Preparation and characterization of expanded graphite polymer composite films for thermoelectric applications

Mingxing Piao, Gyu-Tae Kim, Gary P. Kennedy, Siegmar Roth, Urszula Dettlaff-Weglikowska

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

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 104Sm-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 -25.3μVK-1 were prepared. With a 25wt% ratio of PEI to ExG, the electrical conductivity was measured to be ~103Sm-1, which is remarkably high for n-type polymer composites. Strips of composite films containing 50wt% of ExG in PEDOT:PSS were used as p-type components, and composite films containing 20wt% 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 ~4mV at a temperature gradient of 50K. The module generated 1.7nW power, when a load resistance matched the internal module resistance of 1kΩ. Our results show that chemical functionalization of ExG in thin composite films resulted in more effective thermoelectric properties.

Original languageEnglish
Pages (from-to)2529-2534
Number of pages6
JournalPhysica Status Solidi (B) Basic Research
Volume250
Issue number12
DOIs
Publication statusPublished - 2013 Dec 1

Keywords

  • Chemical doping
  • Expanded graphite
  • Seebeck coefficient
  • Thermoelectric modules

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

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