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Last Updated :2024/09/07

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Master

Affiliation (Master)

  • Faculty of Engineering　Applied Chemistry　Functional Materials Chemistry

Affiliation (Master)

  • Faculty of Engineering　Applied Chemistry　Functional Materials Chemistry

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Kitano

  • Name (Kana)

    Sho

  • Name

    201901001252319028

Achievement

Research Interests

  • Electrochemistry   Photocatalysis   solvothermal synthesis   nanosheet   metal oxide   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Catalytic processes and resource chemistry
  • Nanotechnology/Materials / Energy chemistry

Published Papers

  • Sho Kitano, Hiroya Motohashi, Mana Iwai, Koji Fushimi, Yoshitaka Aoki, Hiroki Habazaki
    Applied Surface Science 2024/10
  • Xiong Zetao, David Quintero, Sho Kitano, Tomoya Nagao, Mana Iwai, Yoshitaka Aoki, Koji Fushimi, Hiroki Habazaki
    Electrochimica Acta 491 0013-4686 2024/07/01 
    Anodizing is gaining popularity as a binder-free fabrication route for obtaining catalyst materials directly on the current collector without using noble metals, binders, or conductive carbon additives. Here, we fabricate promising highly active electrodes for alkaline water electrolysis by anodizing commercial FeNi and FeNiCo alloys (%wt. Fe range between 22 and 63) in an ethylene glycol-based fluoride electrolyte. Anodizing forms metal fluoride coatings, which are converted to OER active compounds (γ-NiOOH:Fe) during potential cycling in an alkaline aqueous solution (1 mol L−1 (M) KOH at 293 K) as a result of leaching of fluoride ions. The morphology, thickness, and number of active sites are influenced by the amount of Fe in the alloy, and the electrode with the highest electrochemical active surface area (Kovar alloy with a 54 %wt. Fe) shows the largest OER activity enhancement by anodizing. The performance evaluation in practical conditions (7 mol L−1 KOH at 343 K) demonstrated a highly active performance with an OER potential as low as 1.52 V at a current density of 600 mA cm−2 even for electrodes obtained in alloys with a low amount of Fe (78-Permalloy with a 22 %wt. Fe), demonstrating that anodizing is an effective way to develop highly active OER electrodes from commercially available alloys. On the other hand, anodizing is a good fluoridation route for transition metals with good results in the formation of F-enriched precursors that efficiently promote active phase formation during the catalytic process, offering the possibility of obtaining catalysts directly on the current collector in a one-step process, easily implemented in industrial applications.
  • Akihiro Fujimura, Masatoshi Abe, Akinori Kawano, Mana Iwai, Sho Kitano, Hiroki Habazaki, Koji Fushimi
    Corrosion Science 227 0010-938X 2024/02 
    The dissolved masses of Fe, Cr, Al, and Si in H2SO4 solution during the polarization of Cr-containing steels were quantified by online ICP-OES. The active dissolution current on 11Cr-2Al/-2Si was smaller than that on 11Cr due to the enrichment of Al/Si on the steel. The Cr dissolution from 11Cr2Al was suppressed in passive state, while that from 11Cr2Si was decreased in active-passive transition because accumulated Al or Si products have different physicochemical effects on the Cr-enrichment of the surface. Roles of Al/Si in corrosion process, especially passivation, were discussed based on quantitative analysis of dissolution products detected by ICP-OES.
  • Chunmei Tang, Ning Wang, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki, Siyu Ye
    Green Energy and Environment 2096-2797 2024 
    Protonic solid oxide electrolysis cells (P-SOECs) are a promising technology for water electrolysis to produce green hydrogen. However, there are still challenges related key materials and anode/electrolyte interface. P-SOECs with Zr-rich electrolyte, called Zr-rich side P-SOECs, possess high thermodynamically stability under high steam concentrations but the large reaction resistances and the current leakage, thus the inferior performances. In this study, an efficient functional interlayer Ba0.95La0.05Fe0.8Zn0.2O3−δ (BLFZ) in-between the anode and the electrolyte is developed. The electrochemical performances of P-SOECs are greatly enhanced because the BLFZ can greatly increase the interface contact, boost anode reaction kinetics, and increase proton injection into electrolyte. As a result, the P-SOEC yields high current density of 0.83 A cm−2 at 600 °C in 1.3 V among all the reported Zr-rich side cells. This work not only offers an efficient functional interlayer for P-SOECs but also holds the potential to achieve P-SOECs with high performances and long-term stability.
  • Quintero, D., Matsuya, H., Iwai, M., Kitano, S., Fushimi, K., Habazaki, H.
    ACS Applied Materials and Interfaces 16 (1) 1944-8252 2024
  • Hadi Sena, Sho Kitano, Hiroki Habazaki, Masayoshi Fuji
    Energy Advances 2 (9) 1495 - 1499 2023/08/08 
    Semiconductor photocatalytic water splitting is a promising method to address the worldwide energy issues. Fast carrier recombination and the limited visible-light absorption are two main challenges to be overcome, and designing p-n heterojunctions is an effective solution. In this study, two direct band gap semiconductors are selected to form a p-n heterojunction. The results show that liquid phase epitaxy of a thick film p-type CuGaO2 on an n-type GaN substrate is effective for the splitting of water into hydrogen and oxygen.
  • Hisato Matsuya, David Quintero, Sho Kitano, Hiroki Habazaki
    ECS Journal of Solid State Science and Technology 12 (7) 2162-8769 2023/07 
    Aluminum solid electrolytic capacitors using a conductive polymer as a cathode material has the advantages of low equivalent series resistance (ESR) and high thermal stability compared to aluminum electrolytic capacitors using liquid electrolytes. A disadvantage of aluminum solid electrolytic capacitors with a conductive polymer is the low breakdown voltages, limiting the operating voltage of the capacitors to ∼100 V or less. In this study, for a possible future increment of the withstand voltages of solid electrolytic capacitors, PEDOT:PSS-coated aluminum with an amorphous or crystalline alumina layer formed at 500 V has been characterized using SEM, STEM/EDS, and conductive AFM to understand the distribution of PEDOT:PSS conductive polymer and its influence on the electric properties. The crystalline alumina layer, developed beneath a porous hydrated alumina layer, contains many voids, which increase the leakage current compared to the void-less amorphous alumina layer. However, the crystalline alumina layer with PEDOT:PSS exhibits a higher breakdown voltage than the amorphous one. The limited incorporation of PEDOT:PSS into the inner part of the porous hydrated alumina layer may introduce a resistive surface layer, possibly contributing to the increased dielectric breakdown.
  • Laras Fadillah, Damian Kowalski, Sho Kitano, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    Electrochemistry Communications 149 1388-2481 2023/04 
    This study demonstrates the highly enhanced photocatalytic activity of Fe2O3 nanotubes by making a heterojunction with Fe2WO6 and doping of W6+ ions into the α-Fe2O3 phase for water splitting and decomposition of an organic pollutant. Both nanotubular and compact Fe2O3/Fe2WO6 films are formed by anodizing the magnetron-sputtered Fe-9 at% W alloy in fluoride-containing ethylene glycol electrolyte and subsequent annealing at 450 °C. Their photocatalytic activities are compared with W-free nanoporous Fe2O3 film formed on high-purity Fe. The nanotubular Fe2O3/Fe2WO6 film exhibits a markedly enhanced photoelectrochemical oxygen evolution reaction and photocatalytic degradation of methylene blue compared with the nanoporous W-free Fe2O3 film. Because of the larger surface area, the nanotubular Fe2O3/Fe2WO6 film reveals further increased activity than the compact Fe2O3/Fe2WO6 film. The STEM study discloses the dispersion of Fe2WO6 nanoparticles in the α-Fe2O3 phase after annealing at 450 °C, and XRD analysis shows the possible doping of W species into α-Fe2O3. The formation of the W-doped α-Fe2O3/Fe2WO6 heterojunction likely promotes the separation of photogenerated electron-hole pairs, enhancing photocatalytic activity. Hence, the nanotubular Fe2O3/Fe2WO6 film is a possible candidate for visible-light-driven photocatalysts.
  • Huijun Yang, Ruijie Zhu, Yang Yang, Ziyang Lu, Zhi Chang, Ping He, Chunyu Zhu, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki, Haoshen Zhou
    Energy and Environmental Science 1754-5692 2023 
    The re-evaluation of zinc (Zn)-based energy storage systems satisfies emerging demands in terms of safety and cost-effectiveness. However, the dendritic Zn morphology and resulting short circuits within the cell remain long-standing challenges. Moreover, diverse Zn dendrite propagation exacerbates the situation, particularly during high-capacity battery operation. The high-capacity Zn deposition/dissolution process involves numerous sites and interfaces, which leads to disordered Zn dendrite growth because of the inherent diffusion-limited aggregation mechanism. Here, we demonstrate a robust polymer separator that serves as both a physical barrier to stress-governed metal electrodeposition and an ionic charge carrier for fast Zn2+ diffusivity. These insights enable an ultra-high Zn reversibility (99.97%) for 2000 cycles at 20.0 mA cm−2 and 4.0 mA h cm−2, and a high-energy-density (115 W h kg−1 based on pouch cell) Zn-MnO2 full battery with an aggressive N/P capacity ratio (1.35). The abundant and environmentally friendly cell components make it a sustainable battery technology for global electrification.
  • Sho Kitano, Yuki Sato, Reiko Tagusari, Ruijie Zhu, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    RSC Advances 13 (16) 10681 - 10692 2023 
    Simple and durable: the multi-metal oxyhydroxide and spinal oxide composite catalyst containing Co, Fe and Ni are synthesized from hydroxide and layered double hydroxide composite precursors and shows excellent bifunctional ORR/OER activities.
  • Katsuya Akimoto, Ning Wang, Chunmei Tang, Kai Shuto, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS APPLIED ENERGY MATERIALS 2574-0962 2022/09 
    Efficient power generation with protonic solid oxide fuel cells (H-SOFCs) remains challenging because the mismatch between the primary ion carriers of the electrolyte and the cathode limits the effective cathode reaction area to the gas-electrolyte-cathode triple-phase boundary (TPB), resulting in large cathodic overpotentials at low operating temperatures. Herein, we report the role of functional layers between an electrolyte and a cathode in reducing the cathodic reaction resistance at the TPB. Thin-film fuel cells with BaZr0.1Ce0.7Y0.1Yb0.1O3-delta (BZCYYb1711) electrolytes were fabricated using a dense La0.5Sr0.5Co0O3-delta (LSC) nanofilm (approximately 100 nm) as a cathode functional layer (CFL) with the typical oxide ion/electron mixed conductor La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF), LSC, and the less-active Sb0.1Sn0.9O2 (ATO). The peak power densities of the cells increased by >100% when using a CFL, and cells having an LSC cathode and CFL achieved power densities of 500 mW cm(-2) at 500 degrees C. The distribution of relaxation times in the impedance spectra revealed the CFL's effect on the ohmic and polarization resistances. Crucially, cells without a CFL had large ohmic resistances because the proton-accessible electrode areas were confined to the gas-cathode-electrolyte TPB. However, the resistance decreased with the CFL because coupled partial proton conductivity and electrocatalytic activity of the LSC nanofilms increased the proton-accessible electrode area. The cells without a CFL showed a large polarization resistance because of the sluggish diffusion of O adatoms over the cathode resulting from the increased TPB length. This resistance decreased by >70% with an LSC CFL because the cells did not require long-range O diffusion because of the significantly extended proton-accessible reaction area near the gas-CFL-cathode TPB. Thus, using interfacial layers is an alternative way to design new cathode materials having low cathodic polarization for H-SOFCs.
