过渡金属氮化物纳米线/石墨烯杂化结构微电极及其电催化特性

Transition metal nitrides have attracted great attention in developing non-precious metal fuel cells due to their distinct electrocatalysis characteristics which are similar to those of precious metals. Performance of nanoscale catalyst is expected to be drastically enhanced by combining with graphene due to coupling effect. In this project, our goal is to realize the controlled growth of transition metal nitride nanowires/graphene nanoplatelets hybrid arrays based on chemical vapour deposition ，solution and electrodeposition, unveiling the correlation between experimental parameters, growth mechanism and structure of the hybrid. The effect of the hybrid structure and nanowires/graphene coupling effect on the electrocatalysis and reaction kinetics of the electrode will be investigated. Single proton exchange membrane fuel cell system will be assembled making use of the hybrid of transition metal nitride nanowires/graphene nanoplatelets as the electrode materials. Some key performance parameters of the cell will be evaluated including voltage-current density (V-i), power-current density(P-i) and cell life, and the effect of operation conditions on the dynamic responses of the cell will also be investigated as well. The performance parameters of the cell will be evaluated based on the theoretical model of commercial cell to explore the potential of the hybrid in practical applications. The work in this project will not only explore fundamental understandings on the nanostructured transition nitride/graphene hybrid in terms of electrocatalysis, but also promote the development of putting the hybrid into practical applications to replace precious metal catalysts of proton exchange membrane fuel cells.

过渡金属氮化物的电催化特性类似于贵金属，对非贵金属燃料电池的发展起着至关重要的作用；由于耦合作用，石墨烯有望对纳米结构催化剂的性能有显著增强。本项目以过渡金属氮化物与石墨烯为研究对象，把气相沉积、溶液法与电沉积相结合，实现氮化物纳米线/石墨烯微片杂化结构的三维微阵列的可控生长，探索合成条件、生长机理与杂化结构的关系；揭示不同生长条件下，纳米线与石墨烯的结构与耦合对杂化物电催化特性和动力学的影响及其内在关联。制作以氮化物纳米线/石墨烯微片为电极材料的质子交换膜燃料电池单电池装置，测试包括电压-电流密度，功率-电流密度，电池寿命以及操作条件对电池动态响应的影响，并对比于真实电池理论模型，揭示金属氮化物纳米线/石墨烯杂化结构作为电池电极材料的实际应用价值。本项目期望为金属氮化物纳米线/石墨烯杂化结构在新型非贵金属燃料电池中的应用奠定理论和实验基础。

燃料电池是一种将化学能转化为电能的清洁能源转换装置，具有能量密度高、转换效率高、环境友好等优点。但是电极材料需要使用贵金属作为催化剂，存在着成本过高的技术瓶颈。由于过渡金属氮化物在电子结构和催化特性上和贵金属Pt相类似，因此本项目的研究将磁控溅射、化学气相沉积和水热合成相结合获得了三维过渡金属氮化物纳米线/纳米带阵列（包括W2N纳米线、TiN纳米线、Mo2N纳多孔纳米带等）；另一方面采用真空湿球墨法和溶液法获得了尺度可控、低含氧量和表面功能化的石墨烯纳米片。在此基础上将纳米尺度金属氮化物与石墨烯纳米片进行杂化生长获得了三维金属氮化物/石墨烯纳米杂化结构电极材料。研究结果表明这种杂化纳米结构可以有效提高电极材料的表面催化活性，其中三维氮掺杂石墨烯/氮碳化钨纳米线阵列结构在不担载贵金属的情况下可以对甲醇的氧化具有良好的电催化活性，电催化电流密度是具有类铂催化特性的碳化钨的2.15倍；而W2N纳米线/石墨烯杂化结构相对于氮化之前具有更好的氧还原特性，氧化电位由0.60V正移到0.71V，电催化电流是氮化前的1.4倍；TiN纳米线在沉积了Pt纳米线后对甲醇氧化催化的电流密度达到83.57A/g，明显高于商用Pt/C催化剂的电流密度23.07A/g。这些研究结果显示纳米尺度过渡金属氮化物纳米线/石墨烯杂化结构对于甲醇氧化和氧还原具有优良的催化活性。动力学分析结果表明，所获得的纳米尺度过渡金属氮化物/石墨烯杂化结构能够将纳米尺度金属氮化物的电催化特性与石墨烯高电导、高比表面积特点相结合，有利于燃料分子的快速扩散与表面催化分解，从而提高电极材料的表面催化活性和能量转换效率，在非贵金属和低贵金属燃料电池电极材料的领域具有令人期待的发展前景。另一方面本项目从表面功能化的角度对石墨烯进行了选择性表面修饰与复合，并探究了其表面对电荷存储和快速转移的特性。从而为发展能量转换/存储一体化的新型纳米结构与器件提供了一种新的思路。