As highly efficient energy conversion devices with the capability for power/heat co-generation and fuel flexibility, solid-oxide fuel cells (SOFCs) have received considerable attention recently as a keystone of the future energy economy. Nowadays, lack of a proper cathode with high performance at intermediate temperature (IT) has become the main obstacle in realizing this fascinating technology. Here we present (La(0.8)Sr(0.2))(0.95)Ag(0.05)MnO(3-delta) as a novel CO(2) tolerant cathode of IT-SOFCs, which shows silver intercalation/de-intercalation capability. Under cathodic polarization, silver can be extracted from perovskite lattice to form a 5-15 nm silver modified A-site cation deficient (La(0.8)Sr(0.2))(0.95)MnO(3-delta) electrode with superior electrocatalytic activity and improved stability. Any performance degradation due to silver sintering can be easily in situ restored by re-intercalating silver into the perovskite lattice under anodic polarization. Through electrochemically adjusting the oxidation state and location of silver, we introduce a way for the development of high-performance silver-modified cathode for IT-SOFCs, which may contribute significantly to a sustainable future.