Issue 33, 2023

Designing n-type all-ionic thermoelectric polymers with improved air stability via a solution-processing anion exchange technique

Abstract

Current thermoelectrics technologies are dominated by inorganic materials that can efficiently harvest low-grade waste heat and realize electrical energy conversion; however, their toxicity, rigidity, rare element-based compositions and energy-intensive processing limit their wide applications. Organic thermoelectrics, with the advantages in mechanical flexibility, material abundance and low-temperature/pressure processing, offer solutions to resolve these limitations. Among organic thermoelectrics, the less well-studied ionic polymers possessing intrinsically high Seebeck coefficients are beneficial for charging supercapacitors or batteries, and hence motivated the present study. Its main purpose is to design and develop air-stable n-type all-ionic thermoelectric polymers with suitable ionic conductivity and high Seebeck coefficients. Our initial focus was on two commercially available, water-processable Cl based cationic polyelectrolytes, polydiallyldimethylammonium chloride (PDADMAC) and poly(2-(dimethylamino)ethyl methacrylate) methyl chloride quaternary salt (MADQUAT); however, their instability to moisture led to transient, irreproducible Seebeck coefficients. To tackle this challenge, which is in fact quite common among n-type ionic polymers, we adopted a facile, solution-based anion exchange technique by replacing the smaller and unstable Cl ions with bulkier, more hydrophobic tetrafluoroborate (BF4) and hexafluorophosphate (PF6) ions in the polymer systems. We also conducted comparative experimental studies of the thermoelectric behaviors of post-anion exchanged polyelectrolytes under dry (15% relative humidity) and more humid (40% relative humidity) atmosphere. Results have confirmed that the thermoelectric properties of the post-exchange systems are humidity-dependent. In particular, BF4-based MADQUAT and PF6-based PDADMAC showed good ionic conductivity, reliable, reproducible Seebeck coefficients and outstanding power factors at 40% relative humidity with significant improvement in air stability. This opens up opportunities for the further development of all-ionic polymer systems to be applied in a variety of applications, such as sensors, storage, wearable electronics, and batteries.

Graphical abstract: Designing n-type all-ionic thermoelectric polymers with improved air stability via a solution-processing anion exchange technique

Supplementary files

Article information

Article type
Paper
Submitted
11 Jul 2023
Accepted
04 Aug 2023
First published
04 Aug 2023

J. Mater. Chem. A, 2023,11, 17550-17559

Author version available

Designing n-type all-ionic thermoelectric polymers with improved air stability via a solution-processing anion exchange technique

N. (. Chen, Y. Song, T. Lee, S. Mayarambakam and H. E. Katz, J. Mater. Chem. A, 2023, 11, 17550 DOI: 10.1039/D3TA04091G

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