The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kazunari Domen - One of the best experts on this subject based on the ideXlab platform.
-
efficient Redox Mediator free z scheme water splitting employing oxysulfide photocatalysts under visible light
ACS Catalysis, 2018Co-Authors: Song Sun, Takashi Hisatomi, Jingyuan Liu, Qian Wang, Shanshan Chen, Swarnava Nandy, Tsutomu Minegishi, Masao Katayama, Kazunari DomenAbstract:Oxysulfides, which exhibit intense visible light absorption and high photocatalytic activity during hydrogen evolution, are promising photocatalysts for Z-scheme water splitting. However, the realization of efficient Z-scheme water splitting using oxysulfides as hydrogen evolution photocatalysts (HEPs) has been hampered by backward reactions involving reversible Redox couples, the low efficiency of interparticle electron transfer, and a lack of knowledge regarding the means of promoting hydrogen evolution activity under nonsacrificial conditions. In this study, La5Ti2CuS5O7 was found to realize water splitting without any Redox Mediator by constructing Z-scheme-type photocatalyst sheets with BiVO4 as the oxygen evolution photocatalyst. It is also demonstrated that p-type doping and the formation of a La5Ti2Cu0.9Ag0.1S5O7 solid solution effectively enhance the water-splitting activity of the photocatalyst sheet. An apparent quantum yield of 4.9% at 420 nm and a solar to hydrogen energy conversion efficienc...
-
a Redox Mediator free solar driven z scheme water splitting system consisting of modified ta3n5 as an oxygen evolution photocatalyst
Chemistry: A European Journal, 2013Co-Authors: Su Su Khine, Masashi Tabata, Kazuhiko Maeda, Takashi Hisatomi, Akihiko Kudo, Kazunari DomenAbstract:Tantalum nitride (Ta3N5) modified with various O2-evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a Redox-Mediator-free Z-scheme water-splitting system. Ta3N5 was prepared by nitriding Ta2O5 powder under a flow of NH3 at 1023–1223 K. The activity of Ta3N5 for water oxidation from an aqueous AgNO3 solution as an electron acceptor without cocatalyst was dependent on the generation of a well-crystallized Ta3N5 phase with a low density of anionic defects. Modification of Ta3N5 with nanoparticulate metal oxides as cocatalysts for O2 evolution improved water-oxidation activity. Of the cocatalysts examined, cobalt oxide (CoOx) was found to be the most effective, improving the water-oxidation efficiency of Ta3N5 by six to seven times. Further modification of CoOx/Ta3N5 with metallic Ir as an electron sink allowed one to achieve Z-scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle Redox Mediator in combination with Ru-loaded SrTiO3 doped with Rh as a H2-evolution photocatalyst.
-
overall water splitting under visible light through a two step photoexcitation between taon and wo3 in the presence of an iodate iodide shuttle Redox Mediator
Chemsuschem, 2011Co-Authors: Ryu Abe, Masanobu Higashi, Kazunari DomenAbstract:A two-step, photocatalytic water splitting system consisting of Pt-loaded TaON (a H(2) evolution photocatalyst), Pt-loaded WO(3) (an O(2) evolution photocatalyst), and an iodate-iodide (IO(3)(-)/I(-)) shuttle Redox Mediator is investigated under visible light irradiation. Photocatalytic oxidation of water to O(2) and reduction of IO(3)(-) to I(-) proceeded with good selectivity over the Pt-WO(3) photocatalyst, even in the presence of a considerable amount of I(-) anions in the solution. The key difference between the adsorption properties of IO(3)(-) and I(-) anions on WO(3) strongly suggested that the photoexcited electrons could react efficiently with IO(3)(-) adsorbed on WO(3), whereas the photogenerated holes selectively reacted with water molecules owing to the low adsorptivity of I(-) on WO(3). Photocatalytic H(2) evolution on Pt-TaON proceeded efficiently, accompanied by I(-) oxidation to IO(3)(-) due to a substantial amount of adsorption of I(-) anions on the surface, whereas H(2) evolution was significantly inhibited by the competitive adsorption of IO(3)(-), which consumes photoexcited electrons. It was also found that WO(3) photocatalysts loaded with platinum oxide (PtO) showed a much higher activity for O(2) evolution in the presence of the electron acceptor IO(3)(-), compared to those loaded with Pt metal. Overall water splitting at a steady rate was demonstrated using a combination of Pt-TaON and Pt(PtO)-WO(3) in an aqueous NaI solution with neutral or weakly acidic pH values, where the concentration of NaI significantly affected the efficiency.
