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 µg h−1　mgcat.−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　1H　NMR　spectra　and　ion　chromatography.　Isotopic　labeling　identifies　that　the　N　atom　of　the　formed　NH3　originates　from　N2.　The　controlled　experiments　confirm　a　strong　interaction　between　Mo-PTA　and　N2　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　N2　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.　©　2021　Wiley-VCH　GmbH