High temperature proton conductors. Note I: Boron and aluminum phosphates

• Published in: Solid state ionics 1986, Vol.18, p.994-1002
• Main Authors: Montoneri, E., Salzano, F.J., Findl, E., Kulesa, F.
• Format: Article
• Language: English
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/0167-2738(86)90298-5

The chemical stability and conductivity of boron and aluminum phosphates in steam are reported for P/B and P/Al atomic ratios greater than unity at temperatures from 100° to 280°C and steam pressures to 5 atmospheres. Al(PO 3) 3 and H 2 AlP 3O 10 undergo the reactions Al (PO 3) 3 + H 2O ⇄ 2 AlP 3 O 10 and H 2 AlP 3 O 10 → AlPO 4 + H 2 O· P 2 O 5↑ At 280°C and a steam pressure of 5 atmospheres gauge the product is a mixture of AlPO 4 and H 2AlP 3O 10, while the conductivity of this solid is in the range of 10 −2 ohm −1.cm −1. The boron phosphates lose material and exhibit poor conductivity under similar conditions due to the instability of the BPO 4 phase as a result of the reaction 2 BPO 4 + 6 H 2 O → B 2 O 3·3 H 2 O↑ + P 2 O 5·3 H 2O↑ . As a result of dehydration or hydrolytic reactions an increase in water vapor pressure does not always lead to increased conductivity even at higher temperature.