The　low　efficiency　of　photogenerated　charge　separation　significantly　hinders　the　photocatalytic　nitrogen　(N2)　fixation.　Local　polarization　electric　field　(LPEF)　induced　by　defects　has　been　known　to　enhance　charge　separation,　yet　the　synergistic　effects　and　mechanisms　related　to　different　types　of　defects　in　pure　phases　remain　poorly　understood.　In　this　study,　defect-free　bismuth　oxybromide　(BiOBr;　BOB),　together　with　single　vacancy　(BOB-VBr　and　BOB-VO)　and　dual　vacancy　(BOB-VBrO)　analogues,　were　successfully　synthesized,　and　the　presence　of　these　specific　vacancies　was　comprehensively　characterized.　Notably,　the　dual　vacancy　BOB-VBrO　exhibited　the　highest　photocatalytic　NH3　generation　rate　of　266　μmol　g-1　h-1　in　a　liquid-solid　biphasic　system,　which　was　6.1,　1.5,　and　1.4　times　higher　than　those　of　BOB,　BOB-VBr,　and　BOB-VO,　respectively.　Furthermore,　the　NH3　generation　capacity　of　BOB-VBrO　reached　an　impressive　rate　of　978　μmol　g-1　h-1　in　a　gas-liquid-solid　triphasic　system.　Photoelectrochemical　tests　revealed　that　BOB-VBrO　demonstrated　the　highest　light　conversion　efficiency,　followed　by　BOB-VO,　BOB-VBr,　and　BOB.　The　relative　intensity　of　the　internal　electric　field　in　BOB-VBrO　was　also　significantly　high,　being　1.8,　2.4,　and　3.9　times　greater　than　those　of　BOB-VO,　BOB-VBr,　and　BOB,　respectively.　The　Br　and　O　vacancies　synergistically　induced　LPEF　between　the　[O]/[Br]　and　[Bi]　layers.　In　situ　irradiation　X-ray　photoelectron　spectroscopy　indicated　that　O　and　Br　vacancies　of　the　oligomers　could　synergistically　enhance　the　LPEF,　thereby　facilitating　the　transfer　of　photogenerated　electrons　from　O/Br　to　Bi.　Additionally,　the　practical　feasibility　of　BOB-VBrO　in　photocatalytic　N2　fixation　was　validated　to　produce　liquid　nitrogenous　fertilizer　for　plant　growth,　revealing　its　potential　application　in　agricultural　production.　©　2025　American　Chemical　Society.