As　the　N　equivalent　to　N　bond　in　N-2　is　one　of　the　strongest　bonds　in　chemistry,　the　fixation　of　N-2　to　ammonia　is　a　kinetically　complex　and　energetically　challenging　reaction　and,　up　to　now,　its　synthesis　is　still　heavily　relying　on　energy　and　capital　intensive　Haber-Bosch　process　(150-350　atm,　350-550　degrees　C),　wherein　the　input　of　H-2　and　energy　are　largely　derived　from　fossil　fuels　and　thus　result　in　large　amount　of　CO2　emission.　In　this　paper,　it　is　demonstrated　that　by　using　Au　sub-nanoclusters　(approximate　to　0.5　nm)　embedded　on　TiO2　(Au　loading　is　1.542　wt%),　the　electrocatalytic　N-2　reduction　reaction　(NRR)　is　indeed　possible　at　ambient　condition.　Unexpectedly,　NRR　with　very　high　and　stable　production　yield　(NH3:　21.4　mu　g　h(-1)　mg(cat.)(-1),　Faradaic　efficiency:　8.11%)　and　good　selectivity　is　achieved　at　-0.2　V　versus　RHE,　which　is　much　higher　than　that　of　the　best　results　for　N-2　fixation　under　ambient　conditions,　and　even　comparable　to　the　yield　and　activation　energy　under　high　temperatures　and/or　pressures.　As　isolated　precious　metal　active　centers　dispersed　onto　oxide　supports　provide　a　well-defined　system,　the　special　structure　of　atomic　Au　cluster　would　promote　other　important　reactions　besides　NRR　for　water　splitting,　fuel　cells,　and　other　electrochemical　devices.