EuAsC2S-12/S11-2-OP3 Proton-Conducting Oxide and Applications to Hydrogen Energy Devices

Ion-conducting solids are useful for sensing, mass transport, and energy conversion. For example, secondary batteries, fuel cells, and etc., utilize ion conduction in solids effectively to convert chemical energy to electrical one. Gas sensing is of another importance for controlling energy devices and ensuring safe operation. We should pay attention to the fact that these materials need electrochemistry to work, i.e., electrochemical cells are the essential mechanism. For example, water electrolysis is an electrochemical process many people are familiar with, but we should notice that it can proceed only in electrochemical manner; in the other cases, the water splitting is not a spontaneous reaction and will never proceed under ordinary conditions. On the other hand, increasing emission of carbon dioxide, a major green-house-effect gas other than water vapour in the air, is a serious problem for the sustainability of human beings. We should change the primary energy source from fossil fuel to the so-called renewable energies, such as solar energy and wind energy. In addition, the reducing reliability and controversy of nuclear power these days give more reason for the introduction of these renewable energies. The use of these energies, however, needs efficient methods of energy storing and restoring, since the sun is not always shining and winds change every moment. “Hydrogen energy system ” (Fig. 1