【作者】 李柯；

【导师】 朱红；

【作者基本信息】 北京化工大学 ， 化学， 2018， 硕士

【摘要】 在当今社会,环境污染和能源短缺成为威胁人类生存的两大问题,所以开发新能源就显得尤为重要。氢能因其高效、无污染等优点而备受关注,而燃料电池可以直接利用氢能源,并且安全环保,能源转化效率高,因而可以替代内燃机成为新一代动力系统。目前,质子交换膜燃料电池的正常运转极其依赖铂基催化剂,而铂元素的成本及储量问题大大限制了其大规模应用,碱性膜燃料电池可以使用非贵金属催化剂替代铂基催化剂,但是其对非贵金属催化剂的活性和稳定性要求非常之高。因此,为了加快燃料电池大规模应用的步伐,研究兼顾成本低和高的ORR活性的非贵金属催化剂就显得非常重要。基于以上研究背景,本论文制备了三种不同体系的非贵金属催化剂:(1)通过溶胶-凝胶法合成了一类具有网状结构的三聚氰胺甲醛凝胶,采用这种凝胶对氧化钴进行包覆,然后在最外层包裹一层碳粉并作为载体,最后对该前驱体进行高温热解得到了一系列Co2O3@MF-C催化剂,并考察了氧化钴含量及锻烧温度对催化剂ORR活性的影响,最后发现:在氧化钴含量为20%,煅烧温度为650℃条件下制备的催化剂,即20%Co2O3@MF-C-650具有最好的ORR活性,其在酸性条件下的起始还原电位和半波电位分别为0.83V和0.71V,在碱性条件下的起始还原电位和半波电位分别为1.02V和0.94V,酸性和碱性条件下的电子转移数分别为3.67和3.96,均是以4-电子反应过程为主,并且具有比较好的稳定性和抗甲醇性能;(2)通过加热搅拌法合成一类新型的具有长方体结构的Co-bpdc晶体(金属有机骨架配合物,简称MOFs材料),通过对其进行高温锻烧得到了一系列催化剂,发现Co-bpdc-600在碱性条件下具有最好的ORR活性,在此基础上合成了 Co-bpdc/MWCNTs复合材料,将该复合材料于600℃下煅烧,并探究了 MWCNTs含量对ORR活性的影响,结果发现钴原子均匀分布在MWCNTs表面,Co-bpdc/MWCNTs-100具有最好的ORR活性,在酸性条件下的起始还原电位和半波电位分别为0.81V和0.71V,在碱性条件下起始还原电位和半波电位为0.98V和0.92V,Co-bpdc/MWCNTs-100在酸性和碱性条件下的电子转移数分别为3.73和3.98,均是以4-电子反应过程为主,并且具有比较好的稳定性和抗甲醇性能;(3)通过常温搅拌法合成了一类新型的片状的Co-phen晶体,通过溶胶-凝胶法合成了具有高比表面积的碳气凝胶,采用碳气凝胶对Co-phen进行包覆然后置于高温下锻烧制备了一系列高比表面积的催化剂,并探究了 Co-phen与碳气凝胶的比例以及煅烧温度对ORR活性的影响,结果证明在Co-phen与碳气凝胶比例为4:10,煅烧温度为700℃条件下制备的催化剂,即4Co-phen@10CA-700具有最好的ORR活性;4Co-phen@10CA-700在酸性条件下的起始还原电位和半波电位分别为0.82V和0.75V,在碱性条件下起始还原电位和半波电位分别为0.99V和0.91V,4Co-phen@10CA-700酸性和碱性条件下的电子转移数分别为3.93和3.97,均是以4-电子反应过程为主,并且具有比较好的稳定性和抗甲醇性能。更多还原

