Improved performance of microbial fuel cells using a gradient porous air cathode: An experiment and simulation study

Area of Science:

• Electrochemistry
• Materials Science
• Energy Conversion

Background:

• High carbon catalyst loadings in air-cathode catalyst layers (CLs) are essential for performance comparable to platinum but lead to thicker CLs, hindering mass transfer.
• Limited mass transfer in conventional CLs restricts the efficiency of microbial fuel cells (MFCs).

Purpose of the Study:

• To develop and investigate a novel porosity-gradient catalyst layer (CL) for air-cathodes in MFCs.
• To passively enhance mass transfer within the CL and improve MFC performance.

Main Methods:

• Computational modeling to simulate oxygen and hydroxide ion transport in porosity-gradient CLs.
• Fabrication and experimental testing of MFCs with different CL structures: increasing porosity (CL-IP), decreasing porosity (CL-DP), and homogeneous CL.

Main Results:

• Computational results indicated that CL-IP improved oxygen transport, while CL-DP enhanced OH^- transport, both alleviating concentration overpotentials.
• Experimental MFCs with CL-IP achieved a maximum power density of 1781 ± 92 mW/m^-2.
• CL-IP outperformed CL-DP (1614 ± 72 mW/m^-2) and homogeneous CL (1183 ± 205 mW/m^-2).

Conclusions:

• A porosity-gradient CL is an effective strategy to passively enhance mass transfer in MFC air-cathodes.
• The CL with increasing porosity (CL-IP) demonstrated superior performance, leading to significantly higher power density in MFCs.