Nanocomposites with p- and n-Type Conductivity Controlled by Type and Content of Nanotubes in Thermosets for Thermoelectric Applications.

Katharina Kröning,Beate Krause,Bodo Fiedler,Petra Pötschke

doi:10.3390/nano10061144

Abstract

In this work, composites based on epoxy resin and various carbon nanotubes (CNTs) were studied regarding their thermoelectric properties. The epoxy composites were prepared by infiltration of preformed CNT buckypapers. The influence of different types of CNTs on the Seebeck coefficient was investigated, namely lab-made and commercially available multi walled carbon nanotubes (MWCNTs), lab-made nitrogen doped MWCNTs (N-MWCNT) and commercially available single walled carbon nanotubes (SWCNTs). It was found that only by varying the lab-made MWCNT content could both n- and p-type composites be produced with Seebeck coefficients between −9.5 and 3.1 µV/K. The incorporation of N-MWCNTs resulted in negative Seebeck coefficients of −11.4 to −17.4 µV/K. Thus, the Seebeck coefficient of pure SWCNT changed from 37.4 to −25.5 µV/K in the epoxy/1 wt. % SWCNT composite. A possible explanation for the shift in the Seebeck coefficient is the change of the CNTs Fermi level depending on the number of epoxy molecules on the CNT surface.

Highlights

The thermoelectric (TE) effect, discovered in 1821 by Thomas Johann Seebeck, describes the direct conversion of temperature differences into electrical voltage and vice versa via a thermocouple.Thermoelectric devices (TED) create a voltage when there is a different temperature on each side of the constituent materials
Different kinds of lab-made nitrogen-doped multi walled carbon nanotubes (MWCNTs) show n-type behavior deduced from negative. This is in good agreement with other investigations of nitrogen doped MWCNTs (N-MWCNT) reported in Krause et al [12,13]
This is in good agreement with other investigations of N-MWCNT reported in Krause et al The thermoelectric properties of epoxy composites were strongly dependent on the carbon nanotubes (CNTs) content

Summary

Introduction

The thermoelectric (TE) effect, discovered in 1821 by Thomas Johann Seebeck, describes the direct conversion of temperature differences into electrical voltage and vice versa via a thermocouple. Thermoelectric devices (TED) create a voltage when there is a different temperature on each side of the constituent materials. Thereby, the applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side. This effect can be used to generate electricity or measure temperature. The Seebeck coefficient (S), defined as the ratio of the generated thermoelectric voltage and the temperature gradient, is a material constant and can be positive or negative, depending on the charge carriers (holes (p-type) or electrons (n-type)). The power factor considers the Seebeck coefficient (S) and the electrical conductivity (σ) and is defined by Equation (1)

Methods

Results

Discussion

Conclusion