Water-unlocked formation of active oxygen vacancies in perovskite fuel-cell cathodes

Authors:
Preprint
Publisher website
Google Scholar
Abstract
Not all oxygen vacancies are equal, yet metal oxide catalysts are usually designed as if they were. In perovskite fuel-cell cathodes, oxygen vacancies near redox-active and redox-inactive cations play distinct roles in oxygen reduction reaction, ion transport and hydration, but they are usually lumped into one bulk-averaged property. By partially substituting Y with less electronegative Yb in the benchmark BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3− δ cathode, we reveal that oxygen vacancies near redox-inactive Y/Yb control the vacancy formation near redox-active Co/Fe, and that water in air unlocks such formation. In dry air, the vacancies near Y/Yb can switch off their inductive effects and thus block the formation of vacancies near Co/Fe, whereas in humid air, these vacancies tend to be occupied by water, unlocking the inductive effect and promoting active vacancies. This water-unlocked formation of vacancies near Co/Fe doubles the oxygen reduction reaction activity in humid air and enables a protonic ceramic fuel cell to generate a peak power density of 700 mW cm − 2 at 600°C and a stable operation beyond 2,450 h. Our findings suggest that oxygen vacancies are not independent but coupled, with water acting as a switch that turns this coupling into new active sites.

This publication has 42 references indexed in Scilit: