A Three-Dimensional ZnO/CdS/NiFe Layered Double Hydroxide Photoanode Coupled with a Cu2O Photocathode in a Tandem Cell for Overall Solar Water Splitting

An integrated tandem photoelectrochemical (PEC) cell, composed of a three-dimensional (3D) ZnO/CdS/NiFe layered double hydroxide (LDH) core/shell/hierarchical nanowire arrays (NWAs) photoanode and a [Formula: see text]-Cu 2 O photocathode, was designed for unassisted overall solar water splitting in this study. The optical and photoelectrochemical characteristics of ZnO-based photoanodes and Cu 2 O photocathode were investigated. The results show that ZnO/CdS/NiFe LDH nanostructures offer significantly enhanced performances with a photocurrent density reaching 5.8[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] at 0.9[Formula: see text]V and an onset potential as early as 0.1[Formula: see text]V (versus RHE). The enhancement can be attributed to the existence of CdS nanoparticles (NPs) which boosts the light absorption in visible region and enhances charge separation. Moreover, the introduction of NiFe LDH nanoplates, with unique hierarchical mesoporous architecture, promotes electrochemical reactions by providing more active sites as co-catalyst. On the above basis, the ZnO/CdS/NiFe LDH–Cu 2 O two-electrode tandem cell system was established. At zero bias, the device shows a photocurrent density of 0.4[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text] along with the corresponding solar-to-hydrogen (STH) conversion efficiency reaching 0.50%. Our results indicate that the tandem PEC cells consisting of metal–oxide–semiconductor photoelectrodes based on Earth-abundant and low-cost materials hold promising application potential for overall solar water splitting.