Decoration of ZnO Nanorod Arrays with Heterojunction of Graphene Quantum Dots and MoS₂ Nanoparticles for Photoelectrochemical Water Splitting

Conversion of sunlight to a chemical fuel through photoelectrochemical (PEC) water splitting is deemed to be a promising solution to satisfy future energy needs. In this study, a photoanode based on the triple heterojunction of MoS2/graphene quantum dots/ZnO nanorods (MoS2/GQD/ZnO) was prepared to compare its PEC performance with its well-studied two component counterparts and pristine ZnO. In this hybrid configuration, ZnO nanorods mainly act as the scaffold for further deposition steps, GQDs act as the charge transport layer, and MoS2 nanoparticles act as the visible light absorber. After the addition of GQDs and MoS2 nanoparticles to ZnO nanorods through electrophoretic deposition, the suitable band alignment between these materials along with the formation of a type-II junction between each of the two parts highly facilitates charge separation and increases the carrier density. Although GQD/ZnO and MoS2/ZnO exhibit superior performance compared to bare ZnO, the formation of a triple structure outperforms the former photoanodes in terms of overpotential and kinetics. Consequently, MoS2/GQD/ZnO represented the highest efficiency and generated 4.36 mA/cm2 photocurrent density, which is 4.1 and 1.3 times higher than that of GQD/ZnO (1.07 mA/cm2) and MoS2/ZnO (3.66 mA/cm2) photoanodes, respectively.