Segregation Resistant Perovskite Oxides with Surfaces Modified by Binary Oxides and Heterogeneous Doping

Technology #17791

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The area specific resistance to surface oxygen exchange reaction at 530 degrees Celsius in air as a function of time on LSC thin film cathodes with the different elements (Mn, Fe, Nb, Zr, Co, V, Ti, Hf) deposited at the surface and on the bare unmodified LSC. Note that the oxygen exchange reaction rate is inversely proportional to the plotted area specific resistance.
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Inventors
Professor Bilge Yildiz
Department of Materials Science and Engineering, MIT
External Link (web.mit.edu)
Nikolai Tsvetkov
Laboratory For Electrochemical Interfaces, MIT
Qiyang Lu
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Segregation Resistant Perovskite Oxides With Surface Modification

PCT Patent Application Filed
Publications
Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface
Nature Materials, June 13, 2016
Improved electrochemical stability at the surface of La0.8Sr0.2CoO3 achieved by surface chemical modification
Faraday Discussions, April 9, 2015

Applications

This invention would be of interest to industries dealing with the application of perovskite oxide materials, including solid oxide fuel and electrolysis cells, catalysts for thermochemical splitting of water and carbon dioxide, oxygen permeation membranes and chemical looping, batteries, and magnetic and catalytic devices. 

Problem Addressed

Existing solid oxide fuel cells and electrolysis cells (SOFC, SOEC) have proven that the surface of such perovskite oxides are not stable. These surfaces undergo segregation and phase separation of dopant oxides at and above 400 degrees Celsius. The degradation of the chemical surface is harshly detrimental due to the consequent formation of a layer that blocks charge transfer. Choosing suitable dopants will therefore hinder the secondary phase segregation.  This technology prevents elastic and electrostatic interactions, the key driving forces behind dopant segregation, by using a suitable surface additive cation that decreases the surface oxygen vacancy concentration at the surface. 

Technology

Perovskite oxides can be stabilized through the application of a thin film of oxidizing metal ions on the material's surface. The size mismatch, between the dopant and host cations and the associated elastic energy minimization push the larger or smaller dopants to free surface or interfaces. In addition, oxygen vacancies and the net positive charge at the surface of perovskite oxides drive the negatively charged dopants in the form of point defects to the surface. To minimize the electrostatic interactions that drive dopant segregation, this technology decreases the amount of the oxygen vacancies that can be equilibrated at the material surface. The surface positive charge is then reduced by putting more oxidizing metal cations at the surface, which lessens the amount of oxygen vacancies present, and thus, the electrostatic attraction of the dopants to the surface is weakened. By choosing a suitable surface additive cation, the stability of the perovskite oxide surface could be improved and the final surface oxygen exchange reaction coefficient is increased up to 30 times. 

Advantages

  • Minimizes or completely avoids segregation and phase separation of dopant cations at the surface
  • Improves chemical stability
  • Able to function at temperatures above 300 degrees Celsius
  • Improves surface charge transfer properties