Faculty Profiles - Yamakata Akira

Papers - Yamakata Akira

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Designing and Understanding Biphasic TiO2 Composites for a Long-Lasting Photocatalytic Air Purification Reviewed

Ulfi Muliane, Shi Nee Lou, Shinbi Lee, Fei He, Shen Zhao, Kosaku Kato, Akira Yamakata, Wonyong Choi

ACS ES&T Engineering 2025.4

Boosted Photocatalytic Water Oxidation over BaTaO2N Produced from Perovskite Oxides Based on Photoinduced Charge Carriers

Junie Jhon M. Vequizo, Kosaku Kato, Shanshan Chen, Takashi Hisatomi, Zheng Wang, Tsuyoshi Takata, Akira Yamakata, Kazunari Domen

Energy & Fuels 2025.4

Conduction Band and Defect Engineering for the Prominent Visible‐Light Responsive Photocatalysts Reviewed

Akira Yamakata, Kosaku Kato, Takafumi Ogawa, Kanta Ogawa, Makoto Ogawa, Daichi Kato, Chengchao Zhong, Akihide Kuwabara, Ryu Abe, Hiroshi Kageyama

Angewandte Chemie International Edition 2024.12

Authorship：Lead author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：Wiley

Controlling trap depth is crucial to improve photocatalytic activity, but designing such crystal structures has been challenging. In this study, we discovered that in 2D materials like BiOCl and Bi4NbO8Cl, composed of interleaved [Bi2O2]2+ and Cl‐ slabs, the trap depth can be controlled by manipulating the slab stacking structure. In BiOCl, oxygen vacancies (VO) create deep electron traps, while chlorine vacancies (VCl) produce shallow traps. The depth is determined by the coordination around anion vacancies: VO forms strong σ bonds with Bi‐6p dangling bonds below the conduction band minimum (CBM), while those around Cl are parallel, forming weak π‐bonding. The strong re‐hybridization makes the trap depth deeper. In Bi4NbO8Cl, VCl also creates shallow traps, but VO does not produce deep traps although Bi‐6p orbitals are also forming strong σ bonding. This difference is attributed to the difference of energy level of CBM. In both cases, CBM consists of Bi‐6p orbitals extending into the Cl layers. However, these orbitals are isolated in BiOCl, but those in Bi4NbO8Cl are bonded with each other between neighboring [Bi2O2]2+ layers. This unique bonding‐based CBM prevents the formation of deep electron traps, and significantly enhances H2 evolution activity by prolonging lifetime of highly reactive free electrons.

DOI： 10.1002/anie.202419624

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Zeolite-decorated black TiOx quantum dots for photocatalytic degradation of organic cationic dyes under LED light irradiation Reviewed

Mohammad Rahim Pour, Mohammad Fereidooni, Supareak Praserthdam, Piyasan Praserthdam, Victor Marquez, Kaito Uesaka, Akira Yamakata, C.V. Paz, Nattawut kamjam, Pongsakorn kanjanaboos

Journal of Alloys and Compounds 1008 176797 - 176797 2024.12

Surface Modifications of Layered Perovskite Oxysulfide Photocatalyst Y₂Ti₂O₅S₂ to Enhance Visible‐Light‐Driven Water Splitting Reviewed

Xizhuang Liang, Junie Jhon M. Vequizo, Lihua Lin, Xiaoping Tao, Qiulian Zhu, Mamiko Nakabayashi, Daling Lu, Hiroaki Yoshida, Akira Yamakata, Takashi Hisatomi, Tsuyoshi Takata, Kazunari Domen

Advanced Science 2024.11

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

Abstract

Increasing the efficiency of visible‐light‐driven water splitting systems will require improvements in the charge separation characteristics and redox reaction kinetics associated with narrow‐bandgap photocatalysts. Although the traditional approach of loading a single cocatalyst on selective facets provides reaction sites and reduces the reaction overpotential, pronounced surface charge carrier recombination still results in limited efficiency increases. The present study demonstrates a significant improvement in the hydrogen evolution activity of the layered single‐crystal photocatalyst Y₂Ti₂O₅S₂. Increased performance is obtained through sequential loading of Pt cocatalysts using a two‐step process followed by photodeposition of Cr₂O₃ nanolayers. The stepwise deposition of Pt involved an impregnation‐reduction pretreatment with subsequent photodeposition and produced numerous hydrogen production sites while promoting electron capture. The Cr₂O₃ shells formed on Pt nanoparticles further promoted electron transfer from the Pt to the water and inhibited surface carrier recombination. Importantly, it is also possible to construct a Z‐scheme overall water splitting system using the optimized Y₂Ti₂O₅S₂ in combination with surface‐modified BiVO₄ in the presence of [Fe(CN)₆]^3−/4−, yielding a solar‐to‐hydrogen energy conversion efficiency of 0.19%. This work provides insights into precise surface modifications of narrow‐bandgap photocatalysts as a means of improving the solar water splitting process.