  • Masahiro Nishimoto, Zetao Xiong, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 427 0013-4686 2022/09 
    This study investigates the oxygen evolution reaction (OER) activity of the FeNiCo alloy anodized at several temperatures in a fluoride-containing ethylene glycol electrolyte. When the alloy is anodized at 10 V, the OER activity in KOH electrolyte is highly enhanced on the alloy anodized at 15 and 20 degrees C, at which non-uniform film growth proceeds. The fraction of the locally thick film regions increases with anodizing time, enhancing the OER activity. Only thin porous films are formed at >= 30 degrees C even though the anodizing current is high because of the promotion of film dissolution at high electrolyte temperatures. Because of the thickness limitation, the OER activity is relatively low when the anodic films are formed at >= 30 degrees C. A good correlation is found between the OER activity and the electric double-layer capacitance; thicker porous anodic films enhance the OER activity. The anodic film formed at each temperature consists of a rutile-type (FeNiCo)F-2 phase, but in KOH electrolyte, it is converted readily to an oxyhydroxide phase, which is OER active. A similar to 2 mu m-thick film obtained under the optimum anodizing condition reduces the overpotential of OER to 245 mV at 10 mA cm(-2) in 1.0 mol dm(-3) KOH electrolyte.
  • Tatsuyuki Takano, Hisato Matsuya, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    Applied Surface Science 592 0169-4332 2022/08/01 
    Hydration treatment of aluminum in hot water is important for its corrosion protection, and also this treatment is a crucial pretreatment in forming dielectric crystalline alumina films on the aluminum anode in aluminum electrolytic capacitors. In this study, a two-layer hydrated film formed on high purity aluminum by hot water treatment was examined using a combination of glow discharge (GD) sputtering and Raman spectroscopy. In addition, the anion penetration behavior through the hydrated alumina layer during anodizing aluminum in several electrolytes was investigated. The results indicate that the outer layer, with a nanosheet-like morphology, consists of a crystalline pseudo-boehmite phase, whereas the relatively compact inner layer is amorphous or poorly crystalline. The inner amorphous layer plays a crucial role in the incorporation of the anions, which is found for the first time. When hydrated aluminum is anodized in phosphate, silicate, and tungstate electrolytes, the inner hydrated alumina layer impedes the penetration of these electrolyte anion species. In contrast, boron species readily penetrate the hydrated alumina layer into the barrier layer formed by anodization in boric acid. This anion-specific incorporation behavior is discussed in terms of ion-selective permeation in the amorphous hydrated alumina layer.
  • Hajime Toriumi, Genki Kobayashi, Takashi Saito, Takashi Kamiyama, Takaaki Sakai, Takahiro Nomura, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    CHEMISTRY OF MATERIALS 34 (16) 7389 - 7401 0897-4756 2022/08 
    Oxyhydrides have excellent potential as electrochemical and catalytic materials owing to the synergistic effects of the conductivity and redox activity of the hydride (H-) ion. However, harsh preparation conditions and their pyrolytic nature limit their applications. Herein, we discover highly durable oxyhydride perovskite BaZr0.5In(II)(0.5)O2.25H0.5 with enhanced H- ion-electron mixed conductivity. BaZr0.5In-(III)O-2.75, as the parent phase, was reductively hydrogenated to BaZr(0.5I)n(II)(0.5)O2.25H0.5 as via simple H-2 gas annealing at 800 degrees C under an ambient pressure with the incorporation of H- ions with simultaneous oxygen vacancy formation. Membrane devices comprising dense BaZr0.5In0.5O2.25H0.5 films on porous Ni-cermet supports were fabricated by conventional sintering and postreduction because low lattice contraction (-0.07%) following hydrogenation allowed for the bulk hydrogenation of BaZr0.5In0.5O2.75 sinters without structural collapse. The resulting devices exhibited higher hydrogen permeability than protonic ceramic ones at 500 degrees C because BaZr0.5In(II)(0.5)O2.25H0.5, allows H- ion hopping between the nearest-neighbor anion sites due to the significantly high oxygen deficiency (25% of O sites are vacant), giving rise to a H- ion conductivity of 10(-3) S cm(-1). Given their superior H- ion conductivity and ease of manufacturing, the synthesized materials have great potential for applications in mixed conducting electrodes and hydrogen-permeable membrane supports of ceramic electrochemical cells.
  • Chunmei Tang, Ning Wang, Ruijie Zhu, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    Journal of Materials Chemistry A 10 (29) 15719 - 15730 2050-7488 2022/07/04 
    Protonic solid oxide electrolysis cells (P-SOECs) are one of the most efficient devices for hydrogen production from renewable electricity, but the lack of suitable anodes has led to serious concerns in terms of high anodic overpotentials and low conversion efficiencies. Herein, we demonstrated that both the steam electrolysis performances and efficiency of P-SOECs based on a BaZr0.6Ce0.2Y0.1Yb0.1O3−δ electrolyte can be significantly improved by employing a Ba0.95La0.05Fe0.8Zn0.2O3−δ (BLFZ) H+/O2−/e− triple-conductor thin film at the anode/electrolyte interface as an anode functional layer (AFL). A broad survey of electrolysis performances was conducted for cells with various AFLs, including H+/O2−/e− triple conductors and O2−/e− double conductors. This investigation clarified that BLFZ can significantly decrease the ohmic and polarization resistances, and thus, greatly increase the electrolysis current. Because of the high proton conductivity and excellent electrochemical kinetics, the BLFZ AFL can allow the anodic reactions to occur over the surfaces of the BLFZ AFL without the long-range diffusion of oxygen species over the anode. Moreover, the BLFZ AFL can depress the hole injection in the electrolyte because the water partial pressure remained relatively high in comparison to the oxygen partial pressure at the AFL/electrolyte interface due to the excellent proton conductivity. Hence, the BLFZ cell offered a high electrolysis current of 570 mA cm−2 at 1.3 V, and an increased efficiency of 75% from 46% for a cell without the BLFZ AFL at 500 °C. These results reveal that an effective AFL can boost the anodic reaction and optimize the efficiency of obtaining P-SOECs with excellent performances and outstanding ability for hydrogen production. Transition metal oxides combining high proton and low oxide ion conductivities could be promising AFLs for highly efficient P-SOECs.
  • Hiroyuki Okada, Etsushi Tsuji, Miho Hisada, Sho Kitano, Hiroki Habazaki, Satoshi Suganuma, Naonobu Katada
    SUSTAINABLE ENERGY & FUELS 6 (11) 2709 - 2717 2398-4902 2022/05 
    Towards the development of active and robust electrocatalysts for the oxygen evolution reaction (OER) to realize water splitting and CO2 electroreduction by renewable energies under practical conditions, brownmillerite-type composite oxide Ca2Fe2-xCoxO5 was synthesized by a sol-gel method and examined for the OER under neutral conditions. A pure brownmillerite-type Ca2Fe2-xCoxO5 phase, which was categorized as an oxygen-deficiency-ordered perovskite-type structure, was synthesized in a range of x = 0-1.25. Brownmillerite-type Ca2FeCoO5 showed higher activity and durability for the OER in a neutral solution than perovskite-type LaFe0.5Co0.5O3 and SrFe0.5Co0.5O3-delta. Furthermore, the durability of Ca2Fe2-xCoxO5 was drastically improved by increasing the Co content from x = 1 to 1.25. Ca2Fe0.75Co1.25O5 was remarkably durable for about 70 h during the OER in a neutral solution whereas Ca2FeCoO5 lost activity within 20 h, and perovskite-type oxides lost activity within a few hours. The detailed analysis of structures and compositions of local regions of Ca2Fe2-xCoxO5 and their changes by the reaction based on electron microscopy clarified the important role of the brownmillerite structure itself in catalytic activity under neutral conditions, while, under alkaline conditions, it has been known that the amorphous phase derived from brownmillerite mainly played the role of active species.
  • Ruijie Zhu, Zetao Xiong, Huijun Yang, Tianhong Huang, Seongwoo Jeong, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki, Chunyu Zhu
    Energy Storage Materials 46 223 - 232 2405-8297 2022/04 
    Rechargeable aqueous zinc (Zn) batteries have attracted great interests because of its inherent safety and costeffectiveness. However, the uncontrollable Zn dendrite formation in aqueous electrolyte restricts its reversibility for long-life application. The bulge or passivation layer in pristine Zn surface serves as nuclei for large amount of Zn crystal aggregation and inhomogeneous Zn electrodeposition. Here, for the first time, we demonstrate a simple, effective, and non-corrosive electropolishing strategy to develop a smooth and clean Zn metal as compared with burdensome and unreliable mechanical polishing method in lab-scale research. After removing the primitive passivation layer, the fresh Zn anode can survive at a high current density of 40 mA cm(-2) over 6000 times. Moreover, the electropolished Zn gains more consistent and reliable electrochemical behaviors which contributes to study the mechanism of Zn electrodeposition and clarify the effectiveness of protective strategies in the follow research.
  • Sho Kitano, Tomohiro G. Noguchi, Masamichi Nishihara, Kazutaka Kamitani, Takeharu Sugiyama, Satoru Yoshioka, Tetsuya Miwa, Kazunari Yoshizawa, Aleksandar Staykov, Miho Yamauchi
    Advanced Materials 34 (16) 2110552 - 2110552 0935-9648 2022/03/11 
    Abstract The oxygen evolution reaction (OER) is a critical element for all sorts of reactions that use water as a hydrogen source, such as hydrogen evolution and electrochemical CO2 reduction, and novel design principles that provide highly active sites on OER electrocatalysts push the limits of their practical applications. Herein, Au‐cluster loading on unilamellar exfoliated layered double hydroxide (ULDH) electrocatalysts for the OER is demonstrated to fabricate a heterointerface between Au clusters and ULDHs as an active site, which is accompanied by the oxidation state modulation of the active site and interfacial direct OO coupling (“interfacial DOOC”). The Au‐cluster‐loaded ULDHs exhibit excellent activities for the OER with an overpotential of 189 mV at 10 mA cm−2. X‐ray absorption fine structure measurements reveal that charge transfer from the Au clusters to ULDHs modifies the oxidation states of trivalent metal ions, which can be active sites on the ULDHs. The present study, supported by highly sensitive spectroscopy combining reflection absorption infrared spectroscopy and modulation‐excitation spectroscopy and density functional theory calculations, indicates that active sites at the interface between the Au clusters and ULDHs promote a novel OER mechanism through interfacial DOOC, thereby achieving outstanding catalytic performance.
  • Hajime Toriumi, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS Omega 2470-1343 2022/03/09
  • Yoshitaka Aoki, Shinichi Nishimura, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki
