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Polyoxometalates (POMs) have attracted extensive interests as solid-state proton conductors due to their high conductivity and good thermal stability. However, the low humidity stability and poor mechanical property of crystalline POMs greatly hinder their practical application. Herein, on the basis of the remarkable improvement of the humidity stability that can be achieved by hybridizing POMs with organic components, we prepared a new POM-based inorganic–organic hybrid, H[Zn(Hapca)3][PW12O40]·7H2O 1 (Hapca = 3-aminopyrazine-2-carboxylic acid), composed of Keggin-type PW12O403− anions and Zn(Hapca)32+ cations. Compound 1 exhibits a proton conductivity of 1.16 × 10−4 S·cm−1 at 55 °C, which remains stable at a relative humidity of 95%. To construct POM-based conductive materials with good mechanical property, we introduced 1 into a poly(vinyl alcohol) (PVA)/glycerol (Gly) hydrogel and obtained the hydrogel composites 1@PVA/Gly-x (x = 20%, 30%, and 40%, where x is the percentage of the mass of 1 to the total mass of 1 and PVA). Remarkably, the hydrogel composites 1@PVA/Gly-x combine the merits of their components. The proton conductivity of 1@PVA/Gly-40% reaches 1.11 × 10−2 S·cm−1 at ambient humidity and 75 °C, outperforming most POM-based composite materials reported to date. Moreover, 1@PVA/Gly-40% displays good elasticity and toughness and high strain sensitivity. Additionally, we assembled 1@PVA/Gly-40% into a strain sensor for the effective monitoring of various human activities. This work provides a new platform for the transformation of crystalline POM-based inorganic–organic hybrids into materials with good mechanical properties.


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Construction of hydrogel composites with superior proton conduction and flexibility using a new POM-based inorganic–organic hybrid

Show Author's information Yuxin WangYing Lu ( )Wensha ZhangTianyi DangYanli YangXue BaiShuxia Liu ( )
Key Laboratory of Polyoxometalate and Reticular Material Chemistry of Ministry of Education, College of Chemistry, Northeast Normal University, Changchun 130024, China

Abstract

Polyoxometalates (POMs) have attracted extensive interests as solid-state proton conductors due to their high conductivity and good thermal stability. However, the low humidity stability and poor mechanical property of crystalline POMs greatly hinder their practical application. Herein, on the basis of the remarkable improvement of the humidity stability that can be achieved by hybridizing POMs with organic components, we prepared a new POM-based inorganic–organic hybrid, H[Zn(Hapca)3][PW12O40]·7H2O 1 (Hapca = 3-aminopyrazine-2-carboxylic acid), composed of Keggin-type PW12O403− anions and Zn(Hapca)32+ cations. Compound 1 exhibits a proton conductivity of 1.16 × 10−4 S·cm−1 at 55 °C, which remains stable at a relative humidity of 95%. To construct POM-based conductive materials with good mechanical property, we introduced 1 into a poly(vinyl alcohol) (PVA)/glycerol (Gly) hydrogel and obtained the hydrogel composites 1@PVA/Gly-x (x = 20%, 30%, and 40%, where x is the percentage of the mass of 1 to the total mass of 1 and PVA). Remarkably, the hydrogel composites 1@PVA/Gly-x combine the merits of their components. The proton conductivity of 1@PVA/Gly-40% reaches 1.11 × 10−2 S·cm−1 at ambient humidity and 75 °C, outperforming most POM-based composite materials reported to date. Moreover, 1@PVA/Gly-40% displays good elasticity and toughness and high strain sensitivity. Additionally, we assembled 1@PVA/Gly-40% into a strain sensor for the effective monitoring of various human activities. This work provides a new platform for the transformation of crystalline POM-based inorganic–organic hybrids into materials with good mechanical properties.

Keywords:

polyoxometalates, proton conduction, inorganic–organic hybrid, hydrogel
Received: 07 July 2022 Revised: 12 August 2022 Accepted: 25 August 2022 Published: 15 September 2022 Issue date: September 2022
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Publication history

Received: 07 July 2022
Revised: 12 August 2022
Accepted: 25 August 2022
Published: 15 September 2022
Issue date: September 2022

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© The Author(s) 2022. Polyoxometalates published by Tsinghua University Press.

Acknowledgements

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos. 22071019, 21872021, and 22172022)

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