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Effect of electrode properties on coulombic efficiency of microbial fuel cell (MFC)

pubblicazioni - Poster

Effect of electrode properties on coulombic efficiency of microbial fuel cell (MFC)

Microbial fuel cell (MFC) is a promising technology capable of treating wastewater and generating electricity. An important parameter to indicate the MFC performance is the coulombic efficiency (CE) that is the ratio between the electrons transported from the organic substrates to the anode electrode and the maximum electrons if all the substrates are degraded and converted to useful electrical current [1]. Different operating conditions have been analyzed in order to optimize the CE in MFCs [2-6]. In this study, the effects of electrode properties, including anode area (2-40 cm2 geometric area), cathode area (1.25-10 cm2 geometric area) [2], PTFE external layers [3], cathode platinum (Pt) loading (0.005-1 mgPt/cm2) [4-5], and chemical oxygen demand (COD) concentration (0.1-3 gCOD/l) [4-5] on power generation were investigated in single chamber MFCs. The increase in anode area didn’t clearly affect the CE values (variation<5%), while the increase in cathode area led to a slight increase in power generation (20% higher) [2] and a significant increase in COD removal (from 50% to 90%) [2], which was caused by a greater aerobic biofilm activity on the larger cathode surface (9 times greater). However, greater aerobic activity in MFCs led to less efficient transformation of organic substrates to useful electricity. Thus, the CE decreased with the cathode area (from 40% to 20%). The addition of external PTFE layers on the cathode surface led to a lower oxygen transport through the cathode and a lower formation of aerobic biofilms. The power generation and the COD removal decreased as shown previously [3]. In contrast, the removal of those PTFE layers accelerated the oxygen reduction reaction on cathodes, consequently the power generation and COD removal efficiency increased [3]. The overall CE values were slightly higher in the MFCs with PTFE external layers, probably due to lower aerobic activity and lower COD removal efficiency. Different cathode Pt loadings have been tested in MFCs with wastewater and wastewater with sodium acetate (NaOAc) [4-5]. The results showed a higher power generation with the increase in Pt loadings, but no clear trend for COD removal at different Pt loadings [4-5]. Consequently, the CE increased with the cathodic Pt loading. Moreover, the MFCs fed with wastewater and NaOAc had almost one order of magnitude higher power generation than the MFCs fed with raw wastewater alone, due to a greater quantity of easily degradable organic substrates in the MFCs [4-5]. Consequently the CE values increased consistently with the decrease in COD concentration in the MFCs. This work showed that electrode (anode/cathode) properties and COD concentrations affect the CE values and power generation of MFCs, and are important to optimize the transformation of organic substrates to in electricity in MFCs.

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