Preparation Of Air Cathodes With Different Capacitance Characteristics And Their Application In Microbial Fuel Cells

Bioelectrochemical systems（BESs）have good applications in the field of wastewater treatment,which can be used to remove organic matter in water or as biosensor for some substances.Electrode material is one of the important factors that affect the performance of BESs.The capacitance of the electrode indicates the ability of the electrode to store charge.During the operation of BESs,the capacitance of the electrode affect the electron transfer process,and then affect the electricity generation of BESs.In this study,different capacitive cathodes were prepared,and the effects of cathode capacitance characteristics on the application of BESs in wastewater treatment and toxicity monitoring were studied.Microbial fuel cells（MFCs）are typical of BESs.In this study,different carbon powders were used as MFCs.Through the corresponding electrochemical characterization methods,the effects of different carbon catalysts,different methods of adding catalytic layer and different cathode matrix on the cathode capacitance were compared.The results showed that the capacitance of air cathode made by adding catalytic layer in the way of dumping was twice as much as the capacitance of air cathode made by traditional coating method,and the internal resistance is smaller.The voltage of single chamber MFCs with high capacitance cathode was about 450 m V,which is comparable to that of some modified carbon catalysts.In 40 hours,the removal efficiency of chemical oxygen demand（COD）and ammonia nitrogen by high capacitance cathode single chamber MFCs was very excellent,which reached about 95%,much better than that of low capacitance cathode MFCs.But they could not effectively remove phosphorus in water.The voltage of MFCs with low capacitance cathode was about 320 m V.The maximum voltage of double chamber MFCs with high capacitance cathode was about 350 m V,and the coulomb efficiency was more than 50%.It was found that MFCs with low capacitance cathode had high tolerance to Cu²⁺,while MFCs with high capacitance cathode were more easily inhibited,which indicated that the microbial composition of MFCs with different capacitance cathode might be different.The two-hour removal rate of Cu²⁺reached 95%,but the removal rate of Pb²⁺was very low.X-ray photoelectron spectroscopy（XPS）analysis showed that the valence state of Cu²⁺was changed on the anode and proton exchange membrane.MFCs with high capacitance cathode not only have better electricity generation performance,but also more sensitive to Cu²⁺,so they are more suitable as MFC biosensors for monitoring Cu²⁺.Voltage inhibition rate was suitable as the response signal.Low capacitance cathode MFCs are more suitable for Cu²⁺removal from water.Therefore,the capacitance performance of electrode should be considered as an important factor when using bioelectrochemical method for wastewater treatment or substance monitoring.