Ammonia　(NH3)　is　an　easy　to　store,　zero-carbon　emission　hydrogen　carrier.　The　current　primary　challenges　in　enhancing　the　yield　and　faradaic　efficiency　of　the　electrocatalytic　nitrogen　reduction　reaction　(NRR)　for　ammonia　synthesis　are　widely　recognized　to　be　the　inhibition　of　the　competing　hydrogen　evolution　reaction　(HER)　and　the　activation　of　N　≡　N　to　facilitate　its　cleavage.　Here　we　select　perovskite　oxide　materials　La0.6Sr0.4Co0.2Fe0.8+xO3−δ　(LSCF0.8+x,　x　=　0-0.1)　as　the　NRR　electrode　for　the　proton-conducting　solid　oxide　electrolyzer　cells　(PCECs).　We　construct　a　more　effective　metal　oxide　interface　via　in　situ　exsolution　of　CoFe　alloy　nanoparticles　(NPs),　which　promotes　N　≡　N　activation　and　cleavage　by　applying　a　certain　voltage　at　500　°C,　thereby　accelerating　the　gradual　synthesis　of　NH3　with　proton　H+.　At　500　°C　and　0.8　V,　the　maximum　NH3　synthesis　rate　is　3.75　×　10−9　mol　s−1　cm−2　while　the　highest　faradaic　efficiency　is　3.05%,　and　there　is　no　damage　to　the　microstructure　after　continuously　working　for　100　h,　indicating　that　this　material　as　the　electrode　is　beneficial　to　the　electrocatalytic　synthesis　of　ammonia　in　PCECs.　©　2024　The　Royal　Society　of　Chemistry.