Air-cathode MFCs

The cathodic reaction of a MFC is an electron consumption or reduction process (Figure 5.2). For a typical air cathode MFC, Pt is usually used as the catalyst for oxygen reduction. Under Pt catalysis, the electrons from the anode and protons transported from the anodic compartment will reduce the oxygen, which is accompanied by water generation. The chemical reaction occurring on the air cathode is O2 + + e H2O (Figure 5.2). Recently,... 

Nitrobenzene originates from numerous industrial and agricultural activities, and can be abiotically removed at a cathode coupled to microbial oxidation of acetate at an anode, as shown by Mu et al. [140]. Finally, a model antibiotic (ceftriaxone) was shown to be oxidatively removed and to boost current production from glucose in the anode in an air-cathode MFC [137]. 

Cheng SA, Kiely P, Logan BE. Pre-acclimation of a wastewater inoculum to cellulose in an aqueous-cathode MEC improves power generation in air-cathode MFCs. Bioresour Technol 2011 102 367-371. 

Another challenge are the low reaction kinetics of oxygen. Performance of air-cathode MFCs is mostly limited by the air-cathode, which degrades the performance of the MFC. Fan et al (2007) changed the size of the air-cathode, and reported that as anode/cathode area ratio reduces from 1 1 to 1 7, the areal power density increased from 1.04 W m to 6.71 W m (normalized to the anode area). Thus, enhancing the reaction kinetics of oxygen is critical. 

The theoretical maximum cell voltage for an acetate-fed air-cathode MFC is 1.1 V (Eemf/ obtained in terms of Nernst equation). However, the measured MFC voltage is considerably lower than this value. In an open circuit when... 

On the cathode electrode, oxygen reduction prefers alkaline conditions to obtain a lower reduction overpotential. Both Puig et al. [85] and He et al. [86] reported the highest current and power generation at pH 9.0-9.5 in two-chamber air-cathode MFCs. Differences in the above results may arise from the different operating conditions (such as substrates, electrolyte conductivity, temperature) and MFC configurations in these studies. 

For an air cathode MFC, we find the OCV does not vary appreciably, and thus the main factor affecting power is From eq. 4-10, we see that power if / ,= Rext, then max emf I Rint Thus, the maximum power is produced for the smallest internal... 

Testing of the smaller brush electrode in a cube-type MFC produced the highest power density yet achieved for an air cathode MFC of 2400 mW/m at a current density of 0.82 mA/cm (R xi = 50 Q) Logan et al. 2007). The power was 73 W/m based on normalizing power to the reactor liquid volume. Ce ranged from 40% to 60% depending on current density. 

---