Dual electric fields in Ni-CdS@Ni(OH)2 heterojunction: A synergistic spatial charge separation approach for enhanced coupled CO2 photoreduction and selective toluene oxidation

Abstract

Simultaneously inducing dual built-in electric fields (EFs) both within a single component and at the heterojunction interface creates a dual-driving force that is crucial for promoting spatial charge separation. This is particularly significant in challenging coupled systems, such as CO₂ photoreduction integrated with selective oxidation of toluene to benzaldehyde. However, developing such a system is quite challenging and often requires a precise design and engineering. Herein, we demonstrate a unique Ni-CdS@Ni(OH)₂ heterojunction synthesized via an in-situ self-assembly method. Comprehensive mechanistic and theoretical investigations reveal that the Ni-CdS@Ni(OH)₂ heterojunction induces dual electric fields (EFs): an intrinsic polarized electric-field within the CdS lattice from Ni doping and an interfacial electric-field from the growth of ultrathin nanosheets of Ni(OH)₂ on Ni-CdS nanorods, enabling efficient spatial charge separation and enhanced redox potential. As proof of concept, the Ni-CdS@Ni(OH)₂ heterojunction simultaneously exhibits outstanding bifunctional photocatalytic performance, producing CO at a rate of 427 ​μmol ​g⁻¹ ​h⁻¹ and selectively oxidizing toluene to benzaldehyde at a rate of 1476 ​μmol ​g⁻¹ ​h⁻¹ with a selectivity exceeding 85%. This work offers a promising strategy to optimize the utilization of photogenerated carriers in heterojunction photocatalysts, advancing synergistic photocatalytic redox systems.