An optimized approach to producing lattice-matched heterointerfaces for electrocatalytic hydrogen evolution has not yet been reported. Herein, we present the synthesis of lattice-matched Mo2C-Mo2N heterostructures using a gradient heating epitaxial growth method. The well lattice-matched heterointerface of Mo2C-Mo2N generating near-zero hydrogen adsorption free energy and facilitating water dissociation in acid and alkaline. Thus, the lattice-matched Mo2C-Mo2N heterostructures display ultralow overpotentials of 73 mV and 80 mV at 10 mA cm-2 in acid and alkaline solutions, respectively, comparable to the commercial Pt/C.Moreover, a novel photothermal-electrocatalytic water vapor splitting device adopting lattice-matched Mo2C-Mo2N heterostructure as hydrogen evolution electrocatalyst displays a competitive cell voltage in the electrocatalytic water splitting equipment. This work opens a novel pathway for designing efficient electrocatalysts with lattice-matched heterointerface.