A comprehensive study on improved power materials for high-temperature thermoelectric generators

Abstract

Dense Ca 3 Co 4 O 9 -Na x CoO 2 -Bi 2 Ca 2 Co 2 O 9 (CCO-NCO-BCCO) nanocomposites were produced from sol-gel derived powder by three methods: Spark plasma sintering, hot-pressing and pressureless sintering under O 2 atmosphere. The SPS processed product showed a thermoelectric power factor of 6.6 µW • cm -1 • K -2 at 1073 K in air. A dense nanocomposite with all-scale hierarchical architecture and enhanced thermoelectric properties is only obtained from pressureless sintering under O 2 atmosphere. The resulting nanocomposite enables the simultaneous increase in isothermal electrical conductivity σ and Seebeck coefficient α, and it delivers a thermoelectric power factor of 8.2 µW • cm -1 • K -2 at 1073 K in air. The impact of materials with enhanced electrical conductivity and power factor on the electrical power output of thermoelectric generators was verified in prototypes. A high electrical power output and power density of 22.7 mW and 113.5 mW•cm -2 , respectively, were obtained, when a hot-side temperature of 1073 K and a temperature difference of 251 K were applied. Different p-and n-type materials were used to verify the effect of the thermoelectric figure of merit zT and power factor on the performance of thermoelectric generators.

High Power Factor vs. High zT—A Review of Thermoelectric Materials for High-Temperature Application

“…In contrast, the power factor is proportional to the maximum achievable power output of a material and the temperature difference T [ 20 ]: …”

“…In this review, we take a closer look at these promising materials for high-temperature applications (>700 K), e.g., power plants, industrial processes, and the automobile industry [ 20 , 42 ]. Therefore, oxide-based materials and several intermetallic compounds such as Zintl phases and half-Heusler compounds will be discussed and compared in terms of the power factor and the figure of merit zT .…”

Redox-Promoted Tailoring of the High-Temperature Electrical Performance in Ca3Co4O9 Thermoelectric Materials by Metallic Cobalt Addition

“…With the discovery of attractive TE properties in Na x CoO 2 ceramics in 1997 [15], a lot of effort has been put in the research and development of CoO-based materials, as well as other transition metal oxides [16], which have important 'default' advantages (abundance, low-cost, environmental 'friendliness', low reactivity and high thermochemical stability) over established TE materials, enabling them to be considered for power generation applications at high temperatures and in oxidizing conditions [17][18][19][20][21]. While the best performing n-type TE oxides were found in the family of perovskite-type titanates [22][23][24][25], manganites [26][27][28][29] and ZnO-based materials [30][31][32], one of the most promising p-type TE materials (considered as the best choice for a p-type leg in a high-temperature TE module) continues to be the so-called Ca 3 Co 4 O 9 compound, belonging to the family of misfit-layered cobaltites [26].…”

Performance of a Thermoelectric Module Based on n-Type (La0.12Sr0.88)0.95TiO3−δ and p-Type Ca3Co4−xO9+δ

“…A high power factor of above 7 lW/cm K 2 is reported at 900°C for In 1.9 Sn 0.05 Al 0.05 O 3 (air), also representing a promising n-type TE material. 9 Pure SrTiO 3 is a dielectric material due to a large band gap (3.2 eV), 10 but the material demonstrates high n-type electrical conductivity at reducing conditions due to the introduction of oxygen vacancies and delocalized electrons caused by Ti 3+ formation.…”