    ACS Applied Energy Materials 5 (2) 1385 - 1389 2574-0962 2022/01/18 
    This study is the first to report the development of hydrogen-permeable metal support electrolysis cells (HMECs) bearing a heterojunction of H+-conducting BaZrxCe0.8-xY0.2O3-delta (BZCY) electrolyte and H-permeable Pd. The HMECs could conduct galvanostatic steam electrolysis at 0.15 A cm(-2); the HMECs maintained a voltage of similar to 1.2 V and achieved a Faradaic efficiency of similar to 80% at 500 degrees C, which are higher than the values predicted for H+-conducting ceramic electrolysis cells with porous cathodes and anodes. The relatively high efficiency of HMECs could be attributed to a decrease in the hole carriers due to the defect thermodynamic equilibria near the BZCY/Pd heterointerface.
  • Zhu, R., Xiong, Z., Yang, H., Wang, N., Kitano, S., Zhu, C., Aoki, Y., Habazaki, H.
    Advanced Functional Materials 33 (8) 1616-3028 2022 
    Rechargeable aqueous zinc (Zn)-ion batteries (RAZIBs), which use non-flammable aqueous electrolytes and low-cost electrode materials, show great potential to boost the development of safe, cost-effective, and highly efficient energy storage systems. The adoption of lightweight and inexpensive aluminum (Al) as current collectors seems to be a good vision, but Al exhibits an easily-corroded nature and a high impedance in aqueous electrolytes, making it a challenge to realize the utilization of Al current collector in RAZIBs. In this study, through the direct current magnetron sputtering, niobium (Nb) coated Al (Al-Nb) foils are prepared, which shows superior corrosion-resistance in an aqueous solution, while maintaining a satisfying electronic conductivity. Moreover, the Al-Nb foils can be adopted to both anode and cathode current collectors while exhibiting high coulombic efficiency and good cycling stability even when they are tested under a condition that can meet the real-world application demands, e.g., the Zn||Al-Nb half-cell shows an average coulombic efficiency of 99.17% in 320 cycles under a current density of 25 mA cm−2 and a galvanizing capacity of 6.25 mAh cm−2. The superior performance of the modified Al current collectors may mark a significant step toward the development of high-energy-density aqueous batteries.
  • Shinichi Hata, Yuki Sakai, Nanami Tani, Sho Kitano, Hiroki Habazaki, Akari Hirakawa, Hinako Tanaka, Yusuke Inomata, Toru Murayama, Masatake Haruta, Yukou Du, Yukihide Shiraishi, Naoki Toshima
    ACS Applied Nano Materials 5 (11) 16231 - 16241 2022 
    Bimetallic or alloyed nanoparticles (NPs) are important materials that often exhibit chemical properties different from those of their monometallic counterparts. However, access to uniformly alloyed bimetallic particles, particularly in the Pd-Rh system, is difficult because of the thermodynamic immiscibility of the individual metals. Herein, we propose a method for accumulating Pd-Rh alloy particles on the surface of zeolite imidazolide framework-67 (ZIF-67), a chemically stable metal-organic framework, under mild conditions at 25 °C. The degradation of methyl orange was used to test the applicability of the resultant material as a heterogeneous catalyst. A turnover frequency of 38.5 h-1 was recorded for Pd0.12Rh0.88/ZIF-67, which is higher than that of catalysts with either Pd (17.2 h-1) or Rh (16.5 h-1). The acceleration of methyl orange decomposition was attributed to electron transfer from Pd to Rh in the alloy particles due to the differences in Pauling electronegativity and an increase in metallic Rh on the catalyst surface. No metal leakage or structural degradation of the ZIF-67 support was observed during the catalytic reaction. Pd0.12Rh0.88/ZIF-67 could actively degrade methyl orange, congo red, and methylene blue. The structure of the catalyst remained intact even when a mixed solution of all three dyes was circulated for 60 min in a fixed-bed system, and the catalyst conversion rate exceeded 99.7%. Our results collectively demonstrate the successful preparation of Pd-Rh-supported catalysts and their application to the continuous reduction of multicomponent dye mixtures. The metal NP-MOF composites prepared using the proposed approach are free from MOF pore damage and can maintain their specific surface area. Therefore, this strategy could give impetus to research on catalytic applications of NP-MOF composites.
  • Yuki Sato, Naohito Yamada, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    Journal of Materials Chemistry A 10 (15) 8208 - 8217 2050-7488 2022 
    This study revealed excellent corrosion resistance of the highly graphitized platelet-type carbon nanofibers due to hydroxyl passivation of the carbon edge plane.
  • Ruijie Zhu, Huijun Yang, Wei Cui, Laras Fadillah, Tianhong Huang, Zetao Xiong, Chunmei Tang, Damian Kowalski, Sho Kitano, Chunyu Zhu, Daniel R. King, Takayuki Kurokawa, Yoshitaka Aoki, Hiroki Habazaki
    Journal of Materials Chemistry A 10 (6) 3122 - 3133 2050-7488 2022 
    Although shear modulus of gel electrolytes is generally far less than that of Zn metal, a modified mechanical suppression effect of hydrogel on the growth of Zn dendrites still can be confirmed, and a Zn–MnO2 cell with high capacity is achieved.
  • Masahiro Nishimoto, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS Sustainable Chemistry and Engineering 9 (28) 9465 - 9473 2168-0485 2021/07/19 
    Developing highly active and durable electrocatalysts, consisting of earth-abundant elements, for oxygen evolution reaction (OER) is pivotal for large-scale water splitting for hydrogen production. Herein, we report that the commercially available FeNiCo alloy can be converted to a highly active electrocatalyst for OER by galvanostatic anodizing in a fluoride-containing ethylene glycol electrolyte. Anodizing of the alloy develops a porous film consisting of the (FeNiCo)F2 phase, which is readily converted to a highly active porous oxyhydroxide during anodic polarization in a KOH electrolyte. The anodized alloy exhibits high activity and high durability for OER with an overpotential as low as 0.26 V at a current density of 10 mA cm-2. The present study demonstrates that a simple and cost-effective anodizing process can be used to form a highly active OER electrode from a low-cost, practical, iron-based alloy. In addition, we found that fluorides containing Fe, Ni, and Co are excellent precursors for the formation of oxyhydroxides exhibiting high OER activity and durability.
  • Shinichi Hata, Keita Iwamoto, Sho Kitano, Hiroki Habazaki, Akari Hirakawa, Nanami Tani, Yukou Du, Yukihide Shiraishi, Naoki Toshima
    Colloids and Interface Science Communications 43 2021/07 
    A room-temperature wet chemical method was developed for preparing a catalyst comprising Pd nanoparticles (NPs) supported on a zeolite imidazolide framework-8 (ZIF-8) surface (Pd/ZIF-8). The Pd/ZIF-8 catalyst exhibited a large surface area and high crystallinity, almost equal to those of pristine ZIF-8. The binding of the Pd NPs deposited on the ZIF-8 surface was shown to occur at the ZIF-8 particle surface rather than throughout the metal–organic framework (MOF) structure. The method was also suitable for complexing ZIF-8 with several other, nano-sized noble metals. The Pd/ZIF-8 heterogeneous catalyst was applied in the NaBH₄-reduction of isomeric nitrophenols in both batch and fixed-bed systems. The catalyst was universally active against the isomeric nitrophenols, with a catalytic conversion of 99.7% after 1 h of cycling in the fixed-bed system. Thus, we have demonstrated the preparation of stable, supported catalysts and their application to the continuous reduction of multi-component nitrophenol mixtures.
  • Chunmei Tang, Katsuya Akimoto, Ning Wang, Laras Fadillah, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    Journal of Materials Chemistry A 9 (24) 14032 - 14042 2050-7488 2021/06/28 
    Protonic solid oxide steam electrolysis cells (P-SOECs) based on BaZrxCe0.8−xYb0.1Y0.1O3−δproton conductors are promising to produce “green” hydrogen from renewable energy at intermediate temperatures. Herein, we demonstrate that the electrolysis performances of a cell with a high-Zr-content electrolyte, BaZr0.6Ce0.2Y0.1Yb0.1O3−δ(BZCYYb6211), can be significantly improved by using a La0.5Sr0.5CoO3−δ(LSC) thin film (∼90 nm) as an anode functional layer (AFL). Electrochemical measurements indicated that LSC-AFL significantly reduced the barrier height for the electrochemical proton incorporation reaction at the gas-electrolyte-electrode triple-phase boundary. Hence, both the ohmic and polarization resistances of the BZCYYb6211 cell decreased from 0.52 and 0.98 Ω cm2to 0.26 and 0.57 Ω cm2, respectively, with the LSC-AFL at 600 °C. In addition, the BZCYYb6211 cell achieved a high electrolysis current of 1.22 A cm−2at 1.3 V with a Faraday efficiency of approximately 80%, which was equivalent to that (1.13 A cm−2) of the cell with a state-of-the-art electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3−δ(BZCYYb1711). BZCYYb6211 with LSC-AFL showed good durability at 500 °C under high steam conditions with an applied current of 1 A cm−2for 100 h. These results revealed that the introduction of an AFL is an effective method to obtain P-SOECs with excellent performances and durability.
  • Ruijie Zhu, Huijun Yang, Laras Fadillah, Zetao Xiong, Damian Kowalski, Chunyu Zhu, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    Journal of Materials Chemistry A 9 (22) 13332 - 13343 2050-7488 2021/06/14 
    On the way to achieve a practical lithium (Li) metal anode for next-generation batteries, the formation and accumulation of inactive “Dead Li” is an unavoidable issue. The accumulation of “Dead Li” leads to increased internal mass-transfer resistance which seriously deteriorates the performance of Li metal batteries during long-term cycling. In this study, by accommodating Li metal into a copper oxide coated carbon scroll host with a vertically aligned framework which possesses a unique low-tortuosity structure, the cycling stability of the Li anode can be significantly improved. It is demonstrated that the mass-transfer resistance and the concentration polarization near the Li metal surface can be greatly alleviated by using this low-tortuosity anode structure design. “Dead Li” that is formed on the electrode surface can automatically fall into the inner tunnel of the carbon host, endowing the anode with the capability of “Dead Li” self-cleaning. As a result, our new Li electrode can remain electrochemically active even after 1000 h in a symmetric cell measurement from 1 mA cm−2to 1 mA h for 500 cycles. The as-reported structure design of the Li anode in this work is compatible with most of the modification technologies that have been applied to conventional Li foil electrodes, providing this new Li anode with a great potential to be applied in subsequent Li anode studies.
  • Yoshitaka Aoki, Kentaro Takase, Hisao Kiuchi, Damian Kowalski, Yuki Sato, Hajime Toriumi, Sho Kitano, Hiroki Habazaki
    Journal of the American Chemical Society 0002-7863 2021/04/23
  • Seong Woo Jeong, Ning Wang, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    Advanced Energy Materials 1614-6832 2021 
