Dramatically enhanced oxygen surface exchange kinetics of mixed conducting SOFC cathode by surface modification

Abstract

Lanthanum-strontium-cobalt-ferrite (LSCF) mixed conducting perovskite have been widely studied as cathode material for intermediate temperature solid oxide fuel cells (SOFC). The performance of LSCF cathode is restrained by oxygen surface exchange process, which is the rate determining step of oxygen reduction reaction. Inspired by the past work, in this study La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ dense electrode is coated with La 2 NiO 4+δ nanoparticle electrolyte. The La 2 NiO 4+δ has relatively high ionic conductivity at intermediate temperature range, 0.0014 S.cm−1 to 0.0371 S.cm−1 at 500 °C to 800 °C, respectively, hence increase of surface reaction sites promotes the oxygen reduction reaction. The electrical conductivity relaxation (ECR) technique is used to study the oxygen surface exchange kinetics of bare LSCF and coated with La 2 NiO 4+δ . The results show that the oxygen surface exchange kinetics of LSCF is affected by the coating. At 800 °C, pO 2 (bar) step change from 0.2 to 0.8, the oxygen surface exchange coefficient, k chem , of LSCF coated with La 2 NiO 4+δ increases by a factor 7. The enhancement in k chem is found comparable as reported values by T. Hong et al. It has been concluded that the ionic conductivity of the coating phase is the key factor responsible for the improvement of surface exchange kinetics. High ionic condusctive oxide coating promotes the oxygen surface exchange kinetics of mixed conducting oxide and improves the performance of electrochemical devices such as solid oxide fuel cell.