含氧石墨烯负载铂基合金催化剂的氧还原反应机理研究

发布时间：2019-06-12 19:24

【摘要】：燃料电池是一种既有较高能源利用效率又不污染环境的能源利用方式，在能源短缺、资源争夺激烈的今天有着巨大的发展潜能。然而，阴极缓慢的氧还原反应制约了燃料电池大规模商业化的发展进程，寻找高效低耗的氧还原电催化剂成为燃料电池的研究重点。新型负载型合金催化剂的开发，减小了贵金属尤其是铂的担载量，降低了燃料电池的成本，一定程度上加快了燃料电池的发展；但由于缺乏对氧还原反应机理与动力学的认识，负载型合金催化剂活化氧还原反应的机制尚不清楚，不仅如此，系统研究氧还原的机理与动力学对氧还原电催化剂的有效设计也具有重要的指导意义。 本文基于密度泛函理论，系统地研究了含氧石墨烯担载铂及铂合金的负载型合金催化剂催化氧还原反应的机理，主要内容如下： 在含氧石墨烯中，氧的存在破坏了石墨烯平面的均一性质，造成电荷分布不均匀，产生的缺陷位成为金属负载的活性位点。金属团簇Pt4，Pt3Ti，Pt3V，Pt3Cr，Pt3Mn，Pt3Fe，Pt3Co和Pt3Ni负载于含氧石墨烯表面后吸附自由态氧分子，活化后的氧分子以O-O过渡态的形式存在于Pt4，Pt3Ti，Pt3Mn，Pt3Fe，Pt3Co和Pt3Ni团簇表面，却在含氧石墨烯负载的Pt3V和Pt3Cr表面发生了完全解离，形成了两个独立的吸附态氧原子。过渡金属原子（Ti，V，Cr，Mn，Fe，Co，，Ni）的存在均能有效促进电子向吸附态氧的转移。 在含氧石墨烯担载Pt4，Pt3V，Pt3Cr，Pt3Fe，Pt3Co团簇的氧还原反应机理研究中，中间体HOO*不能稳定存在于催化剂表面，而是会解离成共吸附状态的HO*和O*。随后，在含氧石墨烯担载的Pt4，Pt3Cr，Pt3Co表面，氧还原过程均能形成共吸附的HO*和共吸附的H2O*与O*，两种还原路径都有可能发生，且以共吸附HO*的还原路径为热力学有利。在含氧石墨烯担载的Pt3Fe表面，氧还原的过程不仅能形成共吸附的HO*和共吸附的H2O*与O*，且这两种还原路径在热力学上不分优劣，处于竞争关系。而在含氧石墨烯担载的Pt3V表面，氧还原的过程不能稳定形成共吸附的H2O*与O*，而只能以共吸附的HO*还原路径为主导。此外，本文的理论研究结果证实了实验上观察到的石墨烯负载Pt3Cr和Pt3Co纳米催化剂对活化氧还原反应的增强机制。
[Abstract]:Fuel cell is a kind of energy utilization mode which has high energy efficiency and does not pollute the environment. It has great development potential in the shortage of energy and fierce competition for resources. However, the slow oxygen reduction reaction of cathode restricts the development of large-scale commercialization of fuel cell, and the search for high efficiency and low consumption oxygen reduction electrocatalyst has become the research focus of fuel cell. The development of new supported alloy catalysts reduces the loading of precious metals, especially platinum, reduces the cost of fuel cells, and accelerates the development of fuel cells to a certain extent. However, due to the lack of understanding of the mechanism and kinetics of oxygen reduction reaction, the mechanism of oxygen reduction activated by supported alloy catalyst is not clear, not only that, the systematic study of oxygen reduction mechanism and kinetics is also of great significance to the effective design of oxygen reduction electrocatalyst. Based on density functional theory, the mechanism of oxygen reduction catalyzed by platinum supported platinum and platinum alloy catalysts containing oxygen graphene has been systematically studied in this paper. the main contents are as follows: in oxygen graphene, the existence of oxygen destroys the homogeneous property of graphene plane, resulting in uneven charge distribution, and the defect site becomes the active site of metal loading. Metal clusters Pt4,Pt3Ti,Pt3V,Pt3Cr,Pt3Mn,Pt3Fe,Pt3Co and Pt3Ni adsorbed free oxygen molecules on the surface of oxygen-containing graphene. The activated oxygen molecules existed on the surface of Pt4,Pt3Ti,Pt3Mn,Pt3Fe,Pt3Co and Pt3Ni clusters in the form of O 鈮

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