    Among several types of low-temperature solid oxide fuel cells, hydrogen-permeable metal-supported fuel cells (HMFCs) are devices that can achieve outputs of approximately 1.0 W cm−2 at 400 °C. This work clarifies the mechanism for promoting the cathode reaction on proton-conducting ceramics at such low temperatures. Combined numerical and electrochemical analyses demonstrate that blocking minor oxide ion conduction at metal/oxide heterojunctions promotes proton transfer at the cathode/electrolyte interfaces, thereby enhancing the turnover frequency of the cathode reaction at the triple-phase boundary. The electrolyte membrane in HMFCs is forced to gain extra protons to compensate for the charge of oxide ions that accumulate because of the blocking, resulting in an increment of the proton concentration gradients near the cathode/electrolyte interfaces so as to eject the excess amount of proton. The interfacial proton concentration gradient increases and thus the cathode polarization resistance of HMFCs decrease with the cell bias. An HMFC with a highly oxygen-deficient BaZr0.5Sc0.5O3−δ electrolyte accumulates a large amount of oxide ions, thereby developing large concentration gradients. Thus, it achieves a cathode reaction resistance of 0.54 Ω cm2 at 400 °C with conventional cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ. These findings demonstrate that HMFCs can efficiently utilize overpotential.
  • Kensuke Sakuraba, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS Applied Materials and Interfaces 13 (37) 45089 - 45096 1944-8244 2021 
    Slippery liquid-infused porous surfaces (SLIPSs) can be formed by impregnating lubricants in porous surfaces with low surface energy. In this study, SLIPSs have been obtained on practically important aluminum with a porous anodic alumina layer by impregnating lubricants containing organic additives. The additive-containing lubricants change the surface slippery even without prior organic coating of the porous alumina surface. The additive-containing SLIPSs reveal a low water sliding angle of <5° and markedly improved corrosion resistance in an acetic acid solution containing chloride. The SLIPSs are formed by the in situ adsorption of the organic additives on the porous alumina surface. The scratched defects induce corrosion of the organic coating-type SLIPSs, whereas the additive-containing SLIPSs sustain high corrosion resistance even after introducing scratch defects. The adsorption of the organic additive in lubricants and refilling of the lubricant are responsible for the self-healing of the corrosion resistance. Thus, the additive-containing SLIPSs are promising self-healing corrosion-resistant surfaces.
  • Sho Kitano, Mei Lee Ooi, Tomokazu Yamamoto, Syo Matsumura, Miho Yamauchi
    Bulletin of the Chemical Society of Japan 94 (4) 1292 - 1299 0009-2673 2021 
    Electrooxidation of NH has gained extensive attention for energy and environmental applications such as fuel cells and water purification. In this study, carbon-supported simple metal-nanoparticle, binary- and ternary-nanoalloy (NA) catalysts composed of Fe-group elements, i.e., Fe, Co and Ni, were synthesized and their catalytic performance for NH electrooxidation in alkaline media was investigated. Cyclic voltammetry and chronoamperometry revealed that Ni-containing catalysts show appropriate activities for NH electrooxidation and the catalytic performances of Fe-group catalysts depend on affinity between constituent metals and nitrogen. Each Fe-group element exhibited distinctive catalytic features for the NH electrooxidation, i.e., Ni ensured chemical stability, Fe effectively reduced overpotential and Co increased current density. The ternary NA catalyst showed excellent activities due to combination of all the catalytic features and synergetic effects exerted by the alloying. 3 3 3 3
  • Ning Wang, Hajime Toriumi, Yuki Sato, Chunmei Tang, Takashi Nakamura, Koji Amezawa, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS APPLIED ENERGY MATERIALS 4 (1) 554 - 563 2574-0962 2021/01 
    Highly efficient mixed H+/e(-)/O2- triple conducting air electrodes are indispensable for improving the electrochemical performance of protonic ceramic fuel cells and electrolysis cells (PCFC/ECs) operating at intermediate temperatures. This study demonstrates that single perovskite-type La0.8Sr0.2Co1-xNixO3-delta families (LSCN, x = 0-0.3) are efficient H+/e(-)/O2- triple conductors due to a pronounced hydration ability at elevated temperatures with a related enthalpy of -107 kJ mol(-1). Thermogravimetry confirmed that the oxides were capable of a 0.01 mole fraction proton uptake at 600 degrees C and p(H2O) of 0.023 atm. Reversible protonic ceramic cells were fabricated using these oxides as an air electrode and exhibited promising performance with a peak power density of 0.88 W cm(-2) in fuel cell mode and an electrolysis current of 1.09 A cm(-2) at a thermal neutral voltage in electrolysis cell mode at 600 degrees C. Impedance analysis confirmed that the polarization resistance of the La0.8Sr0.2Co0.2Ni0.3O3-delta cell was 0.09 Omega cm(2) under an open circuit potential at 600 degrees C, which is much smaller than the polarization resistances reported for cells with a single or double perovskite-type triple conductor. The current results indicate that mixed H+/e(-)/O2- triple phase conducting LSCN oxides are promising air electrodes for protonic ceramic cells operating in the intermediate temperature region at approximately 600 degrees C.
  • Ryota Yamamoto, Damian Kowalski, Ruijie Zhu, Keisuke Wada, Yuki Sato, Sho Kitano, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED SURFACE SCIENCE 537 0169-4332 2021/01 
    Copper is an important practical metal with a high thermal conductivity that is widely used as a heat exchanger material. However, a liquid film often forms on the Cu surface through water vapor condensation, causing a large resistance to heat transfer. To address this issue, a superhydrophobic Cu metal nanowire surface is developed herein via Cu anodizing in a KOH electrolyte to form Cu(OH)(2) nanowires, followed by hydrogen reduction at an elevated temperature and the application of a wet organic coating. The hydrogen treatment reduces the hydroxide to the metal while maintaining the nanowire morphology. The superhydrophobic Cu metal nanowire surface exhibits effective removal of water droplets formed through water vapor condensation. Furthermore, the metal nanowire surface exhibits highly improved heat transfer compared with the Cu(OH)(2) nanowire surface. Therefore, the combined process of anodizing and hydrogen reduction is a simple approach that forms an effective superhydrophobic Cu surface with high thermal conductivity.
  • Naohito Yamada, Sho Kitano, Yuya Yato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS APPLIED ENERGY MATERIALS 3 (12) 12316 - 12326 2574-0962 2020/12 
    A simple anodizing technique has been employed to develop highly active electrocatalysts that can be applied to the oxygen evolution reaction (OER) in alkaline media. NiFe alloys were electrodeposited and anodized to form a porous electrocatalytic layer. This approach produces highly active electrodes without the need for noble metals, binders, or conductive carbon additives. The as-anodized electrode initially exhibits poor OER activity in 1.0 mol dm(-3) KOH; however, the effects of potential cycling improve the OER activity to an extent that an overpotential as low as 0.26 V at 10 mA cm(-2) is observed for the anodized Ni-11.8 at. % Fe electrode. Although significant in situ activation is achieved with anodized NiFe electrodes, this activation is less significant for as-deposited NiFe or anodized Ni electrodes. Furthermore, OER activity is observed to be composition-dependent, with the Ni-11.8 at. % Fe electrode exhibiting the greatest activity. A porous fluoride-rich, Fe-doped Ni oxyfluoride layer produced by anodizing is converted via potential cycling to an amorphous or poorly crystalline Fe-doped Ni(OH)(2) layer with a nanoflake-like morphology. The high activity is maintained even after the removal of most of the fluoride. Thus, the F-rich, Fe-doped Ni oxyfluoride is a promising precursor to develop a highly active OER electrode.
  • Ryoya Masuda, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Taisuke Nozawa, Hiroki Habazaki
    COATINGS 10 (11) 2020/11 
    In this study, zinc is anodized at different voltages in 0.1 mol center dot dm(-3) KOH electrolyte to form nanoporous anodic films. Dark-colored anodic films are formed at anodizing voltages <= 6 V, whereas colorless anodic films are developed at voltages >= 7 V. The anodic films formed at all voltages consist of crystalline ZnO, which was identified by X-ray diffraction and Raman spectroscopy. The Raman spectra of the dark-colored anodic films show the enhanced intensity of the LO phonon mode due to electric-field-induced Raman scattering, which may be associated with the presence of metallic Zn nanoparticles in the anodic films. Scanning electron micrographs and transmission electron micrographs of the cross-section of the dark-colored anodized zinc reveal the formation of two-layer porous anodic films with a highly rough metal/film interface. In contrast, nanoporous anodic films of uniform thickness with a relatively flat metal/film interface are formed for the colorless anodized zinc. The transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS) analysis suggested the presence of zinc nanoparticles in the dark-colored anodic films. The non-uniform anodizing and the formation of metal-nanoparticle-dispersed porous anodic films cause the formation of dark-colored anodic films on zinc.
  • Takashi Fukushima, Manabu Higashi, Sho Kitano, Takeharu Sugiyama, Miho Yamauchi
    Catalysis Today 351 12 - 20 0920-5861 2020/07/01 
    Performance of a polymer electrolyte alcohol electrosynthesis cell (PEAEC) using a glycolic acid (GC)/oxalic acid (OX) redox couple was enhanced via the multiscale approach, i.e., increase of reaction rate on an anode by employing nanometer-scale (nanoscale) IrO catalysts and increase of selectivity for GC production via optimization of cell structures, i.e., a millimeter-scale approach. We prepared nanoscale IrO anode catalyst, which is mixture of IrO nanoparticles (d = 3.7 ± 1.8 nm) and their agglomerates (d < 200 nm). The linear sweep voltammetry measurement for water oxidation revealed that the nanoscale IrO catalyst deposited on a porous carbon paper reduces overpotential for water oxidation by 196 mV from that obtained with an anode composed of commercial microscale IrO grans. Furthermore, application of the nanoscale IrO catalyst on porous titanium paper not only improved durability but also doubly enhanced water oxidation performance. We examined various PEAEC architectures composed of the nanoscale IrO applied Ti anode. Both nanometer- and millimeter-scale approaches realized the best PEAEC performance for GC production, i.e., 59.4% of energy conversion efficiency with 97.1% of Faradaic efficiency for the GC production at 1.8 V and 98.9% of conversion for 3 M OX, which is an almost saturated aqueous solution at operating temperature of the PEAEC (60 °C). 2 2 2 2 2 2 2
  • Yuki Sato, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Naoko Fujiwara, Tsutomu Ioroi, Hiroki Habazaki
    ELECTROCHEMISTRY 88 (6) 566 - 573 1344-3542 2020 
    Development of highly active bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is required for air electrodes of zinc-air secondary batteries (ZAB). In this study, we synthesize spinel-type MnCo2O4 (MCO) nanoparticles on highly graphitized platelet-type carbon nanofibers (pCNF) via a solvothermal method. The pCNF is selected as carbon support in this study because of the excellent stability against anodic degradation under the OER condition. The MCO nanoparticles of 2-5 nm in diameter are uniformly dispersed on pCNF and the catalyst exhibits high activities for ORR due to strong interaction pCNF and MCO, in addition to the improvement of OER activities. The MCO/carbon hybrids show comparable electrocatalytic performances to state-of-the-art bifunctional electrodes for OER and ORR. (C) The Author(s) 2020. Published by ECSJ.
  • J. F. Cheng, J. Yang, S. Kitano, G. Juhasz, M. Higashi, M. Sadakiyo, K. Kato, S. Yoshioka, T. Sugiyama, M. Yamauchi, N. Nakashima
    ACS Catalysis 9 (8) 6974 - 6986 2155-5435 2019/08 [Refereed][Not invited]
     
