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

结合人类活动的发展，为防止二氧化碳排放引起的全球变暖，我们提出了一个二氧化碳回收系统。该系统由二氧化碳的甲烷化组成，这些二氧化碳在燃料消耗点（如发电厂）回收。甲烷化需要高活性催化剂和氢气，而氢气可从太阳能电解海水中获得。为了在全球范围内实现这一体系，我们需要开发低成本、高效率的催化剂和电极，用于海水电解的析氢和析氧反应。本研究的目的是开发这种新的催化剂和电极物质。对比Ni- mo和Ni- mo -O合金电极在Ni衬底上制备的结果表明，少量O的存在使电极的析氢反应活性更高，耐久性也更高。另一个候选电极是Ni-Fe-C合金体系。在5万a /m^2的高电流密度下，经过两年的加速试验，氢过电位几乎没有增加。在浓氢氧化钠溶液中反复停止电解，在高温下也不受腐蚀。我们在国际上首次成功地将二氧化锰型氧化物电极安装在钛基上，制备出了100%析氧效率的海水电解电极。在海水电解过程中，Mo和W的联合添加对选择性析氧更有效，并且我们能够成功地降低电解电压。此外，我们发现非晶Ni-Zr合金制备的甲烷化催化剂具有较高的甲烷化活性。以Ni-Zr-Sm非晶态合金为前驱体，成功研制出活性更高的催化剂。结果表明，钐稳定了氧化锆的四方相，并增强了Ni粒子的分散性。

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.