-
modified ta3n5 powder as a photocatalyst for o2 evolution in a two step water splitting system with an iodate iodide shuttle Redox Mediator under visible light
Langmuir, 2010Co-Authors: Masashi Tabata, Kazuhiko Maeda, Masanobu Higashi, Ryu Abe, Tsuyoshi Takata, Kazunari DomenAbstract:Modification of tantalum nitride (Ta3N5), which has a band gap of 2.1 eV, with nanoparticulate iridium (Ir) and rutile titania (R-TiO2) achieved functionality as an O2 evolution photocatalyst in a two-step water-splitting system with an IO3−/I− shuttle Redox Mediator under visible light (λ > 420 nm) in combination with a Pt/ZrO2/TaON H2 evolution photocatalyst. The loaded Ir nanoparticles acted as active sites to reduce IO3− to I−, while the R-TiO2 modifier suppressed the adsorption of I− on Ta3N5, allowing Ta3N5 to evolve O2 in the two-step water-splitting system.
-
two step water splitting into h2 and o2 under visible light by atao2n a ca sr ba and wo3 with io3 i shuttle Redox Mediator
Chemical Physics Letters, 2008Co-Authors: Masanobu Higashi, Ryu Abe, Tsuyoshi Takata, Kentaro Teramura, Bunsho Ohtani, Kazunari DomenAbstract:Abstract Two-step water splitting into H 2 and O 2 under visible light irradiation is examined combining Pt–ATaO 2 N (A = Ca, Sr, Ba) as a H 2 evolution photocatalyst and Pt–WO 3 as an O 2 evolution photocatalyst by IO 3 - / I - shuttle Redox-Mediator. Overall water splitting proceeds when Pt–CaTaO 2 N or Pt–BaTaO 2 N is used for H 2 evolution photocatalyst, whereas photo-induced self-oxidative decomposition is predominant for Pt–SrTaO 2 N. The onset wavelengths of H 2 evolution almost accord with the absorption edges of CaTaO 2 N and BaTaO 2 N. The available wavelength of light for H 2 evolution in the present two-step water splitting system has been extended to 660 nm by using BaTaO 2 N.
Ryu Abe - One of the best experts on this subject based on the ideXlab platform.
-
highly dispersed ruo2 hydrates prepared via simple adsorption as efficient cocatalysts for visible light driven z scheme water splitting with an io3 i Redox Mediator
ACS Catalysis, 2017Co-Authors: Hajime Suzuki, Shinnosuke Nitta, Osamu Tomita, Masanobu Higashi, Ryu AbeAbstract:Loading a cocatalyst onto a photocatalyst is a well-known effective way to improve the efficiency of both one-step water splitting and Z-scheme water splitting with a Redox Mediator. In Z-scheme water splitting systems with an IO3–/I– Redox couple, the reduction of IO3– on O2-evolving photocatalysts via a six-electron process often represents the rate-determining step of the overall process and therefore necessitates effective cocatalysts such as PtOx and RuO2. However, these cocatalysts cannot be loaded onto thermally unstable materials via conventional impregnation processes involving calcination. In the present study, we introduce a Ru-based cocatalyst that can be loaded without calcination and effectively promotes the reduction of IO3– on various photocatalysts, including nonoxide materials. The results reveal that the Ru species adsorbed via simple stirring of photocatalyst particles such as WO3 in an aqueous RuCl3 solution effectively trigger O2 generation in the presence of IO3– as electron accepto...
