Thermocells Driven by Phase Transition of Hydrogel Nanoparticles

Abstract

Thermoelectric conversion of low temperature, delocalized, and abundant thermal sources is crucial for the development of the Internet of Things (IoT) and/or a carbon-free society. Thermocells are of great interest in thermoelectric conversion of low-temperature heat due to the low cost and flexibility of components. However, significant improvement of the conversion efficiency is required for the practical use of the cells. Here, we report thermo-electrochemical cells driven by volume phase transition (VPT) of hydrogel nanoparticles (NPs). Entropically driven VPT of poly(N-isopropylacrylamide) NPs containing carboxylic acids and amines generates a pH gradient of up to 0.049 and −0.053 pH K −1 , respectively, around physiological temperature. The pH gradient triggers the proton-coupled electron transfer (PCET) reactions of quinhydrone on the electrodes, resulting in the highly efficient thermoelectric conversion with a Seebeck coefficient (S e ) of −6.7 and +6.1 mV K −1 . Thermocells driven by phase transition of hydrogels provide a nontoxic, flexible, and inexpensive charger that harvests carbon-free energy from abundant energy sources such as solar, body and waste heat.

High Positive Seebeck Coefficient of Aqueous I–/I3– Thermocells Based on Host–Guest Interactions and LCST Behavior of PEGylated α-Cyclodextrin

“…It then decreased to +2.4 mV/K by further increasing the temperature above 37 °C (i.e., ΔT higher than 12 K). The S e value of +4.2 mV/K is the highest value next to our previous result (+6.1 mV/K) 26 using a polymer additive, and highest among the thermocells consisting of purely low-molecular-weight compounds. It is also worth noting that no precipitation appeared in the whole temperature range, which contrasts with the previously reported CD or Et 18 -α-CD-based thermocells.…”

Hofmeister Effect and Electrostatic Interaction Enhanced Ionic Conductive Organohydrogels for Electronic Applications

“…Hydrogel is also widely used in thermoelectric applications. [38,39] Figure 4d shows the working principle of common hydrogel-based cells based on the temperature gradient between the two electrodes. Considering the stable charge channels and inorganic salts remaining in the organohydrogels, the thermopower of the AV/LiCl organohydrogel-based cell (Figure S13, Supporting Information) for thermoelectric applications is investigated.…”

High‐Precision Ionic Thermocouples Fabricated Using Potassium Ferri/Ferrocyanide and Iron Perchlorate

“…Instead, the thermogalvanic process can be utilized, in which the electrode potential varies with temperature for a given redox reaction. When a temperature difference is applied between the two electrodes in the cell, a voltage given by Δ V = − S e Δ T [ 4,20–25 ] is generated, where S e is the temperature coefficient of the redox potential or the ionic Seebeck coefficient. The coefficient, S e , is related to the change in the entropy of the cell reaction (), defined as where n is the number of electrons transferred in the reaction and F is Faraday's constant.…”