It is challenging to develop highly efficient, multifunctional and low-cost cocatalysts to accelerate transfer, separation and utilization of charge carriers for fundamentally boosting photocatalytic H-2 evolution. So far, the famous metallic MPx (M = Fe, Co or Ni) H-2-evolution cocatalyst have never been used as interface electron transfer channels between semiconductors and cocatalysts. Herein, we, for the first time, demonstrated that metal phosphide (MP) cocatalyts could be used as an interface electronic bridge to greatly enhance the photocatalytic H-2 evolution over 2D/2D g-C3N4/MoS2 layered heterojunctions. The results clearly prove that Ni2P could serve as much better interface electron transfer channel than CoP and Fe2P. The highest hydrogen production rate of ternary g-C3N4-1%Ni2P-1.5%MoS2 could reach 532.41 mu molg(-1)h(-1), which was 2.47 and 5.15 times than those of g-C3N4-1.5%MoS2 and g-C3N4-1%Ni2P, respectively. More importantly, the bi-functional roles of MP cocatalyts in boosting photocatalytic H-2 evolution were also carefully revealed. Apparently, the metallic MP cocatalyts could not only serve as normal cocatalysts to boost the H-2-evolution kinetics through decreasing the overpotential, but also can act as excellent interface electron transfer channels to achieve efficient transfer of more electrons from g-C3N4 to the surface active sites of MoS2, thus synergistically leading to the significantly boosted H-2 evolution. This work would open up opportunities to develop high-efficiency and low-cost photocatalytic system using the rationally designed metallic earth-abundant cocatalysts as the interface electron bridge.