Showing papers by "Kazuhiko Maeda published in 2022"
TL;DR: In this article , the authors describe recent progress in the development of new mixed-anion compounds for various applications related to energy, with emphasis on their interdisciplinary collaboration in a national project on mixed anion materials.
Abstract: Mixed-anion compounds, in which multiple anions such as O2−, N3−, and H− are contained in the same compound, have recently attracted attention. Because mixed-anion compounds have a unique crystal structure with multiple anions coordinated to cations, materials with fundamentally new and innovative functions are expected to be developed for various chemistry and physics applications, including catalysts, batteries, and superconductors. In this Account, recent progress in the development of new mixed-anion compounds by the MEXT mixed-anion project is described, with emphasis on results related to the development of materials used as photocatalysts/photoelectrodes, phosphors, secondary battery components, conductors, and thermoelectric materials. Mixed-anion compounds containing more than one anionic species in the same phase can exhibit emergent properties and/or functions that are unattainable with their single-anion counterparts. This Account describes recent progress in the development of new mixed-anion compounds for various applications related to energy, with emphasis on our interdisciplinary collaboration in a national project on mixed-anion materials.
29 citations
TL;DR: In this article , a modification of Ru dye-sensitized, Pt-intercalated HCa2Nb3O10 nanosheets with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the solar-to-hydrogen (STH) energy conversion efficiencies.
Abstract: While dye-sensitized metal oxides are good candidates as H2 evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remain low because of uncontrolled charge recombination reactions. Here, we show that modification of Ru dye–sensitized, Pt-intercalated HCa2Nb3O10 nanosheets (Ru/Pt/HCa2Nb3O10) with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO3-based O2 evolution photocatalyst and an I3−/I− redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa2Nb3O10. By using the optimized photocatalyst, PSS/Ru/Al2O3/Pt/HCa2Nb3O10, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and comparable to conventional semiconductor-based suspended particulate photocatalyst systems.
10 citations
TL;DR: In this paper , the use of a widespread soil mineral, alpha-iron(III) oxyhydroxide (α‐FeOOH; goethite), loaded onto an Al2O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (λ>400 nm) in the presence of a RuII photosensitizer and an electron donor.
Abstract: Abstract Photocatalytic conversion of CO2 into transportable fuels such as formic acid (HCOOH) under sunlight is an attractive solution to the shortage of energy and carbon resources as well as to the increase in Earth's atmospheric CO2 concentration. The use of abundant elements as the components of a photocatalytic CO2 reduction system is important, and a solid catalyst that is active, recyclable, nontoxic, and inexpensive is strongly demanded. Here, we show that a widespread soil mineral, alpha‐iron(III) oxyhydroxide (α‐FeOOH; goethite), loaded onto an Al2O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (λ>400 nm) in the presence of a RuII photosensitizer and an electron donor. This system gave HCOOH as the main product with 80–90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm, as confirmed by isotope tracer experiments with 13CO2. The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO2.
10 citations
TL;DR: In this paper , the relationship between the structure and power density of Ruddlesden-Popper-type perovskite-related compounds and their electrochemical properties was investigated.
Abstract: All-solid-state fluoride-ion batteries (FIBs) that use fluoride ions as carrier ions offer a new horizon for next-generation energy storage devices owing to their high specific capacities. Materials that utilize topochemical insertion and desorption reactions of fluoride ions have been proposed as cathodes for FIBs; among them, Ruddlesden–Popper-type perovskite-related compounds are promising cathode materials owing to reversible fluoride-ion (de)intercalations with low volume expansion compared to conversion-type cathode materials. Although it is essential to improve the power density of the compounds for practical application, the relationship between the structure and power density is still not clearly understood. In this study, we synthesized chemically fluorinated Ruddlesden–Popper compounds, LaSrMnO4 and apical-site-substituted oxyfluoride Sr2MnO3F, and examined the correlations between their structures and electrochemical properties; Sr2MnO3F showed better power density. Open-circuit voltage measurements, X-ray absorption spectroscopy, and synchrotron X-ray diffraction revealed that electrochemical F– insertion into LaSrMnO4 proceeds via a two-phase reaction with relatively high volume expansion, whereas that into Sr2MnO3F proceeds via a solid-solution reaction with relatively low volume expansion. The substitution of oxygen in the apical sites with fluorine suppressed phase transitions with large volume changes, resulting in improved power density.
