Nano-flower like CoFe-layered double hydroxide@reduced graphene oxide with efficient oxygen reduction reaction for high-power air-cathode microbial fuel cells

Microbial fuel cells (MFCs) are "self-sufficient" renewable energy sources that utilize the redox processes inherent in microbial metabolism to generate an electrical potential. However, the cathodic region of these fuel cells typically utilizes an oxygen reduction reaction (ORR) operating at high overpotential and slow reaction kinetics significantly, restricting the power generation capacity of MFCs. Herein, to improve the cathodic reduction efficiency, we synthesized CoFe-layered double hydroxides (LDH) on partially-reduced graphene oxide (p-rGO) via electrostatic interaction. In contrast to pure CoFe-LDH, CoFe-LDH@p-rGO composite possessed a three-dimensional uniform porous nanoflower-like morphology, giving the catalyst a high surface area for efficient catalysis. The proportions of CoFe-LDH to p-rGO were optimized to minimize layer stacking through strong π-π bond and van der Waals force, maximizing the overal electron transfer numbers n (3.66), with the lowest charge transfer resistance Rct (38.5 Ω). As a result, this novel catalyst combined the rich Co/Fe metal center catalytic active sites and interlayer structure of CoFe-LDH, with the high electrical conductivity of p-rGO to accelerate the electron transfer rate of ORR. Air-cathode microbial fuel cell (ACMFC) utilizing CoFe-LDH@p-rGO catalyst showed comparable output voltage of 423 mV to Pt/C catalyst, and a comparably high-power density of 204 mW m−2. This work provides a new path towards development of nanostructured non-noble metal catalysts for the optimization of oxygen reduction reaction in high-power ACMFCs.