【Abstract】 In contemporary society,the environmental pollution and energy shortage have become two major issues that threaten the survival of mankind,so the researchment of new energy is particularly important.Hydrogen energy has attracted much attention due to its high efficiency,non-pollution,and other advantages.Fuel cells can use hydrogen energy directly,safely,and environmentally friendly,and have high energy conversion efficiency.Therefore,they have a large potential to replace the internal combustion engine as a new generation of power systems.At present,the normal running of proton exchange membrane fuel cells is extremely dependent on platinum-based catalysts,and the cost and storage of platinum elements greatly limit its large-scale application.Alkaline membrane fuel cell can use non-precious metal catalysts instead of platinum-based catalysts,but it requires the non-precious metal catalysts have very high activity and stability.Therefore,in order to speed up the large-scale application of the fuel cell,it is very important to develop a non-precious metal catalyst that contain inexpensive and high ORR activity simultaneously.Based on the above research background,this paper prepared three different systems of non-precious metal catalysts:(1)A melamine formaldehyde gel with a network structure was synthesized by a sol-gel method.Cobalt oxide was coated with this gel,and then carbon black was used to wrap the above material and worked as a carrier.Finally,a series of Co2O3@MF-C catalysts were obtained by pyrolying the precursor at high temperaturethe.We also investigated the effect of cobalt oxide content and calcinating temperature on the ORR activity of the catalyst.Finally,we found that the optimal preparation conditions of the catalyst were that the cobalt oxide content is 20%and the calcination temperature is 650℃.In other words,20%Co2O3@MF-C-650 has the most excellent ORR activity,and its initial reduction potential and half-wave potential under acidic conditions were 0.79 V and 0.60 V,respectively,and its initial reduction potential and half-wave potential under alkaline conditions were 1.02 V and 0.94 V,respectively.The electron transferred number of 20%Co2O3@MF-C-650 under acidic and alkaline conditions are 3.67 and 3.96,respectively,which are based on 4-electron reaction process,and the test results also indicate the prepared catalysts have better stability and methanol resistance;(2)A series of novel Co-bpdc crystals(Metal-organic frameworks,abbreviated as MOFs)with cuboid structure were synthesized by heating and stirring method.A series of catalysts were obtained by high-temperature calcination and it was found that Co-bpdc-600 has the most excellent ORR activity under alkaline conditions.On this basis,Co-bpdc/MWCNTs composites were synthesized under the same reaction conditions.The composites were calcined at 600℃,and the effect of MWCNTs content on ORR activity was investigated.It was found that cobalt atoms were uniformly distributed on the surface of MWCNTs and the Co-bpdc/MWCNTs-100 has the most excellent ORR activity,and its initial reduction potential and half-wave potential under acidic conditions were 0.79 V and 0.60 V under acidic conditions,and its initial reduction potential and half-wave potential of 0.98 V and 0.92 V under alkaline conditions.The electron transferred number of Co-bpdc/MWCNTs-100 under acidic and alkaline conditions were 3.73 and 3.98,respectively,which were based on 4-electron reaction process,and the test results also indicate the prepared catalysts have better stability and methanol resistance;(3)A novel sheet-like Co-phen crystal was synthesized by stirred at room temperature method and carbon aerogel with high specific surface area was synthesized by sol-gel method.We use carbon aerogel wrap Co-phen,and then A series of high specific surface area catalysts were prepared by calcinating it at high temperature.We also investigated the effect of the ratio of Co-phen and carbon aerogels and calcinating temperature on the activity of the catalyst.we found that the optimal preparation conditions of the catalyst were that the ratio of Co-phen and carbon aerogel was 4:10 and the calcination temperature was 700℃.In other words,4Co-phen@l0CA-700 has the most excellent ORR activity,and its initial reduction potential and half-wave potential under acidic conditions were 0.82 V and 0.75 V,respectively,and its initial reduction potential and half-wave potential under basic conditions were 0.99 V and 0.91 V,respectively.The electron transferred number of 4Co-phen@10CA-700 under acidic and alkaline conditions is 3.93 and 3.97,respectively,which are based on the 4-electron reaction process,and the test results also indicate the prepared catalysts have better stability and methanol resistance更多还原