Hydrogen Storage Alloy / Cr Doped Preparation And Photoelectrochemical Performance Of The Composite Oxide Semiconductor Electrode

As global energy and environmental issues, in order to obtain the low cost and high efficiency solar energy conversion and storage, recently a great deal of interest has been aroused in semiconductor photocatalysts used in photoelectrochemical cell. In this present work, homogeneously mixed Cr-doped Ba₄In₂O₇ nanorod/In₂O₃ nanoparticle composite (Cr-BIO) was synthesized by an optimized simple sol-gel method and Cr-InNbO₄: NiO was synthesized by solid state reaction. The hydrogen storage alloy/semiconductor photoelectrode was then fabricated and the photo-electrochemical characteristics were investigated.Composite semiconductor photocatalysts were reported to have high activity as the higher degree of charge carrier separation. However, most previous approaches to the preparation of homogeneously mixed composite semiconductor photocatalysts need high-temperature or multi-step reactions. Therefore, in this work, an optimized simple sol-gel method of synthesizing homogeneously mixed Cr-BIO was developed. The as prepared Cr-BIO was comprised of Cr-Ba₄In₂O₇ nanorods (5-50 nm in diameters, 50-150 nm in lengths) and Cr-In₂O₃ nanoparticles (30-90 nm in diameter). The rods and particles mix homogeneously in large scale and have sufficient physical contact with each other, suggesting the enhanced degree of charge carrier separation. The Cr-BIO composite showed a wide photo absorption range with a main absorption edge around 480 nm. The Cr-BIO/Cu and Cr-BIO/Ni photoelectrodes was fabricated and the photocurrent was measured.The HSA/Cr-BIO photoelectrode was then fabricated and the photo-assisted electrochemical behavior was investigated. In the electrochemical cyclic voltammetry curve the reduction current increased remarkably under the xenon light irradiation. In the charge-discharge tests, for the electrode irradiated by light and charged with current simultaneously, the discharge time is about 11.4 h, much longer than that (about 8.7 h) charged only with current, indicating obvious photo-assisted chargeability of the electrode. The additional discharge capacity is contributed to the photocharge of photogenerated electrons and holes. The photo-assisted chargeability of Cr-BIO composite may be resulted from the improved degree of charge carrier separation, which is due to both the sufficient physical contact in the homogeneously mixed Cr-BIO composite and the existence of potential offsets between the band edges of individual Cr-doped Ba₄In₂O₇ and Cr-doped In₂O₃.The Cr-doped InNbO₄ powder synthesized by a solid-state reaction show a wide light absorption range with a main absorption edge around 470 nm and a relatively weak absorption at around 530 nm. The 1.0 wt.% NiO nanoparticle was then well dispered on the Cr-InNbO₄ particle surface by an impregnation method. The HSA/Cr-BIO photoelectrode was then fabricated and the photo-assisted electrochemical behavior was investigated. In the electrochemical cyclic voltammetry curve the reduction current increased remarkably under the xenon light irradiation. In the charge-discharge tests, the electrode exhibited obvious photo-assisted chargeable properties. The high photocatalytic activity may be resulted from the increase of visible light absorption. And the well dispered NiO particles on the Cr-InNbO₄ particle surface were also able to increase the photocatalysed activity as they will form the electron traps to improve the degree of charge carrier separation.