Plasma surface modification of single-atom Fe active sites on nano-sized graphene platelets for advanced oxygen reduction reaction
Sungho Lee1, *, Seonghee Kim1, *, Jin Hong Lee2, Heechae Choi3, Nozomi Takeuchi4, **, Oi Lun Li1, **
* Co-first authors having the equal contribution to this paper. ** The authosr to whom correspondence should be addressed.
1 School of Materials Science and Engineering, Pusan National University, South Korea
2 School of Chemical Engineering, Pusan National University, South Korea
3 Institute of Inorganic Chemistry, University of Cologne, Germany
4 Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Japan
Abstract
Single-atom Fe-doped carbon nanographene demonstrates promising results as an oxygen reduction reaction (ORR) electrocatalyst in fuel cells and rechargeable metal-air batteries. In this study, plasma-in-liquid process was applied to modify the surface of graphene nanoplatelet (GNP) with iron (II) Phthalocyanine as the Fe precursor and mixed into 1- Methyl-2-pyrrolidone (solvent) for 20 minutes. During the plasma modification, tiny discharge bubbles were observed, where the emission of C2, CH, CN, and H radicals were identified by the optical emission spectrum. From the highresolution TEM and the corresponding EDS elemental mapping images, the isolated Fe were successfully anchored as single-atom on GNP between 0.50 ~ 0.82 at.%. The ORR activity greatly enhanced after plasma modification, where the single-atom Fe-doped GNP demonstrated extremely high onset potential (Eonset) and half-wave potential (E1/2) of 0.95 - 0.98 V and 0.87 - 0.90 V vs RHE, respectively. Most importantly, plasma-modified Fe-GNP catalysts showed superior ORR catalytic activity compared to other single-atom Fe with similar metal loading catalysts reported in recent studies. The unique plasma-induced chemical reaction via active radicals not only successfully anchored atomic Fe onto the surface but also created certain defects of GNP, which created a synergic effect on the ORR catalytic activities.Keywords - Plasma modification, single-atom doped graphene, oxygen reduction reaction, electrocatalysts.