Undercoordinated　sites　on　metal　catalysts　are　pivotal　for　enhancing　electrocatalytic　reactions,　particularly　in　processes　like　coreduction,　where　multiple　intermediates　must　be　generated　and　coupled.　Traditional　synthesis　methods,　however,　are　limited　in　their　ability　to　produce　these　low-coordination　sites.　In　this　study,　we　developed　an　amorphous　indium　catalyst　(A-In@BO　x　)　using　a　boron　oxide-assisted　method　that　achieves　a　uniquely　low　coordination　number　(CN　=　3.6)　with　a　high　density　of　67.2　wt　%.　This　structural　characteristic　significantly　enhances　the　catalytic　efficiency　for　urea　synthesis,　achieving　a　yield　rate　of　2317.58　mu　g　h-1　mgcat　-1　and　a　Faradaic　efficiency　of　51.43%　at　-0.45　V　versus　RHE.　The　undercoordinated　indium　sites　(UC-In)　on　A-In@BO　x　improve　the　conversion　of　NO3　-　to　NO2　-,　effectively　generating　*NO2　as　a　crucial　nitrogen　intermediate　for　carbon-nitrogen　coupling,　while　the　inherently　limited　activity　for　CO2　reduction　maintains　*CO2　as　the　primary　carbon　intermediate.　Our　integrated　in　situ　spectroscopy　and　theoretical　simulations　show　that　electron　transfer　from　UC-In　to　*NO2　markedly　reduces　the　free　energy　barrier　for　CO2　protonation　from　1.77　to　0.04　eV,　thus　promoting　the　formation　of　the　key　*COOH-NO2　intermediate.　This　breakthrough　not　only　offers　a　fresh　pathway　for　optimizing　urea　synthesis　but　also　elucidates　the　coreduction　mechanisms　at　undercoordinated　metal　sites,　paving　the　way　for　the　design　of　highly　selective　catalysts.