Synergistic mechanism of facet junction and p-n junction optimizing charge transfer for enhanced photocatalytic hydrogen production in the CuCo2O4/Cd0.5Zn0.5S system

Herein, CuCo 2 O 4 hollow porous nanospheres (HPN), nanosheets (NS), and nanowires (NW) were synthesized via solvothermal and calcination processes, and were used to construct efficient heterojunctions with Cd 0.5 Zn 0.5 S. Interestingly, the unique hollow porous structure exhibits enhanced light absorption, large pore diameter (12.57 nm), and strong hydrophilicity (10.05°). Photocatalytic results indicate that CuCo 2 O 4 HPN/Cd 0.5 Zn 0.5 S achieves the optimal hydrogen production rate, which is 5.4, 1.2, and 1.3 times than that of pure Cd 0.5 Zn 0.5 S, CuCo 2 O 4 NW/Cd 0.5 Zn 0.5 S and CuCo 2 O 4 NS/Cd 0.5 Zn 0.5 S, respectively. High-resolution TEM and theoretical calculations confirm that (311)/(111) facet junctions in CuCo 2 O 4 nanospheres form a work function difference (0.24 eV), which significantly facilitates charge transfer and separation. Mott-Schottky and Ultraviolet photoelectron spectroscopy analyses indicate that p-type CuCo 2 O 4 and n-type Cd 0.5 Zn 0.5 S have staggered energy levels and a distinct Fermi level difference (1.85 eV), which leads to rearrangement of the Fermi energy level and modulation of charge transfer pathway. The resulting energy band bending and built-in electric field promote charge transfer at the heterojunction interface more effectively. The synergistic mechanism of the facet junction and p-n junction finally achieves high-efficiency hydrogen production. This work provides new insights into how to construct efficient p-n heterojunction photocatalysts and presents the synergistic mechanism of facet junction and p-n junction.