A hierarchical porous graphene/nickel anode that simultaneously boosts the bio- and electro-catalysis for high-performance microbial fuel cells

The microbial fuel cell (MFC) is an extremely attractive green energy source, which has gained considerable research interest, since it cleans the environment by using wastewater and/or organic wastes as fuels while harvesting electricity; however, a MFC has much lower power density than conventional fuel cells. In this study, a hierarchical porous graphene/nickel (G/Ni) composite electrode with a hierarchical porous structure over distributed pore sizes of 20 nm to 50 mu m is developed by a freeze-drying assisted self-assembly process for MFC anodes. Since a MFC anode involves both electro- and bio-catalytic processes, the beauty of this G/Ni anode is its unique nanostructure that provides a high active surface area for efficient electrocatalysis, while its macroporous structure with strong biocompatibility allows bacteria growing in the pores to have high biocatalyst loading to boost biocatalysis. Thus, this binder-free hierarchical porous G/Ni anode delivers a maximum power density of 3903 mW m(-2) in Shewanella putrefaciens (S. putrefaciens) MFCs, which is similar to 13-fold higher than that of conventional MFC carbon cloth anode. Considering the low cost of porous Ni and the low weight percentage of graphene (5 wt%), this composite electrode offers great promise for practical, high-performance, cost-effective and mass-manufacturable MFCs.