-
overall water splitting under visible light through a two step photoexcitation between taon and wo3 in the presence of an iodate iodide shuttle Redox Mediator
Chemsuschem, 2011Co-Authors: Ryu Abe, Masanobu Higashi, Kazunari DomenAbstract:A two-step, photocatalytic water splitting system consisting of Pt-loaded TaON (a H(2) evolution photocatalyst), Pt-loaded WO(3) (an O(2) evolution photocatalyst), and an iodate-iodide (IO(3)(-)/I(-)) shuttle Redox Mediator is investigated under visible light irradiation. Photocatalytic oxidation of water to O(2) and reduction of IO(3)(-) to I(-) proceeded with good selectivity over the Pt-WO(3) photocatalyst, even in the presence of a considerable amount of I(-) anions in the solution. The key difference between the adsorption properties of IO(3)(-) and I(-) anions on WO(3) strongly suggested that the photoexcited electrons could react efficiently with IO(3)(-) adsorbed on WO(3), whereas the photogenerated holes selectively reacted with water molecules owing to the low adsorptivity of I(-) on WO(3). Photocatalytic H(2) evolution on Pt-TaON proceeded efficiently, accompanied by I(-) oxidation to IO(3)(-) due to a substantial amount of adsorption of I(-) anions on the surface, whereas H(2) evolution was significantly inhibited by the competitive adsorption of IO(3)(-), which consumes photoexcited electrons. It was also found that WO(3) photocatalysts loaded with platinum oxide (PtO) showed a much higher activity for O(2) evolution in the presence of the electron acceptor IO(3)(-), compared to those loaded with Pt metal. Overall water splitting at a steady rate was demonstrated using a combination of Pt-TaON and Pt(PtO)-WO(3) in an aqueous NaI solution with neutral or weakly acidic pH values, where the concentration of NaI significantly affected the efficiency.
-
modified ta3n5 powder as a photocatalyst for o2 evolution in a two step water splitting system with an iodate iodide shuttle Redox Mediator under visible light
Langmuir, 2010Co-Authors: Masashi Tabata, Kazuhiko Maeda, Masanobu Higashi, Ryu Abe, Tsuyoshi Takata, Kazunari DomenAbstract:Modification of tantalum nitride (Ta3N5), which has a band gap of 2.1 eV, with nanoparticulate iridium (Ir) and rutile titania (R-TiO2) achieved functionality as an O2 evolution photocatalyst in a two-step water-splitting system with an IO3−/I− shuttle Redox Mediator under visible light (λ > 420 nm) in combination with a Pt/ZrO2/TaON H2 evolution photocatalyst. The loaded Ir nanoparticles acted as active sites to reduce IO3− to I−, while the R-TiO2 modifier suppressed the adsorption of I− on Ta3N5, allowing Ta3N5 to evolve O2 in the two-step water-splitting system.
-
two step water splitting into h2 and o2 under visible light by atao2n a ca sr ba and wo3 with io3 i shuttle Redox Mediator
Chemical Physics Letters, 2008Co-Authors: Masanobu Higashi, Ryu Abe, Tsuyoshi Takata, Kentaro Teramura, Bunsho Ohtani, Kazunari DomenAbstract:Abstract Two-step water splitting into H 2 and O 2 under visible light irradiation is examined combining Pt–ATaO 2 N (A = Ca, Sr, Ba) as a H 2 evolution photocatalyst and Pt–WO 3 as an O 2 evolution photocatalyst by IO 3 - / I - shuttle Redox-Mediator. Overall water splitting proceeds when Pt–CaTaO 2 N or Pt–BaTaO 2 N is used for H 2 evolution photocatalyst, whereas photo-induced self-oxidative decomposition is predominant for Pt–SrTaO 2 N. The onset wavelengths of H 2 evolution almost accord with the absorption edges of CaTaO 2 N and BaTaO 2 N. The available wavelength of light for H 2 evolution in the present two-step water splitting system has been extended to 660 nm by using BaTaO 2 N.
-
stoichiometric water splitting into h2 and o2 using a mixture of two different photocatalysts and an io3 i shuttle Redox Mediator under visible light irradiation
Chemical Communications, 2001Co-Authors: Kazuhiro Sayama, Ryu Abe, Kazuaki Mukasa, Yoshimoto Abe, Hironori ArakawaAbstract:The stoichiometric splitting of water into H2 and O2 (H2/O2 = 2) under visible light irradiation (lambda > 420 nm) took place for the first time using a mixture of Pt-WO3 and Pt-SrTiO3 (Cr-Ta-doped) photocatalysts and an IO3-/I- shuttle Redox Mediator.
Lukáš Richtera - One of the best experts on this subject based on the ideXlab platform.
