Proton conducting ceramics: Recent advances

Abstract

Abstract.A general introduction into the field of high temperature ceramic proton conductors (HTPCs) is given. Results of two typical studies involving these HTPCs are discussed. In the first part a study of the processes occurring during water vapor exposure of bulk ceramic proton conductors, Bafeo.9YoAO2.95 (BCY10) and BaCe0.8Y0.202.9 (BCY20), is presented. A disc of a HTPC was connected to a mass spectrometer in a vacuum system permitting the identification of the species crossing the ceramic-vacuum interface. Exposing the other side of the sample to D20 led to a strong signal of D20 + after a certain lag time. From these lag times the tracer diffusivity of hydrogen could be determined as a function of temperature. The permeation of steam consisted of two components: a fast component, given by the diffusivities of deuterons (protons), and a slow component, assigned to chemical diffusion of deuterons (protons) coupled to oxygen vacancies. The data also suggested the possibility of participation of even more complex defects in this chemical diffusion. Dilatometry measurements of different specimens of BCY10 and BCY20 also revealed quite clearly this two-phase pattern during protonation. Diffusion measurements on protonic ceramic membranes using H2180 permitted the determination of the tracer diffusivity of oxygen. All of the above measurements were interpreted in the light of the chemical diffusion model developed by Kreuer et al.The second part deals with composites of proton conductors and inorganic compounds such as carbonates, hydroxides, chlorides, and fluorides following the work of B. Zhu. Conductivities of such composites are presented. Nernst potentials of various electrochemical cells with these composites are discussed.

Breakthrough fuel cell technology using ceria-based multi-functional nanocomposites

“…The SDC-BCY20 electrolyte CFCs reached a performance of 0.25 W cm À2 at 550°C [84]. In this similar composite system, Schober and Ringel [64] observed a super-ionic conduction at ca. 560°C, which is agrees with the above fuel cell results.…”

“…Using these materials the CFC could function at lower temperatures, e.g., close 0.3 W cm À2 obtained at 400°C and even at a temperature as low as 200°C [45][46][47][48]. Schober and Ringel [64,65] have also made extensive examples of a BCY-carbonate composite system; they reported various BCY-carbonate composites that showed super-ionic conduction. For example, Y-doped Ba cerate with a Li 2 CO 3 -Na 2 CO 3 (2:1) Mixture, a BCY20 + Li 2 CO 3 composite, a BCY20 + NaOH composite, a BCY20-LiCl composite, and GDC + 20wt.% Li 2 CO 3 + Na 2 CO 3 .…”

“…The composite electrolytes are mixtures of two or more materials/phases. These are also called heterogeneously doped materials or dispersed electrolytes [64][65][66]. These composite electrolytes are considered a new type of electrolyte with high conductivity which occurs through interfaces but at significantly lower temperatures.…”

“…Composite solid electrolytes have got more attention as compared to pure electrolytes due to their higher conductivity and enhanced mechanical strength [64][65][66][67][68][69][70][71]. The control of the electrolyte properties through the variability of the conductance type is very flexible.…”

Effect of indium content on the properties of BaSn0.5Y0.5−xInxO2.75 proton conductor

“…The BaCeO 3 -based proton conductors exhibit the high proton conductivity, but they have a poor chemical stability in H 2 O-and CO 2 -containing atmospheres [5][6][7]. BaZrO 3 -based proton conductors show the good chemical stability, but their poor sintering ability and high grain boundary resistance hinder the application in SOFCs [8][9][10]. Therefore, the development of a material with both a good chemical stability and excellent proton conductivity becomes the urgent demand.…”