Fabrication of Junction type Photoanode and the Application to Photoelectrochemical Water Splitting

Abstract

The photoelectrochemical (PEC) cell is a highly promising system to produce hydrogen and oxygen from water using solar energy. In fabrication of the photoelectrode for PEC cells, prompt separation of photo-generated electrons and holes is extremely important to fully utilize the photoresponse of the material. Tantalum oxynitride photoanode is fabricated and modified with calcium ferrite to form a heterojunction anode for a photoelectrochemical water splitting cell. The synthesized powders are loaded sequentially to the transparent conducting glass by electrophoretic deposition, which is advantageous to form a uniform layer and a junction structure. X-ray diffraction, UV-Vis DRS, scanning electron microscopy, and impedance spectroscopy analysis are conducted to investigate the structural, morphological, and electrochemical characteristics of the anode. The introduction of CaFe2O4 overlayer onto TaON electrode increases the photocurrent density about five times at 1.23V vs. RHE without any co-catalyst. Impedance spectroscopy analysis indicates that the junction formation increased photocurrent density by reducing the resistance to the transport of charge carriers and thereby enhancing the electron-hole separation. This photocurrent generation is a result of the overall water splitting as confirmed by evolution of hydrogen and oxygen in a stoichiometric ratio. From the study of different junction configurations, it is established that the intimate contact between TaON and CaFe2O4 is critical for enhanced performance of the heterojunction anode for photoelectrochemical water oxidation under visible light.