Fig. 6. (a) Polarization and (b) power curves using SS (black) (inset), SS–Gr–PD (blue), and CP-Pt (red) air cathodes. Carbon fibre (2 g) was used in the anodic chamber, n = 6 for each sample, and error bars show the standard error. (c) Polarization curve and (d) power curve for MFCs using graphene at both electrodes, with A-CMC–Gr–PD in the anodic chamber and SS–Gr–PD as an air cathode, n = 3 and error bars show the standard error.