Stability, mixed conductivity, and thermomechanical properties of perovskite materials for fuel cell electrodes based on La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta), La0.5Ba0.5Ti0.5Fe0.5O3-delta, and (La0.5D0.5)(0.95)Cr0.5Fe0.5O3-delta (A = Ca, Ba)

Abstract

For materials based on ferrites and manganites with DD degrees(2+) and D'D degrees(2+) cations substituted into D sublattice, the functional properties are studied and the prospects as electrode materials for solid-oxide fuel cells are assessed. The electronic conductivity of materials based on La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) is shown to decrease with the increase in the ionic radius of alkali-earth substituent; however, for La0.5D'D degrees 0.5Mn0.5Ti0.5O3-delta and La0.5D'D degrees 0.5Fe0.5Ti0.5O3-delta, the appearance of n-conduction is observed during reduction, which may provide adequate conductivity under anodic conditions. Under the conditions of fuel cell operation, the thermal expansion coefficients of these materials are (13.0-13.5) x 10(-6) K-1. The thermal and chemical expansion increases with the increase in the radius of alkali-earth cation; the latter value does not exceed 0.2%, which is acceptable for preparation of electronic layers. The transition of oxygen through membranes based on materials studied is determined to the large extent by the kinetics of surface exchange which depends on the rate of delivery of oxygen vacancies to the surface. Doping of ferrites with chromium or titanium decreases the electronic and ionic conductivity; however, the presence of substituents in D' sublattice makes it possible to stabilize the perovskite phase in a wide range of NEuro(D-2), decrease the thermal and chemical expansion, and prevent to the large extent the ordering of oxygen vacancies, which allows one to consider these materials as the candidates for electrodes in symmetrical solid-oxide fuel cells.