Further enhancing current and power density

Miniaturized MF Cs have demonstrated plenty of promise and indeed much progress has prevailed for such a short period of time yet, miniaturized MFCs face many different challenges to overcome, including further enhancing current and power density, applying air-cathodes to replace potassium ferricyanide, and autonomous operation. 

Enhancing current/power density requires lowering internal resistance and areal resistivity. The reported internal resistance and areal resistivity of miniaturized MFCs are still rather high, in the order ofkS2 and 100si2cm, respectively. The internal resistance is composed of three parts ohmic resistance, activation resistance and concentration resistance. 

Ohmic resistance can be divided into resistance of anode Ra, cathode R, electrolyte R and ion exchange membrane R . For simplicity of comparison, all the resistances are normalized to the surface area of the anode to be areal resistivity  

The anode resistivity, is attributed to electrode resistivity, and to the resistivity associated with the electron transfer from the exoelectrogen to the anode (it can also be seen as the contact resistance. Resistance of the biofilm is also incorporated into the electron transfer resistivity). For a conductive anode, such as gold, CNT, carbon, etc., the electrode resistivity is negligible. Consequently, the main source of the anode resistivity comes from the electron transfer from the exoelectrogen to the anode. 

In the future, other 3D electrodes, such as electrodes made from 3D printing, electrospun nano-wire, 3D electrodes of conductive sponge, etc., can be used to fiilly take up the volume of the anode chamber, offering a larger surface area to volume ratio. 

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