Selectively tuning ionic thermopower in all-solid-state flexible polymer composites for thermal sensing

Abstract

There has been increasing interest in the emerging ionic thermoelectric materials with huge ionic thermopower. However, it’s challenging to selectively tune the thermopower of all-solid-state polymer materials because the transportation of ions in all-solid-state polymers is much more complex than those of liquid-dominated gels. Herein, this work provides all-solid-state polymer materials with a wide tunable thermopower range (+20~−6 mV K−1), which is different from previously reported gels. Moreover, the mechanism of p-n conversion in all-solid-state ionic thermoelectric polymer material at the atomic scale was presented based on the analysis of Eastman entropy changes by molecular dynamics simulation, which provides a general strategy for tuning ionic thermopower and is beneficial to understand the fundamental mechanism of the p-n conversion. Furthermore, a self-powered ionic thermoelectric thermal sensor fabricated by the developed p- and n-type polymers demonstrated high sensitivity and durability, extending the application of ionic thermoelectric materials.

Mesogenic polymer composites for temperature-programmable thermoelectric ionogels

“…By applying a temperature gradient (Δ T ) through an ionic polymer film, the thermodiffusion of ionic carriers from hot to cold parts generates a voltage due to the Soret effect. 3–7 To identify the major ion carrier in the LCI film, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was carried out for surface analysis in negative ion mode (Fig. S13, ESI†), and samples for both ends near the electrode were prepared by applying Δ T = 8.2 K at 80 °C and 80% RH followed by drying.…”

“…1,2 Among the possible power sources for intelligent devices, ionic thermoelectrics (iTEs) composed of ionic polymers are emerging as competitive candidates in terms of a high thermovoltage generation compared to traditional organic thermoelectrics due to their potential as soft wearable electronics and Seebeck voltages that are large enough to operate low-voltage driving electronics from a small thermal gradient between the environment and iTEs. 3–11 The thermoelectric performance of materials is defined using the thermoelectric figure of merit, , where S is the Seebeck coefficient, σ is the carrier conductivity, T is the absolute temperature, and κ is the thermal conductivity. 12 Generally, the electric thermoelectric performance of polymers depends on the power factor (PF = S 2 σ ) due to their intrinsically low thermal conductivity.…”

Thermo-electrochemical cells for heat to electricity conversion: from mechanisms, materials, strategies to applications

“…With the same polymer as a gel and ionic liquid Na:TFSI as an energy carrier, Chi and his co-workers reported a change in S i from 20 to −6 mV K −1 (namely from the p-type to n-type) by adding TPFPB into the gel, which effectively traps the migration of Na + cations. 107 In another interesting investigation, Liu et al reported a giant and bidirectionally tunable S i value in non-aqueous ionogels by ion doping. 42 In his work, the same S i value (−4 mV K −1 , n-type) is reported in the EMIM:TFSI/PVDF-HFP ionogel due to the anion dominated thermodiffusion.…”

“…Recently, researchers have widely utilized TCCs in thermal sensing based on their giant thermopower. 106,107 As shown in Fig. 10E, a thermal sensor is successfully developed for early fire alarming.…”

“…Apart from boosting S i via the abovementioned strategies, efforts should also be made in the improvement of s eff , where the inferior s eff (only at the level of mS cm À1 , particularly in the gel-based electrolyte) has significantly obstructed the performance of TECs. 27,100,107 To improve s eff without sacrificing S i and k eff , researchers should investigate effective strategies from electrode optimization, where it relates the kinetics of the chemical reaction. On the suppression of k eff , not only the thermal separators and gel-based TECs should be focused on, but also other strategies should be proposed to the promising TECs.…”