High-performance solid-state electrochemical thermal switches with earth-abundant cerium oxide

Thermal switches, which electrically turn heat flow on and off, have attracted attention as thermal management devices. Electrochemical reduction/oxidation switches the thermal conductivity (\k{appa}\) of active metal oxide films. The performance of the previously proposed electrochemical thermal switches is low; on/off \k{appa}\-ratio is mostly less than 5 and \k{appa}\-switching width is less than 5 W/mK. We used CeO2 thin film as the active layer deposited on a solid electrolyte YSZ substrate. When the CeO2 thin film was reduced once (off-state) and then oxidized (on-state), \k{appa}\ was about 2.2 W/mK in the most reduced state, and \k{appa}\ increased with oxidation to 12.5 W/mK (on-state). This reduction (off-state)/oxidation (on-state) cycle was repeated 100 times and the average value of \k{appa}\ was 2.2 W/mK after reduction (off-state) and 12.5 W/mK after oxidation (on-state). The on/off \k{appa}\-ratio was 5.8 and \k{appa}\-switching width was 10.3 W/mK. The CeO2-based solid-state electrochemical thermal switches would be potential devices for thermal shutters and thermal displays.