Microbial Fuel Cells (MFCs)

A MFC is a device that directly converts chemical energy into electricity through the catalytic activities of microorganisms. A traditional two-chamber MFC consists of an anode, a cathode, a proton or cation exchange membrane and an electrical circuit. It can be a single-chamber MFC if membrane is removed as demonstrated in following figure.

Microorganisms are used at anode as catalyst to oxidize organic substrate to release protons and electrons as the following reaction:

Anode: CxHyOz + H2O = CO2  +  e-  +  H+

The electrons are then transferred to the anode and flow to the cathode where they combine with protons and oxygen to produce water as the following reaction:

Cathode: O2  + 4 H+  + 4 e-  = 2 H2O

During this process, electricity can be captured at the external circuit.

Microbial Electrolysis Cells (MECs)

Based on an MFC, when a small voltage (>0.2V in practice) is applied between the anode and cathode and keep totally anaerobic condition, Hydrogen gas will be produced at the cathode. This is process is similar to the water electrolysis. Hence it is referred to Microbial electrolysis, and the reactors are called Microbial Electrolysis Cells (MECs) demonstrated as the Figure 2.

MECs hold multiple advantages over water electrolysis to produce hydrogen:

Reduce the energy requirement

– Bio-electrolysis: 0.6 KWh/m3 (0.2 mol H2 energy/mol-H2 produced)

– Water electrolysis: 4.5-5 KWh/m3 (1.5-1.7 mol H2 energy/mol-H2 produced)

No precious metal catalysts at anode

– Bio-electrolysis: self-sustaining microbial biocatalyst

– Water electrolysis: precious metal catalyst, e.g Platinum

Using waste biomass as energy source

– Any biodegradable organic material can potentially be used as substrate.

–Harvesting energy and waste deduction