Interfacial Electron Transfer from the Outer Membrane Cytochrome OmcA to Graphene Oxide in a Microbial Fuel Cell: Spectral and Electrochemical Insights

A microbial fuel cell (MFC) is able to convert waste energy into electricity, and its performance is mainly constrained by extracellular electron transfer (EET) at biological/inorganic interfaces. In this work, the interaction process between the microbe’s outer membrane cytochrome (OmcA) and graphene oxide (GO) is investigated in vitro to elucidate the EET mechanism in the MFC. The feasibility of the electron transfer from the purified OmcA to GO is examined by protein film voltammetry tests. Stopped flow analysis demonstrates that the EET kinetic process obeys the Michaelis–Menten equation and exhibits the characteristics of enzyme catalysis. The structural changes of OmcA/GO monitored by a circular dichroism spectroscopy combined with infrared spectroscopy techniques indicate that the formation of a hydrogen bond between the −NH2 group of the residues and the −COOH/–OH group of GO shortens the electron-transfer distance to mitigate the energy barrier. These results help to understand the EET mechanism at the molecular level for harvesting energy from wastes.