H2O2 production on a carbon cathode loaded with a nickel carbonate catalyst and on an oxide photoanode without an external bias.

Efficient H2O2 production both on a carbon cathode modified with various metal salts and on an oxide photoanode was investigated. The cathodic current density and faradaic efficiency for H2O2 production (FE(H2O2)) on a carbon cathode in KHCO3 aqueous solution were significantly improved by the loading of an insoluble nickel carbonate basic hydrate catalyst. This electrode was prepared by a precipitation method of nickel nitrate and KHCO3 aqueous solution at ambient temperature. The nickel carbonate basic hydrate electrode was very stable, and the accumulated concentration of H2O2 was reached at 1.0 wt% at a passed charge of 2500C (the average FE(H2O2) was 80%). A simple photoelectrochemical system for H2O2 production from both the cathode and a BiVO4/WO3 photoanode was demonstrated without an external bias or an ion-exchange membrane in a one-compartment reactor under simulated solar light. The apparent FE(H2O2) from both electrodes was calculated to be 168% in total, and the production rate of H2O2 was approximately 0.92 µmol min-1 cm-2. The solar-to-chemical energy conversion efficiency for H2O2 production (STCH2O2 ) without an external bias was approximately 1.75%.

High-throughput screening using porous photoelectrode for the development of visible-light-responsive semiconductors.

A high-throughput screening system for new visible-light-responsive semiconductors for photoelectrodes and photocatalysts was developed in this study. Photoelectrochemical measurement was selected to evaluate visible-light responsiveness, and an automated semiconductor synthesis system that can be used to prepare porous thin-film photoelectrodes of various materials was also developed. As an example application of our system, iron-based binary oxides were selected as target materials for n-type semiconductors. Fe-Ti, Fe-Nb, and Fe-V with various composition ratios were synthesized. Fe-Ti and Fe-Nb binary oxide systems have been studied previously, and our results showed good consistency with previous reports, demonstrating the capability of our system. In the Fe-V system, the highest photocurrent was observed with 50% vanadium. This ratio corresponds to FeVO4, which is expected to be a new visible-light-responsive material. As another example, screening targets of bismuth-based binary oxides were investigated for p-type semiconductor photoelectrodes, and CuBi2O4 was found as a new visible-light-responsive p-type semiconductor.

Synthesis of tubular titanate via a self-assembly and self-removal process.

Novel morphology titanate tubes were successfully synthesized via a self-assembly and self-removal process. After the product was treated by calcinating and washing, crystalline TiO2 tubes were obtained. In this study, two new concepts are applied to design the synthetic route: (i) titanium glycolate rods obtained from an ethylene glycol-mediated process and titanate sheets synthesized using the hydrothermal process were used as the template and the precursor, respectively, and ii) the template was directly removed in the reaction without posttreatment. Furthermore, a possible mechanism was proposed for the formation of tubular structures.

Synthesis of single-crystal manganese dioxide nanowires by a soft chemical process.

α- and ß-MnO(2) single-crystal nanowires have been successfully synthesized through a soft chemical process, which involves no catalysts or templates. The diameters of the nanowires are about 10-40 nm and the lengths up to several tens of micrometres. Experimental results showed that MnO(2) polymorphic forms can be synthesized by selected-control reaction temperatures and their crystal phases in the nanowires were confirmed by XRD and TEM measurement. Further, the formation process of nanowires is discussed.