PROTON CONDUCTOR ELECTROLYTES BASED ON CsH2PO4 AND THERMALLY STABLE POLYMERS

1,2 Irina Bagryantseva, 1,2Valentina Ponomareva, 1,2 Anna Gaydamaka

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia,

2 Novosibirsk State University, Novosibirsk, Russia

E-mail: ponomareva@solid.nsc.ru

Introduction

The family of acid salts of alkali metals with the common formula MnHm(AO4)p (A = P, S, Se) presents an important class of proton conductors with high proton conductivity ~10-2 S/cm in the medium temperature range 130-250°С due to the superprotonic phase. Among them CsH2PO4 and its composites undoubtedly have a great potential for use as a proton-conducting membrane in fuel cells (FCs) [1]. Recently, the systems based on CsH2PO4 and polymer additive have been intensively studied [2-4]. The thin-film flexible membranes are preferable for improving the electrochemical characteristics of FCs. Such systems combine high proton conductivity of the acid salt with the flexibility, hydrophobicity, mechanical stability and flexibility of the polymer. Mechanically strong membranes with the thickness less than100 μm can be obtained by the solvent casting technique. Due to the pure solubility of CsH2PO4 in common solvents such membranes are a physical dispersion of acid salt particles in the polymer matrix. For this purpose the fine salt particles should be obtained. The conductivity of CsH2PO4-based polymer systems is determined by the morphology and the nature of the distribution of salt particles in the volume of the membrane depending on the energy of adhesion similarly to the composites based on acid salts and highly dispersed inorganic oxide (SiO2, TiO2 etc.) [5].

Results and Discussion

This work is devoted to the investigation of the mechanism of formation of new high-conductive polymer membranes based on CsH2PO4 and thermally stable polymers of different composition such as fluoropolymers and butyral. The synthesis conditions were studied and optimized. The investigation of electrotransport, structural, thermal properties and the mechanism of proton conductivity of the polymer composites were carried out. The proton conductivity and changes in structural properties of «CsH2PO4-polymer» systems with varying polymer matrix were examined. The small content of the polymer results in the conductivity remaining at the level of the initial salt in the superionic phase. But the high polymer concentrations lead to the percolation threshold of the "conductor-insulator" type with the further decrease in the electrotransport characteristics. The different ways of particle size reduction was examined. The range of different water partial pressure on the proton conductivity was studied for the suppression of CsH2PO4 dehydration and extension of superionic phase stability. The changes of structural characteristics of the salt in the polymer matrices were studied by XRD. The addition of a polymer matrix results in a partial amorphization of the CsH2PO4. The particle size and its distribution in the volume of the membrane have been characterized by electron microscopy. The addition of appropriate amount of polymer matrix also provides the flexibility of the membrane, increasing of hydrolytic stability, sufficient mechanical strength and gas permeability while maintaining high proton conductivity.

This work was carried out with a partial financial support from RFBR grant 18-08-01279.

References

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