Performance of Membrane Electrode Assembly Microbial Fuel Cells Using Activated Carbon Cathodes with Various Diffusion Layers

Open Access
Author:
Hays, Sarah Elizabeth
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 03, 2011
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
Keywords:
  • membrane electrode assembly
  • microbial fuel cells
  • carbon mesh anode
Abstract:
A microbial fuel cell (MFC) is a device that uses bacteria to generate electricity through the oxidation of organic matter. MFCs continue to be extensively researched with various chemical feed sources using a conventional setup with widely spaced electrodes, and cathodes containing platinum. However, these specifications make scale-up expensive and difficult to construct. Many anode and cathode materials have been used in different configurations in the past; however, most of these studies chose to use idealized substrates, which is unrealistic for practical applications. In this study, a membrane electrode assembly (MEA) MFC was constructed using activated carbon (AC) cathodes and either a carbon brush or flat carbon mesh anode, and domestic wastewater as a feed substrate. The use of carbon brush anodes produced consistently higher voltage and power density results than carbon mesh anodes. Over time, the average voltage from the carbon brush anode reactor configurations was 360 ± 63 mV, while the carbon mesh anode configuration was 200 ± 81 mV. The average decrease in power density over time (89 days) from the carbon brush anode reactor configurations was 15 mW/m2, while the carbon mesh anode configuration dropped 190 mW/m2 over time. The maximum Coulombic efficiency (CE) for the mesh anode configuration was 22 ± 0.4%, while for the brush anode configuration it was 13 ± 2.9%.The CE for the mesh anode decreased 17% over time and the average CE was only 7.8 ± 7.1%. The average CE for the brush anode configuration was 8.6 ± 2.9% with a 4.6% decrease over time. Brush anodes measured consistently higher average COD removal values per cycle (80 ± 3%) than carbon mesh anodes (58 ± 7%). To optimize the use of carbon mesh anodes, additional diffusion layers (DLs) were added to the AC cathodes. This hindered oxygen diffusion to the anode, which was expected to be contributing to the decline in performance of reactors using carbon mesh anodes. Increased voltage and power generation correlated directly to an increase in the number of diffusion layers added. The setup which allowed the least oxygen diffusion used two layers of generic cling wrap (G2-PG), and achieved an average voltage of 310 ± 52 mV and a maximum power density of 160 mW/m2. CE values positively correlated with the addition of diffusion layers. However, as seen with the original setups which did not have additional DLs, there was a steady decrease in CE over time. The addition of DLs positively correlated to lower effluent BOD5 values. These findings showed that the addition of diffusion layers improved the performance of carbon mesh anodes in a MEA reactor configuration. However, the use of brush anodes provided more consistent, reliable results over time than the use of thinner carbon mesh anodes with domestic wastewater.