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Papers by Author: Tatsumi Ishihara

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Reversible Solid State Fe-Air Rechargeable Battery Using LaGaO₃ Based Oxide Ion Conducting Electrolyte

Authors: Tatsumi Ishihara, Atsushi Inoishi, Sintaro Ida

Abstract: The combination of solid oxide fuel cell technology with Fe-air battery concept was proposed by using H₂/H₂O as a redox mediator and LaGaO₃ based oxide for electrolyte. Since large internal resistance and large degradation during charge and discharge cycles are observed on anode, improvement in discharge potential and cycle stability are strongly required by improving stability of anode. In this study, cermet anode consisting of Ni-Fe alloy combined with oxide ion conductor was investigated. It was found that by using cermet anode of Ni-Fe combined with Ce_0.6Mn_0.3Fe_0.1O₂(CMF), the observed energy density of the cell is improved to be 1109 Wh/Kg-Fe at 10 mA/cm², 873 K, which is about 92% of the theoretical energy density assuming the formation of Fe₃O₄ (1290 Wh/Kg-Fe). Cycle stability was also much improved on the cell using Ni-Fe-CMF anode comparing with that of Ni-Fe metal because of suppressed aggregation of Ni by mixing with CMF. Electrochemical charge-discharge measurement at 773 K showed excellent cycle stability over 30 cycles with high energy density (Round trip efficiency is higher than 80 %). The excellent performance and stability with operating at lower temperature promise this Fe-air solid oxide battery as the next generation energy storage device for averaging electricity and electric vehicle.

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Ni-Fe-LaGaO₃ Based Alloy Anode Cermet for Direct Hydrocarbon Type Solid Oxide Fuel Cell Using LaGaO₃ Electrolyte

Authors: Hao Zhong, Tatsumi Ishihara, Hiroshige Matsumoto

Abstract: Cermet anode of NiFe(9:1)-La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) (90:10 weight ratio) was studied for direct CH4 fueled SOFC operating at intermediate temperature. In case of NiFe bimetal anode, power density of the cell decreased drastically after operation under CH4 feeding condition. On the other hand, mixing Sm doped CeO2, MgO, or LSGM is effective for improving the long term stability. The cell with NiFe-LSGM anode exhibited much stable power density under CH4 feeding condition. Deposition of coke was also studied by Raman spectroscopy and no coke deposition was observed after 15 h operation. Since the surface activity of this anode is high, power density was hardly dependent on PCH4.It was found that NiFe-LSGM10 shows a high tolerance against the coke deposition under CH4 feeding condition.

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Development of Intermediate-Temperature Solid Oxide Fuel Cells Using Doped Lanthanum Gallate Electrolyte

Authors: Hiroyuki Eto, Taner Akbay, Jun Akikusa, Gakuji Uozumi, Norihisa Chitose, Toru Inagaki, Tatsumi Ishihara

Abstract: Intermediate-temperature(IT) solid oxide fuel cells(SOFCs) were developed using lanthanum gallate electrolyte, samarium cobaltite cathode and the cermet anode of nickel and ceria. High efficiency operation below 800°C was enabled using planar disk type cells with unique seal less stack design. The first 10 kW-class combined heat and power (CHP) system provided AC output power of 10 kW with electrical and overall efficiency of 41 and 82 %HHV, respectively. Optimization of cell-stack components to increase the output power density is in progress.

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Intermediate Temperature Steam Electrolysis Using Doped Lanthanum Gallate Solid Electrolyte (2) Effects of CeO₂ Interlayer on Activity

Authors: Nitiphong Jirathiwathanakul, Hiroshige Matsumoto, Tatsumi Ishihara

Abstract: Steam electrolysis is attracting much interest method to produce hydrogen and also the new energy recovery process of wasted heat energy. Up to now, Y2O3 stabilized ZrO2 (YSZ) has been used for a solid electrolyte and so the operating temperature is limited down to 1273K. This study is focused on increasing the performance of steam electrolysis by using LaGaO3 based oxide for electrolyte at intermediate temperature of 873 K, which is upper limit of the obtainable wasted heat. It was found that the formation amount of H2 is almost obeyed the Faraday law up to 1.8 V suggesting that the ionic transport number of oxide ion in LaGaO3 was kept to be 1 under the steam electrolysis condition. The electrolyzing current is improved as following order; La0.6Sr0.4CoO3

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Development of Honeycomb-Type Solid Oxide Fuel Cell Consisting of LaGaO₃ Electrolyte

Authors: Hao Zhong, Hiroshige Matsumoto, Tatsumi Ishihara, Akira Toriyama

Abstract: La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) -based honeycomb cell was first time successfully built and operated in the case of single-wall used condition and the full 4-walls cell one. Power generation characteristic of this honeycomb cell was measured from 700°C to 900°C by using various electrochemical techniques including polarization, current interruption and impedance spectrometry. The LSGM honeycomb cell shows the exact high power density compared with the ZrO2 based cell at the operating temperature range, and its value is 394 and 252 mW/cm2 at 800°C and 700°C, respectively. Thermal stability of this honeycomb cell is also studied and it is seen that the good performance through several times thermal cycling is observed. The 4-walls’s cell stack is successfully working at 800°C, and the volumetric power density is achieved to a value of about 700 mW/cm3.

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Effects of Dye Mixing on Photocatalytic Splitting of H₂O into H₂ and O₂ on KTaO₃

Authors: Hidehisa Hagiwara, Hiroshige Matsumoto, Tatsumi Ishihara

Abstract: Effects of mixing dye sensitizer for the photocatalytic activity of dye-sensitized Pt/K0.95Ta0.92Zr0.08O3 was investigated. It was found that the photocatalytic activity was greatly improved by mixing dye sensitizer on the catalyst, and among the examined combination of organic dyes, the highest photocatalytic activity was obtained by mixing Cr-tetraphenylporphyrin (Cr-TPP) and Pentametylene bis[4-(10, 15, 20-triphenylporphine-5-yl)benzoate] dizinc(ΙΙ) (Zn-TPP dimer). In order to identify the effect of dye sensitizer, photovoltaic behavior of the dye-sensitized KTaO3 was investigated. The lifetime of the photo-exited electron and hole can be improved by coating with dye sensitizer. Thus, the effect of porphyrinoids would be explained by the improved efficiency of charge separation.

Ni-Fe Bimetallic Anode for Intermediate Temperature Solid Oxide Fuel Cells Using LaGaO₃ Based Oxide Electrolyte

Authors: Tatsumi Ishihara, Masashi Shinagawa, Akira Kawakami, Hiroshige Matsumoto

Abstract: Effects of various additives to Ni anode on SOFC using La0.9Sr0.1Ga0.8Mg0.2O3 based oxide were investigated in this study. Among the examined additives, it was found that the addition of small amount of Fe is highly effective for increasing the anodic activity. When 5 wt% Fe was added to Ni anode, the anodic overpotential was as small as 34 mV at 873 K, 0.1A/cm2, which is almost half of pure Ni anode. Since the estimated activation energy for anodic reaction decreased, addition of Fe to Ni seems to be effective for increasing the activity of Ni for anodic reaction. XRD measurement after power generating property suggests that added Fe was formed alloy with Ni. SEM observation shows the high dispersion of Ni metal was sustained by addition of small amount of Fe. Consequently, this study reveals that Ni-Fe bimetal is highly active for anodic reaction of SOFCs at decreased temperature.

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