Solid-State Electrochemical Thermal Transistor based on Oxygen Sponge SrCoO_x (2 ≦ x ≦ 3)

Thermal transistors are devices that can electrically switch “heat flow” on and off, like a semiconductor transistor that switches “electric current” on and off. We can reuse waste heat exhausted to the environment using devices composed of thermal transistors such as thermal shutters and thermal displays^[1]. Although several thermal transistors have been demonstrated thus far, the use of liquid electrolytes (or ionic liquids or ion gels) may limit the application from the viewpoint of reliability or liquid leakage^[2−4]. Very recently, we demonstrated a solid-state thermal transistor that can electrochemically control the heat flow with an on-to-off ratio of the thermal conductivity (<i>κ</i>) of ~4 without using any liquid^[5]. The thermal transistor is composed of a multilayer film composed of an upper electrode (Pt), strontium cobaltite (SrCoO<i>_x</i>), solid electrolyte (YSZ), and bottom electrode (Pt). An electrochemical redox treatment at 280 °C in air repeatedly modulates the crystal structure and <i>κ</i> of the SrCoO_<i>x</i> layer. The fully oxidized perovskite-structured SrCoO₃ layer shows a high <i>κ</i> ~3.8 W m⁻¹ K⁻¹, whereas the fully reduced defect perovskite-structured SrCoO₂ layer shows a low <i>κ</i> ~0.95 W m⁻¹ K⁻¹. We believe that all-solid-state electrochemical thermal transistors have the potential to become next-generation devices for future thermal management technology, and we are currently working on improving their characteristics^{[6, 7]}.<br/><br/><b>References</b><br/>[1] T. Swoboda <i>et al.</i>, <i>Adv. Electron. Mater.</i> <b>7</b>, 2000625 (2021).<br/>[2] J. Cho <i>et al</i>., <i>Nat. Commun.</i> <b>5</b>, 4035 (2014).<br/>[3] A. Sood <i>et al</i>., <i>Nat. Commun.</i> <b>9</b>, 4510 (2018).<br/>[4] Q. Y. Lu <i>et al</i>., <i>Nat. Mater.</i> <b>19</b>, 655 (2020).<br/>[5] Q. Yang, <u>H. Ohta</u> <i>et al</i>., <i>Adv. Funct. Mater.</i> <b>33</b>, 2214939 (2023).<br/>[6] Z. Bian, <u>H. Ohta</u> <i>et al</i>., <i>ACS Appl. Mater. Interfaces</i> <b>15</b>, 23512 (2023).<br/>[7] M. Yoshimura, <u>H. Ohta</u> <i>et al</i>., <i>ACS Appl. Electron. Mater.</i> <b>5</b>, 4233 (2023).