Oxygen reduction mechanism and performance of Y₁Ba₂Cu₃O_7−d as a cathode material in a high-temperature solid-oxide fuel cell

Abstract

The high-Tc Y₁Ba₂Cu₃O_7−δ superconductor with oxygen ion vacancies was employed as the cathode for a high-temperature solid-oxide fuel cell (SOFC). The cathodic current-overpotential characteristics were studied in the temperature range from 500 to 800 °C and the oxygen pressure range from 10⁻⁴ to 0.21 atm. The delocalization of the triple-phase boundary and the oxygen reduction mechanism were identified. The delocalized triple-phase boundary of Y₁Ba₂Cu₃O_7−δ improves the cathodic polarization in SOFCs. By using a mathematical simulation and a particular experimental design, the oxygen adsorption step in the oxygen reduction process was demonstrated to be rate limiting. A layer of strong oxygen-adsorption catalyst such as Pt or Ag coated on the Y₁Ba₂Cu₃O_7−δ electrode was found to be able to largely enhance the activity of oxygen reduction by improving the ability of oxygen to be adsorbed on the electrode surface.