Thermoelectric Power Generation from Lanthanum Strontium Titanium Oxide at Room Temperature through the Addition of Graphene

Abstract

The applications of strontium titanium oxide based thermoelectric materials are currently limited by their high operating temperatures of >700 °C. Herein, we show that the thermal operating window of lanthanum strontium titanium oxide (LSTO) can be reduced to room temperature by the addition of a small amount of graphene. This increase in operating performance will enable future applications such as generators in vehicles and other sectors. The LSTO composites incorporated one percent or less of graphene and were sintered under an argon/hydrogen atmosphere. The resultant materials were reduced and possessed a multiphase structure with nanosized grains. The thermal conductivity of the nanocomposites decreased upon the addition of graphene, whereas the electrical conductivity and power factor both increased significantly. These factors, together with a moderate Seebeck coefficient, meant that a high power factor of ∼2500 μWm(-1)K(-2) was reached at room temperature at a loading of 0.6 wt % graphene. The highest thermoelectric figure of merit (ZT) was achieved when 0.6 wt % graphene was added (ZT = 0.42 at room temperature and 0.36 at 750 °C), with >280% enhancement compared to that of pure LSTO. A preliminary 7-couple device was produced using bismuth strontium cobalt oxide/graphene-LSTO pucks. This device had a Seebeck coefficient of ∼1500 μV/K and an open voltage of 600 mV at a mean temperature of 219 °C.

Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

“…Below 800 K the electrical conductivity and the Seebeck coefficient of polycrystalline STO (without graphene) are beyond the limits of the instruments used here. Literature data sources: lanthanum doped STO single crystal (LSTO SC), reduced graphene oxide/STO nanocomposite (RGO/STO), graphene/lanthanum doped STO nanocomposite (G/LSTO), reduced graphene oxide/niobium doped STO nanocomposite (RGO/NSTO) …”

“…The grain boundary effect is significantly reduced with the addition of only 0.11 vol% pristine graphene, and the weighted mobility matches that of single crystals above 700 K. At higher graphene concentrations (around 0.22 vol%,) the grain boundary effect is completely eliminated above room temperature. The weighted mobilities of the G/STO, G/LSTO, [27] and RGO/ NSTO [28] nanocomposites are the same as that of STO single crystals. This observation suggests the charge transport in the nanocomposites is now governed by acoustic phonon scattering, whereas without graphene, grain boundary scattering limits the mobility in the low temperature range.…”

Anisotropy and enhancement of thermoelectric performance of Sr0.8La0.067Ti0.8Nb0.2O3−δceramics by graphene additions

“…We have previously reported that the incorporation of graphene in La doped SrTiO 3 ceramic (sintered conventionally in a reducing atmosphere of Ar/5% H 2 ) resulted in signicant improvement in ZT values. 46 The highest ZT of 0.12 at 1000 K for the base ceramic was improved to values of $0.26 (approximately temperature-independent) from ambient to 1000 K for a graphene loading of 0.6 wt%. More recently Feng et al 47 reported a ZT value of 0.09 at 760 K for pure SrTiO 3 containing RGO, and Okhay et al 48 reported a ZT value of 0.29 at 1160 K for Nb-doped SrTiO 3 containing RGO.…”

Mg Deficiency in Grain Boundaries of n‐Type Mg3Sb2 Identified by Atom Probe Tomography

“…Other impurities may alter the surface energy in ways that could also control the boundary composition and resultant charge state. Other grain boundary engineering strategies such as adding metallic, nanoscale grain boundary phases such as graphene may also improve conductivity and therefore zT .…”