Self-Powered and Green Ionic-Type Thermoelectric Paper Chips for Early Fire Alarming

Abstract

Early fire alarming is of vital importance to lower the damages led by forest fires. Thus far, methods to monitor the forest fires at their early stage are mainly focused on artificial ground patrol, unmanned aerial vehicle cruise monitoring, observation by watchtower, or satellite inspection, whereas these methods are practically encountered with the problems of untimely feedback before the forest fires are out of control. This work proposes a particular kind of self-powered, low-cost, and green thermoelectric paper chips based on the principle of self-assembly and disassembly of ionic liquids on the surface of gold electrodes. By adjustment of the species of ionic liquids, both "nand p-type" thermoelectric behaviors have been exploited that correspond to the opposite open-circuit voltages. Owing to the fluidic nature of ionic liquids, those "nand p-type" thermoelectric units can be readily connected in series on one paper chip, leading to remarkable voltage signals in the presence of the temperature difference of 35 K. Followed by signal acquisition and transmission, such a thermoelectric paper chip successfully affords immediate electrical alarming at the early stage of an afire circumstance.

Thermoelectric Converters Based on Ionic Conductors

“…When heating one electrode, new ion adsorption‐desorption equilibrium will be established, following with the change of the ion density and rearrangement of the ion distribution in comparison with the other unheated electrode. As illustrated in Figure 3a, [30] if cations interact more strongly with the electrode, they desorb less than anions on the heated electrode surface, accordingly resulting in the potential increase of the hot‐end electrode. Whereas the arrangement of the ions on the other electrode remains unchanged, corresponding to an unchanged potential, thus generating a potential difference between two electrodes.…”

“…(c) and (d) are the illustration of thermally induced ion desorption of n‐type and p‐type of ionic liquids from the electrode, respectively. Reproduced with permission [30] . Copyright 2020, American Chemical Society.…”

“…Though the Seebeck coefficient of I‐TE materials is promising, which can readily reach the order of mV/K, the thermoelectric converter made up of only one I‐TE device is still far from achieving satisfactory thermoelectric voltages. Studies using ionic liquids as I‐TE materials have shown the possibility of screening out constituents with opposite thermoelectric behaviors (Figure 6b) [30] …”

“…(b) The thermal sensing device based on I‐TE materials for the fire alarm. Reproduced with permission [30] . Copyright 2020, American Chemical Society.…”

Soft Electronics Based on Liquid Conductors

“…One exciting example was reported lately, using ionic liquid-based thermoelectric converter to monitor the early forest fire. [151] As illustrated in Figure 22e, ten pairs of p-type ([EMIm] [Ac]) and n-type ([EMIm][TFSI]) ionic liquids were deposited on a piece of A4 paper alternatively while being connected through Au electrodes. This paper chip was further bridged with external circuit composed of conversion module, signal acquisition module, transmitter, receiver, and alarm module and sticked on a tree.…”