-
bis 2 2 bipyridil copper ii chloride complex tyrosinase biomimetic catalyst or Redox Mediator
Materials, 2020Co-Authors: Milan Sýs, Atripan Mukherjee, Granit Jashari, Vojtěch Adam, Amir M. Ashrafi, Miroslav Novák, Lukáš RichteraAbstract:In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)2Cl]Cl∙5H2O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a Redox Mediator?
Yungeun Sung - One of the best experts on this subject based on the ideXlab platform.
-
Discharging a Li-S battery with ultra-high sulphur content cathode using a Redox Mediator
'Springer Science and Business Media LLC', 2018Co-Authors: Kwi Ryong Kim, Kugseung Lee, Chiyeong Ahn, Yungeun SungAbstract:Lithium-sulphur batteries are under intense research due to the high specific capacity and low cost. However, several problems limit their commercialization. One of them is the insulating nature of sulphur, which necessitates a large amount of conductive agent and binder in the cathode, reducing the effective sulphur load as well as the energy density. Here we introduce a Redox Mediator, cobaltocene, which acts as an electron transfer agent between the conductive surface and the polysulphides in the electrolyte. We confirmed that cobaltocene could effectively convert polysulphides to Li 2 S using scanning electron microscope, X-ray absorption near-edge structure and in-situ X-ray diffraction studies. This Redox Mediator enabled excellent electrochemical performance in a cathode with ultra-high sulphur content (80 wt%). It delivered 400 mAh g -1 cathode capacity after 50 cycles, which is equivalent to 800 mAh g -1 S in a typical cathode with 50 wt% sulphur. Furthermore, the volumetric capacity was also dramatically improved. © The Author(s) 20165
-
discharging a li s battery with ultra high sulphur content cathode using a Redox Mediator
Scientific Reports, 2016Co-Authors: Kwi Ryong Kim, Kugseung Lee, Chiyeong Ahn, Yungeun SungAbstract:Lithium-sulphur batteries are under intense research due to the high specific capacity and low cost. However, several problems limit their commercialization. One of them is the insulating nature of sulphur, which necessitates a large amount of conductive agent and binder in the cathode, reducing the effective sulphur load as well as the energy density. Here we introduce a Redox Mediator, cobaltocene, which acts as an electron transfer agent between the conductive surface and the polysulphides in the electrolyte. We confirmed that cobaltocene could effectively convert polysulphides to Li2S using scanning electron microscope, X-ray absorption near-edge structure and in-situ X-ray diffraction studies. This Redox Mediator enabled excellent electrochemical performance in a cathode with ultra-high sulphur content (80 wt%). It delivered 400 mAh g−1cathode capacity after 50 cycles, which is equivalent to 800 mAh g−1S in a typical cathode with 50 wt% sulphur. Furthermore, the volumetric capacity was also dramatically improved.
Michael Gratzel - One of the best experts on this subject based on the ideXlab platform.
-
alternative bases to 4 tert butylpyridine for dye sensitized solar cells employing copper Redox Mediator
Electrochimica Acta, 2018Co-Authors: Parnian Ferdowsi, Yasemin Saygili, Shaik M Zakeeruddin, Javad Mokhtari, Michael Gratzel, Anders Hagfeldt, Ladislav KavanAbstract:Abstract Novel facile synthetic protocol is developed to prepare electrochemically and optically clean Cu(tmby)2TFSI and Cu(tmby)2TFSI2 in a mixture (tmby = 4,4,6,6-tetramethyl-2,2-bipyridine; TFSI = trifluoromethylsufonylimide). This pure Cu(II/I) Redox Mediator exhibits improved charge-transfer rate at the counterelectrode (PEDOT) and faster diffusion transport in the solution. Four pyridine derivatives: 4-tert-butylpyridine, 2,6-bis-tert-butylpyridine, 4-methoxypyridine and 4-(5-nonyl)pyridine are evaluated as electrolyte additives. Base-specific electrochemical properties of the Redox Mediator are found for Cu(tmby)22+/+, but not for Co(bpy)33+/2+ which is used as control system. Due to steric hindrance, 2,6-bis-tert-butylpyridine has the smallest influence on the Mediator's electrochemistry, but is also ineffective for the VOC enhancement through TiO2 conduction band upshift. Charge-transfer rates at PEDOT surface and diffusion resistances correlate with the basicity (pKa) of the used pyridine derivatives. The dye (Y123)-sensitized solar cells are evaluated by solar conversion performance in addition to electron lifetime, charge extraction and long-term stability tests. The optimization of pyridine bases for the Cu-mediated solar cells represents interplay of basicity and coordination ability. In turn, this allows for tuning of the charge transfer rate at counterelectrode and the mass transport in the electrolyte solution. The 4-(5-nonyl)pyridine is outperforming all the remaining bases in performance metrics of the corresponding solar cells.
