Electrochemical　nitrogen　reduction　reaction　(eNRR)　is　recognized　as　a　promising　approach　for　ammonia　synthesis,　which　is,　however,　impeded　by　the　inert　nitrogen　and　the　unavoidable　competing　hydrogen　evolution　reaction　(HER).　Here,　a　Mo-PTA@CNT　electrocatalyst　in　which　Mo　species　are　anchored　on　the　fourfold　hollow　sites　of　phosphotungstic　acid　(PTA)　and　closely　embedded　in　multi-walled　carbon　nanotubes　(CNT)　for　immobilization　is　designed　and　synthesized.　Interestingly,　the　catalyst　presents　a　high　ammonia　yield　rate　of　51　+/-　1　mu　g　h(-1)　mg(cat.)(-1)　and　an　excellent　Faradaic　efficiency　of　83　+/-　1%　at　-0.1　V　versus　RHE　under　ambient　conditions.　The　concentrations　of　NH4+　are　also　quantitatively　calculated　by　H-1　NMR　spectra　and　ion　chromatography.　Isotopic　labeling　identifies　that　the　N　atom　of　the　formed　NH3　originates　from　N-2.　The　controlled　experiments　confirm　a　strong　interaction　between　Mo-PTA　and　N-2　with　an　adsorption　energy　of　50.46　kJ　mol(-1)　and　activation　energy　of　21.36　kJ　mol(-1).　More　importantly,　due　to　CNT＇s　gas　storage　and　hydrophobicity　properties,　there　is　a　fourfold　increase　in　N-2　content.　The　concentration　of　H2O　is　reduced　by　more　than　half　at　the　interface　of　the　electrode.　Thus,　the　activity　of　eNRR　can　be　significantly　improved　with　ultrahigh　electron　selectivity.