成果報告書詳細
管理番号20150000000320
タイトル*平成26年度中間年報 水素利用等先導研究開発事業 高効率水素製造技術の研究 次世代水素製造システムの研究
公開日2016/2/19
報告書年度2014 - 2014
委託先名エクセルギーパワーシステムズ株式会社 国立大学法人東京大学
プロジェクト番号P14021
部署名新エネルギー部
和文要約
英文要約Title: Advancement of Hydrogen Technologies and Utilization Project. High-Efficiency Hydrogen Production Research and Development. Next-generation Hydrogen Production System (FY2014-FY2015) FY2014 Annual Report

A novel electrochemical reactor for hydrogen production is proposed based on a fuel cell/battery (FCB) system. The hydrogen evolution and oxidation reactions in the system occur at solid/liquid and solid/gas two-phase boundaries using a metal hydride negative electrode. This leads to high energy efficiency for hydrogen production by reducing the electrode overpotential. We thus investigated electrochemical charge performance at various current densities by fabricating an experimental cell. The fabricated cell was composed of negative and positive electrodes with a 1:3 capacity ratio. Hydrogen gas was produced in a linear manner during the charge process. The energy conversion efficiency of hydrogen production at a current density of 37.0 A/m2 was 98.3%. This value is higher than that of conventional water electrolysis. We also investigated the effect of particle size (3 and 40 μm), optimum composition weight ratio (between active material, carbon black, and binder), and types of metal hydride (MmNi3.6Co0.7Mn0.4Al0.1 and La0.6Pr0.2Nd0.1Mg0.1Ni4.1Al0.1) for the negative electrode. From our experiments, it was found that the overpotential for hydrogen production decreased with reduction of the metal hydride particle size and use of MmNi3.6Co0.7Mn0.4Al0.1. It was also found that the optimum composition ratio of metal hydride, carbon black, and binder was 100:5:5 by weight. For a positive electrode of the novel electrochemical reactor, the active material should be able to store oxygen gas by chemical reactions and have a good electrochemical properties. From our previous studies, we have found that manganese dioxide (MnO2) is a suitable material for positive electrode of the system. However, the rate performance of the positive electrode should be improved in order to satisfy the requirements of the target application. To improve the rate performance of the manganese dioxide positive electrode, we fabricated electrodes by adding small amount (5 and 10 wt%) of nickel hydroxide to the manganese dioxide. Electrochemical characterizations such as galvanostatic measurements and electrochemical impedance spectroscopy were carried out to determine the discharge rate performance and electrical resistance. The electrochemical results indicated that the positive electrode with nickel hydroxide has better rate performance than the pure manganese dioxide electrode. It is considered that the electrical path in the electrode was improved owing to the low electrical resistance of the nickel hydroxide and the bimodal effects between the nickel hydroxide and manganese dioxide particles. Additionally, X-ray diffraction confirmed that the formation of δ-MnO2, which results in electrochemically unreactive Mn3O4 after electrochemical discharging, is inhibited in the presence of nickel hydroxide. For further performance improvement of the positive electrode by increasing the surface area and reducing the overpotential, we are currently fabricating electrodes with a novel fibrous structure.
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