effects of oxygen transport on performance of microbial fuel cells

Open Access
- Author:
- Zhao, Yi
- Graduate Program:
- Environmental Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 18, 2013
- Committee Members:
- John Michael Regan, Thesis Advisor/Co-Advisor
- Keywords:
- microbial fuel cells
oxygen transport
ORR
heliox - Abstract:
- Microbial fuel cells (MFCs) are a promising technology for extracting energy from pollutants in wastewater. The slow oxygen transport in the cathode of a typical air-cathode MFC is one of the limiting factors giving rise to low kinetics of the oxygen reduction reaction (ORR) in these systems. This research was aimed at studying gas-phase oxygen transport in air-cathode MFCs by the comparative performance of heliox- (21% oxygen and 79% helium, which enhances oxygen diffusivity relative) and air-supplied reactors. Identical air-cathode MFCs were operated until they all attained stable electrochemical performance. Two pairs of reactors were then switched to either air- or heliox-fed conditions, with one reactor maintain as an air-cathode control. The cathode potentials of heliox-fed MFCs significantly increased and were higher than those of air-fed reactors. At a gas flow rate of 5 L/h, the highest peak current obtained by heliox-fed MFCs was 10 A/m2, compared to 9.1 A/m2 in air-fed MFCs. The maximum power density of heliox-fed reactors (1320 ± 50 mW/m2) was 26% higher than that of air-fed systems (1050 ± 40 mW/m2). Electrochemical impedance spectroscopy (EIS) was performed to characterize cathode and system impedances. The internal resistance of heliox-fed MFCs was 27% lower than that of air-fed reactors at a cathode potential of 0.4 V and 51% lower at 0 V. A significant decrease in diffusion resistance-the dominant component of internal resistance–was measured for heliox systems relative to air-fed reactor. Heliox-fed MFCs also had slightly better chemical oxygen demand (COD) removal efficiencies, and both gas conditions had comparable Coulombic efficiencies (CEs). Collectively, these results demonstrate that heliox improved oxygen transport to the cathode catalyst by decreasing the diffusion resistance, without inducing negative effects associated with excessive oxygen intrusion to the MFCs.