Microbial Fuel Cells

Microbial fuel cells (MFCs) are bioelectrochemical devices that generate electricity by exploiting the metabolic processes of electrogenic bacteria. These systems provide a renewable energy source and serve as an innovative method for treating organic waste, such as wastewater.

A typical MFC consists of two chambers: an anoxic (oxygen-free) compartment that houses the bacteria and an oxic (oxygen-rich) compartment that contains oxygen as the terminal electron acceptor. Many MFCs use proton exchange membranes to separate the two chambers, although other separators or membrane-less designs are also used. The system provides an organic carbon substrate while limiting essential nutrients (e.g., nitrogen or phosphorus), suppressing biomass production, and shifting metabolism toward catabolic energy generation via redox electron transfer.

Electrogenic bacteria, such as Geobacter sulfurreducens and Shewanella oneidensis, oxidize organic substrates in the anoxic chamber. The electrons generated during this process are transferred to the external electrode, the anode, via extracellular electron transfer mechanisms—either directly through conductive pili or indirectly via redox-active molecules. From the anode, the electrons travel through an external circuit to the cathode in the oxic chamber, producing an electric current.

Simultaneously, the protons released in the anoxic chamber diffuse through the proton exchange membrane to the cathode. At the cathode, a catalysts such as platinum or manganese oxide facilitate the reaction between oxygen, electrons, and protons to form water. This completes the circuit and maintains charge balance.

Microbial fuel cells can use a variety of organic waste materials as substrates, making them especially valuable in environmental cleanup efforts. Their ability to simultaneously degrade waste and produce electricity makes MFCs suitable for applications such as powering remote sensors or supplementing energy needs in wastewater treatment facilities. Despite their promise, challenges such as low power density, high costs of electrode materials, and system scalability must be addressed to enhance their practical viability.