Integrating 2D/2D CdS/α-Fe2O3 ultrathin bilayer Z-scheme heterojunction with metallic β-NiS nanosheet-based ohmic-junction for efficient photocatalytic H2 evolution

Water splitting for hydrogen production on noble metal-free photocatalysts remains a big challenge. Herein, we present for the first time a 2-dimensional/2-dimensional (2D/2D) Z-scheme photocatalyst formed by in situ growing CdS nanosheets on α-Fe2O3 nanosheets. The former was additionally modified with metallic β-NiS cocatalyst, which creates a Ohmic-based heterojunction and functions as hydrogen-evolution sites. The resultant β-NiS-decorated CdS/α-Fe2O3 ultrathin 2D/2D heterojunction showed a remarkable hydrogen production rate of 45 mmol h−1 g−1 and a high quantum efficiency of 46.9 % at 420 nm. The excellent photocatalytic performance is attributed to: (1) intimate and large interfaces between CdS and α-Fe2O3 nanosheets for facilitated charge transfer, (2) promoted charge separation in the Z-scheme heterojunction, and (3) large quantity of Ohmic-junction hydrogen-evolution sites over metallic β-NiS cocatalyst. Overall, this work demonstrates a promising strategy for improving charge dynamics and hydrogen-production efficiency, through rational design and integration of multiple built-in electric fields over 2D semiconductor nanosheets.