Influence of ZnO addition on microstructure and proton electrical conductivity of BaZr0.8Y0.2O3-δ ceramics

Sintering aids are widely used to promote densification and grain growth for electrolytes based on yttriumdoped barium zirconate. However, there are some discrepancies in the literature about the influence of these sintering aids on the microstructure development. Some authors consider that ZnO remains on grain boundaries, forming an amorphous phase that promotes sintering, and others proposed that ZnO forms a solid solution with barium zirconate. Even considering different mechanisms, it was proposed that ZnO addition compromised protonic conductivity. In this work BaZr0.8Y0.2O3-? (BZY20) was prepared by conventional oxide mixture (solid state sintering), adding ZnO as sintering aid. We proposed a mechanism for the ZnO actuation on the microstructure development, by the formation of a liquid phase during sintering and formation of a vitreous phase throughout grain boundaries during cooling. This could be the reason for poor protonic conductivity in comparison to the undoped BZY20 electrolytes. The proposed mechanism was established through the scanning electron microscopy analyses and electrical conductivity measurements under several different atmospheres by impedance spectroscopy. High density samples were obtained by using ZnO, but with compromised electrical conductivity compared to the undoped samples.

Synthesis and high proton conductive performance of indium-substituted Keggin-type quaternary heteropoly acid

The synthesis and characterization of indium-substituted Keggin structure quaternary heteropoly acid, H4[In(H2O)PW9Mo2O39]·11H2O (PMo9W2In), is reported. At 18 °C with 80% relative humidity, PMo9W2In displays the protonic conductivity as 2.32 ×10-4...

Tailoring the protonic conductivity of porous yttria-stabilized zirconia thin films by surface modification

Porous yttria-stabilized zirconia (YSZ) thin films were prepared by pulsed laser deposition to investigate the influence of specific surface area on the electrical and protonic transport properties.

High Surface Proton Conduction in Nanostructured ZIF-8

The zeolitic imidazolate framework-8 (ZIF-8) combines a significantly high microporosity with an excellent thermal, chemical, and hydrothermal stability. Here, we demonstrated that ZIF-8 can display significant levels of protonic conductivity through a water-mediated surface transport mechanism associated to the presence of di-coordinated Zn ions revealed by X-ray photoelectron spectroscopy. A set of powders with particle sizes from 2.8 µm down to 80 nm studied by dynamic water vapour sorption analysis was used to demonstrate that water adsorbs predominantly in the micropore cavities of microcrystalline ZIF-8, whereas adsorption on the external surface becomes the dominant contribution for the nanostructured material. Impedance spectroscopy in turn revealed that the protonic conductivity of the nanocrystalline ZIF-8 was two orders of magnitude higher than that of the micron-sized powders, reaching approximately 0.5 mS·cm−1 at 94 °C and 98% relative humidity. Simple relations were derived in order to estimate the potential gains in water uptake and conductivity as a function of the particle size. This new strategy combining particle nanostructuring with surface defects, demonstrated here for one of the most know metal organic framework, is of general application to potentially boost the conductivity of other materials avoiding chemical functionalization strategies that in most if not all cases compromise their chemical stability, particularly under high humidity and high temperature conditions.