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.　(c)　2025,　Dalian　Institute　of　Chemical　Physics,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.　All　rights　reserved.