Microalgal cycling in the cathode of microbial fuel cells (MFCs) induced oxygen reduction reaction (ORR) and electricity: A biocatalytic process for clean energy

Abstract

Development in electricity generation technologies is necessary to ensure a safe and sustainable future. Catalytic activity of oxygen reduction reaction (ORR) is still the key challenge in microbial fuel cells (MFCs) which has not improved significantly even upon the application of catalysts. In this study, microalgae as biocatalysts (i.e., availability of electron acceptors and maintain ORR) were applied for spontaneous bioelectricity generation. Microalgal cycling was performed at various concentrations (5, 10, 15, and 20 % vv−1) in the cathode whereas, 2 % fat, oil, and grease (FOG) were added in the anode. Electrochemical and next-generation sequencing (NGS) analyses along with biological parameters were studied to fully understand the anodic and cathodic behavior towards electrogenesis. Continuous microalgal cycling resulted in the highest power density (21.0 mW m−2) and current density (245 mA m−2) in the reactor loaded with 2 % FOG + 15 % vv−1 microalgae. Electrochemical analysis showed the potential of 2 % FOG + 15 % vv−1 microalgae via exhibiting Ohmic resistance of 34. 9 Ω and charge transfer resistance of 100 Ω with improved ORR activity. NGS revealed that Clostridium (7–16.5 %), Bacteroidetes (4.54–12.87 %), and Geobacter (6.5–22.7 %) were the dominant species involved in the electron transport mechanism. CoA ligase, acetyl-CoA C-acetyltransferase, and acetate kinase were the major enzymes involved in β-oxidation and electrogenesis. This study demonstrated the baseline for the use of microalgae as biocatalyst in cathode of MFCs to improve the catalytic efficiency of ORR.