Yu Katayama
Kyoto University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Yu Katayama.
Science | 2017
Jonathan Hwang; Reshma R. Rao; Livia Giordano; Yu Katayama; Yang Yu; Yang Shao-Horn
Catalysts for chemical and electrochemical reactions underpin many aspects of modern technology and industry, from energy storage and conversion to toxic emissions abatement to chemical and materials synthesis. This role necessitates the design of highly active, stable, yet earth-abundant heterogeneous catalysts. In this Review, we present the perovskite oxide family as a basis for developing such catalysts for (electro)chemical conversions spanning carbon, nitrogen, and oxygen chemistries. A framework for rationalizing activity trends and guiding perovskite oxide catalyst design is described, followed by illustrations of how a robust understanding of perovskite electronic structure provides fundamental insights into activity, stability, and mechanism in oxygen electrocatalysis. We conclude by outlining how these insights open experimental and computational opportunities to expand the compositional and chemical reaction space for next-generation perovskite catalysts.
Langmuir | 2015
Toshiaki Matsui; Shohei Suzuki; Yu Katayama; Kosuke Yamauchi; Takeou Okanishi; Hiroki Muroyama; Koichi Eguchi
The electrochemical oxidation of ammonia over Pt electrode in alkaline aqueous solutions was studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. In 0.1 M NH3-1 M KOH, the band ascribable to the HNH bending mode of adsorbed NH3 was confirmed at 1662-1674 cm(-1) in the potential range of 0.1-1.1 V. The intensity of this band decreased continuously with a rise in potential, indicating the oxidative consumption of adsorbed ammonia. In response to this behavior, the band at 1269 cm(-1) appeared alternatively above 0.2 V, and its intensity reached the local maximal value at ca. 0.4 V. Note that this potential of ca. 0.4 V agreed well with the onset potential of ammonia oxidation, ca. 0.45 V, in the linear sweep voltammogram. This 1269 cm(-1) band was assigned to the NH2 wagging mode of N2H4, which was one of the active intermediates, N2H(x+y,ad) (x = 1 or 2, y = 1 or 2), according to the mechanism proposed by Gerischer and Mauere. To the best of our knowledge, this is the first report for the detection of N2H4 as a reaction intermediate over Pt electrode. Furthermore, the formation of bridged NO was also observed above the onset potential of ammonia oxidation, ca. 0.5 V. Such adsorbed NO species probably inhibit the electrochemical reaction due to the occupation of reaction sites at higher potential.
Energy and Environmental Science | 2017
Michal Tulodziecki; Graham M. Leverick; Chibueze V. Amanchukwu; Yu Katayama; David G. Kwabi; Fanny Bardé; Paula T. Hammond; Yang Shao-Horn
Lithium iodide has been studied extensively as a redox-mediator to reduce the charging overpotential of Li–oxygen (Li–O2) batteries. Ambiguities exist regarding the influence of lithium iodide on the reaction product chemistry and performance of lithium–oxygen batteries. In this work, we examined the role of lithium iodide on the reduction product chemistry under two conditions: (i) mixing KO2 with lithium salts and (ii) discharging Li–oxygen batteries at high and low overpotentials, in the presence of an ether-based electrolyte with different ratios of H2O : LiI. The addition of iodide to electrolytes containing water was found to promote the formation of LiOOH·H2O, LiOH·H2O and LiOH at the expense of Li2O2. At low H2O : LiI ratios (lower than 5), LiOH instead of Li2O2 was formed, which was accompanied by the oxidation of iodide to triodide while at high H2O : LiI ratios (12, 24, 134), a mixture of Li2O2, LiOOH·H2O and LiOH·H2O was observed and no triiodide was detected. The reaction between peroxide Li2O2 and/or superoxide LiO2 with H2O to form LiOH is facilitated by increased water acidity by strong I−–H2O interactions as revealed by 1H NMR and FT-IR measurements. This mechanism of LiOH formation in the presence of LiI and H2O was also found upon Li–O2 cell discharge, which is critical to consider when developing LiI as a redox mediator for Li–O2 batteries.
