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The interfacial synergy effect caused by the space charge transfer of heterojunctions can effectively modify the catalytic activity. Herein, a composite heterojunction catalyst of CoTe 2 /CoP with moderate Gibbs free energy of hydrogen adsorption is designed based on interfacial effects driven by work function difference between CoTe 2 and CoP. As expected, CoTe 2 /CoP only needs overpotentials of 80 mV at 10 mA cm−2 and stability for continuous catalysis at the current density of 100 mA cm−2 for 20 h in hydrogen evolution reaction (HER). The experimental results and theory calculations identify that the built-in field drives the transfer of electrons from CoTe 2 to CoP at the interface, which realizes electronic redistribution with increased electron density on the Co atoms in CoP and optimizes the adsorption-free energy of the reaction intermediates, thereby, accelerating HER kinetics. Besides, the CoTe 2 /CoP heterostructure also behaves the excellent catalytic activity towards water splitting. [Display omitted] • CoTe 2 /CoP is prepared via one-step phosphotellurization method. • Built-in field drives the transfer of electrons from CoTe 2 to CoP at the interface. • Electronic redistribution optimizes the adsorption-free energy of the reaction intermediates. • CoTe 2 /CoP exhibits the boosted hydrogen evolution reaction (HER) performance. [ABSTRACT FROM AUTHOR]