P-N switchable thermoelectric ionogels enabled by microphase separation for intelligent thermal sensing.

Ionic thermoelectric (iTE) materials have emerged as powerful candidates for thermal sensing due to their high thermopowers, low thermal conductivity, and ease of production. However, the monotonic thermoelectric behavior of conventional iTE materials hinders their multi-scenario applications as thermal sensors, especially in the design of intelligent thermopiles that require feedback at certain temperatures. Here, we report an ionogel with bipolar switchable thermopowers from +7.71 to -3.77 mV K^-1 induced by a lower critical solution temperature phase behavior. These thermoresponsive ionogels exhibit nonlinear thermal voltages once the phase separation occurs, which can be used for intelligent over-temperature protection sensors. Moreover, thermopiles with high-sensitive heat flux detection are prepared by integrating p-n pairs in series. A prototype wearable device integrated with 24 p-n pairs achieves a total thermopower of 0.22 V K^-1 and a heat flux sensitivity of up to 2 V m W^-1. These nonvolatile ionogels with bipolar switchable thermopower offer great prospects for applications such as intelligent thermal sensing.