfonate?SDBS?can not only improve the morphology of PPy as soft templates,but also as dopant into PPy chain.When SDS is used as soft template,the optimal concentration of SDS is 0.025 M and the ZTmaxax value is 0.23×10-33 at 325 K.When SDBS as soft template,the optimal concentration of SDBS is 0.030 M,the maximum ZT value of 0.17×10-33 was acquired at 400 K.FESEM images show that the two anionic surfactants formed different PPy micro-morphology,primarily due to SDS and SDBS hydrophilic lipophilic balance,?HLB?value is distinct.HLB value of SDS and SDBS are 40,10.638,respectively.Therefore,the hydrophilicity of SDS is better,the size of the micelles in the aqueous solution is larger,resulting in bigger particle size of PPy.And the SDBS micelles formed in the aqueous solution are small,and the benzene ring of SDBS can stabilize the micelles,so the particle size of PPy is small.Meanwhile,owing to the different decomposition temperature of SDS and SDBS,SDS will aggravate the decomposition of PPy,and SDBS will improve the thermal stability of PPy.Considering the steric hindrance effect caused by SDBS long molecular chain which can form a stable dispersion system,so PPy/MWCNT and PPy/rGO composites were successfully prepared by using SDBS as dispersant,multi-walled carbon nanotubes?MWCNT?and reduction graphene oxide?rGO?as composite materials.The highest thermoelectric figure of merit ZT is 1.411×10-33 when the MWCNT mass ratio is 7 wt%,22 times higher than that of pure PPy.When the rGO mass ratio is 9 wt%,ZTmaxax value of 1.534×10-33 is 24 times as high as that of pure PPy at 325 K.The percolation thresholds phenomenon in polymer composites limits the amount of MWCNT and rGO,so it is necessary to control the content of MWCNT and rGO in order to obtain the best thermoelectric properties of PPy.Beside,thanks to the excellent thermal stability MWCNT and rGO,and the 3D network of PPy-MWCNT and PPy-rGO formed by?-?interaction limits the thermal vibration of PPy chain,both of which can enhance the thermal stability of PPy significantly. |
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