Capacitive Bioanodes Enable Renewable Energy Storage in Microbial Fuel Cells

We developed an integrated system for storage of renewable electricity in a microbial fuel cell (MFC). The system contained a capacitive electrode that was inserted into the anodic compartment of an MFC to form a capacitive bioanode. This capacitive bioanode was compared with a noncapacitive bioanode on the basis of performance and storage capacity. The performance and storage capacity were investigated during polarization curves and charge–discharge experiments. During polarization curves the capacitive electrode reached a maximum current density of 1.02 ± 0.04 A/m², whereas the noncapacitive electrode reached a current density output of only 0.79 ± 0.03 A/m². During the charge–discharge experiment with 5 min of charging and 20 min of discharging, the capacitive electrode was able to store a total of 22 831 C/m², whereas the noncapacitive electrode was only able to store 12 195 C/m². Regarding the charge recovery of each electrode, the capacitive electrode was able to recover 52.9% more charge during each charge–discharge experiment compared with the noncapacitive electrode. The capacitive electrode outperformed the noncapacitive electrode throughout each charge–discharge experiment. With a capacitive electrode it is possible to use the MFC simultaneously for production and storage of renewable electricity

Fluidized Capacitive Bioanode As a Novel Reactor Concept for the Microbial Fuel Cell

The use of granular electrodes in Microbial Fuel Cells (MFCs) is attractive because granules provide a cost-effective way to create a high electrode surface area, which is essential to achieve high current and power densities. Here, we show a novel reactor design based on capacitive granules: the fluidized capacitive bioanode. Activated carbon (AC) granules are colonized by electrochemically active microorganisms, which extract electrons from acetate and store the electrons in the granule. Electricity is harvested from the AC granules in an external discharge cell. We show a proof-of-principle of the fluidized capacitive system with a total anode volume of 2 L. After a start-up period of 100 days, the current increased from 0.56 A/m² with 100 g AC granules, to 0.99 A/m² with 150 g AC granules, to 1.3 A/m² with 200 g AC granules. Contact between moving AC granules and current collector was confirmed in a control experiment without biofilm. Contribution of an electro-active biofilm to the current density with recirculation of AC granules was limited. SEM images confirmed that a biofilm was present on the AC granules after operation in the fluidized capacitive system. Although current densities reported here need further improvement, the high surface area of the AC granules in combination with external discharge offers new and promising opportunities for scaling up MFCs