Construction Of MXene/Metal Organic Frameworks Derived Carbon Composites And Their Application As Catalysts For Oxygen Reduction Reaction

Since the 21st century,human society has developed rapidly.Traditional energy sources such as coal and oil gradually deviate from the concept of green and sustainable development of contemporary human civilization due to their limited reserves,serious pollution and low utilization rate.In recent years,proton exchange membrane fuel cell(PEMFC)has been widely favored by all walks of life because of its high power density,ultra-low pollution and high efficiency.However,due to the slow kinetic process of its core semi reaction Oxygen Reduction Reaction(ORR),the operation of the battery often needs the help of catalysts.At present,the mainly used catalyst is commercial Pt/C.Because of its high cost and poor stability,it greatly hinders the wide popularization of proton exchange membrane fuel cells.Therefore,developing cheap and efficient alternatives to commercial catalysts has become the mission of scientific researchers.In this paper,MXene,which are very popular in recent years,are studied and compounded with Metal Organic Frameworks(MOFs)to explore the application of MXene in the field of oxygen reduction catalysts.The specific work includes the following three parts:1.Fe-doped ZIF-8/Ti3AlC2 was synthesized by liquid phase growth method,then calcined and etched to obtain Fe-N-C/Ti3C2Tx.Then,the spatial structure relationship and phase information were analyzed by SEM and XRD;The chemical coupling was analyzed and clarified by XPS,and the optimization mechanism was revealed.Finally,the oxygen reduction performance was analyzed by rrde and compared with commercial Pt/C and pure Fe-N-C catalysts.The excellent performance of the catalyst was demonstrated from the aspects of electrochemical impedance spectroscopy,cycle stability and electrochemical active area.The starting potential of the synthesized Fe-N-C/Ti3C2Tx was 0.94 V and the half wave potential was 0.86 V(vs.RHE),and the half wave potential attenuated only 10 mV after 10000 cycles.2.Fe doped ZIF-8 was synthesized by liquid phase growth method,and fe-n-c was prepared by pyrolysis.Then Fe-N-C particles were anchored by the adsorption of electronegative functional groups on the surface of Ti3C2Tx,and Fe-N-C@Ti3C2Tx was obtained after calcination again.This method not only ensures the quality of Fe-N-C active sites,but also improves the utilization of Ti3C2Tx surface.The morphology of the material was clearly observed by SEM and TEM.Fe-N-C particles were evenly distributed on the surface of Ti3C2Tx,which greatly improved the surface utilization of Ti3C2Tx and was conducive to exposing more active sites;The chemical coupling between Fe-N-C and Ti3C2Tx and the mechanism of catalyst performance optimization were analyzed and clarified by XPS and Raman.Owing to the formation of Ti-O-N bond,oxygen is more easily adsorbed and dissociated on the surface of Ti3C2Tx.Its initial potential was 0.97 V,half wave potential was 0.88 V(vs.RHE),and the half wave potential did not decay after 10000 cycles.3.ZIF-67/Ti3C2Tx was synthesized by liquid phase growth method,then calcined and pickled to obtain Co-N-C/Ti3C2Tx.The phase,structure and morphology of the composite catalyst were analyzed by XRD and SEM.The active sites were better coated on the surface of Ti3C2Tx;The valence state of Co in the catalyst was analyzed by XPS to reveal the key reasons for the optimization of catalyst performance.Finally,the oxygen reduction catalytic activity was analyzed by RRDE,and compared with commercial Pt/C and pure co-n-c catalysts.Based on its huge specific surface area,abundant and uniform Co-Nx active sites and excellent conductivity,Co-N-C/Ti3C2Tx showed excellent catalytic activity.The initial potential was 0.94 V,the half wave potential was 0.85 V(vs.RHE),and the half wave potential attenuated only 5 mV after 10000 cycles.