Thermal Transport and Thermoelectric Effect in Composites of Alumina and Graphene-Augmented Alumina Nanofibers.

Ali Saffar Shamshirgar,Roman Ivanov,Girish C Tewari,Pilar Miranzo,Maarit Karppinen,Jani Seitsonen,Irina Hussainova,Manuel Belmonte,Rocío E Rojas Hernández

doi:10.3390/ma14092242

Abstract

The remarkable tunability of 2D carbon structures combined with their non-toxicity renders them interesting candidates for thermoelectric applications. Despite some limitations related to their high thermal conductivity and low Seebeck coefficients, several other unique properties of the graphene-like structures could out-weight these weaknesses in some applications. In this study, hybrid structures of alumina ceramics and graphene encapsulated alumina nanofibers are processed by spark plasma sintering to exploit advantages of thermoelectric properties of graphene and high stiffness of alumina. The paper focuses on thermal and electronic transport properties of the systems with varying content of nanofillers (1–25 wt.%) and demonstrates an increase of the Seebeck coefficient and a reduction of the thermal conductivity with an increase in filler content. As a result, the highest thermoelectric figure of merit is achieved in a sample with 25 wt.% of the fillers corresponding to ~3 wt.% of graphene content. The graphene encapsulated nanofibrous fillers, thus, show promising potential for thermoelectric material designs by tuning their properties via carrier density modification and Fermi engineering through doping.

Highlights

Accepted: 23 April 2021Almost all energy conversion systems are associated with waste of energy in the form of heat
In graphene-augmented alumina nanofibers (GAIN) structures the full width at half maximum (FWHM) of the 2D peak centered at 2669 cm−1 is ~116, almost five times that of the 2D peak of a common single-layer graphene, which together with the presence of a notable first order D peak at 1342 cm−1 corresponds to the results reported for turbostratic carbon [25]
Raman spectroscopy on GAIN fibers have shown that the 2D peak is 21 cm−1 downshifted attributed to the physical strain exerted on graphene by γ-Al2 O3 substrate, and the G peak is 5 cm−1 upshifted as compared to free standing single layer graphene, which was attributed to the doping effect of the substrate and surface physisorbed water

Summary

Introduction

Accepted: 23 April 2021Almost all energy conversion systems are associated with waste of energy in the form of heat. Thermoelectric (TE) conversion is an attractive and technologically viable solution to directly harvest this waste heat. The thermoelectric effect is described as the conversion of heat (temperature gradient) to a voltage potential through the Seebeck effect and vice versa through the Peltier effect. The efficiency of a TE material is defined by the thermoelectric figure-of-merit which is proportional to the Seebeck coefficient and electrical conductivity of the material, and inversely to its thermal conductivity. High electrical conductivity, and low thermal conductivity. Electrical conductivity increases by increasing carrier density through the following relationship σ = neμ. An increase in carrier density results in a decline in Seebeck coefficient. An increase of the carrier density increases the electrical contribution to the thermal conductivity and subsequently a decline in the thermoelectric Figure of Merit [1]. Many of the applicable semiconductor materials including but not limited to Bi2 Te3 [4], PbTe [5], and Sb2 Te3 [6] are Published: 27 April 2021

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Conclusion