DEVELOPMENT OF NOVEL MATERIALS FOR ENVIRONMENTAL PROTECTION AND ENERGY SUPPLY GLOBAL CARBON DIOXIDE RECYCLING

我们建议建立一个CO_2回收系统，以防止CO_2排放与人类活动的发展相结合造成的全球变暖。该系统包括CO_2的甲烷化，这些CO_2在燃料消耗场所（如发电厂）回收。甲烷化需要高活性的催化剂和氢气，而氢气可以利用太阳能电解海水获得。为了在全球范围内实现这一系统，我们需要开发低成本的催化剂和电极，用于海水电解的析氢和析氧反应。通过对Ni基Ni-Mo和Ni-Mo-O合金电极的比较，发现少量O的存在既提高了电极的析氢活性，又提高了电极的耐久性。另一种电极候选物是Ni-Fe-C合金系统。即使在50，000 A/m^2的高电流密度下加速试验两年，氢过电位也几乎没有增加。在钛基MnO_2型氧化物电极上，首次成功地制备出析氧效率为100%的海水电解用电极。同时发现Mo和W的复合添加对海水电解中的选择性析氧更有效，并能成功地降低电解电压，同时发现非晶态Ni-Zr合金制备的甲烷化催化剂具有较高的甲烷化活性。我们还成功地开发了以非晶态Ni-Zr-Sm合金为前驱体的活性更高的催化剂。结果表明，钐稳定了氧化锆的四方相，提高了镍颗粒在四方相上的分散性。

We are proposing a CO_2 recycling system for preventing global warming caused by CO_2 emissions in conjunctions with development of human activities. The system consists of methanation of CO_2 which are recovered at fuel consumers sites such as power plants. Methanation needs highly active catalysts and hydrogen which can be obtained from seawater electrolysis using solar energy. To substantiate this system in global scale, we need to develop low cost catalysts and electrode with high efficiency for hydrogen evolution and oxygen evolution reactions at seawater electrolysis. The objectives of this investigation are to develop such new catalysts and electrode substances.Comparison between Ni-Mo and Ni-Mo-O alloy electrodes fabricated on Ni substrate showed existence of small amount of O imparts both higher activity for hydrogen evolution reaction and higher durability. Another electrode candidate was Ni-Fe-C alloy system. It showed almost no increase in hydrogen overpotential even after accelerating test for two years at a high current density of 50,000 A/m^2. It was also stable and suffered no corrosion even after repeated stoppage of electrolysis in a concentrated NaOH solution at high temperature.For the first time in the world, we have succeeded in preparation of electrodes with 100 % oxygen evolution efficiency for seawater electrolysis using MnO_2 type oxide electrode installed on titanium substrate. It was also found combined addition of Mo and W was more effective for selective oxygen evolution at seawater electrolysis and we were able to reduce electrolysis voltage successfully.Moreover, we found methanation catalysts prepared from amorphous Ni-Zr alloys had high activity sfpr methanation. We have also succeeded in develop more active catalyst using amorphous Ni-Zr-Sm alloys as precursors of the catalysts. It was clarified that samarium stabilize tetragonal phase of zirconia on which dispersion of Ni particles were also enhanced.