Cerium Oxide-based Solid-State Thermal Transistors with Wide Switching Width of 9.5 W/mK

Thermal transistors that electrically switch heat flow on and off have attracted attention as thermal management devices. Electrochemical reduction/oxidation switches the thermal conductivity ({appa}) of active metal oxide layers. The {appa}-switching width (difference between on-state and off-state {appa}) of the previously proposed electrochemical thermal transistors is narrow, less than 5 W/mK. Here, we show solid-state electrochemical thermal transistors with a wide {appa}-switching width of 9.5 W/mK. We used CeO2 thin film as the active layer directly deposited on a solid electrolyte YSZ substrate. A Pt thin film was deposited on the surface of the CeO2 thin film and the back surface of the YSZ substrate to create a solid-state electrochemical thermal transistor. When the CeO2 thin film was once reduced (off-state) and then oxidized (on-state), the {appa} was approximately 2.5 W/mK in its most reduced state, and {appa} increased with oxidation to 11.8 W/mK (on-state). This reduction (off-state)/oxidation (on-state) cycle was repeated five times and the average value of {appa} was 2.5 W/mK after reduction (off-state) and 12 W/mK after oxidation (on-state). The {appa}-switching width was 9.5 W/mK. The CeO2-based solid-state electrochemical thermal transistors are potential materials for thermal shutters and thermal displays.