Ruddlesden-Popper　oxide　La2NiO4+δ　(LNO)　has　a　high　ionic　conductivity　and　good　thermal　match　with　the　electrolyte　of　solid　oxide　fuel　cells　(SOFCs);　however,　LNO　suffers　from　performance　decay　owing　to　the　La　surface　segregation　under　the　operation　conditions　of　SOFCs.　Herein,　we　report　an　in　situ　electrochemical　decoration　strategy　to　improve　the　electrocatalytic　activity　and　durability　of　LNO　cathodes.　We　show　that　the　electrochemical　polarization　leads　to　in　situ　construction　of　the　LNO@Pt　core-shell　structure,　significantly　suppressing　the　detrimental　effect　of　La　surface　segregation　on　the　LNO　cathode.　The　initial　peak　power　density　of　a　single　cell　with　the　LNO　cathode　is　0.71　W　cm-2　at　750　°C,　increasing　to　1.39　W　cm-2　by　the　in　situ　construction　of　the　LNO@Pt　core-shell　structure　after　polarization　at　0.5　A　cm-2　for　20　h.　The　LNO@Pt　core-shell　structure　is　also　highly　durable　without　noticeable　performance　degradation　over　the　duration　of　the　test　for　180　h.　The　findings　shed　light　on　the　design　and　fabrication　of　highly　active　and　durable　LNO-based　cathodes　for　SOFCs.　©　2023　American　Chemical　Society