Abstract
Polyoxometalate based solids are promising candidates of proton-conducting solid electrolytes. In this work, a Preyssler-type polyoxometalate is crystallized with potassium ions and poly(allylamine), which is also a good proton conductor, from aqueous solutions. Here we show that the hygroscopicity induced low durability of polyoxometalate and poly(allylamine) can be circumvented by the electrostatic interaction between the polyoxometalate and protonated amine moieties in the solid state. Crystalline compounds are synthesized with poly(allylamine) of different average molecular weights, and all compounds achieve proton conductivities of 10−2 S cm−1 under mild-humidity and low-temperature conditions. Spectroscopic studies reveal that the side-chain mobility of poly(allylamine) and hydrogen-bonding network rearrangement contribute to the proton conduction of compounds with poly(allylamine) of low and high average molecular weights, respectively. While numbers of proton-conducting amorphous polyoxometalate-polymer composites are reported previously, these results show both structure-property relationship and high functionality in crystalline composites.
Highlights
Polyoxometalate based solids are promising candidates of proton-conducting solid electrolytes
Poly(allylamine) (PAA) is utilized as a polymer because (1) amine groups contribute to increase the number of protonation sites and to extend the hydrogen-bonding network, which results in efficient proton transport and (2) PAA would be positively charged by protonation, and structural stability may improve via electrostatic interaction with POM
The chemical formula of the crystal was determined as K8H4[Bi(H2O)P5W30O110]0.03PAA500019H2O [I] by inductively coupled plasma optical emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS), CHN combustion analysis, and thermogravimetry (TG) (Supplementary Figure 2)
Summary
Polyoxometalate based solids are promising candidates of proton-conducting solid electrolytes. Nafions, which are sulfonated fluorocarbon polymers, have achieved great success commercially in polymer electrolyte fuel cells (PEFCs): Nafions show high proton conductivity (>10−2 S cm−1) under high-humidity (relative humidity (RH) 100%) and low-temperature (
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