Gradhdiyne as an electronic bridge to facilitate built-in electric field in NiS/ ZnCdS S-Scheme heterostructure for efficient photocatalytic hydrogen evolution

Graphdiyne (GDY) as an emerging carbon allotrope with abundant acetylenic linkages, has been proven to be an excellent substrate and electron transport material for improving the photocatalytic activity. In this work, an Sscheme GDY/NiS/ZnCdS (GDY/NiS/ZCS) heterojunction with GDY as an electron bridge was synthesized using a simple mixing method. GDY nanosheets serve as an effective electron bridge to accelerate electron transfer between NiS and ZnCdS. ZnCdS and NiS form an S-Scheme heterojunction due to the alignment of their conduction bands. Benefitted from the difference in Fermi levels between the NiS and ZnCdS induces band bending, thereby creating an internal electric field on the interface of NiS/ZnCdS S-Scheme heterojunction. The S-Scheme charge transfer mechanism of GDY/NiS/ZCS heterojunction was strongly confirmed by in situ irradiated XPS. Photogenerated charge carriers can be carried along a more advantageous S-Scheme pathway with the help of the synergistic impact of internal electric field and GDY electron bridge, hence greatly increasing the photocatalytic activity. A maximum hydrogen evolution rate of 32.1 mmol g- 1 h- 1 was attained over 1.5 wt%GDY/ NiS/ZCS with exceptional stability, which is 2.84 times greater than NiS/ZCS and 5.26 times higher than pure ZnCdS. This work provides a new perspective on employing GDY as an electron bridge for constructing S-Scheme heterojunction with internal electric fields to improve photocatalytic performance.