SocMan Ho-Kimura

An Fe ₂ O ₃ /BiVO ₄ heterojunction was found to be successfully formed by placing a haematite underlayer on a BiVO ₄ anode. This composite anode has a significant improvement in PEC photocurrent in the low bias region.

In the synthesis method of a BiVO₄ photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO₄ particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO₄ does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V₂O₅ among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO₄ crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO₄ photoanode was 2.2 mA/cm² at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm² illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO₃:Rh–BiVO₄ photocatalyst sheet prepared by the BiVO₄ synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation.

A simplistic and low-cost method that dramatically improves the performance of solution-grown hematite photoanodes for solar-driven water splitting through incorporation of nanohybrid metal oxide overlayers was developed. By heating the α-Fe₂O₃/SnO₂–TiO₂ electrode in an inert atmosphere, such as argon or nitrogen, the photocurrent increased to over 2 mA/cm² at 1.23 V versus a reversible hydrogen electrode, which is 10 times higher than that of pure hematite under 1 sun (100 mW/cm², AM 1.5G) light illumination. For the first time, we found a significant morphological difference between argon and nitrogen gas heat-treated hematite films and discussed the consequences for photoresponse. The origin for the enhancement, probed via theoretical modeling, stems from the facile incorporation of low formation energy dopants into the Fe₂O₃ layer at the interface of the metal oxide nanohybrid overlayer, which decreases recombination by increasing the electrical conductivity of Fe₂O₃. These dopants diffuse from the overlayer into the α-Fe₂O₃ layer readily under inert gas heat treatment. This simple yet effective strategy could be applied to other dopants to increase hematite performance for solar energy conversion applications.

Despite the great success of Li‐ion batteries (LIBs) up to now, higher demand has been raised with the emergence of the new generation electrics, such as portable devices and electrical vehicles. Even with the improvement on anodes, the cathodes with high capacity and long‐lastingness still remain a challenge. New 3D NiCo₂O₄@V₂O₅ core–shell arrays (CSAs) on carbon cloth as cathodes in LIBs have been reported in this work. The nanodesigned materials realize the theoretical specific capacity of V₂O₅ with high power rate based on the total mass of the framework and amount of active materials. The electrodes achieve superb cycling stability, among the most stable cathodes for LIBs ever reported. From both in situ transmission electron microscopy and quantum level calculations, the 3D NiCo₂O₄ nanosheet frameworks provide high electron conductivity and the skeleton of the robust CSAs without participating in the lithiation/delithiation; the thickness of the layered V₂O₅ plays a key role for Li diffusivity and the capacity contribution of electrodes. The structures herein point to new design concepts for high‐performance nanoarchitectures for LIB cathodes.

A novel wide spectrum responsive BiVO₄–TiO₂ junction composite photoanode has been successfully synthesized by a simple, solution-based metal–organic decomposition (MOD) method. The photocurrent was increased by ∼4 times using the junction with respect to bare BiVO₄ under 100 mW cm⁻² illumination, resulting in ∼5-fold enhancement in IPCE at 400 nm which is nearly double the value reported recently. These enhancements in both IPCE and stability are due to the ultrafine film structure and more importantly, facile rectifying electron transfer across the junction.