Faculty Profiles - Yamakata Akira

Papers - Yamakata Akira

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固体表面の動力学に追る時間分解中赤外分光 Invited Reviewed

山方啓, 加藤康作

光学 51 448 - 454 2022.10

Effects of a Nanoparticulate TiO2 Modifier on the Visible-Light CO2 Reduction Performance of a Metal-Complex/Semiconductor Hybrid Photocatalyst Reviewed

Mitsuhiko Shizuno, Kosaku Kato, Shunta Nishioka, Tomoki Kanazawa, Daiki Saito, Shunsuke Nozawa, Akira Yamakata, Osamu Ishitani, Kazuhiko Maeda

ACS Applied Energy Materials 5 ( 8 ) 9479 - 9486 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society ({ACS})

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 (lambda > 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 similar to 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.

DOI： 10.1021/acsaem.2c01052

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One-Step Excitation Overall Water Splitting over a Modified Mg-Doped BaTaO2N Photocatalyst Reviewed

Huihui Li, Jiadong Xiao, Junie Jhon M. Vequizo, Takashi Hisatomi, Mamiko Nakabayashi, Zhenhua Pan, Naoya Shibata, Akira Yamakata, Tsuyoshi Takata, Kazunari Domen

ACS Catalysis 12 ( 16 ) 10179 - 10185 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

BaTaO2N responds to visible light up to 650 nm and exhibits photocatalytic activity during the hydrogen and oxygen evolution reactions. However, the difficulty in promoting both processes simultaneously hinders the realization of overall water splitting (OWS) over this material. Herein, we demonstrate the activation and stabilization of BaTaO2N-based photocatalysts for visible-light-driven OWS by combining flux-assisted nitridation with Mg doping and co-loading of Cr2O3/(Na)Rh and IrO2 co-catalysts. RbCl-assisted nitridation produced single-crystal BaTaO2N particles doped with Mg and so promoted charge transfer to the co-catalysts. The coloading of Cr2O3/(Na)Rh and IrO2 at moderate temperatures as co-catalysts to promote the hydrogen and oxygen evolution reactions, respectively, allowed the BaTaO2N photocatalyst to evolve hydrogen and oxygen simultaneously from water. This work highlights the importance of carefully tuning semiconducting and catalytic properties to realize effective charge transfer when preparing narrow-bandgap oxynitrides for OWS.

DOI： 10.1021/acscatal.2c02394

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Effect of Surface Plasmon Resonance and the Heterojunction on Photoelectrochemical Activity of Metal-Loaded TiO2 Electrodes under Visible Light Irradiation Reviewed

Chia-Yu Chang, Akira Yamakata, Wenjea J. Tseng

The Journal of Physical Chemistry C 126 12450 - 12459 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

This study examines the influence of surface plasmon resonance (SPR) and the semiconducting heterojunction on the photoelectrochemical (PEC) activity of metal-loaded TiO2 electrodes under visible light irradiation. Different metal nanoparticles (including Au, Ag, Rh, and Cu) have been selected deliberately and deposited on the TiO2 electrode layers via photodeposition and subsequent annealing at 300 degrees C. UV-vis spectra show an increased absorbance in the visible light region with the metal loading. X-ray photon spectroscopy reveals the formation of CuO, Ag2O, and Ru2O3 after annealing, while only Au remains in its metallic state. The PEC activity increases in the ascending order of Cu < Au < Rh < Ag. This is consistent with the electrochemical impedance measurement where the Ag-loaded TiO2 electrode shows the lowest charge transfer resistance together with the highest ion diffusion rate. Our findings suggest that the presence of semiconducting p-n heterojunctions with associated oxygen-vacancy defects facilitates the enhanced PEC activity by reducing the electron-hole recombination in addition to the SPR effect.

DOI： 10.1021/acs.jpcc.2c02649

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Eliciting the contribution of TiN to photoelectrochemical performance enhancement of Imma-LaTiO2N at neutral pH Invited Reviewed

Mirabbos Hojamberdiev, Juan Manuel Mora-Hernandez, Ronald Vargas, Eva Maria Heppke, Kunio Yubuta, Akira Yamakata, Zukhra Kadirova, Leticia Torres-Martinez, Katsuya Teshima, Martin Lerch

