Standard Article

Impact of impurities and interface reaction on electrochemical activity

Advances in Electrocatalysis, Materials, Diagnostics and Durability

Materials for high temperature fuel cells

Materials durability

  1. M. Mogensen,
  2. K. V. Hansen

Published Online: 15 DEC 2010

DOI: 10.1002/9780470974001.f500036a

Handbook of Fuel Cells

Handbook of Fuel Cells

How to Cite

Mogensen, M. and Hansen, K. V. 2010. Impact of impurities and interface reaction on electrochemical activity. Handbook of Fuel Cells. .

Author Information

  1. Technical University of Denmark, Roskilde, Denmark

Publication History

  1. Published Online: 15 DEC 2010

Abstract

The surfaces and interfaces of usual electrolytes for solid oxide fuel cells (SOFCs) such as stabilized zirconia and doped ceria tend to be covered strongly by glassy phases consisting of SiO2, Na2O, and other glass-forming oxides. Even in case of very clean single crystals a “monolayer” of impurities of similar “glassy” composition is usually observed on the surface of yttria-stabilized zirconia (YSZ). Furthermore, dopants like Y2O3 in YSZ and Gd2O3 in ceria gadolinia oxide (CGO) segregate to the grain boundaries as well as to the interface between the bulk crystal and the glassy surface layer. Perovskite electrode materials, ABO3, where A is a big and B is a small metal ion, exhibit surface layers enriched in A-oxides. Generally, the electrode polarization resistance increases with increasing amount of surface segregations. Deleterious reactions between the segregated impurities and the cell components may take place at the interfaces, and the viscous glassy phases may act as diffusion paths that allow solid-state reactions, which otherwise would be kinetically hindered. The driving forces for both impurity and dopant segregations are, in general, the changes in interface free energy between clean and covered interfaces.

Keywords:

  • solid oxide fuel cell;
  • segregation of impurities;
  • segregation of constituents;
  • electrode kinetics