Cathode Performance as a Factor in Electricity Generation in Microbial Fuel Cells

Abstract

Although microbial fuel cells (MFCs) generate much lower power densities than hydrogen fuel cells, the characteristics of the cathode can also substantially affect electricity generation. Cathodes used for MFCs are often either Pt-coated carbon electrodes immersed in water that use dissolved oxygen as the electron acceptor or they are plain carbon electrodes in a ferricyanide solution. The characteristics and performance of these two cathodes were compared using a two-chambered MFC. Power generation using the Pt-carbon cathode and dissolved oxygen (saturated) reached a maximum of 0.097 mW within 120 h after inoculation (wastewater sludge and 20 mM acetate) when the cathode was equal size to the anode (2.5 x 4.5 cm). Once stable power was generated after replacing the MFC with fresh medium (no sludge), the Coulombic efficiency ranged from 63 to 78%. Power was proportional to the dissolved oxygen concentration in a manner consistent with Monod-type kinetics, with a half saturation constant of K(DO) = 1.74 mg of O2/L. Power increased by 24% when the cathode surface areas were increased from 22.5 to 67.5 cm2 and decreased by 56% when the cathode surface area was reduced to 5.8 cm2. Power was also substantially reduced (by 78% to 0.02 mW) if Pt was not used on the cathode. By using ferricyanide instead of dissolved oxygen, the maximum power increased by 50-80% versus that obtained with dissolved oxygen. This result was primarily due to increased mass transfer efficiencies and the larger cathode potential (332 mV) of ferricyanide than that obtained with dissolved oxygen (268 mV). A cathode potential of 804 mV (NHE basis) is theoretically possible using dissolved oxygen, indicating that further improvements in cathode performance with oxygen as the electron acceptor are possible that could lead to increased power densities in this type of MFC.

High Power Density from a Miniature Microbial Fuel Cell Using Shewanella oneidensis DSP10

“…This calculation reveals that the mini-MFC, while using a ferricyanide catholyte and GF electrodes, produced 160 and 1960 times more current and power density than previously reported for a pure culture Shewanella putrefaciens MFC. The use of dissolved oxygen in the cathode chamber could reduce this difference by up to 8-fold (27), but significant differences in performance remain. Based on the comparisons stated above, we believe that the mini-MFC demonstrates that small footprint devices that take advantage of shorter diffusion paths and higher surface area-to-chamber volume ratios could present significant advantages over larger, less efficient designs.…”

Studies on Sustainable Power Estimation from Local Waste Waters Using Microbial Fuel Cells

“…The variation of Dissolved oxygen with time is depicted in Fig 7. Results showed that dissolved oxygen increased from 2.5 mg/L to 4.2 mg/L. The reason for increase in the Dissolved oxygen of waste water sample is due to decrease in the levels of BOD and COD in the waste water sample and aeration [18][19][20][21][22][23][24][25][26][27]. …”

Microbial fuel cells in bioelectricity production

“…Cathodes usually used in MFCs are either Pt-coated carbon electrodes immersed in water of just plain carbon electrodes in ferricyanide solution (Oh et al 2004). Carbon cloth is most commonly used as material for electrode in MFC along with Pt as catalyst but are expensive in nature.…”