Transformation of an oxygen ion conductor to a proton conductor by solid state reaction

It is shown that starting from a thin, gas tight layer of an oxygen ion conductor such as 8YSZ a thin, gas tight layer of a proton conductor can be obtained by coating the original layer with BaCO3 or BaO followed by sintering. Generally, a homogeneous Zr1–xYxO2–y ceramic compound will react with BaO to form the desired proton conductor BaZr1–xYxO3–x/2. This procedure obviates the deposition of proton conducting layers starting from fine powders which in view of the poor sinterabilty of the common proton conductors was a difficult endeavor in the past. It also permits the construction of larger components (reactors etc.) covered with a proton conductor. The present technique is also applicable to the formation of CZI10 (CaZr0.9In0.1O3–y) layers. The latter compound is an excellent proton conductor for potentiometric purposes and has seen commercial use in hydrogen sensors in molten aluminium (5).