    Iridium oxide (IrOx)-based materials are the most suitable oxygen evolution reaction (OER) catalysts for water electrolysis in acidic media. There is a strong demand from industry for improved performance and reduction of the Ir amount. Here, we report a composite catalyst, IrOx-TiO2-Ti (ITOT), with a high concentration of active OH species and mixed valence IrOx on its surface. We have discovered that the obtained ITOT catalyst shows an outstanding OER activity (1.43 V vs RHE at 10 mA cm(-2)) in acidic media. Moreover, no apparent potential increase was observed even after a chronopotentiometry test at 10 mA cm(-2) for 100 h and cyclic voltammetry for 700 cycles. We proposed a detailed OER mechanism on the basis of the analysis of the in situ electrochemical X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements as well as density functional theory (DFT) calculations. All together, we have concluded that controllable Ir-valence and the high OH concentration in the catalyst is crucial for the obtained high OER activity.
  • Hadi Razavi-Khosroshahi, Sara Mohammadzadeh, Mirabbos Hojamberdiev, Sho Kitano, Miho Yamauchi, Masayoshi Fuji
    ADVANCED POWDER TECHNOLOGY 30 (7) 1290 - 1296 0921-8831 2019/07 [Refereed][Not invited]
     
    The accumulation of organic pollutants in surface water, groundwater, and even drinking water has raised as a serious issue in recent decades. Semiconductor-based photocatalysis has emerged as a green and sustainable approach to find remediate solutions for environmental and energy issues. However, the fast recombination rate of photogenerated charge carriers reduces the photocatalytic efficiency of photocatalysts. In this study, a hydrothermal synthesis method is proposed for preparing four types of p-n heterojunctions, BiVO4/BiOX (X = F, Cl, Br, I). BiVO4 is an n-type semiconductor and BiOX is a p-type semiconductor. Photocatalytic activity tests showed that the BiVO4/BiOF has the best photocatalytic performance under visible light, and photoluminescence spectra confirmed the lowest recombination rate of photogenerated charge carriers for BiVO4/BiOF as compared with others. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
  • Hadi Razavi-Khosroshahi, Sara Mohammadzadeh, Mirabbos Hojamberdiev, Sho Kitano, Miho Yamauchi, Masayoshi Fuji
    DALTON TRANSACTIONS 48 (25) 9284 - 9290 1477-9226 2019/07 [Refereed][Not invited]
     
