Boosted activity of graphene encapsulated CoFe alloys by blending with activated carbon for oxygen reduction reaction.

The slow oxygen reduction reaction (ORR) hampers the efficiency of microbial fuel cells (MFCs) to a large extent, which usually requires catalysts to facilitate the electron transfer. The major challenge of the existed non-precious metals in place of the noble metal catalysts (Pt, Pd, Au et al.) for ORR is their low efficiency, which urgently needs special route to tackle this issue. Herein, we report a simple and convenient technique using prussian blue analogues as precursor to directly synthesize the N-doped graphene encapsulated CoFe alloy which is present in "Core-Shell" structure via calcination of Co2 Fe(CN)6 in inert condition. The encapsulation of metal alloy within graphene shell immensely promotes the electron transfer from the encapsulated metals to the graphene surface. It efficiently optimizes the electronic structure of the as-synthesized catalyst and thereby triggers high ORR activity. The surrounding activated carbon (AC) contributes to the large pore structure and further offers a commodious route for the oxygen to gain electron. Therefore, the total resistance of air cathodes is significantly reduced from 17.300 Ω to 9.551 Ω and the electrochemical activity is greatly improved. The power performances of MFCs indicate that CoFe/C-10% presents the highest maximum power density (MPD) of 1616 mW m-2 , which is 5 times larger than that of the bare AC. It is well concluded that the graphene encapsulated CoFe alloy can be recognized as potential ORR catalyst for MFCs.