Polymer gels with tunable ionic Seebeck coefficient for ultra-sensitive printed thermopiles

Dan Zhao,Xavier Crispin,Thomas Fischer,Anna Martinelli,Magnus P Jonsson,Diana Bernin,Maryam Shahi,Andreas Willfahrt,Simone Fabiano,Zia Ullah Khan,Joseph Brill

doi:10.1038/s41467-019-08930-7

Abstract

Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. Traditional thermopiles can provide accurate and stable temperature reading but they are based on brittle inorganic materials with low Seebeck coefficient, and are difficult to manufacture over large areas. Recently, polymer electrolytes have been proposed for thermoelectric applications because of their giant ionic Seebeck coefficient, high flexibility and ease of manufacturing. However, the materials reported to date have positive Seebeck coefficients, hampering the design of ultra-sensitive ionic thermopiles. Here we report an “ambipolar” ionic polymer gel with giant negative ionic Seebeck coefficient. The latter can be tuned from negative to positive by adjusting the gel composition. We show that the ion-polymer matrix interaction is crucial to control the sign and magnitude of the ionic Seebeck coefficient. The ambipolar gel can be easily screen printed, enabling large-area device manufacturing at low cost.

Highlights

Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes
The self-diffusion coefficients of cations (D+) and anions (D–) were determined by Pulsed field gradient (PFG)-nuclear magnetic resonance (NMR) spectroscopy (Fig. 2a, details can be found in Methods and Supplementary Figure 4)
We found that both D+ and D− initially increase for small amounts of added polyethylene glycol (PEG)

Summary

Introduction

Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. 1234567890():,; Thermoelectric materials enable direct conversion of heat to electrical signals and can be used for heat flux and temperature sensing[1] These technologies are based on the Seebeck effect, i.e., the creation of a voltage across a material subject to a temperature gradient. The low electrical conductivity of insulators (lower than 10–12 Ω cm−1) makes it very challenging to perform reliable thermovoltage measurements There is yet another special class of electronic insulators emerging for thermoelectric applications: electrolytes. Several groups reported extraordinary high values of ionic Seebeck coefficient in electrolytes, reaching +10 mV K−1, and their ionic conductivity is large enough to ensure easy thermovoltage measurements[4,5,6]. The thermodiffusion of ions produces a large constant voltage that can be used for heat flux sensing or temperature measurements

Methods

Results

Conclusion