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Preparation and characterization of expanded graphite polymer composite films for thermoelectric applications
Author(s) -
Piao Mingxing,
Kim Gyutae,
Kennedy Gary P.,
Roth Siegmar,
DettlaffWeglikowska Urszula
Publication year - 2013
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201300078
Subject(s) - seebeck coefficient , materials science , thermoelectric effect , pedot:pss , polyvinyl alcohol , composite number , composite material , graphite , doping , conductive polymer , polymer , optoelectronics , thermal conductivity , physics , thermodynamics
This report demonstrates application of expanded graphite (ExG) for thermoelectric energy conversion, where it serves as a filler for both p‐ and n‐type organic materials. Thin ExG composite films showing improved thermoelectric properties were prepared. In particular, composites with intrinsically conducting polymer poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) yielding high electrical conductivity (up to 10 4 S m −1 ) and enhanced thermopower (Seebeck coefficient) provided promising p‐type material. Chemical doping experiments performed on ExG dispersed in polyvinyl alcohol (PVA) revealed that the exfoliated graphitic sheets can be efficiently n‐doped with polyethyleneimine (PEI). As a result, n‐type ExG/PVA/PEI composite thin films showing improved n‐type characteristics with thermopower values as high as −25.3 µV K −1 were prepared. With a 25 wt% ratio of PEI to ExG, the electrical conductivity was measured to be ∼10 3 S m −1 , which is remarkably high for n‐type polymer composites. Strips of composite films containing 50 wt% of ExG in PEDOT:PSS were used as p‐type components, and composite films containing 20 wt% of ExG in PVA doped with PEI were used as n‐type components in thermoelectric modules to demonstrate thermoelectric voltage with one, two, and three p‐n couples connected in series. The testing modules produced an output voltage of ∼4 mV at a temperature gradient of 50 K. The module generated 1.7 nW power, when a load resistance matched the internal module resistance of 1 kΩ. Our results show that chemical functionalization of ExG in thin composite films resulted in more effective thermoelectric properties.