Abstract
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.
Highlights
The development of nonprecious metal catalysts with high oxygen reduction reaction (ORR) activity and stability has been a major focus of fuel cell research
It was proposed that the active sites are the Fe ions coordinated by four nitrogen atoms, which are incorporated to graphitic carbon and have the same local structure of Fe-porphyrin catalysts [5]
4/carbon nanotube (CNT) catalytic activities for ORR were investigated by theoretical calculations at the on Fe−N4 /CNTs catalytic activities for ORR were investigated by theoretical calculations at the BLYP/DZP level
Summary
The development of nonprecious metal catalysts with high oxygen reduction reaction (ORR) activity and stability has been a major focus of fuel cell research. It was proposed that the active sites are the Fe ions coordinated by four nitrogen atoms, which are incorporated to graphitic carbon and have the same local structure of Fe-porphyrin catalysts [5]. These Fe−N4 /C catalytic sites in graphitic carbon matrix were demonstrated to have excellent ORR catalytic performance [2,6,7,8,9]. CNTs areand highly related to the tube diameter and to length, which can obviously influence geometrical influence the geometrical and electronic structures of there. The tube diameter and length influence the ORR activity and stability of Fe−N4 /CNTs nano-catalysts.
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