In this work

a novel NiP

2

/g-C

3

N

4

heterojunction

via

homogeneous precipitation method assisted by thermal phosphorization reaction was designed and constructed

and the optimized sample showed the excellent photocatalytic H

2

evolution activity under visible-light irradiation

which was nearly 112 times higher than that of pristine g-C

3

N

4

sample. Experimental characterizations and DFT calculations demonstrated that the NiP

2

nanoparticles covered on the g-C

3

N

4

surface can form a built-in electric field at the interface to accelerate the transfer of photoexcited electrons from g-C

3

N

4

to NiP

2

crucial for hindering the recombination of electron-hole pairs. Moreover

the energy barrier of hydrogen evolution reaction can also vastly reduce when combined NiP

2

and g-C

3

N

4

to construct NiP

2

/g-C

3

N

4

heterojunction. This work represents a method through combing experimental and theoretical tools to thoroughly investigate the mechanism of photocatalytic process.