DOI： 10.1002/advs.202412326

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Simultaneous Structural and Electronic Engineering on Bi‐ and Rh‐co‐doped SrTiO3 for Promoting Photocatalytic Water Splitting Reviewed

Zhenhua Pan, Junie Jhon M. Vequizo, Hiroaki Yoshida, Jianuo Li, Xiaoshan zheng, Chiheng Chu, Qian Wang, Mengdie Cai, Song Sun, Kenji Katayama, Akira Yamakata, Kazunari Domen

Angewandte Chemie International Edition 2024.8

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

<jats:p>Activating metal ion‐doped oxides as visible‐light‐responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)‐molten (dopants) reaction to synthesize Bi‐ and Rh‐codoped SrTiO3 (SrTiO3:Bi,Rh) particles. Our investigation reveals that SrTiO3:Bi,Rh manifests as single‐crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well‐stabilized Rh3+ energy state for visible‐light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high‐concentration and long‐lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3:Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9% at 420 nm, setting a new benchmark among Rh‐doped‐based SrTiO3 materials. Furthermore, when integrated into an all‐solid‐state Z‐scheme system with Mo‐doped BiVO4 and reduced graphene oxide, SrTiO3:Bi,Rh enabled water splitting with an AQY of 7.1% at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid‐molten reaction as a viable approach for this purpose.</jats:p>

DOI： 10.1002/anie.202414628

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Nonfullerene Acceptors Bearing Spiro-Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy. Reviewed International journal

Kai Wang, Seihou Jinnai, Takumi Urakami, Hirofumi Sato, Masahiro Higashi, Sota Tsujimura, Yasuhiro Kobori, Rintaro Adachi, Akira Yamakata, Yutaka Ie

Angewandte Chemie (International ed. in English) e202412691 2024.8

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

The development of nonfullerene acceptors (NFAs), represented by ITIC, has contributed to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Although tuning the electronic structures to reduce the exciton binding energy (Eb) is considered to promote photocharge generation, a rational molecular design for NFAs has not been established. In this study, we designed and developed two ITIC-based NFAs bearing spiro-substituted bithiophene or biphenyl units (named SpiroT-DCI and SpiroF-DCI) to tune the frontier molecular orbital (FMO) distribution of NFAs. While the highest occupied molecular orbitals (HOMOs) of SpiroF-DCI and ITIC are delocalized in the main π-conjugated framework, the HOMO of SpiroT-DCI is distributed on the bithiophene unit. Reflecting this difference, SpiroT-DCI exhibits a smaller Eb than either SpiroF-DCI or ITIC, and exhibits greater external quantum efficiency in single-component OSCs. Furthermore, SpiroT-DCI shows improved PCEs for bulk-heterojunction OSCs with a donor of PBDB-T, compared with that of either SpiroT-DCI or ITIC. Time-resolved spectroscopy measurements show that the photo-induced intermolecular charge separation is effective even in pristine SpiroT-DCI films. This study highlights the introduction of spiro-substituted bithiophene units that are effective in tuning the FMOs of ITIC, which is desirable for reducing the Eb and improving the PCE in OSCs.

DOI： 10.1002/anie.202412691

PubMed

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Development of Non-Fullerene Acceptors with π-Extended Central Unit for Organic Photovoltaic Devices Reviewed

Tomokazu Umeyama, Motohisa Kubota, Haoxuan Zhang, Rintaro Adachi, Akira Yamakata, Tomoyuki Koganezawa, Hiroshi Imahori

Journal of Photopolymer Science and Technology 37 ( 2 ) 197 - 204 2024.6

Atomically dispersed low-valent Au boosts photocatalytic hydroxyl radical production Reviewed

Zhenyuan Teng, Hongbin Yang, Qitao Zhang, Wenan Cai, Ying-Rui Lu, Kosaku Kato, Zhenzong Zhang, Jie Ding, Han Sun, Sixiao Liu, Chengyin Wang, Peng Chen, Akira Yamakata, Ting-Shan Chan, Chenliang Su, Teruhisa Ohno, Bin Liu

