High‐power microbial‐fuel‐based hybrid cells with three‐dimensional graphene‐coated iron foam as an anode control Fe 3 + release

Microbial fuel cells (MFCs) benefit from the introduction of iron in the anode, as its multiple valence states and high electron‐catalytic activity led to improved power densities in MFCs. However, the effect of long‐term Fe 3+ release into the electrolyte on the power density of MFCs is often overlooked. Herein, an anode consisting of a three‐dimensional iron foam uniformly coated by reduced graphene oxide (rGO/IF) with a suitable loading density (8 g/m 2 ) and a large specific surface area (0.05 m 2 /g) for high‐density bacterial loading was prepared. The hybrid cells based on the rGO/IF anode exhibit a maximum power density of 5330 ± 76 mW/m 2 contributed by MFCs and galvanic cells. The rGO/IF anode enables continuous Fe 3+ release for high electron‐catalytic activity in the electrolyte during the discharging of the galvanic cells. As a result, the hybrid cells showed a power density of 2107 ± 64 mW/m 2 after four cycles, facilitated through reversible conversion between Fe 3+ and Fe 2+ in the electrolyte to accelerate electron transfer efficiency. The results indicate that the rGO/IF anode can be used for designing and fabricating high‐power MFCs by optimizing the rate of release of Fe 3+ in the electrolyte.