New medium-temperature proton electrolytes based on CsH2PO4 and silicophosphate matrices

Silicophosphate gels ranging widely in P₂O₅ content and specific surface area have been synthesized by a sol-gel process. We have demonstrated the possibility of producing medium-temperature high-conductivity systems based on silicophosphate matrices and CsH₂PO₄. The thermal, structural, and transport properties of composite proton electrolytes have been investigated. The results indicate that the electrical conductivity of the composites based on matrices with Si : P = 1 : 0.5 increases by up to three and half or four orders of magnitude and that their proton conductivity is ～10^?3 to 3 × 10^?2 S/cm at temperatures from 90 to 220°C and a water vapor content of ?0.6–1 mol % in air. The additive suppresses the superionic phase transition of CsH₂PO₄. The increase in conductivity at low contents of the heterogeneous component is due to both CsH₂PO₄ dispersion and the presence of protonated centers on the matrix surface. When the mole fraction of the additive exceeds 0.3, the composites contain CsH₅(PO₄)₂, a compound with a lower thermal stability, which is responsible for their high conductivity in a limited temperature range.