A　highly　efficient　and　stable　electrocatalyst　with　the　novel　heterostructure　of　Co-embedded　and　N-doped　carbon　nanotubes　supported　Mo2C　nanoparticles　(Mo2C/NCNTs@Co)　is　creatively　constructed　by　adopting　the　one-step　metal　catalyzed　carbonization-nitridation　strategy.　Systematic　characterizations　and　density　functional　theory　(DFT)　calculations　reveal　the　advanced　structural　and　electronic　properties　of　Mo2C/NCNTs@Co　heterostructure,　in　which　the　Co-embedded　and　N-doped　CNTs　with　tunable　diameters　present　electron-donating　effect　and　the　work　function　is　correspondingly　regulated　from　4.91　to　4.52　eV,　and　the　size-controlled　Mo2C　nanoparticles　exhibit　Pt-like　4d　electronic　structure　and　the　well　matched　work　function　(4.85　eV)　with　I-/I3-　redox　couples　(4.90　eV).　As　a　result,　the　conductive　NCNTs@Co　substrate　with　fine-tuned　energy　level　alignment　accelerates　the　electron　transportation　and　the　electron　migration　from　NCNTs@Co　to　Mo2C,　and　the　active　Mo2C　shows　high　affinity　for　I3-　adsorption　and　high　charge　transfer　ability　for　I3-　reduction,　which　reach　a　decent　synergetic　catalytic　effect　in　Mo2C/NCNTs@Co　heterostructure.　The　DSSC　with　Mo2C/NCNTs@Co　CE　achieves　a　high　photoelectric　conversion　efficiency　of　8.82%　and　exceptional　electrochemical　stability　with　a　residual　efficiency　of　7.95%　after　continuous　illumination　of　200　h,　better　than　Pt-based　cell.　Moreover,　the　synergistic　catalytic　mechanism　toward　I3-　reduction　is　comprehensively　studied　on　the　basis　of　structure-activity　correlation　and　DFT　calculations.　The　advanced　heterostructure　engineering　and　electronic　modulation　provide　a　new　design　principle　to　develop　the　efficient,　stable,　and　economic　hybrid　catalysts　in　relevant　electrocatalytic　fields.　©　2019　American　Chemical　Society.