Optimization strategy for CdSe@CdS core–shell nanorod structures toward high performance water splitting photoelectrodes

[Display omitted] •Simple cost effective wet chemical method to fabricate CdSe@CdS NRs photoanode.•Test of achievable maximum photocurrent density from tandem photoanode structure of given energy gaps.•Band diagram analysis of CdS/CdSe tandem in relation with photoelectrochemical reaction. Photoelectrochemical (PEC) water splitting offers a promising strategy for converting solar energy to chemical fuel of hydrogen. Herein, we report about the successful synthesis of hexagonal CdSe@CdS core–shell nanorod (NR) structures by facile two-step chemical synthesis of hydrothermal and chemical bath growth. Structural, morphological, optical, and electrical properties of the NR structures are thoroughly investigated, thereby heterojunction characteristics can be elaborated. Compared with the bare CdS NRs, the CdSe@CdS core–shell NR-heterostructures exhibit far enhanced photoelectrode performance mainly owing to the small bandgap energy of CdSe and the optimized CdSe layer thickness. The CdSe@CdS core–shell NRs reveal the PEC current density of 11.0 mA/cm2 at 0 V vs. SCE, which is more than twice of that of the bare CdS NRs (4.3 mA/cm2). The enhancement in the PEC performance is elucidated by the energy band diagrams of the various heterostructures, which can be assessed by the Mott-Schottky and electrochemical impedance spectroscopy measurements.