Significant Reduction in the Switching Time of Solid-State Electrochemical Thermal Transistors

Thermal transistors have the remarkable ability to electrochemically switch the thermal conductivity (κ) of an active material. Several thermal transistors have been reported to control heat flow, but they are impractical because they use liquid electrolytes. Recently, we realized a solid-state thermal transistor that electrochemically controls the κ of SrCoO x (2 ≤ x ≤ 3) using 0.5-mm-thick yttria-stabilized zirconia (YSZ) single crystal substrates as a solid electrolyte at 280 °C. The applicable electric current is low (50 μA) due to the high electrical resistivity of YSZ at 280 °C. Consequently, κ switching is slow (∼3 min). Herein, we aim to reduce the switching time by examining several SrCoO x -based thermal transistors using YSZ substrates with varied thicknesses. The x in SrCoO x is controlled between 2 and 3, and the κ switches between 0.97 and 3.86 W m –1 K –1 . The overall electrical resistance decreases as the YSZ thickness decreases. For a 0.1-mm-thick YSZ substrate, the applicable current increases to 1 mA and the switching time is significantly reduced to ∼10 s.