成果報告書詳細
管理番号20160000000167
タイトル*平成27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2016/12/27
報告書年度2015 - 2015
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-FY2017) FY2015 Annual Report

We have proposed a novel electrochemical reactor for hydrogen production/power generation. The electrochemical reactor is composed of metal hydride and nickel hydroxide as negative and positive electrodes, respectively. This is based on nickel-metal hydride batteries but the amount of the negative electrode can be reduced significantly (ratio of negative and positive electrodes capacity is less than 0.5). In the previous study, we reported that this novel electrochemical reactor had a high energy conversion efficiency for hydrogen production, which was 98.3% at 37.0 A/m2 with a lab scale single cell (active electrode area: 32.5 cm2). For a real system application, however, it is necessary for the electrochemical reactor to have a high responsiveness toward higher voltage and higher current. In this study, therefore, we developed a 1 kW-class electrochemical reactor for hydrogen production by stacking 20 single cells using bi-polar plates. Also, a particle electrode fabrication method was developed for the fabrication of large (active electrode area: 15×20 cm2) and thick (thickness: ~0.8 mm) electrodes. To evaluate of the electrode and the 20-cell stack, we recorded scanning electron microscopy and energy dispersive X-ray spectroscopy micrographs and measuring the galvanostatic performance. The experimental results show that the particle electrode exhibits an excellent charge performance despite being relatively thick and high porosity. The 20-cell stack also showed high hydrogen production efficiency with a maximum current efficiency for hydrogen production of 95.3% and hydrogen evolution amount per unit input electrical energy of 259.1 cc/Wh.
We also proposed a novel electrochemical water-splitting cycle consisting of two-step electrochemical reactions for oxygen and hydrogen production by introducing an intermediate electrode. Two-step water electrolysis offers the following advantages: (i) higher-purity hydrogen can be obtained because hydrogen and oxygen gases are generated in different steps and (ii) high energy conversion efficiency for hydrogen production can be achieved by reducing the ohmic overpotential between the electrodes through the use of a thinner separator than a conventional one. Furthermore, a pulsed current can be supplied to the electrolysis cell, which leads to a low concentration overpotential by increasing the reacting species concentration in a diffusion layer. In the present study, manganese dioxide (MnO2) was selected as the intermediate electrode because its oxidation-reduction potential is located between the potentials of the hydrogen and oxygen evolution reactions.
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