Papers by Keyword: Water Splitting

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Authors: Alfonsina Pappacena, Marta Boaro, Olga Šolcová, Alessandro Trovarelli
Abstract: A novel surfactant-assisted synthesis method was developed in our laboratory to enhance the oxygen storage capacity (OSC) and the thermo stability of a TWC catalyst based on zirconia and rare earth oxides. The same procedure was used to prepare ceria-zirconia compositions with different amount of ceria, either undoped or doped with La and Nd. The potential use of these materials in a two steps solar thermochemical water splitting cycle for the production of H2 was investigated. For this proposal the O2 release of the materials was measured through thermogravimetric analysis in N2 at 1573K. Then all prepared compositions were subjected to an aging treatment at temperature above 1573K in air or in N2 flow and their activity in producing H2 via water splitting at 1073K was evaluated with respect their structural evolution. The results obtained highlight that the reactivity depends on the temperature and atmosphere of the treatments and on the composition. The best result was obtained for the ceria rich composition treated at 1573K in N2 and for the corresponding doped composition treated in air.
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Authors: Tomonari Yasuda, Masashi Kato, Masaya Ichimura
Abstract: Hydrogen energy attracts attention as an eco-friendly energy resource. The water splitting by semiconductor materials can generate hydrogen without CO2 emission. However, the hydrogen conversion efficiency using conventional materials is not high enough, or the materials corrode easily even if they show high efficiency. On the other hand, silicon carbide (SiC) is expected to be a water splitting material showing high conversion efficiency without corrosion. In this study, we characterized band edge potentials for 4H-, 6H- and 3C-SiC, and we revealed that they are capable of water splitting. We also estimated conversion efficiencies by photocurrent measurements in electrolytes for bulk 4H- and 6H-SiC.
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Authors: Chin Wei Lai, Kung Shiuh Lau, Sharifah Bee Abd Hamid
Abstract: Nowadays, hydrogen production using solar-driven photoelectrochemical (PEC) water splitting has attracted considerable attention since the introduction of TiO2 photoelectrodes. However, TiO2 is not able to split water on its own because the cleavage requires more than 1.4 V or even up to 1.9 V, including the redox potential of water (1.23 V) and unavoidable over-potentials. Many semiconductors have been studied, but only a very few large band gap materials can generate enough photo-voltage to cleave water for a single photoelectrode PEC water splitting cell especially processing under solar illumination. In the present study, development of WO3-loaded TiO2 nanotubes (WTNT) is a possible solution to generate a voltage that is high enough to split the water while absorbing more light (photons) from a greater part of solar spectrum. Furthermore, WTNT offered several advantages over the pure TiO2 photoelectrode, such as excellent chemical and thermal stability, active at room temperature as well as responsive to UV and visible illumination. The paper concludes by presenting the comparison results between unmodified TiO2 and WTNT photoelectrode in term of morphology, phase, elemental analysis, electrical properties, and electrochemical properties for the tandem solar-driven water splitting cell.
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Authors: Listra Yehezkiel Ginting, Mohammad Kemal Agusta, Nugraha, Ahmad H. Lubis, Hermawan Kresno Dipojono
Abstract: Photocatalytic hydrogen generation holds promise as the future source of environmentally friendly and economically feasible energy source. In order to conduct more efficient photocatalytic reaction, anatase TiO2 doped with transition metals is proposed as catalyst. Investigation was conducted by using density functional theory (DFT) augmented with Hubbard U treatment to correct the band gap of TiO2. Emergence of new states inside the band gap of doped anatase TiO2 can lead to a material with a better photocatalytic property, i.e., able to work at visible light than that of pristine TiO2 which is sensitive to UV light only. The investigated materials comply with standard hydrogen electrode (SHE), thus can be used as photocatalyst in water splitting reaction. Out of the two options tested, TiO2 doped with Fe produces a material with the better photocatalytic properties.Keywords: DFT + U, anatase TiO2, photocatalytic, water splitting, band gap
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Authors: Leigh Russell Sheppard, Marta Bello Lamo, Thomas Dittrich, Richard Wuhrer
Abstract: This investigation was aimed at identifing the scope for exploiting segregation phenomena to improve the ability of doped TiO2 to separate photo-generated charge carriers. By applying several controlled conditions of temperature and oxygen activity during the annealing of Nb-doped TiO2 (0.65 at. %), compositional gradients were imposed within the surface and near-surface regions due to solute segregation. These compositional gradients were characterised using secondary ion mass spectrometry (SIMS) and Xray photoelectron spectroscopy (XPS), and then tested for charge separation abilities using surface photovoltage spectroscopy (SPS). This investigation has revealed that processing Nb-doped TiO2 under conditions that favour the depletion of Nb from the surface and near-surface region yields stronger charge separation. While this is attributed to the formation of a homo-junction that is providing additional driving force for charge separation, the altered impact of Nb5+ and related defect disorder may also play a role. This investigation has provided encouraging preliminary outcomes to stimulate further investigations.
