Abstract: Cathode performance will gradually decrease during long-term operation of microbial fuel cells (MFCs), to answer why cathode performance decrease is of significant for practical application of MFCs. In this paper, nickel foam air-cathodes were used in a MFC to search the reason causing the degradation. It was found that power density of MFC with a nickel foam air-cathode was 22% less for after 4 months operation than for after 1 week operation. Electrode polarization curves measured showed that cathode performance degradation was the main reason leading to decrease in power density. At -0.2 V (vs Ag/AgCl), current density of a new cathode was 12.3 A·m^-2, and decreased to 4.2 A·m^-2 after 4 months operation. Cathode performance decreased with increase of operation time, which showed mainly in the high current range [>-0.05 V (vs Ag/AgCl)]. Scanning electron microscope (SEM) images indicated that there was no biofilm on cathode surface, implying that the decrease of oxygen diffusion rate through cathodes was the main reason causing the decrease of cathode performance. From energy dispersive spectrometer (EDS) measurement it was found that there was phosphate precipitation inside the cathode after 4 months operation. These results indicated that salt precipitation increased with increase of operation time could clog micro-pores of cathode and decreased oxygen diffusion rate, leading to degradation of cathode performance.

Key words: nickel foam cathode, microbial fuel cells, long-term operation, salt crystallization

摘要： 微生物燃料电池（MFC）阴极性能在长期运行过程中逐渐下降，查明其下降原因对MFC技术的实际应用具有重要意义。采用泡沫镍阴极研究了阴极长期运行过程中阴极下降的原因。研究发现：MFC运行4个月之后功率密度相比运行1周的MFC下降达22%，测试电极极化曲线发现阴极性能的下降是导致MFC功率密度下降的主要因素。线性伏安扫描（LSV）结果显示：运行初期在-0.2 V电势下阴极电流密度为12.3 A·m^-2，而运行4个月后，阴极电流密度下降为4.2 A·m^-2，阴极性能随运行时间增加而降低主要表现在大电流区域[>-0.05 V （vs Ag/AgCl）]。对阴极表面和内部进行扫描电子电镜（SEM）分析发现：阴极表面没有明显的生物膜，氧扩散实验发现阴极氧扩散量明显降低是造成阴极性能下降的主要原因；通过能谱分析（EDS）可知阴极内部有磷酸盐析出。这些结果说明阴极内部在长期运行过程中逐渐析盐，而析盐导致泡沫镍阴极内孔隙堵塞，阻碍氧扩散到催化层，从而使阴极性能降低。

关键词: 泡沫镍阴极, 微生物燃料电池, 长期运行, 析盐