Nature Chemistry 16 ( 8 ) 1250 - 1260 2024.6

Double‐Hollow Au@CdS Yolk@Shell Nanostructures as Superior Plasmonic Photocatalysts for Solar Hydrogen Production Reviewed

Yi‐An Chen, Yuhi Nakayasu, Yu‐Chang Lin, Jui‐Cheng Kao, Kai‐Chi Hsiao, Quang‐Tuyen Le, Kao‐Der Chang, Ming‐Chung Wu, Jyh‐Pin Chou, Chun‐Wei Pao, Tso‐Fu Mark Chang, Masato Sone, Chun‐Yi Chen, Yu‐Chieh Lo, Yan‐Gu Lin, Akira Yamakata, Yung‐Jung Hsu

Advanced Functional Materials 2024.6

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：Wiley

Abstract

Structural engineering has proven effective in tailoring the photocatalytic properties of semiconductor nanostructures. In this work, a sophisticated double‐hollow yolk@shell nanostructure composed of a plasmonic, mobile, hollow Au nanosphere (HGN) yolk and a permeable, hollow CdS shell is proposed to achieve remarkable solar hydrogen production. The shell thickness of HGN@CdS is finely adjusted from 7.7, 18.4 to 24.5 nm to investigate its influence on the photocatalytic performance. Compared with pure HGN, pure CdS, a physical mixture of HGN and CdS, and a counterpart single‐hollow cit‐Au@CdS yolk@shell nanostructure, HGN@CdS exhibits superior hydrogen production under visible light illumination (λ = 400–700 nm). The apparent quantum yield of hydrogen production reaches 8.2% at 320 nm, 6.2% at 420 nm, and 4.4% at 660 nm. The plasmon‐enhanced activity at 660 nm is exceptional, surpassing the plasmon‐induced photoactivities of the state‐of‐the‐art plasmonic photocatalysts ever reported. The superiority of HGN@CdS originates from the creation of charge separation state at HGN/CdS heterojunction, the considerably long‐lived hot electrons of plasmonic HGN, the magnified electric field, and the advantageous features of double‐hollow yolk@shell nanostructures. The findings can provide a guideline for the rational design of versatile double‐hollow yolk@shell nanostructures for widespread photocatalytic applications.

DOI： 10.1002/adfm.202402392

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Carbon Nanotubes as a Solid-State Electron Mediator for Visible-Light-Driven Z-Scheme Overall Water Splitting Reviewed

Lihua Lin, Yiwen Ma, Nobuyuki Zettsu, Junie Jhon M. Vequizo, Chen Gu, Akira Yamakata, Takashi Hisatomi, Tsuyoshi Takata, Kazunari Domen

Journal of the American Chemical Society 146 ( 21 ) 14829 - 14834 2024.5

Trapping of Intermediates of a Photocatalytic Oxygen Evolution Reaction in Overall Water Splitting Reviewed

Fumiaki Amano, Satoshi Nakayama, Souta Suzuki, Akira Yamakata, Kosuke Beppu

ACS Applied Energy Materials 2024.2

Double Hydrogen Atom Transfer Strategy for Catalytic Acceptorless Dehydrogenation of Cycloalkanes Reviewed

Rahul Jagtap, Yuki Nishioka, Stephen Geddis, Yu Irie, Fuki Masaaki, Yasuhiro Kobori, Rintaro Adachi, Akira Yamakata, Harunobu Mitsunuma, Motomu Kanai

2024.2

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

The advancement of an effective hydrogen liberation tech-nology from liquid organic hydrogen carriers (LOHCs), such as cyclohexane and methylcyclohexane (MCH), holds significance in realizing a hydrogen-centric society. However, the attainment of homogeneous catalytic acceptorless dehydrogenation (CAD) characterized by elevated selectivity for thorough aromatization under mild conditions remains unrealized. In this study, a catalyst system, facilitated by a double hydrogen atom transfer (HAT) processes, has been devised for the CAD of inert cycloalkanes at ambient temperature under visible light irradiation. Through the synergistic utilization of tetrabutylammonium chloride (TBACl) and thiophosphoric acid (TPA) HAT catalysts, successful CAD with comprehensive aromatization has been accomplished with high functional group tolerance.

