The　electrochemical　reduction　of　nitrate　(NO3−)　to　ammonia　(NH3)　(NO3RR)　represents　an　environmentally　sustainable　strategy　for　NH3　production　while　concurrently　addressing　water　pollution　challenges.　Nevertheless,　the　intrinsic　complexity　of　this　multi-step　reaction　severely　constrains　both　the　selectivity　and　efficiency　of　NO3RR.　Copper-based　electrocatalysts　have　been　extensively　investigated　for　NO3RR　but　often　suffer　from　nitrite　(NO2−)　accumulation,　which　stems　from　insufficient　NO3−　adsorption　strength.　This　limitation　often　leads　to　rapid　catalyst　deactivation,　hindered　hydrogenation　pathways,　and　reduced　overall　efficiency.　Herein,　we　report　a　one-step　green　chemical　reduction　method　to　synthesize　PtCuSnCo　quarternary　alloy　nanoparticles　with　homogeneously　distributed　elements.　Under　practical　NO3−　concentrations,　the　optimized　catalyst　exhibited　an　impressive　Faradaic　efficiency　approaching　100%　and　an　outstanding　selectivity　of　95.6　±　2.9%.　Mechanistic　insights　uncovered　that　SnCo　sites　robustly　facilitated　NO3−　adsorption,　complemented　by　the　proficiency　of　PtCu　sites　in　NO3−　reduction.　The　synergistic　spatial　neighborhood　effect　between　SnCo　and　PtCu　sites　efficiently　stabilizes　NO3−　deoxygenation　and　suppresses　NO2−　accumulation.　This　tandem　architecture　achieves　a　finely　tuned　balance　between　adsorption　strength　and　deoxygenation　kinetics,　enabling　highly　selective　and　efficient　NO3RR.　Our　findings　emphasize　the　indispensable　role　of　engineered　multi-metallic　catalysts　in　overcoming　persistent　challenges　of　NO3RR,　paving　the　way　for　advanced　NH3　synthesis　and　environmental　remediation.　©　2025　Dalian　Institute　of　Chemical　Physics,　the　Chinese　Academy　of　Sciences