B,P单掺杂和共掺杂石墨烯对O,O_2,OH和OOH吸附特性的密度泛函研究

基于第一性原理的密度泛函理论研究了B,P单掺杂以及B,P共掺杂石墨烯对O,O_2,OH和OOH的吸附特性.通过分析吸附能、键长、态密度以及电荷转移,比较了不同掺杂对燃料电池氧还原反应(ORR)中间物吸附的影响,进而探讨了反应过程,并给出各步反应自由能的变化趋势.结果表明:B,P单掺杂石墨烯对各中间物的吸附能存在线性关系,掺P石墨烯吸附OOH的吸附能为3.26 eV,远大于掺B石墨烯的吸附能0.73 eV;掺P石墨烯较大的吸附能有利于中间物OOH中O—O键的断裂,掺B石墨烯吸附能小有利于中间物OH生成H2O脱附的反应发生;而B,P共掺杂石墨烯的吸附存在协同效应,具有更好的催化ORR的反应能力.

Density functional study on the adsorption characteristics of O,O2, OH,and OOH of B-, P-doped,and B,P co dop ed graphenes

Over past years, the excessive use of fossil fuel has posed serious problems such as greenhouse effect and environmental pollution, which threaten human life. Regarded as an ideal substitution for traditional internal combustion engine, low temperature proton exchange membrane fuel cell (PEMFC) converts chemical energy through electrode reaction directly into electrical energy with high efficiency and low pollution. However, the main problem behind the industrialization of PEMFC, is that oxygen reduction reaction (ORR) occurring on the cathode needs precious metal platinum (Pt) as catalyst, which has a limited reserve and is costly. Owing to high activity and stability, the graphenes doped with non-metal B and P, have proven to be excellent alternatives to Pt experimentally. However, the relevant theoretical work is scarce.Adsorptions of the ORR intermediates, i.e., O, O₂, OH, and OOH, of doped graphenes are essential for the cathode reaction, which also bring some difficulties to the next step reaction. Therefore, in this paper, based on density functional theory, the adsorption characteristics of O, O₂, OH, and OOH of B-doped, P-doped and B, P-codoped graphenes are studied using first-principles calculation code VASP first. By analyzing the adsorption energies, bond lengths, densities of states and charge transfers, the influences of the different dopants on the intermediates are evaluated. Then, the ORR steps are discussed, and the free energy change of each step is further given. The results show that for B-doped and P-doped graphenes, the adsorption energies of various intermediates exhibit similar linear relationships. The adsorption energy of OOH of P-doped graphene (3.26 eV) is much larger than that in B-doped grapheme (0.73 eV). The large adsorption energy of P-doped graphene is beneficial to the fracture reaction of O–O bond in OOH, while the small adsorption energy of B-doped graphene can promote the reaction of OH converting into water. Owing to the synergistic effect, the graphene codoped with B and P possesses better catalyzing ability than single B-and P-doped ones. The results are helpful for understanding the excellent performances of codoped graphenes.