Membraneless Hybrid Biofuel Cells: Integrating Microbial Anode and Enzymatic Cathode
Membraneless and membrane-based (Nafion 117) SCMFC configuration was studied and compared in this experimentation. SCMFCs (volume of 130 ml) fed with PBS and NaOAc were run in a batch mode for a week. The batch mode SCMFC tests showed that the cathode OCP was higher than 0.5 V vs Ag/AgCl in all SCMFCs tested and stabilizes for an hour. The initial cathode polarization curves showed low overpotentials and ohmic resistances at low current generation (Figure 1a). All cathodes had significantly higher performances in comparison to the Pt-based cathode till 0.2 V vs. Ag/AgCl. Greater ohmic and mass-transfer losses during the cathode polarization were observed when a polymeric membrane (Nafion 117) was used. Markedly high power densities (referred to geometric cathode area) up to 200 μW/cm2 (2 W/m2) were reached in membraneless SCMFCs with PBS and sodium acetate (Figure 1b). When a polymeric membrane (Nafion 117) was applied in SCMFCs, the power generation dropped to 24-26 μW/cm2 (0.24-0.26 W/m2), which is most likely due to increased ohmic and diffusional losses given by the presence of a solid barrier.
This study showed the possibility of using enzymatic cathode (bilirubin oxidase) in membraneless SCMFCs with high power generation. The highest power density (2 W/m2) ever reported in a single bottle MFC fed with acetate in phosphate buffer was achieved in this study. The main problem related with the exploration of enzymatic electrodes in wastewater MFCs is the enzymes short lifetime and deactivation cased from contaminants in the wastewater.
Further studies should be conducted in order to enhance the lifetime and the long-term operation efficiency of the developed enzymatic MFCs.
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