α-Fe2O3/Ag/CdS ternary heterojunction photoanode for efficient solar water oxidation

Abstract

The photoelectrochemical (PEC) water oxidation performance of α-Fe₂O₃ photoanodes is jointly restricted by their high charge recombination and sluggish water oxidation kinetics. Herein, through coupling Ag and CdS nanoparticles with an α-Fe₂O₃ nanorod film, a new kind of α-Fe₂O₃/Ag/CdS ternary heterojunction film was constructed and investigated as a photoanode for solar water oxidation. The resultant α-Fe₂O₃/Ag/CdS photoanode can take full advantages of the α-Fe₂O₃/CdS heterojunction and the properties of Ag nanoparticles. Specifically, the formation of the α-Fe₂O₃/CdS heterojunction improves the charge separation and transfer efficiency of the α-Fe₂O₃ photoanode through band potential differences. Meanwhile, the presence of Ag nanoparticles enlarges the absorption edge of α-Fe₂O₃/CdS and decreases the electron–hole recombination through their surface plasmon resonance (SPR) effect. In addition, the electrocatalytic properties of Ag nanoparticles could initiate the water oxidation on the α-Fe₂O₃/Ag/CdS photoanode jointly. As a result, a higher photocurrent density of 3.25 mA cm⁻² at 1.23 V vs. RHE was achieved on the α-Fe₂O₃/Ag/CdS photoanode during water oxidation, which is 2.5 times higher relative to the photocurrent of the α-Fe₂O₃ photoanode. Furthermore, the onset potential of water oxidation on the α-Fe₂O₃/Ag/CdS photoanode was negatively shifted about 220 mV relative to the α-Fe₂O₃ photoanode due to its faster kinetics. With the protection of the amorphous TiO₂ layer, the water oxidation activity of the α-Fe₂O₃/Ag/CdS photoanode can be steadily maintained even after 10 h of reaction at 1.23 V vs. RHE. The present work provides an efficient strategy for the development of α-Fe₂O₃-based ternary heterojunction photoanodes for solar water oxidation.