Journal of Physical Chemistry Letters | 2017
Livia Giordano; Pinar Karayaylali; Yang Yu; Yu Katayama; Filippo Maglia; Simon F. Lux; Yang Shao-Horn
Understanding electrochemical and chemical reactions at the electrode-electrolyte interface is of fundamental importance for the safety and cycle life of Li-ion batteries. Positive electrode materials such as layered transition metal oxides exhibit different degrees of chemical reactivity with commonly used carbonate-based electrolytes. Here we employed density functional theory methods to compare the energetics of four different chemical reactions between ethylene carbonate (EC) and layered (LixMO2) and rocksalt (MO) oxide surfaces. EC dissociation on layered oxides was found energetically more favorable than nucleophilic attack, electrophilic attack, and EC dissociation with oxygen extraction from the oxide surface. In addition, EC dissociation became energetically more favorable on the oxide surfaces with transition metal ions from left to right on the periodic table or by increasing transition metal valence in the oxides, where higher degree of EC dissociation was found as the Fermi level was lowered into the oxide O 2p band.
ACS Applied Materials & Interfaces | 2017
Yu Katayama; Kosuke Yamauchi; Kohei Hayashi; Takeou Okanishi; Hiroki Muroyama; Toshiaki Matsui; Yuuki Kikkawa; Takayuki Negishi; Shin Watanabe; Takenori Isomura; Koichi Eguchi
Over the last few decades, because of the significant development of anion exchange membranes, increasing efforts have been devoted the realization of anion exchange membrane fuel cells (AEMFCs) that operate with the supply of hydrogen generated on-site. In this paper, ammonia was selected as a hydrogen source, following which the effect of conceivable impurities, unreacted NH3 and atmospheric CO2, on the performance of AEMFCs was established. As expected, we show that these impurities worsen the performance of AEMFCs significantly. Furthermore, with the help of in situ attenuated total reflection infrared (ATR-IR) spectroscopy, it was revealed that the degradation of the cell performance was primarily due to the inhibition of the hydrogen oxidation reaction (HOR). This is attributed to the active site occupation by CO-related adspecies derived from (bi)carbonate adspecies. Interestingly, this degradation in the HOR activity is suppressed in the presence of both NH3 and HCO3- because of the bicarbonate ion consumption reaction induced by the existence of NH3. Further analysis using in situ ATR-IR and electrochemical methods revealed that the poisonous CO-related adspecies were completely removed under NH3-HCO3- conditions, accompanied by the improvement in HOR activity. Finally, a fuel cell test was conducted by using the practical AEMFC with the supply of NH3-contained H2 gas to the anode and ambient air to the cathode. The result confirmed the validity of this positive effect of NH3-HCO3- coexistence on CO2-tolerence of AEMFCs. The cell performance achieved nearly 95% of that without any impurity in the fuels. These results clearly show the impact of the chemically induced bicarbonate ion consumption reaction on the realization of highly CO2-tolerent AEMFCs.
Journal of Physical Chemistry Letters | 2018
Katherine R. Phillips; Yu Katayama; Jonathan Hwang; Yang Shao-Horn
The electrochemical CO2 reduction reaction (CO2RR) has gained attention recently due to rising concern over atmospheric carbon levels, but catalyst selectivity and efficiency remain a challenge, particularly for products other than CO. Here, we report the selective formation of formate using a sulfide-derived copper (SD-Cu) catalyst for CO2RR. On the basis of in situ and postelectrolysis spectroscopy, we propose that this selectivity is due to stronger binding of the CO intermediate originating from remaining subsurface sulfur atoms.
Journal of Physical Chemistry C | 2015
Yu Katayama; Takeou Okanishi; Hiroki Muroyama; Toshiaki Matsui; Koichi Eguchi
ACS Catalysis | 2016
Yu Katayama; Takeou Okanishi; Hiroki Muroyama; Toshiaki Matsui; Koichi Eguchi
Electrochimica Acta | 2015
Takeou Okanishi; Yu Katayama; Hiroki Muroyama; Toshiaki Matsui; Koichi Eguchi
Journal of Catalysis | 2016
Yu Katayama; Takeou Okanishi; Hiroki Muroyama; Toshiaki Matsui; Koichi Eguchi