Influence Mechanism And Optimization Of Air Cathode Performance In Microbial Fuel Cells

With the development of the economy,the demand for energy and the increasing water consumption of society has led to increasing pressure on the environment due to water pollution and wastewater discharge.The technology used in wastewater treatment plants today is still the commonly used anaerobic plus aerobic biological combination process,which has problems such as high sludge production and high energy consumption.Microbial fuel cells（MFCs）can treat wastewater and generate energy,and the energy available in wastewater is higher than the energy consumed to treat the same volume of wastewater,so they are receiving more and more attention to save energy and treat wastewater at the same time.Since the air cathode of single chamber microbial fuel cells（SCMFCs）is susceptible to various factors,the air cathode performance is expressed to achieve better development of the MFCs system and to better achieve the goal of expansion and practicality.In this experiment,polytetrafluoroethylene（PTFE）as a binder and carbon black as（CB）gas diffusion layer（GDL）conductive oxygen permeable material were investigated.The catalytic layer,the collector layer,and the gas diffusion layer was rolled together using a roller pressing method.The oxygen reduction reaction of the air cathode is affected by oxygen and proton transfer,and this thesis is divided into three parts to investigate the effect of GDL hydrophobicity,the power generation efficiency of the catalyst layer with a medium iron-nitrogen-carbon activated carbon catalyst and the performance recovery of the contaminated air cathode.Firstly,the effect of GDL on oxygen transfer coefficient and hydrophobicity on proton and oxygen transfer in the catalyst layer were investigated.The ratio of carbon black to PTFE in different GDLs was investigated.The effect of air cathode was derived by electrochemical testing of MFCs,including linear scanning voltammetry,and electrochemical AC impedance,using a combination of several tests such as contact angle testing,nitrogen adsorption and desorption curves,and oxygen transfer,and also monitoring the COD of the system inlet and outlet water.It was shown that excess PTFE hinders the transfer of protons and electrons in the air cathode,while too little PTFE limits the oxygen transfer in the catalyst layer,and the optimum carbon black:PTFE mass ratio in this thesis is 4:1.less PTFE within the gas diffusion layer increases the specific surface and pore size and increases the oxygen transfer coefficient,obtaining a maximum 1431±80.3 m W m^-2 power density with a Coulomb efficiency of 45%.The catalyst-doped iron source with nitrogen source for air cathode was further investigated to enhance the oxygen reduction reaction process.Biological carbon prepared from cigarette waste was used as a carrier,and different air cathodes were prepared by using iron nitrate nonahydrate,and urea as the iron and nitrogen sources,respectively,according to different urea additions.The electrochemical characterization method was used to test the electrochemical properties of the air cathodes,and then the physical characteristics of the catalysts were analyzed using the relevant physical characterizatics of specific surface area,X-ray diffraction,X-ray photoelectron spectroscopy test,and Raman spectroscopy.It was shown that stirring pyrolysis generated Fe-N-C catalysts,which facilitated the air cathode performance and higher power generation,and obtained a power density of up to 2168 m W m^-2 at the optimum addition level.The air cathode contaminated by long-term operation can be treated with lysozyme for attached microorganisms,which can restore part of the power generation performance of the air cathode,up to more than 80%of the initial performance,indicating that lysing microorganisms can restore the performance of the air cathode to some extent.