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.