The low catalytic activity, limited resources, complexity and costs, and non-environmentally friendly nature are key factors limiting the application of non-precious metals and their composites at the cathode in microbial fuel cells (MFCs). This study evaluated the feasibility of graphene-based nano materials (RGO(HI-AcOH) vs. RGO/Ni nanoparticle composite) as novel cathode catalysts in single chamber air-cathode MFCs. A series of MFCs with different catalyst loadings were produced. The electrochemical behavior of the MFCs were evaluated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). As a result, the MFCs with the RGO(HI-AcOH) cathodes showed greater maximum power densities (>37%) than those with the RGO/Ni nanoparticle cathodes. In the MFCs, the highest maximum power density of 1683 +/- 23 mW/m(2) (CE = 72 +/- 3%), which covers 77% of that estimated for Pt/C (2201 +/- 45 mW/m(2), CE = 81 +/- 4%), was obtained from the double loading RGO(HI-AcOH) cathodes. Among the MFCs with the RGO/Ni nanoparticle composite cathodes, those loaded with a double catalyst (1015 +/- 28 mW/m(2), CE = 70 +/- 2%) showed better power performance than the others. Both CV and EIS showed good agreement with the MFC results. This study suggests that the RGO(HI-AcOH) cathode, particularly with a double catalyst loading, is promising for sustainable low-cost green materials, stable power generation and the long-term operation of MFCs. (C) 2016 Elsevier B.V. All rights reserved.