Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University, Chongqing 400030, China; Institute of Engineering Thermophysics, School of Energy and Power Engineering, Chongqing University, Chongqing, China. Electronic address: [Email]
High carbon catalyst loadings are commonly used for the catalyst layer (CL) in air-cathodes to obtain a performance comparable with that using platinum. This results in a much thicker CL, which severely limits mass transfer. In this study, we developed a porosity-gradient CL to passively enhance mass transfer in the air-cathode of microbial fuel cells (MFCs) for the first time. Computational results demonstrated that a cathode CL with increasing porosity (CL-IP) and decreasing porosity (CL-DP) from the water to the air-facing side exhibited improved transport of oxygen and OH-, respectively, alleviating concentration overpotentials in the CL. Experimental results also showed that an MFC that included a cathode with CL-IP achieved a maximum power density of 1781 ± 92 mW m-2, which was higher than that achieved with CL-DP and a homogeneous CL (1614 ± 72 and 1183 ± 205 mW m-2).