Graphene-Polyaniline Nanofibers Composite as Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

The catalytic oxygen reduction reaction (ORR) has engrossed rising attention due to its importance in energy converting system such as fuel cells. However, the commercialization of fuel cells is still mired by several factors, including the insufficient kinetics of ORR, high cost of noble metal catalysts, and the meager stability of the catalysts especially in alkaline medium. Thus, the important task is to develop a low-cost, stable and more active electrocatalysts for the ORR in alkaline fuel cells. Low-Pt loading or non noble metal cathode catalysts are currently receiving more and more research attention^{1, 2}.

The present work reports the synthesis of a novel Pt free cathode catalyst i.e., graphene-polyaniline nanofiber (GP) composite for ORR. Initially, the polyaniline (PANI) nanofibers and graphene sheets are individually synthesized using simple chemical route. Here, the polymer fibers are acting as interconnecting agents between graphene sheets, which are confirmed by Transmission electron microscopy showed in Fig.1A. Further, the catalytic activity and durability of GP composite were evaluated by linear sweep voltammetry in 0.1 M KOH solution, as showed in Fig.1B. The results confirmed that GP composite exhibited a 100 mV shift in ORR onset potential with enhanced activity compared to graphene alone. The possible ORR mechanism may be given as follows:

.

At graphene

H₂O +1/2 O₂ → H₂O₂ (2 electron transfer reaction)

At GP composite

O₂ + 2H₂O  → 4OH^- (4 electron transfer reaction)

 In addition, the GP composite showed good stability during a potential cycling test. Further structural and composition of graphene and GP composite were characterized using Field emission scanning electron microscopy (FESEM) and Raman spectroscopy (Figures are not shown). Fig. 1A shows the schematic of glassy carbon electrode modified with GP composite. Thus, the present composite developed may be a simple, cost effective one that showed a long durability for ORR. Therefore, it may be an excellent catalyst material of choice for practical fuel cells.

Figure caption

Fig.1 (A) Schematic representation of GP composite preparation, and glassy carbon electrode modification. (B) Liner sweep voltammogram curves for ORR in O₂ saturated 0.1 M KOH on (a) Graphene, (b) GP composite and (c) Pt/C 20% . Scan rate 10 mV/s. 

References

1. Y. Bing, H. Liu, L. Zhang, D. Ghosh, and J. Zhang, Chem. Soc.Rev. 39, 2184, 2010.

2. Y. Shao, J. Sui, G. Yin, and Y. Gao, Appl. Catal. B   79, 89, 2008.