Synthesis And Application Of Fe-based MOF-derived Carbon-based Cathodes

Energy shortage and environmental pollution are two challenges that must be overcome to reach the goal of"emission peak and carbon neutrality",and the pursuit of environmentally sustainable energy technologies is imminent.Microbial Fuel Cell（MFC）aims to recover energy from wastewater by using electricity-producing microorganisms to treat pollutants while generating valuable by-products such as electricity and hydrogen,and is a promising environmentally preferable technology.At present,the air cathode MFC with oxygen as the electron acceptor is the most widely researched.The biggest limitation of single-chamber air cathode MFC is the sluggish oxygen reduction reaction（ORR）of the cathode,which limits the performance of MFC.The most effective method to solve this problem is to use catalysts to promote the ORR reaction,and the most effective catalyst is Pt/C,but it has the disadvantages of high price and poor stability,which limits the application of MFC on a large scale.In addition,the microbial electrolysis cell（MEC）technology based on MFC also requires catalysts to improve the overall performance of the electrolysis cell.Therefore,the exploration of efficient and stable cathode catalyst materials is essential to promote the practical application of MFC.Metal-organic frameworks（MOFs）based on Fe have the advantages of high activity of transition metal elements and stable structure,which are ideal precursors for efficient and inexpensive catalysts.Among them,MIL-88B has attracted much attention because of its controllable morphology and excellent stability.In this paper,MIL-88B with spindle morphology was synthesized by hydrothermal method,composite with other materials with high nitrogen content to synthesize a series of derived catalysts,test and analyze the ORR catalytic performance,and apply to MFC and MEC microbial electrochemical techniques.The main research contents and results of this study are as follows:（1）Fluorinated MIL-88B was combined with hydrogen-bonded organic frameworks（HOFs）with high nitrogen content and carbonized to obtain a three-dimensional network carbon structure loaded with Fe₂O₃material.The ORR electrocatalytic performance is comparable to that of conventional Pt/C catalysts,with a four-electron transfer pathway under both alkaline and neutral conditions,and the oxygen reduction peak（-0.10 V,vs.Ag/AgCl）is even higher than that of commercial Pt/C catalysts.The F-MIL-HOF catalyst performed well in stability tests,with only a10.2%decrease in performance,still providing efficient ORR catalytic performance.The MFC voltage was maintained at 0.44 V when F-MIL-HOF was loaded onto the MFC reactor cathode replacing Pt/C.（2）The MCN-1 material loaded with Fe/Fe₃C active nanoparticles was obtained by mixing MIL-88B and g-C₃N₄materials by a simple impregnation method after carbonization at a lower temperature,and the MCN-1 catalyst still maintained the spindle morphology of MIL-88B.the Fe/Fe₃C active material was dispersed on the spindle surface,which made MCN-1 exhibit an excellent performance under alkaline and neutral conditions The double layer capacitance of MCN-1 is 7.03 mF cm^-2and the limiting diffusion current density reaches 7.65 mA cm^-2,which is much higher than that of Pt/C(6.26 mA cm^-2).After loading MCN-1 into the MFC cathode instead of Pt/C,the MFC voltage reached 0.57 V and the power density was 3421.0±67.3mW m^-3,which is better than that of commercial Pt/C catalysts.（3）The MCN-1 catalyst was used on the biocathode of the MEC to improve the hydrogen production rate and sulfate removal capacity.Experimental results showed hydrogen production rates up to 0.47 m³H₂/m³·d and sulfate removal up to 85%.This excellent performance is attributed to the efficient catalytic performance and biocompatibility of MCN-1,which can synergize with microorganisms.