Preparation Of The Catalysts Based On Zinc Containing MOFs And Their Oxygen Reduction/Evolution Performance

The problem of environmental degradation and energy shortage have become increasingly prominent.The development of efficient and clean energy conversion technologies has become the key to solving these problems.Lithium-air battery has attracted wide attention since the high theoretical energy density.However,the OER and ORR at the cathode on have been extremely slow,resulting in its low actual energy density.MOFs has a large specific surface area and a rich channel structure and has great potential for application in the field of electrocatalysis.The boiling point of metal zinc is low.In the process of high temperature treatment,the volatilization of zinc can make the material rich in pores.Based on this point,the zinc containing MOFs material was synthesized in this work,and the catalyst was prepared by doping and carbonizing,and catalytic performance of OER/ORR was studied.MOF-5 was synthesized by a stirring synthesis method,followed by high temperature carbonization and nitrogen doping.The prepared catalyst particles are evenly distributed.In 0.1 M KOH electrolytes,they have good ORR catalytic activity.Among them,the N/CMOF-5-500 catalyst has the best ORR activity,the initial voltage is-0.088 V,the half wave potential is-0.179 V,the limiting current density is-5.510 mA·cm-2,the Tafel fitting slope is-44.2 mV·dec-1,the electron transfer number is 3.91;However,the OER catalytic activity is poor.The doping of nitrogen can significantly increase the ORR activity of the catalyst.Co/ZIF-8 was synthesized by a stirring synthesis method,and then carbonization was carried out at high temperature.The prepared catalysts have high degree of defect.In 0.1 M KOH electrolytes,they have good ORR and OER catalytic activity.Among them,the CoZn-5 catalyst has the best OER/ORR activity,the half wave potential of ORR is-0.141 V,the limiting current density is 4.374 mA·cm-2,Tafel fitting slope is 64.1 mV·dec-1,the electron transfer number is 3.77;Tafel fitting slope of OER is 87.3 mV·dec-1,the current density on 0.8 V is up to 24.357 mA·cm-2.Doping of a certain amount of cobalt element can greatly increase the ORR/OER catalytic activity of the catalyst.Fe/IRMOF-3 was synthesized by solvothermal method and carbonized at high temperature.The prepared catalysts have high defect degree and high content of nitrogen and iron.In the 0.1 M KOH electrolytes,they have good ORR and OER catalytic activity.Amonge them,the FeZn-10 catalyst has the best OER/ORR activity.The half wave potential of ORR is-0.158 V,the limit current density is 5.499 mA·cm-2,the ORR Tafel fitting slope is 64.5 mV·dec-1,and the electron transfer number is 3.96.The Tafel fitting slope of OER is 50.5 mV·dec-1,and the current density at 0.8 V is 16.791 mA·cm-2.By doping a certain amount of iron element,the ORR/OER activity of the catalysts can be improved obviously.