6 citations
TL;DR: In this paper , a more detailed investigation of various polymorphic TiO2 species loaded onto the graphitic carbon nitride nanosheets (NS-C3N4) and the visible-light CO2 reduction activity of the resultant photocatalysts was conducted.
Abstract: Graphitic carbon nitride nanosheets (NS-C3N4) combined with a binuclear Ru(II)–Re(I) complex (RuRe) consisting of a photosensitizer and catalytic units are capable of selectively reducing CO2 to CO under visible light (λ > 400 nm) using triethanolamine as an electron donor. In this system, the grafting of the nanoparticulate rutile TiO2 on the NS-C3N4 surface has previously been shown to enhance photocatalytic performance because of improved charge separation between the NS-C3N4 and the TiO2 and the reinforced adsorption of the RuRe. Here, a more detailed investigation of various polymorphic TiO2 species loaded onto the NS-C3N4 and the visible-light CO2 reduction activity of the resultant photocatalysts was conducted. The experimental results showed that the RuRe/anatase-TiO2/NS-C3N4 outperformed analogues with other TiO2 polymorphs in terms of the CO generation rate, with a maximum catalytic turnover number of ∼100. Transient absorption and emission spectroscopy measurements were carried out to clarify the origin of the different CO evolution activities provided by different TiO2 modifiers. The results revealed that the TiO2 modifiers not only affected the charge separation ability but also controlled the efficiency of back electron transfer from the Ru-photosensitizer unit in the RuRe to the TiO2. The results also showed that, among the investigated TiO2 polymorphs, anatase best facilitated the forward electron transfer from the NS-C3N4 to the TiO2 while suppressing the undesirable back electron transfer reaction.
6 citations
TL;DR: In this article , a metal-sulfur bond with Pb2+, an earth-abundant metal ion, was shown to achieve a high performance photocatalytic CO2 reduction to formate (HCOO) with >99% selectivity and an apparent quantum yield of 2.6% at 400 nm.
Abstract: Metal–organic frameworks (MOFs) and coordination polymers (CPs) are potential candidates for high-performance photocatalysts because of their high tunability of electronic and structural properties. For example, MOFs and CPs having a high specific surface area (∼1000 m2 g–1) have been applied as visible-light-driven photocatalysts for CO2 reduction and water splitting. Herein, we show a unique CP possessing a metal–sulfur bond with Pb2+, an earth-abundant metal ion. Different from ordinary high-surface-area MOFs and CPs, this CP is nonporous and has just 0.7 m2 g–1 surface area. Nevertheless, owing to its capability of absorbing visible light up to ∼500 nm, it efficiently photocatalyzes CO2 reduction to formate (HCOO–) under visible-light irradiation with >99% selectivity and an apparent quantum yield of 2.6% at 400 nm, even without postmodification treatment such as cocatalyst loading. These values are the highest yet reported for a precious-metal-free single-component photocatalyst for the visible-light-driven reduction of CO2 to HCOO–. This work may thus shed light on the great potential of nonporous CPs as building units of photocatalytic CO2 conversion systems.
4 citations
TL;DR: In this paper , a wurtzite-structured Ga1-xZnx(N,O,F) was successfully synthesized by nitridation of mixtures of a Ga-containing oxide and ZnF2.