DOI： 10.26434/chemrxiv-2024-s5n5v

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Suppression of Charge Recombination by Vertical Arrangement of A Donor Moiety on Flat Planar Dyes for Efficient Dye‐Sensitized Solar Cells Reviewed

Qi Guo, Tomohiro Higashino, Rintaro Adachi, Chayanit Wechwithayakhlung, Daniel Packwood, Akira Yamakata, Hiroshi Imahori

ChemSusChem 17 ( 9 ) 2024.1

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

Abstract

In dye‐sensitized solar cells (DSSCs), flat planar dyes (e. g., highly light‐harvesting porphyrins and corroles) with multiple anchoring groups are known to adopt a horizontal orientation on TiO₂ through the multiple binding to TiO₂. Due to the strong electronic coupling between the dye and TiO₂, fast charge recombination between the oxidized dye and an electron in TiO₂ occurs, lowering the power conversion efficiency (η). To overcome this situation, an additional donor moiety can be placed on top of the planar dye on TiO₂ to slow down the undesirable charge recombination. Here we report the synthesis and photovoltaic properties of a triarylamine (TAA)‐tethered gold(III) corrole (TAA‐AuCor). The DSSC with TAA‐AuCor using iodine redox shuttle exhibited the highest η‐value among corrole‐based DSSCs, which is much higher than that with the reference AuCor. The transient absorption spectroscopies clearly demonstrated that fast electron transfer from the TAA moiety to the corrole radical cation in TAA‐AuCor competes with the undesirable charge recombination to generate long‐lived charge separated state TAA⋅⁺‐Cor/TiO₂⋅⁻ efficiently. Consequently, the introduction of the TAA moiety enhanced the η‐value remarkably, demonstrating the usefulness of our new concept to manipulate charge‐separated states toward highly efficient DSSCs.

DOI： 10.1002/cssc.202301661

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Efficient and stable visible-light-driven Z-scheme overall water splitting using an oxysulfide H2 evolution photocatalyst Reviewed

Lihua Lin, Yiwen Ma, Junie Jhon M. Vequizo, Mamiko Nakabayashi, Chen Gu, Xiaoping Tao, Hiroaki Yoshida, Yuriy Pihosh, Yuta Nishina, Akira Yamakata, Naoya Shibata, Takashi Hisatomi, Tsuyoshi Takata, Kazunari Domen

Nature Communications 15 ( 1 ) 2024.1

Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

So-called Z-scheme systems permit overall water splitting using narrow-bandgap photocatalysts. To boost the performance of such systems, it is necessary to enhance the intrinsic activities of the hydrogen evolution photocatalyst and oxygen evolution photocatalyst, promote electron transfer from the oxygen evolution photocatalyst to the hydrogen evolution photocatalyst, and suppress back reactions. The present work develop a high-performance oxysulfide photocatalyst, Sm₂Ti₂O₅S₂, as an hydrogen evolution photocatalyst for use in a Z-scheme overall water splitting system in combination with BiVO₄ as the oxygen evolution photocatalyst and reduced graphene oxide as the solid-state electron mediator. After surface modifications of the photocatalysts to promote charge separation and redox reactions, this system is able to split water into hydrogen and oxygen for more than 100 hours with a solar-to-hydrogen energy conversion efficiency of 0.22%. In contrast to many existing photocatalytic systems, the water splitting activity of the present system is only minimally reduced by increasing the background pressure to 90 kPa. These results suggest characteristics suitable for applications under practical operating conditions.

DOI： 10.1038/s41467-024-44706-4

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Other Link： https://www.nature.com/articles/s41467-024-44706-4

An efficient particulate photocatalyst for overall water splitting based on scandium and magnesium co-doped strontium titanate Reviewed

Shigeru Ikeda, Riku Okamoto, Akira Kimura, Yuhi Nakayasu, Akira Yamakata, Ryota Tomizawa, Taizo Masuda, Koichiro Nakatani

Sustainable Energy & Fuels 8 ( 2 ) 202 - 209 2024

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

A high photocatalytic performance for overall water splitting was demonstrated over a photocatalyst based on a magnesium and scandium co-doped strontium titanate particle composed of a cubic shape having a nanosized step structure on the edge of the particle.

