Proton conductivity in oxides

These studies on the above materials did not however, provide a direct evidence for high-temperature protonic conduction in oxide materials. A conclusive demonstration for high-temperature protonic conduction in oxides was first reported in 1981 by Iwahara et al. (1981a) for rare-earth doped perovskite oxides. 

All in all, proton conductivity in oxides is a matter of compromise in composition and temperature between high concentration of protons (favorable hydration kinetics), high proton mobility, and chemical robustness. In this contribution, we concentrate on a description of protonic defects and their thermodynamics in various perovskite-related oxides, give an overview of the resulting proton... 

Thus, there is the diffusion of two species hydroxyl anions and anion vacancies but if the diffusion is the rate-determining step, it is generally the one of the vacancies because the diffusion of hydroxyl ions takes place by the jitmp of protons from an oxygen to another in the network (phenomenon identical to proton conduction in oxides) and the mobility of these protons is in general larger than the one of the vacancies. 

Iwahara, H., Esaka, T., Uchida, H. and Maeda, N. (1981) Proton conduction in sintered oxides and its application to steam electrolysis for hydrogen production,... 

Iwahara, H. et al.. Proton conduction in sintered oxides based on BaCe03, /. Electrochem. Soc. Solid-State Sci. Technol., 135, 529-533 (1988). 

As with oxygen ion-conducting electrolytes, proton conduction in these electrolytes occurs only within a limited range of hydrogen partial pressures. In addition, as they are oxides, oxygen defects can occur. Figure 13.6 shows the predominant defects in indium-doped calcium zirconate, which were calculated based on an extrapolation of conductivity measurements [79]. Hydrogen conduction occurs by interstitials H ... 

In the area of dense membrane applications for hydrogenation reactions a number of recent studies also report the use of proton conducting solid oxide membranes (Otsuka and Yagi [2.86], Panagos et al. [2.87], Mamellos and Stoukides [2.88]). As noted previously, this is an exciting class of new materials with significant potential applications. 

Shown in Figure 6 is a diagram of a nickel support and a Pt-loaded nanoparticulate oxide acting as a porous cathode. Organic-based fuel cell cathodes often have some Nafion added to improve proton conductivity but at the cost of electrical conductivity. However, we have the reverse problem - we have excellent proton conductivity in the inorganic cathode, but the oxides are electrical insulators. We need to boost the electrical conductivity of the cathode in order to fabricate a total inorganic MEA. This is a major objective of our future work. 

Sata N, Yugami H, Akiyama Y, Sone H, Kitamura N, Hattori T, Ishigame M. Proton conduction in mixed perovskite type oxides. Solid State Ionics. 1999 125 383-387. 

Proton conducting perovskite oxides are the subject of numerous current studies, as these materials have a potential use in a number of electrochemical applications, including fuel cells, electrochromic displays and hydrogen sensors. Perovskite... 

The oxide Ba Inp adopts the brownmillerite structure at lower temperatures (Section 2.4). The structure begins to disorder at approximately 900°C and forms a cubic perovskite phase with a high concentration of oxygen vacancies somewhere above this temperature. Proton conduction in the solid is brought about by the incorporation of water molecules. Water vapour can react directly with the oxide at higher temperatures, following disproportionation at the oxide surface ... 

Doping by aliovalent cations is indispensable for the appearance of protonic conduction in these oxides. It seems that electron holes and oxide ion vacancies formed by doping might play an important role in the formation of protons. For example, substitution of Yb for Ce in SrCeOg may provide oxygen vacancies Vq as a means of charge compensation ... 

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