含CoNx中心的石墨烯电催化氧还原反应机理研究

Study on the Mechanism of Oxygen Reduction Reaction on Graphene with CoNx Centers

中文关键词:  CoN_x-G催化剂  催化机理  反应势垒  氧还原反应  密度泛函理论

英文关键词:CoN_x-G catalysts  catalytic mechanism  reaction barrier  oxygen reduction reaction  density functional theory

中文摘要:

      采用理论计算方法深入研究了两种含三配位CoN_x(x=2,3)中心的石墨烯(CoN_x-G)催化剂在氧还原反应(ORR)中的催化机理. 在这两种催化剂表面, ORR的最低能量反应路径遵循相同的机制: O_{2 (ads)}分子首先加氢还原为OOH_(ads), 随后OOH_(ads)加氢解离为两个OH_(ads), 最终OH_(ads)继续加氢还原为产物水. 在CoN₂-G上, 整条反应路径中OH_(ads)还原为H₂O_(ads)具有最高能垒; 而在CoN₃-G表面, O_2(ads)还原为OOH_(ads)具有最高能垒. 相比CoN₂-G, CoN₃-G具有较低的最高势垒, 更佳的结构对称性, 更负的形成能, 且在ORR过程中Co中心始终保持正电荷, 有利于含氧中间体的活化. 因此, CoN₃-G表现出比CoN₂-G更优良的ORR催化性能, 归因于配位的三个N原子对Co位点电子结构的优化以及体系稳定性的增强.

英文摘要:

      The oxygen reduction reaction (ORR) catalytic mechanism of two graphene (CoN_x-G) catalysts containing CoN_x (x=2,3) centers was investigated using theoretical computational methods. On both catalysts, the lowest-energy reaction pathway for ORR follows the same mechanism: the O_2(ads) molecules are first hydrogenated and reduced to OOH_(ads), which then undergoes hydrogenation and dissociation to produce two OH_(ads) molecules, and finally the OH_(ads) continues to hydrogenate and reduce to form water. The key difference lies in the fact that the reduction of OH_(ads) to H₂O_(ads) on the CoN₂-G structure serves as the highest energy barrier(HEB) step of the entire pathway, whereas on the CoN₃-G structure, the reduction of O_2(ads) to OOH_(ads) is the HEB. Compared to CoN₂-G, CoN₃-G exhibits a lower HEB, a better structural symmetry, more negative formation energy, and maintains a positive charge on the Co centers throughout the ORR process, which facilitates the activation of oxygen-containing intermediate. Consequently, CoN₃-G shows a better ORR catalytic performance than CoN₂-G, which is attributed to the optimization of the electronic structure of the Co sites and the enhancement of system stability through the coordination of three N atoms.