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743 results on '"Takanabe, Kazuhiro"'

203. Enhanced Kinetics of Hole Transfer and Electrocatalysis during Photocatalytic Oxygen Evolution by Cocatalyst Tuning

Author

Nurlaela, Ela, primary, Wang, Hai, additional, Shinagawa, Tatsuya, additional, Flanagan, Sean, additional, Ould-Chikh, Samy, additional, Qureshi, Muhammad, additional, Mics, Zoltán, additional, Sautet, Philippe, additional, Le Bahers, Tangui, additional, Cánovas, Enrique, additional, Bonn, Mischa, additional, and Takanabe, Kazuhiro, additional

Published
2016
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210. Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H2and Buffer Ions

Author

Obata, Keisuke, Stegenburga, Liga, and Takanabe, Kazuhiro

Abstract

Although the electrochemical hydrogen evolution reaction (HER) on a Pt electrode is among the most studied electrocatalytic reactions, its reaction mechanism and exchange current density are still under debate. Particularly on the Pt catalyst, its facile reaction kinetics and lack of effective methods to compensate mass transport make it difficult to isolate kinetic and diffusion contributions. This study focuses on the quantitative description of mass transfer constraints arising from both H2and phosphate buffer ions using a Pt electrocatalyst in near-neutral pH regions, which are overlooked in the literature despite the relevance to various (photo-) electrochemical reactions for water splitting and CO2reduction. The established HER model that uses H+as a reactant quantitatively breaks down the observed overpotentials with diffusion contributions of both hydrogen and buffer species while the intrinsic kinetics on Pt exhibits negligible contribution. The significance of electrolyte engineering, that is, the optimization of the electrolyte identity and molality, is confirmed to determine the overall HER performance. To maximize the HER performance on Pt at ambient temperature, the phosphate-buffer electrolyte should be adjusted to a pH close to pKaof the buffer that effectively minimizes the pH gradient and to the adequate molality of the buffer (typically ∼0.5 M phosphates) that H2diffusion is maximized, which is related with H2solubility and solution viscosity. At pH far from pKa, concentration overpotential of buffer ion dominates the overall performance, which requires highly dense buffer (>1.5 M phosphates) to minimize the pH gradient.

Published
2019
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211. Optoelectronic Structure and Photocatalytic Applications of Na(Bi,La)S2Solid Solutions with Tunable Band Gaps

Author

BaQais, Amal, Tymińska, Nina, Le Bahers, Tangui, and Takanabe, Kazuhiro

Abstract

NaLa1–xBixS2solid solutions with tunable band gaps were synthesized, and their optoelectronic structures and photocatalytic performance were investigated via experimental and theoretical approaches. The solid solution powders with various La/Bi ratios were synthesized with Na2CO3, La2O3, and Bi2O3as precursors and via sulfurization with flowing CS2at 800 °C for 2 h. The Vegard’s law behavior of cell parameters showed a perfect Bi/La solid solution in the cubic NaLa1–xBixS2with the associated linear variation of the lattice constants. On the contrary, the combination of diffuse reflectance ultraviolet–visible spectroscopy with density functional theory (DFT) calculations employing the HSE06 functional reveals a monotonic but nonlinear variation of the band gap of the solid solution. While consistent valence band maximum was obtained in NaLa1–xBixS2—consisting mainly of S 3p orbitals—the conduction band minimum was contributed by discrete Bi orbitals present at more positive potential than La. As a result, the slight inclusion of Bi caused a drastic shift in the band gap, and 24% Bi substitution provided an absorption edge closer to that of pure NaBiS2. Systematic DFT calculations on NaLa1–xBixS2determined the optoelectronic properties for improved photovoltaic and photocatalytic performance with a Bi-rich sample rather than a La-rich counterpart; that is, there were larger absorption coefficients, smaller effective masses, and larger dielectric constants for Bi-rich samples versus La-rich samples. The NaLa1–xBixS2particles decorated with Pt nanoparticles show maximum hydrogen evolution performance with x= 0.02–0.06 of Bi samples consistent with the compensating effects between photon absorption capacity and loss of electromotive force with decreasing band gap.

Published
2019
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214. Electrocatalytic Activity and Stability of M-Fe Catalysts Synthesized by Polymer Complex Method for PEFC Cathode

Author

Ou, Yiwei, Kumagai, Hiromu, Fengxiang, Yin, Okada, Saori, Hatasawa, Haruna, Morioka, Hiroyuki, Takanabe, Kazuhiro, Kubota, Jun, and Domen, Kazunari

Subjects
chemistry.chemical_classification, Materials science, Renewable Energy, Sustainability and the Environment, Inorganic chemistry, Polymer, Condensed Matter Physics, Cathode, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, law.invention, Catalysis, chemistry, law, Materials Chemistry, Electrochemistry
Published
2011

230. A Permselective CeO<italic>x</italic> Coating To Improve the Stability of Oxygen Evolution Electrocatalysts.

Author

Obata, Keisuke and Takanabe, Kazuhiro

Subjects
*ELECTROCATALYSTS, *NICKEL ferrite, *OXYGEN evolution reactions, *PERFORMANCE of anodes, *OXIDATION-reduction reaction
Abstract

Abstract: Highly active NiFeOx electrocatalysts for the oxygen evolution reaction (OER) suffer gradual deactivation with time owing to the loss of Fe species from the active sites into solution during catalysis. The anodic deposition of a CeOx layer prevents the loss of such Fe species from the OER catalysts, achieving a highly stable performance. The CeOx layer does not affect the OER activity of the catalyst underneath but exhibits unique permselectivity, allowing the permeation of OH− and O2 through while preventing the diffusion of redox ions through the layer to function as a selective O2‐evolving electrode. The use of such a permselective protective layer provides a new strategy for improving the durability of electrocatalysts. [ABSTRACT FROM AUTHOR]

Published
2018
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231. Solvent‐Free Synthesis of Quaternary Metal Sulfide Nanoparticles Derived from Thiourea.

Author

Bhunia, Manas K., Abou‐Hamad, Edy, Anjum, Dalaver H., Gurinov, Andrei, and Takanabe, Kazuhiro

Subjects
METAL sulfides, NANOPARTICLES, THIOUREA, HYDROCARBONS, CAPPING proteins
Abstract

Abstract: The synthesis of metal sulfide (MS) materials with sizes in the sub‐10 nm regime often requires capping agents with long hydrocarbon chains that affect their structures and properties. Herein, this study presents a molten‐state synthesis method for a series of transition‐MS nanoparticles using thiourea as a reactive precursor without capping agents. This study also reports the synthesis of MS with single metals (Fe, Co, Ni, Cu, and Zn) and quaternary CuGa2In3S8 using the same synthesis protocol. Thiourea first melts to form a molten‐state condition to serve as the reaction medium at a relatively low temperature (<200 °C), followed by its thermal decomposition to induce a reaction with the metal precursor to form different MS. This synthesis protocol, owing to its dynamic characteristics, involves the formation of a variety of organic carbon nitride polymeric complexes around the MS particles. Dynamic nuclear polarization surface‐enhanced nuclear magnetic resonance spectroscopy is effective to identify the polymeric compositions and structures as well as their interactions with the MS. These results provided thorough structural descriptions of the MS nanoparticles surrounded by the carbon nitride species derived from thiourea, which may find various applications, including photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Published
2018
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