MATERIALS TODAY ENERGY 27 2022.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The presence of defects, which act as the recombination hubs for photogenerated charge carriers, hinders the improvement of photocatalytic activity for oxygen evolution reaction of LaTiO2N under visible light irradiation via a four-electron-transfer reaction pathway. Here, we involve titanium nitride (TiN) in a varying content (0e17.8%) to improve the efficiency of charge separation and transport, influencing the photoelectrochemical performance of LaTiO2N. The characterization results confirm the formation of a strong contact between orthorhombic-LaTiO2N and cubic-TiN particles. The photoelectrochemical (PEC) measurements reveal the inverse dependence between electron transfer phenomena and charge carrier recombination, which allows to understand the trend when modifying LaTiO2N with TiN. In fact, the incorporation of 17.8% TiN in the LaTiO2N:TiN material results in a higher photocurrent. Open-circuit potential (OCP) decay and transient absorption spectroscopy (TAS) studies confirm longer lifetimes of charge carriers for increasing amounts of TiN in the synthesized materials. Thus, the main role of TiN is to improve the properties of the semiconductor-electrolyte interface, having verified its impact on the separation and transport of photogenerated charge carriers. Furthermore, computational studies predict that the adsorption of water molecules is favored at the LaTiO2N:TiN surface compared to the individual TiN and LaTiO2N surfaces. (C) 2022 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.mtener.2022.101053

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Role of Oxygen Vacancy in the Photocarrier Dynamics of WO3 Photocatalysts: The Case of Recombination Centers Reviewed

Kosaku Kato, Yohei Uemura, Kiyotaka Asakura, Akira Yamakata

The Journal of Physical Chemistry C 126 ( 22 ) 9257 - 9263 2022.6

Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society ({ACS})

Defects in powder photocatalysts determine the photocatalytic activity. The addition of defects sometimes enhances the activity, but sometimes decreases it. However, the factors determining the difference between these cases have not been fully elucidated yet. Herein, we investigated the effects of oxygen vacancies on photocarrier dynamics in WO3 powder using broadband transient absorption spectroscopy. It was found that the decay of deeply trapped electrons was accelerated when the number of oxygen vacancies was increased by H-2 reduction. This result suggests that oxygen vacancies in WO3 mainly act as recombination centers. This is in contrast to many other photocatalysts such as TiO2 and SrTiO3, where the carrier lifetime increases with increasing oxygen vacancy concentration. These differences can be attributed to the difference in the distance between oxygen vacancies. When defects are dispersed, trapped electrons need to travel over long distances by repeatedly hopping and tunneling between defects to combine with holes, resulting in decelerated recombination. In contrast, when the defects are connected or located close together, the trapped electrons can readily migrate among defects, leading to enhanced recombination. Control of the distance between defects is thus important for enhancing photocatalytic activity.

DOI： 10.1021/acs.jpcc.2c01662

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Enhanced Overall Water Splitting by a Zirconium‐Doped TaON‐Based Photocatalyst Reviewed

Jiadong Xiao, Shinji Nishimae, Junie Jhon M. Vequizo, Mamiko Nakabayashi, Takashi Hisatomi, Huihui Li, Lihua Lin, Naoya Shibata, Akira Yamakata, Yasunobu Inoue, Kazunari Domen

Angewandte Chemie International Edition 61 ( 17 ) 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Solar-powered one-step-excitation overall water splitting (OWS) using semiconducting materials is a simple means of achieving scalable and sustainable hydrogen production. While tantalum oxynitride (TaON) is one of the few photocatalysts capable of promoting OWS via single-step visible-light excitation, the efficiency of this process remains extremely poor. The present work employed 15 nm amorphous Ta2O5.3.3 H2O nanoparticles as a new precursor together with Zr doping and an optimized nitridation duration to synthesize a TaON-based photocatalyst with reduced particle sizes and low defect densities. Upon loading with Ru/Cr2O3/IrO2 cocatalysts, this material exhibited stoichiometric water splitting into hydrogen and oxygen, with an order of magnitude improvement in efficiency. Our findings demonstrate the importance of inventing/selecting the appropriate synthetic precursor and of defect control for fabricating active OWS photocatalysts.

DOI： 10.1002/anie.202116573

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Identification of a Self-Photosensitizing Hydrogen Atom Transfer Organocatalyst System. Reviewed International journal

Hiromu Fuse, Yu Irie, Masaaki Fuki, Yasuhiro Kobori, Kosaku Kato, Akira Yamakata, Masahiro Higashi, Harunobu Mitsunuma, Motomu Kanai

Journal of the American Chemical Society 144 ( 14 ) 6566 - 6574 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society ({ACS})

We developed organocatalyst systems to promote the cleavage of stable C-H bonds, such as formyl, α-hydroxy, and benzylic C-H bonds, through a hydrogen atom transfer (HAT) process without the use of exogenous photosensitizers. An electronically tuned thiophosphoric acid, 7,7'-OMe-TPA, was assembled with substrate or co-catalyst N-heteroaromatics through hydrogen bonding and π-π interactions to form electron donor-acceptor (EDA) complexes. Photoirradiation of the EDA complex induced stepwise, sequential single-electron transfer (SET) processes to generate a HAT-active thiyl radical. The first SET was from the electron-rich naphthyl group of 7,7'-OMe-TPA to the protonated N-heteroaromatics and the second proton-coupled SET (PCET) from the thiophosphoric acid moiety of 7,7'-OMe-TPA to the resulting naphthyl radical cation. Spectroscopic studies and theoretical calculations characterized the stepwise SET process mediated by short-lived intermediates. This organocatalytic HAT system was applied to four different carbon-hydrogen (C-H) functionalization reactions, hydroxyalkylation and alkylation of N-heteroaromatics, acceptorless dehydrogenation of alcohols, and benzylation of imines, with high functional group tolerance.