    Tantalate semiconductors are potential photocatalysts for hydrogen generation via photocatalytic water splitting reaction because the conduction band of tantalates is composed of the tantalum 5d orbital, which is located at a more negative potential than that of the H+/H-2 half reaction, i.e., 0.0 V vs. NHE. Bi3TaO7 is a stable tantalate under acidic or alkaline conditions, with a band gap suitable for visible light absorption. However, the photocatalytic properties of Bi3TaO7 are only reported based on the dye degradation reactions, probably due to the fast electron/hole recombination losses. 2D crystal-like nanosheets with a thickness of a few nanometers show unique features such as high carrier mobility, the quantum Hall effect, high specific surface area, and excellent electrical/thermal conductivity. 2D structures can also enhance the photocatalytic properties because photo-generated charge carriers in nanosheets are less prone to fast recombinations as compared to their bulk counterparts. In this study, nanosheets of Bi3TaO7 are produced by a liquid exfoliation method and the photocatalytic hydrogen generation reaction is investigated for both the as-synthesized Bi3TaO7 nanoparticles and Bi3TaO7 nanosheets.
  • Kulbir Kaur Ghuman, Kota Tozaki, Masaaki Sadakiyo, Sho Kitano, Takashi Oyabe, Miho Yamauchi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 21 (9) 5117 - 5122 1463-9076 2019/03 [Refereed][Not invited]
     
    Despite many advancements, an inexpensive ammonia synthesis catalyst free from hydrogen and nitrogen poisoning, and capable of synthesizing ammonia under mild conditions is still unknown and is long sought-after. Here we present an active nanoalloy catalyst, RuFe, formed by alloying highly active Ru and inexpensive Fe, capable of activating both N-2 and H-2 without blocking the surface active sites and thereby overcoming the major hurdle faced by the current best performing pure metal catalysts. This novel RuFe nanoalloy catalyst operates under milder conditions than the conventional Fe catalyst and is less expensive than the so far best performing Ru-based catalysts providing additional advantages. Most importantly, by integrating theory and experiments, we identified the underlying mechanisms responsible for lower surface poisoning of this catalyst, which will provide directions for fabricating poison-free efficient NH3 synthesis catalysts in future.
  • M. Yamauchi, S. Hata, H. Eguchi, S. Kitano, T. Fukushima, M. Higashi, M. Sadakiyo, K. Kato
    Catalysis Science and Technology 9 (23) 6561 - 6565 2044-4753 2019 [Refereed][Not invited]
     
