Journal
ACS CATALYSIS
Volume 6, Issue 10, Pages 6804-6813Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.6b01242
Keywords
graphene; heteroatom doping; first-principles calculation; DSCs; triiodine reduction
Categories
Funding
- National Key Basic Research Program of China [2013CB933201]
- National Natural Science Foundation of China [21303052, 21333003]
- Shanghai Rising Star Program [14QA1401100]
- Chen Guang project [13CG24]
- Young Elite Scientist Sponsorship Program by CAST
- Fundamental Research Funds for the Central Universities
- Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund
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Graphene with heteroatom doping has found increasing applications in a broad range of catalytic reactions. However, the doping effects accounting for the enhanced catalytic activity still remain elusive. In this work, taking the triiodide electroreduction reaction as an example, we study systematically the intrinsic activity of graphene and explore the origin of doping-induced activity variation using first principles calculations, in which two typical N and S dopants are tested. The most common graphene structures, basal plane, armchair edge, and zigzag edge, are considered, and it is found that the former two structures show a weak adsorption ability for the iodine atom (the key intermediate in the triiodide electroreduction reaction), corresponding to a low catalytic activity. Doping either N or S can strengthen the adsorption and thus increase the activity, and the codoping of N and S (NS-G) exhibits a synergistic effect. A detailed investigation into the whole process of the triiodide electroreduction reaction at the CH3CN/NS-G interface is also carried out to verify these activity trends. It is found that the zigzag edges which contain spin electrons show a relatively stronger adsorption strength compared with the basal plane and armchair edge, and initial doping would result in the spin disappearance that evidently weakens the adsorption; with the disappearance of spin, however, further doping can increase the adsorption again, suggesting that the spin electrons may play a preliminary role in affecting the intrinsic activity of graphene. We also analyzed extensively the origin of doping-induced adsorption enhancement of graphene in the absence of spin; it can be rationalized from the electronic and geometric factors. Specifically, N doping can result in a more delocalized electron-donating area to enhance I adsorption, while S doping provides a localized structural distortion, which activates the nearest sp(2)-C into coordinatively unsaturated sp(3)-C. These results explain well the improved activity of the doping and the synergistic effect of the codoping. The understandings are generalized to provide insight into the enhanced activity of the oxygen reduction reaction on heteroatom doped graphene. This work may be of importance toward the design of high-activity graphene based material.
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