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Facile synthesis of diamino-modified graphene/polyaniline semiinterpenetrating networks with practical high thermoelectric performance Yen-Hao Lin, Tsung-Chi Lee, Yu-Sheng Hsiao, Wei-Keng Lin, Wha-Tzong Whang, and Chun-Hua Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14890 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 10, 2018
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ACS Applied Materials & Interfaces
Facile synthesis of diamino-modified graphene/polyaniline semiinterpenetrating networks with practical high thermoelectric performance Yen-Hao Lin†, Tsung-Chi Lee†, Yu-Sheng Hsiao*‡, Wei-Keng Lin¶, Wha-Tzong Whang†, ChunHua Chen*†
†Department of Materials Science and Engineering, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu, Taiwan 300, R.O.C. ‡ Department of Materials Engineering, Ming Chi University of Technology, 84 Gungjuan Rd., Taishan Dist. New Taipei City, Taiwan 243, R.O.C. ¶Department of Engineering and system science, National Tsing Hua University, Sec. 2, Kuang-Fu Road, Hsinchu, Taiwan 300, R.O.C. KEYWORDS: Semi-interpenetrating network (S-IPN), Graphene, Polyaniline, Thermoelectric, Conducting polymer. ABSTRACT: p-Phenediamino-modified graphene (PDG) has been newly synthesized via a facile green one-step chemical route as a functionalized graphene-based additive to copolymerize with aniline for fabricating innovative PDG/polyaniline conducting polymer composites (PDG/PANI) containing very special semi-interpenetrating networks (S-IPNs). The S-IPNs which not only provide additional pathways by creating chemically-bonded PDG and PANI for smoothly transporting carriers, but greatly reduce the amount of graphene required to less than a few percent could effectively improve the overall electrical conductivity, Seebeck coefficient and thus the thermoelectric performance. The found optimized thermoelectric figure of merit (ZT) of 0.74 approaches a practical high level which is comparable or much higher than previously reported ones for thermoelectric polymers.
Introduction 1-2
Conjugated polymers, e.g. polyaniline (PANI) , or poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)3-7, have attracted great attention over the past decade not only because of their metal-like conductivity, but also because of their potential for achieving remarkable thermoelectric (TE) figures of merit (ZTs) via chemical functionalization of the polymer chains or doping8-10. ZT is defined as σS2T/κ, where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the thermal conductivity, and T is the absolute temperature. The unique characteristics of the conjugated polymers, such as their liquid base, flexibility, typically low thermal conductivity, high Seebeck coefficient, and more importantly, modifiable functional groups, enable the TE polymers to simply blend with various classes of inorganic TE materials for fabricating unique organic/inorganic TE composites having complementary properties11. Graphene, which exhibits intrinsically high conductivity and mechanical strength and can be readily chemically functionalized, has been one of the most considered candidates among potential heterogeneous dopants for TE polymers12. However, the poor dispersibility of un-modified graphene in solvents, caused by its rare surface functional
moieties and the strong van der Waals forces between graphene layers, leads to difficulties in preparing the desired monodisperse TE polymer/graphene composites. The breakthrough of the chemical modification of graphene made by Ruoff et al. directly promotes the progress of polymer/graphene composites13. Gao14 has also demonstrated the functionalization of graphene oxide (GO) with various functional groups (e.g. hydroxyl, carboxyl, amino, bromine, long alkyl chains, etc.) and the simultaneous reduction of the GO to graphene. The graphene functionalized by these known approaches is well dispersed in different polymer matrices and can generally ameliorate the overall conductivity15, improve the mechanical properties1618 , and increase the thermal stability19. In this work, we newly designed and fabricated a series of p-phenediamino-modified graphene (PDG)/PANI composites comprising very unique semi-interpenetrating networks (S-IPNs) constructed by chemically-bonded 2dimensional (2D) graphene sheets and 1-dimensional (1D) PANI chains for principally improving the TE performance. To achieve these novel hybrid structures, graphene edges were chemically decorated with amino-aniline groups using p-phenylenediamine (p-PD).
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Figure 1. Schematic diagram of semi-interpenetrating networks constructed by chemically-bonded p-phenediamino-modified graphene and linear polyaniline.
The modified graphene then polymerizes with aniline monomers to form unique S-IPNs as illustrated in Figure 1. The S-IPNs in the PDG/PANI composites would significantly reduce the overall resistance when carriers move through the composites and thus enhance the TE performance. The present study provides an economic and environmentally-friendly two-step chemical route for synthesizing well-conductive graphene decorated TE polymers, which is completely different from the conventional complicated approaches. In recent research, the weight ratio of PANI/graphene is 30 wt % to 60 wt %. The thermoelectric properties show a significant improvement because of the high ratio of PANI/graphene. However, the high graphene content causes increased costs and more waste in the production of this graphene, as shown in Table 1. In our experiments, we use a small amount of graphene (