    © 2019 The Royal Society of Chemistry. Ti1-xZrxO2 complex oxide particles with 0.02 ≤ x ≤ 0.1 show superior catalytic performances for the direct power storage into glycolic acid via electroreduction of oxalic acid. The atomic pair distribution function analysis of X-ray total scatterings suggested that structural periodicity is the key factor for the catalytic enhancement.
  • Takashi Fukushima, Sho Kitano, Shinichi Hata, Miho Yamauchi
    Science and Technology of Advanced Materials 19 (1) 142 - 152 1878-5514 2018/12/31 [Refereed][Not invited]
     
    We demonstrated carbon-neutral (CN) energy circulation using glycolic acid (GC)/oxalic acid (OX) redox couple. Here, we report fundamental studies on both catalyst search for power generation process, i.e. GC oxidation, and elemental steps for fuel generation process, i.e. OX reduction, in CN cycle. The catalytic activity test on various transition metals revealed that Rh, Pd, Ir, and Pt have preferable features as a catalyst for electrochemical oxidation of GC. A carbon-supported Pt catalyst in alkaline conditions exhibited higher activity, durability, and product selectivity for electrooxidation of GC rather than those in acidic media. The kinetic study on OX reduction clearly indicated that OX reduction undergoes successive two-electron reductions to form GC. Furthermore, application of TiO2 catalysts with large specific area for electrochemical reduction of OX facilitates the selective formation of GC.
  • Sho Kitano, Masaaki Sadakiyo, Kenichi Kato, Miho Yamauchi, Hiroyuki Asakura, Tsunehiro Tanaka, Keiji Hashimoto, Hiroshi Kominami
    APPLIED CATALYSIS B-ENVIRONMENTAL 205 340 - 346 0926-3373 2017/05 [Refereed][Not invited]
     
    For a rhodium ion-modified TiO2 (Rh3+/TiO2) photocatalyst responding to visible light, control of the structure of the Rh3+ modifier and effects of the structures of the Rh3+ modifier on photocatalytic activities were examined. A TiO2 support was pre-calcined to maintain crystallinity and specific surface area during post-calcination, and the structure of the Rh3+ modifier for Rh3+/TiO2 was changed by post-calcination without causing changes in the crystallinity and specific surface area of the TiO2 support. In mineralization of acetone under irradiation of visible light, the photocatalytic activities of the post-calcined Rh3+/TiO2 showed a volcano-like tendency as a function of post-calcination temperature. The results of this study showed that an atomically isolated structure of the Rh3+ modifier was preferable for high activities and that aggregation of the Rh species led to a decrease in the activities. (C) 2016 Elsevier B.V. All rights reserved.
  • Sho Kitano, Atsuhiro Tanaka, Keiji Hashimoto, Hiroshi Kominami
    APPLIED CATALYSIS A-GENERAL 521 202 - 207 0926-860X 2016/07 [Refereed][Not invited]
     
    Metal ion-modified TiO2 photocatalysts designated by combinations of various metal ions and TiO2 powders that respond to visible light and exhibit controllable photocatalytic oxidative performances were examined. The photocatalytic oxidative performances were evaluated by selective oxidation of benzyl alcohol in water in the presence of O-2 under irradiation of visible light. The TiO2 samples modified with Ru3+, Pd2+ and Rh3+ (Ru3+/TiO2, Pd2+/TiO2 and Rh3+/TiO2) exhibited high levels of photocatalytic activity. The effects of metal ions and the kind of TiO2 on photocatalytic performances of Rh3+/TiO2 and Ru3+/TiO2 were investigated in detail. (C) 2015 Elsevier B.V. All rights reserved.
  • Sho Kitano, Miho Yamauchi, Shinichi Hata, Ryota Watanabe, Masaaki Sadakiyo
    GREEN CHEMISTRY 18 (13) 3700 - 3706 1463-9262 2016 [Refereed][Not invited]
     
    We demonstrate the production of glycolic acid, an industrially important alcoholic compound, via the electrochemical reduction of oxalic acid, which is procurable from biomass, and electro-oxidation of water with the help of renewable light energy for the first time. In principle, this new synthesis system is achievable while minimizing the consumption of fossil resources. We built a precious-metal free electrosynthesis system by employing a TiO2 cathode for oxalic acid reduction and a WO3 photoanode for water oxidation. The alcohol production proceeds during the application of electric power above 2.1 V in the dark. Notably, UV-visible light irradiation of the WO3 photoanode enables glycolic acid electrosynthesis above 0.5 V, which is lower (by 0.6 V) than the theoretical bias, i.e., 1.1 V. Glycolic acid electrosynthesis with an 80% high Faradaic efficiency was achieved on applying a bias of 1.5 V under UV-visible irradiation (lambda > 300 nm).
  • M. Yamauchi, R. Watanabe, S. Hata, S. Kitano, M. Sadakiyo, T. Takeguchi
    ECS Transactions 75 (43) 17 - 21 1938-6737 2016 [Refereed][Not invited]
     
    © The Electrochemical Society. We demonstrated an electric power circulation method that does not emit CO2 and is based on the glycolic acid (GC)/oxalic acid (OX) redox couple. Electric power charge in GC was achieved through OX electro-reduction with high selectivity (>98%) using purely anatase-type Ti02 spheres in the potential region of -0.5 to -0.7 V vs. RHE at 50 °C. We also realized GC production via the combination of electrochemical OX reduction and electro-oxidation of water with the help of renewable light energy for the first time. Furthermore, we succeeded in power generation via the selective electro-oxidation of GC to OX without CO2 emission. These results are the first experimental proof of the carbon-neutral power circulation involving an alcohol/carboxylic acid redox couple.
  • Takeshi Matsumoto, Masaaki Sadakiyo, Mei Lee Ooi, Sho Kitano, Tomokazu Yamamoto, Syo Matsumura, Kenichi Kato, Tatsuya Takeguchi, Miho Yamauchi
    SCIENTIFIC REPORTS 4 2045-2322 2014/07 [Refereed][Not invited]
     
    An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO2-free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO2, produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C-2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4 V vs. the reversible hydrogen electrode (RHE), without CO2 generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system.
  • Sho Kitano, Atsuhiro Tanaka, Keiji Hashimoto, Hiroshi Kominami
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 16 (24) 12554 - 12559 1463-9076 2014 [Refereed][Not invited]
     
    Photocatalytic oxidation of benzyl alcohols in aqueous suspensions of rhodium ion-modified titanium(IV) oxide (Rh3+/TiO2) in the presence of O-2 under irradiation of visible light was examined. In the photocatalytic oxidation of benzyl alcohol, benzaldehyde was obtained in a high yield (97%) with >99% conversion of benzyl alcohol. Rh3+/TiO2 photocatalysts having various physical properties were prepared using commercially available TiO2 powders as supporting materials for Rh3+ to investigate the effect(s) of physical properties of TiO2 on photocatalytic activities of Rh3+/TiO2 for selective oxidation. Adsorption properties of benzyl alcohol, benzaldehyde and benzoic acid on TiO2 were also investigated to understand the high benzaldehyde selectivity over the Rh3+/ TiO2 photocatalyst. The reaction mechanism was discussed on the basis of the results of photocatalytic oxidation of various p-substituted benzyl alcohol derivatives.
  • Sho Kitano, Naoya Murakami, Teruhisa Ohno, Yasufimi Mitani, Yoshio Nosaka, Hiroyuki Asakura, Kentaro Teramura, Tsunehiro Tanaka, Hiroaki Tada, Keiji Hashimoto, Hiroshi Kominami
    JOURNAL OF PHYSICAL CHEMISTRY C 117 (21) 11008 - 11016 1932-7447 2013/05 [Refereed][Not invited]
     
    A rhodium(III) ion (Rh3+)-modified TiO2 (Rh3+/TiO2) photocatalyst, prepared by a simple adsorption method and exhibiting high levels of photocatalytic activity in degradation of organic compounds, was investigated by using X-ray absorption fine structure (XAFS) measurements, (photo)electrochemical measurements, double-beam photoacoustic (DB-PA) spectroscopic measurements, and photoluminescence measurements. Based on the results, the features of the Rh3+ modifier and the working mechanism of the Rh3+/TiO2 photocatalyst are discussed. XAFS measurements revealed that the Rh3+ species were highly dispersed and almost atomically isolated on TiO2. The (photo)electrochemical measurements, DB-PA spectroscopic measurements, and photoluminescence showed a unique bifunction of the Rh3+ modifier as a promoter for O-2 reductions and an electron injector to the conduction band of TiO2 for response to visible light. The reasons for the Rh3+/TiO2 photocatalyst exhibiting higher levels of photocatalytic activity than those of TiO2 photocatalysts modified with other metal ions are also discussed on the basis of obtained results.
  • Sho Kitano, Keiji Hashimoto, Hiroshi Kominami
    CATALYSIS TODAY 164 (1) 404 - 409 0920-5861 2011/04 [Refereed][Not invited]
     
