Moderate-temperature proton conductors

Proton, that is, H+ ion, conductors are of importance as potential electrolytes in fuel cells. There are a number of hydroxides, zeolites, and other hydrated materials that conduct hydrogen ions, but these are not usually stable at moderate temperatures, when water or hydroxyl tends to be lost, and so have only limited applicability. 

Today, there is great interest in fuel cells which can operate at moderately high temperatures (200-350 °C). Since it is almost impossible to find a low-temperature oxide ion conductor below 500-600 °C, efforts must be directed towards proton conductors with high conductivity in the absence of water. The results already obtained with ZrP intercalated with diamines seem to be a promising way to obtain good protonic conductors with stability up to about 200 °C. 

The major problem with ceramic proton conductors is that those that exhibit high proton conductivity, such as the ones we have exemplified so far, are rather basic in nature because Sr and Ba are main components. They are thus vulnerable to destructive reaction with acidic gases such as CO2 or SO2/SO3, especially at moderate temperatures, and may also react with water at moderate and low temperatures to form hydroxides. 

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