Blocking Ion Migration Stabilizes the High Thermoelectric Performance in Cu₂ Se Composites

Area of Science:

• Materials Science
• Solid-State Chemistry
• Thermoelectrics

Background:

• Mixed ionic-electronic conductors (MIECs) are crucial for thermoelectric devices but suffer from phase instability under operational stress.
• High direct current and temperature gradients induce ion migration and phase decomposition, limiting MIEC applications.

Purpose of the Study:

• To stabilize the mixed ionic-electronic conductor copper selenide (Cu₂Se) against phase instability.
• To enhance the thermoelectric performance of Cu₂Se-based materials.

Main Methods:

• Formation of a Schottky heterojunction between Cu₂Se and in-situ-formed BiCuSeO nanoparticles.
• Utilizing an ionic capacitive effect to regulate Cu⁺ ion accumulation and migration.
• Investigating electron transfer dynamics across the heterojunction interface.

Main Results:

• Cu⁺ ion migration was reduced by two orders of magnitude due to ion accumulation at the Schottky junction.
• The heterojunction effectively blocked Cu⁺ reduction to Cu metal, stabilizing the β-Cu₂Se phase.
• Cu₂Se/BiCuSeO composites achieved a peak ZT of ~2.7 at 973 K and an average ZT of ~1.5 (400–973 K).

Conclusions:

• Schottky heterojunctions offer a novel strategy for stabilizing MIECs by controlling ion and electron behavior.
• This approach provides new insights into managing ion migration in ionic-transport-dominated materials for improved thermoelectric applications.