    Rhodium(III) ion (Rh3+)-modified TiO2 (Rh3+/TiO2) samples having various physical properties and structures (anatase and rutile) were prepared using commercially available TiO2 samples. Thus-prepared Rh3+/TiO2 samples were used for degradation of acetaldehyde or mineralization of acetone with a constant vapor pressure under irradiation of visible light and correlations between the photocatalytic activities and physical properties were investigated. Rhodium(III) ion on the surface of TiO2 worked as an inorganic photosensitizer and the Rh3+/TiO2 samples showed a kind of volcano-like tendency against specific surface area of TiO2, indicating that the balance of surface area and crystallinity of TiO2 is important in an Rh3+/TiO2 photocatalyst. The latter reaction system was found to be a simple and convenient method to evaluate the activity of a photocatalyst in a short time. The role of Rh3+ as a catalyst for multi-electron reduction of oxygen is discussed on the basis of results obtained for Rh3+-modified rutile-type TiO2 samples. (C) 2010 Elsevier B. V. All rights reserved.
  • Sho Kitano, Keiji Hashimoto, Hiroshi Kominami
    APPLIED CATALYSIS B-ENVIRONMENTAL 101 (3-4) 206 - 211 0926-3373 2011/01 [Refereed][Not invited]
     
    Using the adsorption method, small amounts of rhodium ion (Rh3+) or copper ion (Cu2+) were loaded on nanocrystalline titanium(IV) oxide (TiO2) with various physical properties prepared by the HyCOM (hydrothermal crystallization in organic media) method and subsequent calcination at various temperatures. In photocatalytic degradation of 2-propanol under visible light irradiation, Rh3+-modified HyCOM-TiO2 samples exhibited higher levels of activity than did Cu2+-modified HyCOM-TiO2 samples and the nitrogen-doped TiO2 sample. The Rh3+-modified HyCOM-TiO2 samples showed a volcano-like tendency with calcination temperature, suggesting that the balance of surface area and crystallinity of TiO2 is important in an Rh3+/TiO2 photocatalyst. Rutile-type TiO2 modified with Cu-2 exhibited the highest level of activity among the Cu2+/HyCOM-TiO2 samples. (c) 2010 Elsevier B.V. All rights reserved.
  • Sho Kitano, Keiji Hashimoto, Hiroshi Kominami
    CHEMISTRY LETTERS 39 (6) 627 - 629 0366-7022 2010/06 [Refereed][Not invited]
     
    Using adsorption method, a small amount of rhodium ion (Rh3+) was loaded on nanocrystalline titanium(IV) oxide (TiO2) with various physical properties prepared by HyCOM and subsequent calcinations at various temperatures. In photocatalytic degradation of 2-propanol under visible light irradiation, Rh3+-modified HyCOM-TiO2 samples exhibited higher levels of activity than did nitrogen-doped TiO2 sample and showed a volcano-like tendency with calcination temperature, suggesting that the balance of surface area and crystallinity of TiO2 is important in an Rh3+/TiO2 photocatalyst.
  • Keiji Hashimoto, Katutoshi Sumida, Sho Kitano, Kazuto Yamamoto, Nobuaki Kondo, Yoshiya Kera, Hiroshi Kominami
    CATALYSIS TODAY 144 (1-2) 37 - 41 0920-5861 2009/06 [Refereed][Not invited]
     
    Titanium(IV) oxide samples modified with platinum or rhodium chloride (H2PtCl6/TiO2 or RhCl3/TiO2) were prepared by an impregnation method and post-calcination at various temperatures and were used for photo-oxidation of nitrogen oxide under irradiation of visible light or UV light. Turnover numbers of both the catalysts were maintained at temperatures Lip to 350 degrees C under 24-h irradiation of visible light, although the specific surface area of the catalysts decreased greatly with increase in post-calcination temperature. The turnover number of H2PtCl6/TiO2 was about two-times larger than that of RhCl3/TiO2. Only a small amount of released NO2 was observed in the RhCl3/TiO2 catalyst, whereas in the H2PtCl6/TiO2 catalyst, the amount of NO2 released to gas phase increased with an increase in oxidation products. The small amount of released NO2 indicates that most of the NOx adsorbed on RhCl3/TiO2 as an adsorption form of nonvolatile NO3, whereas the amount of adsorbed NO2 on H2PtCl6/TiO2 was about four-times larger than that on RhCl3/TiO2. The results indicate that the oxidation rate of NO2 to NO3-over RhCl3/TiO2 was faster than that over H2PtCl6/TiO2. These results strongly suggest that the Cl radical induced by visible light was not directly related to the photo-oxidation of NO to NO2 and NO3 and that the complex species of RhCl3 and H2PtCl6 contributed to the photo-oxidation. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

MISC

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 幅崎 浩樹, 北野 翔
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2022/04 -2025/03 
    Author : 北野 翔
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists
    Date (from‐to) : 2020/04 -2022/03 
    Author : Kitano Sho
     
    Iridium clusters which are active for oxygen evolution reaction were composited with monolayer nanosheets of layered double hydroxide (LDH) and transition metal chalcogenides (TMD) as electrocatalysts. OER revealed that iridium clusters supported on LDH were highly active. We found that electronic states of iridium clusters were changed to reductive on the LDH nanosheets and oxidative on the TMD nanosheets. High OER performances were achieved on the iridium cluster-loaded TMD nanosheets.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists
    Date (from‐to) : 2018/04 -2020/03 
    Author : Kitano Sho
     
    In this study, we synthesized novel highly active electrocatalysts for the oxygen evolution reaction (OER), metal nanoparticle-loaded layered double hydroxide (LDH) nanosheets. Loading of metal nanoparticles enabled to enhance catalytic activities of LDH nanosheets composed of Co2+ or Ni2+ as divalent metal ions. We found that enhancement of catalytic activities was achieved by construction of effective electrode structure for OER and change in electronic states of active sites due to charge transfer between nanosheets and nanoparticles.
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    Date (from‐to) : 2011 -2013 
    Author : 北野 翔
     
    種々の条件で合成したHyCOM-TiO_2を合成し、溶媒やカップリング剤の種類を変更してバスケット構造の構築を検討したが細孔を有するボール型のナノバスケットは構築されなかった。HyCOM-TiO_2の多くが球状のような微粒子ではなく、ある程度の厚みを有した六角板状の構造であるため、バスケット構造の構築が困難であることが原因であると考えられる。 焼成処理によって表面Rh種の状態を制御した高活性なRh^<3+>/TiO_2を用い、可視光照射下において本課題の反応の一つであるニトロベンゼンの光触媒的還元反応を行った。2-プロパノール溶媒を用いてこの反応を行ったところ、反応の進行が確認され、65%の選択率でアミノベンゼンを得ることに成功した。これは可視光照射下において金属イオン修飾TiO_2光触媒系を用いて還元的有機合成を行った初めての例である。また、この反応系はTiO_2をベースにした可視光応答型光触媒による還元反応であるため、既存の反応系への応用や他反応系との様々な組み合わせが期待できる。 金属イオン修飾TiO_2を用いたアルコールの選択酸化反応において、さらなる反応性の向上のために反応系における基質(ベンジルアルコールとその酸化生成物)の吸着特性の解析を行った。その結果、基質の酸化速度はTiO_2上への吸着量に依存することを見出した。金属イオン修飾TiO_2を用いた本反応系において基質の酸化速度は吸着量によって決定され、アルコールとアルデヒドの吸着量の差が、アルデヒド生成の高い選択性に寄与していることが明らかになった。これらの結果は、TiO_2ベースの光触媒を用いるアルコールの選択酸化反応系において、今後の触媒設計指針に大きく貢献すると考えられる。 総括すると、HyCOM-TiO_2を用いたバスケット構造の構築には至らなかったが、金属イオン修飾物の制御や、ソルボサーマル法によって合成した新規可視光応答型光触媒により、当初の計画以上の反応の多様性を得るとともに、今後の可視光応答型光触媒の発展が期待される結果を得た。

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