DOI： 10.1021/jacs.2c01705

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時間分解分光計測を利用した光触媒反応機構の解明 Invited Reviewed

山方啓

分光研究 71 75 - 89 2022.4

Donor-π-Acceptor Type Porphyrin-Fullerene Dyad with Acetylene Bridge for p-Type Dye-sensitized Solar Cell Reviewed

Qi Guo, Tomohiro Higashino, Kosaku Kato, Akira Yamakata, Hiroshi Imahori

Chemistry Letters 51 ( 3 ) 260 - 263 2022.2

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：Oxford University Press (OUP)

Abstract

Donor-π-acceptor type porphyrin-fullerene dyads with an acetylene bridge were designed and synthesized. The dyad was found to produce a charge-separated state with a lifetime of 0.42 µs and a quantum yield of 0.78 in benzonitrile. The p-type dye-sensitized solar cells with the dyad exhibited higher photovoltaic performance than that with the porphyrin reference without the fullerene moiety.

DOI： 10.1246/cl.210717

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Manipulation of charge carrier flow in Bi4NbO8Cl nanoplate photocatalyst with metal loading Reviewed

Kanta Ogawa, Ryota Sakamoto, Chengchao Zhong, Hajime Suzuki, Kosaku Kato, Osamu Tomita, Kouichi Nakashima, Akira Yamakata, Takashi Tachikawa, Akinori Saeki, Hiroshi Kageyama, Ryu Abe

Chemical Science 13 ( 11 ) 3118 - 3128 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

Separation of photoexcited charge carriers in semiconductors is important for efficient solar energy conversion and yet the control strategies and underlying mechanisms are not fully established. Although layered compounds have...

DOI： 10.1039/d1sc06054f

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Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial Visible Light-Induced Photocatalytic H2 and O2 Evolution over BaTaO2N Reviewed

Mirabbos Hojamberdiev, Ronald Vargas, Zukhra C. Kadirova, Kosaku Kato, Hadi Sena, Aleksei G. Krasnov, Akira Yamakata, Katsuya Teshima, Martin Lerch

ACS Catalysis 12 ( 2 ) 1403 - 1414 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：American Chemical Society (ACS)

The doping of foreign cations and anions is one of the effective strategies for engineering defects and modulating the optical, electronic, and surface properties that directly govern the photo-catalytic O-2 and H-2 evolution reactions. BaTaO2N (BTON) is a promising 600 nm-class photocatalyst because of its absorption of visible light up to 660 nm, small band gap (E-g = 1.9 eV), appropriate valence band-edge position for oxygen evolution, good stability under light irradiation in concentrated alkaline solutions, and nontoxicity. Although the photocatalytic and photoelectrochemical water-splitting efficiencies of BaTaO2N have been progressively improved, it is still far from the requirements set for practical applications. Here, we employ a 5% B site-selective doping of aliovalent metal cations (Al3+, Ga3+, Mg2+, and Zr4+) to enhance sacrificial visible light-induced photocatalytic H-2 and O-2 evolution over BaTaO2N. The results of physicochemical characterizations reveal that no significant change in crystal structure, crystal morphology, and optical absorption edge is observed upon cation doping. Therefore, the difference observed in O-2 and H-2 evolution during the photocatalytic reactions over pristine and doped BaTaO2N photocatalysts is explained by examining optical, electronic, and surface properties. Also, molecular dynamics (MD) is used to gain insights into the respective effect of cation doping on adsorption energy of water molecules and formed intermediates (H* for H-2 evolution and HO*, O*, and HOO* for O-2 evolution) on the BaTaO2N surfaces terminated with TaO6, TaN6, and TaO4N2 octahedra. Finally, the experimental reaction rates for H-2 and O-2 evolution are correlated well using a linear energy-performance relationship, elucidating the doping and surface-termination trends observed in the BaTaO2N photocatalysts.