Abstract: Wurtzite-structured Ga1-xZnx(N,O,F) was successfully synthesized by nitridation of mixtures of a Ga-containing oxide and ZnF2. The addition of ZnF2 lowered the nitridation temperature for the synthesis of Ga1-xZnx(N,O,F) to 823 K, even when bulk ZnGa2O4 was used as a paired precursor. This lowering of the synthesis temperature was ascribed to the enhancement of nitridation through the addition of fluorine. The low-temperature nitridation achieved by the addition of fluorine suppressed the volatilization of Zn compared with that during the synthesis of a GaN:ZnO solid solution by a conventional high-temperature ammonolysis reaction. The higher concentration of Zn, as well as the higher N concentration in Ga1-xZnx(N,O,F) achieved through the fluorine-assisted nitridation, led to a redshift of the absorption edge of Ga1-xZnx(N,O,F) to 560 nm compared with that of GaN:ZnO synthesized by the conventional ammonolysis reaction. The visible-light absorption of Ga1-xZnx(N,O,F) can be used to drive the photoelectrochemical oxidation of water.
2 citations
TL;DR: In this article , the synthesis and properties of H--doped perovskite-type stannate with respect to the A-site cation of the material and the preparation conditions were investigated.
Abstract: Narrow-gap semiconductors with visible light absorption capability have attracted attention as photofunctional materials. H--doped BaSn0.7Y0.3O3-δ containing Sn(II) species was recently reported to absorb visible light up to 600 nm, which represents the first demonstration of oxyhydride-based visible-light-absorbers. In the present study, a more detailed investigation was made to obtain information on the synthesis and properties of H--doped perovskite-type stannate with respect to the A-site cation of the material and the preparation conditions. H--doped ASn0.7Y0.3O3-δ (A = Ba, Ba0.5Sr0.5, and Sr) obtained by the reaction of ASn0.7Y0.3O3-δ precursors with CaH2 at 773 K under vacuum conditions was shown to have almost the same bandgap (ca. 2.1 eV), regardless of the A-site cation. Physicochemical measurements and theoretical calculations revealed that the identical bandgaps of H--doped ASn0.7Y0.3O3-δ are due to the simultaneous shift of the midgap states composed of Sn2+ with the conduction band minimum. Experimental results also indicated that the appropriate preparation conditions with respect to Y3+-substitution and the temperature for the synthesis of the ASn0.7Y0.3O3-δ precursors were essential to obtain H--doped products that have a low density of defects.
2 citations
TL;DR: In this article , the Ruddlesden-Popper structure was used as a cathode material for all-solid-state fluoride-ion batteries (FIBs) with a relatively high capacity of 118 mAh g/1 and good cycling stability over 70 cycles.
Abstract: All-solid-state fluoride-ion batteries (FIBs) are expected to become the next generation of battery systems owing to their outstanding energy storage characteristics. However, the volume expansion of the cathode that accompanies the insertion of fluoride ions remains an urgent issue to be addressed. Even if an intercalation-type cathode is applied in FIBs, fluoride-ion insertion into the interstitial sites of two-dimensional materials such as LaSrMnO4 still leads to non-negligible volume expansion. Here, we report a novel intercalation-type material, Sr3Fe2O5F2, possessing the Ruddlesden–Popper structure as a cathode material for FIBs that features not only interstitial sites but also anion vacancies as three-dimensional (3D) percolation sites to accommodate fluoride ions. This material exhibits a relatively high capacity of 118 mAh g–1 and good cycling stability over 70 cycles. Fe2+/Fe3+ redox reactions are responsible for charge compensation during the charging and discharging processes. The crystal structure during the charging process changes from Sr3Fe2O5F0.46 to Sr3Fe2O5F2 by using the 3D percolation sites with an extremely small volume change of approximately 0.17% and thereafter changes to Sr3Fe2O5F3 with a P4/mmm symmetry by using interstitial sites with a large volume change of approximately 11%. Our findings should pave the way for the design of new cathodes with excellent cycling stability and minimal volume expansion based on the percolation mechanism.
1 citations
TL;DR: In this paper , Pb2Ti2O5.4F1.2 was modified with various metal cocatalysts for visible-light H2 evolution and showed 3.2 times greater H2 activity than the previously reported Pt/Pb2Ni2O2O4F 1.2 catalyst.
