Intermediate-temperature proton conductors and their applications to energy and environmental devices

Abstract

The development of proton conductors has proceeded rapidly in recent years. A number of organic or inorganic materials show proton conductivities of ∼10⁻² S cm⁻¹ at temperatures below 100°C. However, although there is great current demand for proton conductors capable of operating in the temperature range of 100–400°C in practical applications, very few materials that can satisfy this demand have been reported to date. Acceptor-doped SnP₂O₇ are promising candidate materials because their proton conductivities reach >10⁻¹ S cm⁻¹ in the temperature range of interest. This paper presents an overview of the current status of acceptor-doped SnP₂O₇, highlighting the mechanism and kinetics of proton conduction and the development of electrochemical devices using these materials. New insights for proton insertion and conduction are proposed that use electrochemical techniques. Two approaches to designing SnP₂O₇-based composite electrolytes with good mechanical properties have also been developed for different operating temperatures. In addition, the benefits of intermediate-temperature operation using these materials are discussed in terms of practical applications, especially in fuel cells, exhaust sensors, and solid catalysts.