摘要/Abstract

杂原子掺杂的Fe-NC催化剂在氧还原反应中表现出优异的性能.本工作采用密度泛函理论研究了S原子掺杂对Fe-NC单原子催化剂电子结构的调控及促进氧还原反应的作用机理，分析了硫原子掺杂后Fe-NC催化剂的稳定构型，S原子对FeN₄活性位点电子结构的调控，以及氧气的吸附和氧还原反应作用机理.研究结果表明，在FeN₄活性位点周围掺杂少量S原子，可以提高催化剂的稳定性.S原子掺杂提高氧还原性能的机理为：（1）S原子的掺杂降低了催化剂的带隙，提高催化剂导电性，有利于电催化氧还原反应；（2）S原子的掺杂可以提高催化剂吸附氧气的能力，有利于氧还原反应；（3）体系中引入四个S原子可以降低氧还原反应的过电位，提高FeN₄位点催化氧还原反应的活性.这项工作可能为基于碳材料的单原子催化剂上杂原子掺杂的调控提供新的思路.
关键词: Fe-NC催化剂, 杂原子掺杂, 氧还原反应, 密度泛函理论
Heteratom-doped Fe-NC catalyst is promising for highly efficiently oxygen reduction reaction (ORR). In this work, density functional theory with the Vienna Ab initio Simulation Package (VASP) has been employed to systematically study the electronic structure regulation mechanism and oxygen reduction promoting mechanism on sulfur atom doped Fe-NC catalyst. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional within a generalized gradient approximation (GGA) was used in this work. The computataional hydrogen electron model was used to calculate the changes in Gibbs free energy. To consider the influence of S doping proportion, we build FeNSx models with 1~4 S atoms. The thermodynamic stability of catalysts was firstly considered based on formation energy, following by electronic structure analysis through Bader charge analysis and densities of states. Then, the oxygen adsorption ability was considered based on oxygen adsorption configurations and energies analyses. At last, reaction overpotentials were calculated based on computational hydrogen electrode model to study activity of catalytic sites. The results show that the catalyst doped with few sulfur atoms around the active sites of FeN4 could remain stable. Three possible ORR promoting mechanisms of S atoms doping were investigated. Firstly, the doping of sulfur atoms would reduce the band gap of the catalyst, thus improving the conductivity of the catalyst, which is beneficial to electrocatalytic oxygen reduction reactions. Secondly, the doping of a small amount of S atoms can improve the affinity between oxygen and the catalysts, which is also important for oxygen reduction reaction. At last, the introduction of four S atoms in the system would reduce the overpotential of ORR, thus improving the activity of the active sites to catalyze the oxygen reduction reaction. Our results predict that few S atoms doping would improve ORR performance of the Fe-NC catalyst through reducing band gap, improving ability to adsorb oxygen, and improving catalytic activity of FeN₄ site. This work may give a new insight into regulation rules of heteratom doping on single atom catalysts based on carbon materials.
Key words: Fe-NC catalyst, heteratom doping, oxygen reduction reaction, density functional theory


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