DOI： 10.1021/acscatal.1c04547

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Overall photosynthesis of H2O2 by an inorganic semiconductor Reviewed

Pan Zhenhua, Junie Jhon, M. Vequizo, Kosaku Kato, Akira Yamakata, Kenji Katayama, Chiheng Chu, Kazunari Domen

Nature Communications 13 ( 1 ) 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PORTFOLIO

Artificial photosynthesis of H2O2 using earth-abundant water and oxygen is a promising approach to achieve scalable and cost-effective solar fuel production. Recent studies on this topic have made significant progress, yet are mainly focused on using organic polymers. This set of photocatalysts is susceptible to potent oxidants (e.g. hydroxyl radical) that are inevitably formed during H2O2 generation. Here, we report an inorganic Mo-doped faceted BiVO4 (Mo:BiVO4) system that is resistant to radical oxidation and exhibits a high overall H2O2 photosynthesis efficiency among inorganic photocatalysts, with an apparent quantum yield of 1.2% and a solar-to-chemical conversion efficiency of 0.29% at full spectrum, as well as an apparent quantum yield of 5.8% at 420 nm. The surface-reaction kinetics and selectivity of Mo:BiVO4 were tuned by precisely loading CoOx and Pd on {110} and {010} facets, respectively. Time-resolved spectroscopic investigations of photocarriers suggest that depositing select cocatalysts on distinct facet tailored the interfacial energetics between {110} and {010} facets and enhanced charge separation in Mo:BiVO4, therefore overcoming a key challenge in developing efficient inorganic photocatalysts. The promising H2O2 generation efficiency achieved by delicate design of catalyst spatial and electronic structures sheds light on applying robust inorganic particulate photocatalysts to artificial photosynthesis of H2O2.

DOI： 10.1038/s41467-022-28686-x

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Improvement of Visible‐Light H2 Evolution Activity of Pb2Ti2O5.4F1.2 Photocatalyst by Coloading of Rh and Pd Cocatalysts Reviewed

Kenta Aihara, Kosaku Kato, Tomoki Uchiyama, Shuhei Yasuda, Toshiyuki Yokoi, Akira Yamakata, Yoshiharu Uchimoto, Kazuhiko Maeda

Chemistry - A European Journal 28 ( 43 ) 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley

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.

DOI： 10.1002/CHEM.202200875

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Influences of pulverization and annealing treatment on the photocatalytic activity of BiVO₄ for oxygen evolution Reviewed

Kazuya Okuno, Hiromu Kumagai, Junie Jhon M. Vequizo, Kosaku Kato, Makoto Kobayashi, Akira Yamakata, Masato Kakihana, Hideki Kato

Sustainable Energy & Fuels 6 ( 7 ) 1698 - 1707 2022

Effects of the rigid and sterically bulky structure of non-fused nonfullerene acceptors on transient photon-to-current dynamics Reviewed

Seihou Jinnai, Kasumi Murayama, Keisuke Nagai, Megumi Mineshita, Kosaku Kato, Azusa Muraoka, Akira Yamakata, Akinori Saeki, Yasuhiro Kobori, Yutaka Ie

Journal of Materials Chemistry A 10 ( 37 ) 20035 - 20047 2022

Photoexcited charge manipulation in conjugated polymers bearing a Ru(ii) complex catalyst for visible-light CO2 reduction Invited Reviewed

Akinobu Nakada, Ryuichi Miyakawa, Ren Itagaki, Kosaku Kato, Chinami Takashima, Akinori Saeki, Akira Yamakata, Ryu Abe, Hiromi Nakai, Ho-Chol Chang

Journal of Materials Chemistry A 10 ( 37 ) 19821 - 19828 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry ({RSC})

Conjugated polymers have emerged as promising candidates for photocatalyst materials. Design principles that maximize the synergy between the conjugated skeleton and catalyst moiety are strongly desired to be established for achieving efficient photocatalysis. Herein, the photoexcited charge manipulation was demonstrated by molecular engineering in conjugated polymers bearing a Ru(II) complex as the CO2 reduction photocatalyst. Combinational studies based on ultrafast spectroscopies and theoretical calculations revealed that the introduction of an electron-donating carbazole (Cz) skeleton in the polymer enables enhanced photoexcited charge trapping on the Ru(II)-complex catalyst moiety. The carbazole-based polymer [Cz-bpyRu](n) facilitates CO2 reduction under visible light even longer than 500 nm and exhibited 7- to 15-fold greater activity than those of phenyl (Ph) and benzothiadiazole (Bt) counterparts. The findings of this study thus provide insights into molecular engineering for photoexcited charge manipulation to achieve efficient photocatalysis.

DOI： 10.1039/D2TA02183H

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Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial Visible Light-Induced Photocatalytic H₂ and O₂ Evolution over BaTaO₂N

Akira Yamakata

ACS Catalysis 2022

One-Step Excitation Overall Water Splitting over a Modified Mg-Doped BaTaO2N Photocatalyst

Akira Yamakata

ACS Catalysis 2022

Harnessing infrared solar energy with plasmonic energy upconversion

Akira Yamakata

Nature Sustainability 2022

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Papers - Yamakata Akira