Novel Cathode Materials for Microbial Fuel Cells

Open Access
Author:
Zhang, Fang
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 09, 2010
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
Keywords:
  • microbial fuel cell
  • current collector
  • cathode
  • poly(dimethylsiloxane)
  • activated carbon
Abstract:
A microbial fuel cell (MFC) is a device for direct bioelectricity generation. A new and simplified approach for making cathodes for microbial fuel cells (MFCs) was developed by using metal mesh current collectors and inexpensive polymer/carbon diffusion layers (DLs). Rather than adding a current collector to a cathode material such as carbon cloth, we constructed the cathode around the metal mesh itself, thereby avoiding the need for the carbon cloth or other supporting material. Poly(dimethylsiloxane) (PDMS) was used as diffusion layer material, preventing water leakage, limiting oxygen transfer through the cathode and improving coulombic efficiency. Multiple PDMS/carbon layers were applied in order to optimize the performance of the cathode. Two PDMS/carbon layers achieved the highest maximum power density of 1610 ± 56 mW/m2 (normalized to cathode projected surface area; 47.0 ± 1.6 W/m3 based on liquid volume). The coulombic efficiency of the mesh cathodes reached more than 80%, and was much higher than the maximum of 57% obtained with carbon cloth. These findings demonstrate that cathodes can be constructed around metal mesh materials such as stainless steel, and that an inexpensive coating of PDMS can prevent water leakage and lead to improved coulombic efficiencies. To further reduce the cost of MFC, an inexpensive activated carbon (AC) air cathode was tested as an alternative to a platinum-catalyzed electrode for oxygen reduction in a MFC. AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. Tests with the AC cathode produced a maximum power density of 1220 mW/m2 (normalized to cathode projected surface area; 36 W/m3 based on liquid volume) compared to 1060 mW/m2 obtained by Pt catalyzed carbon cloth cathode. The coulombic efficiency ranged from 15% to 55%. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs.