ZnO@CdS heterostructures: an efficient photoanode for photoelectrochemical water splitting

Abstract

Solar water splitting devices with high efficiency need to be developed, utilizing low cost and efficient materials. For this purpose, ZnO@CdS heterostructure nanosheets are developed herein as an efficient photoanode for solar water splitting. 2D nanosheets of ZnO are synthesized vertically on fluorine doped tin oxide (FTO) through a simple electrochemical deposition technique. The ZnO nanosheets can generate a photocurrent density of 0.212 mA cm−2 at 0 V vs. Ag/AgCl. The vertically grown interconnected 2D sheets help to enhance light absorbance and allow larger amounts of electrolyte to penetrate inside the anode. ZnO is a wide bandgap (3.3 eV) material and it suffers from low solar light absorbance. To enhance the optical activity under visible light and to ensure efficient charge carrier separation, the surfaces of the ZnO nanosheets are modified with CdS, which has a bandgap of 2.4 eV, using a successive ionic layer adsorption and reaction (SILAR) technique. The amount of CdS on the ZnO surface is varied by increasing the SILAR cycle number and a maximum photocurrent density is observed in the case of ZnO@CdS/20. ZnO@CdS/20 can generate a photocurrent density of 1.15 mA cm−2 at 0 V vs. Ag/AgCl under continuous light illumination. The observed photoconversion efficiency (η) is maximal in the case of ZnO@CdS/20, a value of 0.754%. After the decoration of CdS on ZnO, the carrier density also increases nearly 30 times compared to bare ZnO, which further indicates the higher photoactivity of the heterostructures.