Abstract: Abstract Pb2Ti2O5.4F1.2 modified with various metal cocatalysts was studied as a photocatalyst for visible‐light H2 evolution. Although unmodified Pb2Ti2O5.4F1.2 showed negligible activity, modification of its surface with Rh led to the best observed promotional effect among the Pb2Ti2O5.4F1.2 samples modified with a single metal cocatalyst. The H2 evolution activity was further enhanced by coloading with Pd; the Rh−Pd/Pb2Ti2O5.4F1.2 photocatalyst showed 3.2 times greater activity than the previously reported Pt/Pb2Ti2O5.4F1.2. X‐ray absorption fine‐structure spectroscopy, photoelectrochemical, and transient absorption spectroscopy measurements indicated that the coloaded Rh and Pd species, which were partially alloyed on the Pb2Ti2O5.4F1.2 surface, improved the electron‐capturing ability, thereby explaining the high activity of the coloaded Rh−Pd/Pb2Ti2O5.4F1.2 catalyst toward H2 evolution.
TL;DR: In this article , the synthesis of cobalt phosphate (CoPi) modified, nitrogen-doped TiO2 nanotube arrays (N•TNAs) for photoelectrochemical (PEC) oxygen evolution under visible light is reported.
Abstract: The synthesis of cobalt phosphate (CoPi)‐modified, nitrogen‐doped TiO2 nanotube arrays (N‐TNAs) for photoelectrochemical (PEC) oxygen evolution under visible light is reported. Because of the nitrogen doping, the N‐TNAs exhibit enhanced visible‐light activity toward the PEC water oxidation reaction. However, the performance is diminished as a result of self‐oxidation by photogenerated holes in the valence band of the N‐TNAs. Compared with the N‐TNAs, the CoPi/N‐TNAs prepared under optimal conditions show a twofold improvement in photocurrent generation and are also sensitive to light with wavelengths as long as 580 nm. Stable oxygen evolution with a Faradaic efficiency approaching unity is demonstrated using the CoPi/N‐TNA photoanodes under simulated sunlight for at least 2 h of operation.
TL;DR: In this paper , a novel strategy of first nitridation and subsequent calcination post-treatment method is developed to prepare N,F-codoped TiO2 (TNOF) to efficiently utilize solar energy and catalyze water splitting reaction under visible-light.
Abstract: To efficiently utilize solar energy and catalyze water splitting reaction under visible-light, a novel strategy of first nitridation and subsequent calcination post-treatment method is developed to prepare N,F-codoped TiO2 (TNOF)...
TL;DR: In this article , a perovskite oxyfluoride (Pb3Fe2O5F2) was used for electrochemical oxidation of water, where it exhibited activity for oxidizing water forming O2.
Abstract: A two-dimensional (2D) perovskite oxyfluoride Pb3Fe2O5F2, deposited on a conductive glass substrate, exhibited activity for electrochemical oxidation of water. This 2D oxyfluoride electrode could oxidize water forming O2 at a...
25 Nov 2022
TL;DR: In this paper , a layered nitro-halide β-ZrNBr with a narrow bandgap of ca. 2.3 eV and low defect density was reported to exhibit multifunctionalities for photocatalytic water reduction, water oxidation and CO 2 reduction under visible-light irradiation.
Abstract: Developing mixed-anion semiconductors for solar fuel production has inspired extensive interest, but the nitrohalide-based photocatalyst is still in shortage. Here we report a layered nitro-halide β-ZrNBr with a narrow bandgap of ca. 2.3 eV and low defect density to exhibit multifunctionalities for photocatalytic water reduction, water oxidation and CO 2 reduction under visible-light irradiation. As confirmed by the results of electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations, the formation of anion vacancies in the nitro-halide photocatalyst was inhibited due to its relatively high formation energy. Furthermore, performance of β-ZrNBr can be effectively promoted by a simple exfoliation into nanosheets to shorten the carrier transfer distance as well as to promote charge separation. Our work extends the territory of functional photocatalysts into the nitro-halide, which opens a new avenue for fabricating efficient artificial photosynthesis.
