Chen Xin, Hu Rui, Bai Fan
The Center of New Energy Materials and Technology, College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China.
Materials (Basel). 2017 May 18;10(5):549. doi: 10.3390/ma10050549.
The influences of diameter and length of the Fe-N₄-patched carbon nanotubes (Fe-N₄/CNTs) on oxygen reduction reaction (ORR) activity were investigated by density functional theory method using the BLYP/DZP basis set. The results indicate that the stability of the Fe-N₄ catalytic site in Fe-N₄/CNTs will be enhanced with a larger tube diameter, but reduced with shorter tube length. A tube with too small a diameter makes a Fe-N₄ site unstable in acid medium since Fe-N and C-N bonds must be significantly bent at smaller diameters due to hoop strain. The adsorption energy of the ORR intermediates, especially of the OH group, becomes weaker with the increase of the tube diameter. The OH adsorption energy of Fe-N₄/CNT with the largest tube diameter is close to that on Pt(111) surface, indicating that its catalytic property is similar to Pt. Electronic structure analysis shows that the OH adsorption energy is mainly controlled by the energy levels of Fe 3d orbital. The calculation results uncover that Fe-N₄/CNTs with larger tube diameters and shorter lengths will exhibit better ORR activity and stability.
采用密度泛函理论方法，使用BLYP/DZP基组研究了Fe-N₄修饰的碳纳米管（Fe-N₄/CNTs）的直径和长度对氧还原反应（ORR）活性的影响。结果表明，Fe-N₄/CNTs中Fe-N₄催化位点的稳定性会随着管径的增大而增强，但会随着管长的缩短而降低。管径过小的碳纳米管会使Fe-N₄位点在酸性介质中不稳定，因为由于环向应变，在较小直径下Fe-N键和C-N键必须显著弯曲。ORR中间体的吸附能，尤其是OH基团的吸附能，会随着管径的增加而减弱。管径最大的Fe-N₄/CNT的OH吸附能与Pt(111)表面的相近，表明其催化性能与Pt相似。电子结构分析表明，OH吸附能主要由Fe 3d轨道的能级控制。计算结果表明，管径较大且长度较短的Fe-N₄/CNTs将表现出更好的ORR活性和稳定性。
