Eco‐Friendly Higher Manganese Silicide Thermoelectric Materials: Progress and Future Challenges

Abstract

As a promising thermoelectric material, higher manganese silicides are composed of earth-abundant and eco-friendly elements, and have attracted extensive attention for future commercialization. In this review, the authors firstly summarise the crystal structure, band structure, synthesis method and pristine thermoelectric performance of different higher manganese silicides. After that, the strategies for enhancing electrical performance and reducing lattice thermal conductivity of higher manganese silicides as well as their synergistion are highlighted. The application potentials including the chemical and mechanical stability of higher manganese silicides and their energy conversion efficiency of the assembled thermoelectric modules are also summarised. By analysising the current advances in higher manganese silicides, this review proposes that potential methods of further enhancing zT of higher manganese silicide lie in enhancing electrical performance with simultaneously reducing lattice thermal conductivity via effectively reducing effective mass, optimizing carrier concentration, and nanostrcutre engineering.

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…Specially, the fact that introducing additional secondary phases can make κ l approaching nearly zero needs further clarification from physical and theoretical point, since with such an ultralow κ l , further reducing n H can lead to even higher zT. 3)From the device design and application aspect, most recent theoretical understanding on stability enhancement of Cu 2 X‐based thermoelectric materials as well as the corresponding experimental demonstration can better guide future experimental studies, including welding materials, module design and understanding on the internal Cu concentration gradient. Most importantly, proper module design can further enhance η max and one possible case is assembling different modules into cascade modules …”

“…In p‐type A a B b semiconductors with holes are the main carriers, VECs for holes (as an indicator for the change of carriers) can be defined as VECs (AaBb) = b ⋅[8 − VECs (B) ] − a ⋅VECs (A) , where VECs (A) and VECs (B) are VECs of cations and anions. Increasing VECs indicates increasing n H . Taking p‐type Cu 2 X‐based thermoelectric materials into this equation, VECs of Cu 2 X can be increased through substituting Cu/X with elements having lower VECs or introducing Cu vacancies.…”

“…Tyagi et al measured the fracture toughness of Cu 2 Se being ≈2 ± 0.02 MPa m −1/2 , and the compressive strength being ≈45 MPa with ≈3% plastic strain. The mechanical properties indicate Cu 2 Se and Cu 2 S are physically stable for thermoelectric applications . Additionally, the mechanical properties can be further improved by material‐engineering methods, such as nanoengineering …”

“…The practical applications of thermoelectric materials are highly limited by both their efficiency and cost . Figure c,d shows the calculated maximum energy conversion efficiency (η max ) of Cu 2 X‐based thermoelectric materials (applied as power generators) estimated from peak zT values at corresponding temperatures and the estimated material costs .…”

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

“…In order to achieve high zT , materials should possess high σ, high S , and low κ. However, these three key parameters are strongly interrelated and conflict with each other . As introduced above, increasing n can lead to an increase in σ and κ e , along with a decrease in S (Equation ).…”