Effect of graphene nanofillers on the enhanced thermoelectric properties of Bi₂Te₃ nanosheets: elucidating the role of interface in de-coupling the electrical and thermal characteristics

Abstract

In this report, we investigate the effect of graphene nanofillers on the thermoelectric properties of BiTe nanosheets and demonstrate the role of interface for enhancing the overall figure of merit (ZT) ∼ 53%. The enhancement in the ZT is obtained due to an increase in the electrical conductivity (∼111%) and decrease in the thermal conductivity (∼12%) resulting from increased conducting channels and phonon scattering, respectively at the interfaces between graphene and BiTe nanosheets. A detailed analysis of the thermal conductivity reveals ∼4 times decrease in the lattice thermal conductivity in contrast to ∼2 times increase in the electronic thermal conductivity after the addition of graphene. Kelvin probe measurements have also been carried which reveals presence of low potential barrier at the interface between graphene and BiTe nanosheets which assist the flow of charge carriers thereby, increasing the mobility of the carriers. Thus, our results reveals a significant decrease in the lattice thermal conductivity (due to the formation of interfaces) and increase in the electron mobility (due to conducting paths at the interfaces) strongly participate in deciding observed enhancement in the thermoelectric figure of merit.

Thermoelectric Properties of Reduced Graphene Oxide/Bi2Te3 Nanocomposites

“…It can be seen that as the content of rGO is increased from 0 to 1 wt%, no other peaks appear, which agrees with the results reported in Ref. [16]. by the van der Pauw technique.…”

“…As the content of rGO is increased from 0 to 1 wt%, the electrical conductivity of the rGO/Bi2Te3 nanocomposite bulk materials decreases from 1403 S/cm to 1025 S/cm at room temperature. These values are higher than those of typical values for Bi2Te3/graphene bulk material (~950 S/cm with 0.2 vol.% graphene at 300 K) [14] or Bi2Te3 NW/graphene bulk material (~230 S/cm with 1 wt% graphene at 300 K) [18], but very close to Bi2Te3/rGO bulk material (1440 S/cm at 300 K) [16]. The electrical conductivity for all the samples decreased as the measurement temperature was increased from 25 °C to 300 °C, indicative of degenerate semiconductor behavior [30].…”

“…As the measurement temperature increased, the absolute value of Seebeck coefficient for all the samples first increased and then decreased, e.g., the absolute value of the (negative) Seebeck coefficient of the composite with 1 wt% rGO increased from 96 μV/K at 25 °C to 120 μV/K at 200 °C, and then decreased to 105 μV/K at 300 °C. The absolute value of the (negative) Seebeck coefficient of the composite with 1 wt% rGO (96 μV/K at 25 °C) is higher than that of a Bi2Te3/rGO bulk material (83 μV/K at 300 K) [16]; however, it is lower than that of a Bi2Te3/graphene bulk material (~113 μV/K with 0.2 vol.% graphene at 475 K) [14] and a Bi2Te3 NW/graphene bulk material (~170 μV/K with 1 wt% graphene at 300 K) [18]. The power factor of the samples first increased and then decreased as the measurement temperature was increased from 25 °C to 300 °C (Figure 7c), mainly due to the same trend of the absolute value of Seebeck coefficient and the decreased electrical conductivity.…”

“…Carbon nanotubes and graphene have shown high electrical conductivity, high carrier mobility, and high mechanical properties [10,11], and have been widely used in the research on inorganic TE composite materials [12][13][14][15][16][17][18][19]. For example, Dong et al [12] prepared PbTe/graphene nanocomposite powders by a wet chemical method, and then sintered the as-prepared powders by a spark plasma sintering (SPS) process at 580 • C, and a ZT value of 0.7 was obtained at 670 K for the composite with 5% mass ratio of graphene: PbTe.…”

“…For example, Dong et al [12] prepared PbTe/graphene nanocomposite powders by a wet chemical method, and then sintered the as-prepared powders by a spark plasma sintering (SPS) process at 580 • C, and a ZT value of 0.7 was obtained at 670 K for the composite with 5% mass ratio of graphene: PbTe. Ju et al [13] fabricated Bi 2 Te 3 nanowire (NW)/graphene composite films by wet chemical synthesis combined with a sintering process, and a ZT value of 0.2 was obtained for the composite film with 20 wt% Bi 2 Te 3 NWs at 300 K. Liang et al [14] prepared Bi 2 Te 3 /graphene bulk materials by a hydrothermal process combining SPS method, and a ZT value of 0.21 was obtained for the composite with 0.2 vol.% graphene at 475 K. Agarwal et al [15] prepared Bi 2 Te 3 /graphene bulk materials by a cold pressing method, and a ZT value of 0.92 was obtained for the composite with 0.05 wt% graphene at 402 K. Kumar et al [16] synthesized Bi 2 Te 3 /reduced graphene oxide (rGO) nanocomposites by a refluxing method, and then pressed the as-prepared nanocomposites into pellets; a ZT value of~0.35 was obtained for the pellet at~340 K. Zhang et al [17] reported Bi 0.4 Sb 1.6 Te 3 bulk materials by a high-pressure and high-temperature synthesis and high pressure sintering method, and a ZT value of 1.26 at 423 K was obtained for the composite with 0.05 wt% graphene. Ju et al [18] fabricated Bi 2 Te 3 NW/graphene bulk materials by a wet-chemical synthetic route and subsequent sintering process, and a ZT value of 0.4 was obtained for the composite with 1 wt% graphene at 300 K. Shin et al [19] prepared rGO/Bi 0.36 Sb 1.64 Te 3 composites by a melt spinning process combining SPS method, and a ZT value of 1.16 was achieved for the composite with 0.4 vol.% rGO at 393 K.…”