Chemically Driven Ion Exchanging Synthesis of NaYSiO-Based Glass-Ceramic Proton Conductors.

We have developed 12-membered silica-tetrahedra-ringed NaYSiO-type sodium ion conducting glass-ceramics on the basis of the composition NaRPSiO (R: rare earth elements; denoted as Narpsio); especially, the material of NaYPSiO with the combined parameters of (x, y) = (0.4, 0.2) gives rise to the maximum conductivity of 1 × 10 Scm at 300 °C. Because glass-ceramics generally have the advantage of structural rigidity and chemical durability over sintered polycrystalline ceramics, the present study employed glass-ceramic Narpsio to perform chemically driven ion exchange of Na with protonated water molecules with an aim to produce a proton conductor. The ion exchange was carried out in a hydrochloric acid solution by changing immersion time, temperature, and acid concentration. The ion exchanged NaYPSiO-based glass-ceramics were analyzed by the complex impedance method, and the proton conductivity was found to exhibit 3 × 10 Scm at 300 °C with the activation energy of 59 kJ/mol. The dependence of humidity-sensitive conductivity of the ion exchanged bulk glass-ceramics was also examined; the conductivity increased almost linearly from 0.6 × 10 Scm in dry air to 1.5 × 10 Scm in 75% humid ambience at 300 °C. Thus, the ion exchanged glass-ceramics can be considered to be high temperature proton conductors as well as humidity sensors.