Controllable Preparation Of Oxygen-Catalyzed MOF-Based Porous Carbon Fibers And Their Application In Flexible Zinc-Air Batteries

The continuous development of flexible wearable electronic products in the fields of smart clothing,medical care and mobile communications,and the proposal of the"carbon peaking and carbon neutrality"green economic development model have created an urgent need for environmentally friendly and sustainable flexible energy storage devices.Flexible zinc-air batteries（FZABs）are considered to be extremely promising flexible energy storage devices,due to the advantages of high energy density,good mechanical flexibility and eco-friendly compositions.However,the current development of FZABs is constrained by the sluggish oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）that occur on the air cathode side.Currently,precious metal（such as Pt and Ir,Ru）-based materials are the state-of-the-art ORR/OER catalysts,but their high prices and scarcity seriously hinder their industrial application in a large scale.Therefore,it is of great practical significance to develop oxygen catalysts with low cost,high catalytic activity and excellent stability.Herein,different kinds of metal-organic frameworks（MOFs）derivatives are used as the starting point,a variety of MOFs-based porous carbon nanofibers were prepared through electrospinning technology and post treatment,and used as oxygen catalysts for liquid and flexible zinc-air batteries.The specific research are as follows:1.Taking MOFs-derived transition metal-nitrogen-carbon as the entry point,the Co,N co-doped porous carbon nanofibers（Co@N-HPCFs）was fabricated using electrospinning technology and heat treatment,while using core-shell ZIF-8@67 as the precursor.The as-prepared catalyst possessed a unique one-dimensional fiber and hollow structure,high-density and uniformly dispersed Co nanoparticles and Co@N-C active sites.In alkaline solution,Co@N-HPCF-800 exhibited an efficient four-electron ORR reaction process with a half-wave potential of 0.831 V and a limited diffusion current density of 5.85 m A cm^-2,which is comparable to commercial Pt/C.In addition,the methanol tolerance and electrochemical stability of the catalysts were superior to those of Pt/C.When such MOFs-derived Co-N-C-based porous carbon fibers were used as air cathode catalysts for liquid/solid Zn-air batteries,the batteries exhibited high peak power density,excellent long-term cycling stability,and mechanical flexibility.2.The catalytic activity of the above-mentioned Co-N-C-based porous carbon fibers is comparable to that of commercial Pt/C.However,for the cathode catalysts of zinc-air battery,it is of great significance to have ORR and OER bifunctional oxygen catalytic activity.Herein,we took MOFs-derived carbon-based transition metal oxides as the entry point,synthesized a nitrogen-doped Cu Co₂O₄nanoparticle-embedded 1D beaded-like structure carbon nanofibers（N-Cu Co₂O₄@CNFs）through electrospinning technology and controllable nitrogen doping technique,while using polyacrylonitrile（PAN）as the supporting substrate and bimetallic Cu Co-MOF as the self-sacrificial template and heteroatom doping source.Benefiting from the synergistic effect between interconnected1D hierarchical porous structure and high catalytic activity of N-doped Cu Co₂O₄nanoparticles,the N-Cu Co₂O₄@CNFs catalysts exhibited enhanced ORR/OER reaction kinetics and preferable charge transfer ability.As a result,the as-prepared N-Cu Co₂O₄@CNFs-800 exhibited prominent electrocatalytic ability and superior stability for OER/ORR,even surpassed the commercial Pt/C and Ru O₂.Furthermore,the liquid ZABs employing the N-Cu Co₂O₄@CNFs-800 as bifunctional air cathode catalyst obtained a high peak power density(175.6 m W cm^-2),a low charge-discharge voltage gap（0.82 V）and excellent charge-discharge cycling stability（up to 40 h）.