Electrical conductivity and structural properties of proton electrolytes based on CsH2PO4 and silicophosphate matrices with low phosphorus content

• Published in: Inorganic materials Vol. 50; no. 10; pp. 1056 - 1062
• Main Authors: Ponomareva, V. G., Shutova, E. S.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-10-2014
• Subjects: Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Composite Electrolyte; Lower Phosphorus Content; High Phosphorus Content; Proton Conductivity; Hydrogen Bond System
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168514100136

We have demonstrated that silicophosphate matrices with various P
2
O
5
contents can be used to produce medium-temperature highly conductive CsH
2
PO
4
-based composites. The low-temperature conductivity of all the composites studied is higher than that of the salt at low humidity by up to three and half to four orders of magnitude. The phase transition disappears with increasing additive content. The proton conductivity, thermal characteristics, and phase composition of the salt are shown to depend significantly not only on the composition of the composite but also on that of the silicophosphate matrix. The composites with Si : P = 1 : 0.14 contain disordered CsH
2
PO
4
in the range
x
= 0.1–0.6. Increasing the percentage of the heterogeneous component leads to CsH
2
PO
4
amorphization at
x
= 0.7 and the formation of the CsH
5
(PO
4
)
2
compound at
x
= 0.8–0.9. The thermodynamic properties and thermal stability of the composites vary in accordance with this. We have assessed the thermal stability of the electrolytes of various compositions under isothermal conditions at 200–210°C and water vapor content of ≃0.6–1% in air in prolonged tests. The thermal stability of the materials is shown to depend significantly on both the percentage of the salt in the composite and the composition of the matrix. We have determined the optimal thermal and transport characteristics of the composites based on silicophosphate gel with lower phosphorus content. This opens up the possibility of using them as membranes in medium-temperature hydrogen fuel cells.