TL;DR: Maeda et al. as mentioned in this paper used α-Eisen(III)-Oxyhydroxid auf einem Aluminiumoxidträger als wiederverwertbarer Katalysator für the CO2-Reduktionsreaktion, der mithilfe eines Ruthenium(II)-Photosensibilisators and eines Elektronendonors eine Selektivität von 80 − 0 % and eine effektive Quantenausbeute von 4.3 % bei 460 nm aufweist.
Abstract: Für die Photoreduktion von CO2 zu Ameisensäure wurde ein Oxyhydroxid-Katalysator auf Fe-Basis entwickelt. Wie Kazuhiko Maeda et al. in ihrer Zuschrift berichten (DOI: 10.1002/ange.202204948), dient α-Eisen(III)-Oxyhydroxid auf einem Aluminiumoxidträger als wiederverwertbarer Katalysator für die CO2-Reduktionsreaktion, der mithilfe eines Ruthenium(II)-Photosensibilisators und eines Elektronendonors eine Selektivität von 80–0 % und eine effektive Quantenausbeute von 4.3 % bei 460 nm aufweist.
TL;DR: The composites of cupric oxide (CuO) and NiFe layered double hydroxide (NiFe-LDH) were prepared by three methods including hydrothermal (h) and solid-state reactions (s), as well as physical mixing (m) as mentioned in this paper .
TL;DR: In this paper , a Ruddlesden-Popper phase two-layer perovskite analogous to Li2LaTa2O6N and having a band gap of 2.5 eV was used as a photocatalytic material for water splitting and CO2 conversion.
Abstract: Mixed-anion materials that consist more than one anionic species in a single-phase have attracted attention for various applications. Oxynitrides containing d0- or d10-metal cations are typical example of visible-light-driven photocatalysts for water splitting and CO2conversion. In this presentation, recent progress on the development of mixed-anion materials for water splitting and CO2 conversion made by our group will be given.
While two-dimensional (2D) undoped layered oxynitrides are potential candidates as high performance visible-light photocatalysts, synthesis of 2D layered oxynitrides is generally difficult because most of them are metastable phases and are not chemically very stable. We found an exceptional example of a 2D layered oxynitride, K2LaTa2O6N (more specifically, K2LaTa2O6N·1.6H2O), which is a Ruddlesden-Popper phase two-layer perovskite analogous to Li2LaTa2O6N and has a band gap of 2.5 eV. This material undergoes in situH+/K+ exchange in aqueous solution while keeping its visible light absorption capability. The protonated, Ir-modified K2LaTa2O6N exhibited photocatalytic activity for H2 evolution from aqueous NaI solution under visible light, outperforming Pt/ZrO2/TaON and Pt/SrTiO3:Rh, which are one of the best-performing oxynitride and oxide photocatalysts for H2 evolution, respectively.
The use of mixed-anion materials is of interest not only for photocatalysts but also for catalysts promoting water oxidation and CO2reduction. For example, we found that certain oxyfluorides work as electrocatalysts for water oxidation. A 2D perovskite oxyfluoride Pb3Fe2O5F2 exhibits activity for electrochemical water oxidation to O2, which is 8 times more active than a 3D bulk PbFeO2F.
01 Jun 2022
TL;DR: In this article , an α-iron(III) oxyhydroxide was developed for CO2 photoreduction into formic acid, showing 80-90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm with the aid of a ruthenium(II) photosensitizer and an electron donor.
Abstract: An Fe-based oxyhydroxide catalyst was developed for CO2 photoreduction into formic acid. As reported by Kazuhiko Maeda et al. in their Communication (DOI: 10.1002/anie.202204948), α-iron(III) oxyhydroxide, which is an easily available soil mineral and is loaded onto an alumina support, serves as a recyclable catalyst for the C-O2 reduction reaction, showing 80–90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm with the aid of a ruthenium(II) photosensitizer and an electron donor.
TL;DR: A wide-spread soil mineral, alpha-iron-(III) oxyhydroxide, was found to become a recyclable catalyst for carbon dioxide photoreduction into formic acid as mentioned in this paper .
Abstract: A wide-spread soil mineral, alpha-iron-(III) oxyhydroxide, was found to become a recyclable catalyst for carbon dioxide photoreduction into formic acid. Credit: Professor