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Authors: Ryo Niishiro, Akihiko Kudo
Abstract: This review paper represents photocatalytic properties of metal cation-doped TiO2 (rutile) and SrTiO3 photocatalysts for O2 evolution from an aqueous silver nitrate solution and H2 evolution from an aqueous methanol solution under visible light irradiation. Photocatalytic activities for the O2 evolution of Cr/Sb and Rh/Sb-codoped TiO2 are strongly dependent on the codoping ratio and the amount of doped chromium and rhodium. The codopant controls the oxidation number of doped chromium and rhodium. Rh-doped SrTiO3 in which the doped Rh species possesses a reversible redox property is active for the H2 evolution reaction under visible light irradiation. Overall water splitting under visible light irradiation proceeds with Z-scheme photocatalyst systems consisting of the Rh-doped SrTiO3 as a H2 evolution photocatalyst combined with BiVO4 as an O2 evolution photocatalyst and an Fe3+/Fe2+ electron mediator.
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Authors: Hidehisa Hagiwara, Hiroshige Matsumoto, Tatsumi Ishihara
Abstract: Effects of mixing dye sensitizer for the photocatalytic activity of dye-sensitized Pt/K0.95Ta0.92Zr0.08O3 was investigated. It was found that the photocatalytic activity was greatly improved by mixing dye sensitizer on the catalyst, and among the examined combination of organic dyes, the highest photocatalytic activity was obtained by mixing Cr-tetraphenylporphyrin (Cr-TPP) and Pentametylene bis[4-(10, 15, 20-triphenylporphine-5-yl)benzoate] dizinc(ΙΙ) (Zn-TPP dimer). In order to identify the effect of dye sensitizer, photovoltaic behavior of the dye-sensitized KTaO3 was investigated. The lifetime of the photo-exited electron and hole can be improved by coating with dye sensitizer. Thus, the effect of porphyrinoids would be explained by the improved efficiency of charge separation.
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Authors: Ke Xin Liang, Zu Kun Du, Yu Tan, Sheng Han Zhang
Abstract: Anatase TiO2 nanotube arrays with about 50nm pore diameter were prepared by anodic oxidation. The effect of the donor materials (sodium hydroxide, methanol and ethylene glycol) on electrochemistry impedance spectroscopy (EIS) and the photocurrent responses of TiO2 nanotube arrays photoanode in the photoelectrochemical cell for splitting water hydrogen production were investigated. The results indicate that all the donor materials enhance the photocurrent responses and reduce the internal reaction resistances of the TiO2 nanotube arrays photoanode. The effect of adding organic donor compounds in the anolyte on charge transfer and photocurrent is superior to the inorganic donor compounds and in turn reduces from the ethylene glycol, methanol to sodium hydroxide. Additionally, it should be highlighted that +0.3V vs. open circuit potential of applied potential on the electrode promotes a suitable charge transfer at semiconductor/electrolyte interface. The flat band potentials of TiO2 nanotube arrays photoanode move to negative direction with donor materials adding in the anolyte which indicates beneficial photoelectrocatalytic hydrogen production by water splitting.
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Authors: Mamoru Ohashi, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato
Abstract: Photocatalysts for overall water splitting have great potential in solar energy applications. A variety of photocatalysts have shown activity for water splitting. In particular, oxysulfides are the great interest because of their ability to generate H2 and O2 from water under visible light. However, they are generally synthesized under H2S flow, which is an extremely harmful gas for humans. In this study, La2O2S2 was synthesized at low temperature without H2S gas, and its photocatalytic activity was confirmed by hydrogen generation experiments.
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