-
unveiling iodine based electrolytes chemistry in aqueous dye sensitized solar cells
Chemical Science, 2016Co-Authors: Federico Bella, Michael Gratzel, S Galliano, M Falco, Guido Viscardi, Claudia Barolo, Claudio GerbaldiAbstract:Aqueous dye-sensitized solar cells (DSSCs) have recently emerged as promising systems, which can combine low cost and environmental compatibility with appreciable efficiency, long-term durability and enhanced safety. In the present study, we thoroughly investigate the chemistry behind the iodide/triiodide-based Redox Mediator, which presents – in a completely aqueous environment – several differences when compared to the behavior observed in the conventionally used organic solvents. The speciation of ions, the effect of the concentration of the Redox Mediator and the type of counter-ion are characterized from the electrochemical, spectroscopic, photovoltaic and analytical viewpoints. Furthermore, we demonstrate that aqueous DSSCs, often assumed as unstable, hold the potential to assure unparalleled stability after five months of aging without any addition of stabilizers or gelling agents, thus envisaging the construction of eco-friendly photovoltaic devices free of expensive, flammable and toxic solvents.
-
electrochemical studies of the co iii co ii dbbip 2 Redox couple as a Mediator for dye sensitized nanocrystalline solar cells
Coordination Chemistry Reviews, 2004Co-Authors: Petra J Cameron, Shaik M Zakeeruddin, Laurence M Peter, Michael GratzelAbstract:Abstract The electrochemical properties of the Redox Mediator Co(III)/Co(II)(dbbip)2 (dbbip = 2,6-bis(1′-butylbenzimidazol-2′-yl)pyridine) in a mixed acetonitrile/ethylene carbonate solvent have been studied by a range of techniques in order to determine the rate constants for electron transfer and the diffusion coefficients of the Co(II) and Co(III) species. Platinum, gold, fluorine-doped tin oxide (FTO) and compact TiO2 layers were used as electrode materials. The results have been used to predict the limitations imposed on the performance of dye-sensitized nanocrystalline cells by the electron transfer kinetics and mass transport properties of the Redox Mediator. The Co(III)/Co(II) Redox Mediator is compared with the conventional triiodide/iodide Redox system used in high performance dye-sensitized solar cells.
-
coii dbbip 22 complex rivals tri iodide iodide Redox Mediator in dye sensitized photovoltaic cells
Journal of Physical Chemistry B, 2001Co-Authors: Herve Nusbaumer, Shaik M Zakeeruddin, Jacquese Moser, And Mohammad K Nazeeruddin, Michael GratzelAbstract:Transient absorption spectroscopy was employed to study charge-transfer dynamics in dye-sensitized nanocrystalline solar cells (DSSC) containing a new one-electron Redox Mediator, cobalt(II)-bis[2,6-bis(1‘-butylbenzimidazol-2‘-yl)pyridine]. Photovoltaic cells incorporating this relay have yielded light-to-electricity power conversion efficiencies of up to 5.2%. This rivals the performance of the tri-iodide/iodide couple that is currently almost exclusively used in DSSC. Interception of the dye oxidized state by electron transfer from the Co(II) complex in diluted electrolyte was found to follow a first-order kinetics with a rate constant of km = 5 × 105 s-1. Above a threshold of 10-2 M, under which the cationic relay is essentially adsorbed onto the negatively charged particle surface, larger concentrations of the reduced Mediator resulted in a linear increase of the apparent rate, yielding a second-order rate constant of km‘‘ = 2.9 × 106 M-1 s-1. Dynamics of the recombination reaction between injected co...