DOI： 10.1039/d3se01408h

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Activation of Nonoxide Photocatalyst Sheet Operable under Visible Light Irradiation up to 600 nm by Conductive Bilayer Reviewed

Swarnava Nandy, Hiroka Sandaiji, Shuji Sekimori, Junie Jhon M. Vequizo, Rhauane Almeida Galvão, Natsutogi Iwasa, Swapnil S. Karade, Mamiko Nakabayashi, Tsuyoshi Takata, Takashi Hisatomi, Akira Yamakata, Kazunari Domen

ACS Energy Letters 4708 - 4714 2024

Publishing type：Research paper (scientific journal)

Particulate photocatalyst sheets allow for scalable sunlight-driven overall water splitting. Photocatalyst sheets composed of doped-La5Ti2Cu0.9Ag0.1O7S5 (LTCA), gallium zinc oxynitride (GaN:ZnO), and Au as the hydrogen evolution photocatalyst, oxygen evolution photocatalyst, and conductor layer, respectively, are promising candidates because of their long absorption edge wavelengths (700 and 600 nm, respectively). However, the actual performance of this sheet has been poor due to the large Schottky barrier at the GaN:ZnO/Au interface. Here, we developed a photocatalyst sheet incorporating conductive thin Au and thick Ti bilayer films having high and low work functions, respectively, which increased the activity by a factor of 6 compared with that of a single Au layer sheet. An optimized doped-LTCA/Au/Ti/CoOx/GaN:ZnO sheet modified with CoOx and Cr2O3/Rh cocatalysts exhibited a solar-to-hydrogen energy conversion efficiency of 0.3%. This work provides a key strategy based on the utilization of narrow bandgap oxynitride materials to construct efficient visible-light-driven nonoxide-based sheets.

DOI： 10.1021/acsenergylett.4c01795

Scopus

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Boosting charge separation in organic photovoltaics: unveiling dipole moment variations in excited non-fullerene acceptor layers Reviewed

Akira Yamakata, Kosaku Kato, Takumi Urakami, Sota Tsujimura, Kasumi Murayama, Masahiro Higashi, Hirofumi Sato, Yasuhiro Kobori, Tomokazu Umeyama, Hiroshi Imahori

Chemical Science 15 ( 32 ) 12686 - 12694 2024

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

Neat ITIC films are found to facilitate charge transfer, dissociation, and free carrier formation without the need for donor layers. This process, driven by V-type molecular stacking, significantly boosts organic photovoltaic efficiency.

DOI： 10.1039/d4sc00917g

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Sub-50 nm perovskite-type tantalum-based oxynitride single crystals with enhanced photoactivity for water splitting Reviewed

Jiadong Xiao, Mamiko Nakabayashi, Takashi Hisatomi, Junie Jhon M. Vequizo, Wenpeng Li, Kaihong Chen, Xiaoping Tao, Akira Yamakata, Naoya Shibata, Tsuyoshi Takata, Yasunobu Inoue, Kazunari Domen

Nature Communications 14 ( 1 ) 2023.12

Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

A long-standing trade-off exists between improving crystallinity and minimizing particle size in the synthesis of perovskite-type transition-metal oxynitride photocatalysts via the thermal nitridation of commonly used metal oxide and carbonate precursors. Here, we overcome this limitation to fabricate ATaO₂N (A = Sr, Ca, Ba) single nanocrystals with particle sizes of several tens of nanometers, excellent crystallinity and tunable long-wavelength response via thermal nitridation of mixtures of tantalum disulfide, metal hydroxides (A(OH)₂), and molten-salt fluxes (e.g., SrCl₂) as precursors. The SrTaO₂N nanocrystals modified with a tailored Ir–Pt alloy@Cr₂O₃ cocatalyst evolved H₂ around two orders of magnitude more efficiently than the previously reported SrTaO₂N photocatalysts, with a record solar-to-hydrogen energy conversion efficiency of 0.15% for SrTaO₂N in Z-scheme water splitting. Our findings enable the synthesis of perovskite-type transition-metal oxynitride nanocrystals by thermal nitridation and pave the way for manufacturing advanced long-wavelength-responsive particulate photocatalysts for efficient solar energy conversion.

DOI： 10.1038/s41467-023-43838-3

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Other Link： https://www.nature.com/articles/s41467-023-43838-3

A Quantitative Study on the Relationship of Specific Surface Area and Carrier Lifetime to Photocatalytic Activity of Anatase TiO₂ Nanoparticles Reviewed

Shimpei Naniwa, Kosaku Kato, Akira Yamakata, Akira Yamamoto, Hisao Yoshida

ACS Catalysis 13 ( 22 ) 15212 - 15218 2023.11

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Papers - Yamakata Akira