Solid-State Electrochemical Thermal Transistors with Large Thermal Conductivity Switching Width

Thermal transistors that electrically switch heat flow on and off have attracted growing attention as thermotronic devices such as thermal shutters and thermal displays. In 2023, we demonstrated the world’s first solid-state electrochemical thermal transistors with SrCoO<i>_x</i> (2 ≤ <i>x</i> ≤ 3) as the active layer.^[1-3] The thermal conductivity (<i>κ</i>) on/off ratio was approximately 4 and <i>κ</i> switching width was 2.85 W m⁻¹ K⁻¹. Here, we demonstrate solid-state thermal transistors with a large <i>κ</i> switching width of 9.5 W m⁻¹ K⁻¹. We used CeO₂ thin films as the active layer directly deposited on the solid electrolyte YSZ substrate using the PLD method. A Pt thin film was deposited on the surface of the CeO₂ thin film and the back surface of the YSZ substrate using the sputtering method to create an all-solid-state thermal transistor. When the CeO₂ thin film was once reduced and then oxidized, the <i>κ</i> was approximately 2.5 W m⁻¹ K⁻¹ in the most reduced state, and <i>κ</i> increased with oxidation to 11.8 W m⁻¹ K⁻¹. This reduction/oxidation was repeated 5 times and the average value of <i>κ</i> was 2.5 W m⁻¹ K⁻¹ after reduction and 12 W m⁻¹ K⁻¹ after oxidation. The CeO₂-based solid-state electrochemical thermal transistors might have the potential for thermotronic devices such as thermal shutters and thermal displays.<br/><br/>[1] Q. Yang <i>et al</i>., <i>Adv. Funct. Mater.</i> <b>33</b>, 2214939 (2023).<br/>[2] Z. Bian <i>et al</i>., <i>ACS Appl. Mater. Interfaces</i> <b>15</b>, 23512 (2023).<br/>[3] M. Yoshimura <i>et al</i>., <i>ACS Appl. Electron. Mater.</i> <b>5</b>, 4233 (2023).