Synthesis and Conductivity of Indium-Doped Tin Pyrophosphates

We have synthesized indium-doped tin pyrophosphates as high-temperature anhydrous proton conductors. The ratio of tin to indium was varied using two different synthetic methods. The first is a high-temperature reaction in which a paste containing the reactants in excess phosphoric acid was heated for various amounts of time at various temperatures. The second method is a solution precipitation procedure followed by calcination, which offers several advantages over traditional synthetic techniques. These advantages include better stoichiometric control, lower temperature requirements, and chemically uniform products. Several phosphate sources were investigated, including phosphoric acid, pyrophosphoric acid, and potassium pyrophosphate. The resulting indium-doped tin pyrophosphates had good proton conductivity over a wide temperature range with no humidification.