Separator Characteristics for Increasing Performance of Microbial Fuel Cells

Abstract

Two challenges for improving the performance of air cathode, single-chamber microbial fuel cells (MFCs) include increasing Coulombic efficiency (CE) and decreasing internal resistance. Nonbiodegradable glass fiber separators between the two electrodes were shown to increase power and CE, compared to cloth separators (J-cloth) that were degraded over time. MFC tests were conducted using glass fiber mats with thicknesses of 1.0 mm (GF1) or 0.4 mm (GF0.4), a cation exchange membrane (CEM), and a J-cloth (JC), using reactors with different configurations. Higher power densities were obtained with either GF1 (46 +/- 4 W/m(3)) or JC (46 +/- 1 W/m(3)) in MFCs with a 2 cm electrode spacing, when the separator was placed against the cathode (S-configuration), rather than MFCs with GF0.4 (36 +/- 1 W/m(3)) or CEM (14 +/- 1 W/m(3)). Power was increased to 70 +/- 2 W/m(3) by placing the electrodes on either side of the GF1 separator (single separator electrode assembly, SSEA) and further to 150 +/- 6 W/m(3) using two sets of electrodes spaced 2 cm apart (double separator electrode assembly, DSEA). Reducing the DSEA electrode spacing to 0.3 cm increased power to 696 +/- 26 W/m(3) as a result of a decrease in the ohmic resistance from 5.9 to 2.2 Omega. The main advantages of a GF1 separator compared to JC were an improvement in the CE from 40% to 81% (S-configuration), compared to only 20-40% for JC under similar conditions, and the fact that GF1 was not biodegradable. The high CE for the GF1 separator was attributed to a low oxygen mass transfer coefficient (k(O) = 5.0 x 10(-5) cm/s). The GF1 and JC materials differed in the amount of biomass that accumulated on the separator and its biodegradability, which affected long-term power production and oxygen transport. These results show that materials and mass transfer properties of separators are important factors for improving power densities, CE, and long-term performance of MFCs.

Optimizing the electrode size and arrangement in a microbial electrolysis cell

“…The hydrogen evolution reaction often limits the overall MEC performance and cathodes with a larger surface area have demonstrated an increase in hydrogen production and current density (Call et al, 2009). Also, both MFC and MEC tests have demonstrated that the maximum power output can be increased by reducing the distance between the electrodes (Ghangrekar and Shinde, 2007;Liu et al, 2005a;Zhang et al, 2009).…”

Microbial fuel cells for energy production from wastewaters: the way toward practical application

“…A thick aerobic biofilm on the cathodes may function as a diffusion barrier to H + transfer to the catalyst site (Zhang X. et al, 2009;Ahmed, 2011), and it can severely block OH − transport outside the electrode, resulting in an significant OH − accumulation in the cathode microenvironment and thus a lower cathode potential (Yuan et al, 2013); the aerobic bacteria may consume a portion of the available oxygen at the catalytic sites and thus reduce the oxygen reduction kinetics Yuan et al, 2013); the EPS of attached microorganisms may also cause catalyst poisoning. Up to now, only the mechanisms of blockage of OH − and oxygen transfer by the cathodic biofilms have been demonstrated Yuan et al, 2013), the mechanisms how the aerobic biofilm affects cathode performance still need to be investigated.…”

“…Up to now, only the mechanisms of blockage of OH − and oxygen transfer by the cathodic biofilms have been demonstrated Yuan et al, 2013), the mechanisms how the aerobic biofilm affects cathode performance still need to be investigated. As a result of biofilm growth, an increased internal resistance coupled with a decreased electricity (power) generation of MFCs was obtained in many studies (Cheng et al, 2006;Yang et al, 2009;Zhang X. et al, 2009;Zhang F. et al, 2011a). Therefore, it is important to develop effective methods to minimize the cathode bacterial growth for a better long-term performance of MFCs.…”

“…Fouling and deformation of separator materials (e.g., membranes and various cloths) also impair the long-term stability of MFCs (Zhang X. et al, 2009;2010;Xu et al, 2012). The mechanism how separator fouling affects the performance of MFCs is very complex because physical, chemical, and biological interactions between the contaminants and the separator all occur simultaneously during the fouling process.…”

Recent Development of Miniatured Enzymatic Biofuel Cells 657

“…In this case, Nafion used in the MFCs is not an efficient proton specific membrane but actually a cation specific membrane (Rozendal et al, 2006). Subsequent studies have implied that anion-exchange or bipolar membranes has better properties than cation exchange membranes regarding to cell performance (Zhang et al, 2009). Two promising applications of MFCs in the future are wastewater treatment and electricity generation (Feng et al, 2008 andKaturi &Scott, 2010).…”