Construction And Performance Study Of Self-supported Oxygen Electrode Catalyst

Zinc-air battery is a new type of green electrochemical energy conversion device that is of great significance to solve the current energy and environmental problems because of its high energy density and good safety performance.The kinetics of oxygen reduction and oxygen evolution on the oxygen electrode of zinc-air battery is extremely slow and the resistance of mass transfer and electron transport is large,which make it difficult to achieve the expected output power,energy conversion efficiency and cycle durability.Based on this,this paper proposed a research strategy of self-supporting integrated electrode to solve the above issues.Two controllable methods were established to synthesize self-supporting oxygen electrode catalysts and subsequently their catalytic performances,catalytic mechanisms and potential application in zinc-air battery were studied.An economical and efficient metal-organic framework grafting-derivatization method was innovatively proposed to develop free-standing single-atom catalyst integrated electrode materials.Metal-organic frameworks was grafted on a three-dimensional flexible porous carbon micron tube sponge substrate.The metal-organic frameworks would transform into a thin catalytic layer enriched with Fe-N₅ single-atom sites during high-temperature process.That is a three-dimensional self-supporting single-atom catalyst integrated electrode material was obtained.This self-supporting material consists of porous carbon micron tubes cross-linked to each other,which can shorten the mass and electron transport paths reducing mass transport and i R performance losses when it is directly used as an oxygen electrode.The thin catalytic layer on the wall of the carbon micron tube effectively accelerates the catalytic kinetic processes and enhances the catalytic activities.As a result,the resulting single-atom catalyst integrated electrode exhibits ultra-high oxygen reduction activity(0.942 V@-3 m A cm^-2).When directly used as the oxygen electrodes of liquid-state and solid-state zinc-air batteries,high peak power densities of 183.1 m W cm^-2 and 58.0 m W cm^-2 were respectively achieved,superior to their powder counterparts and commercial Pt/C catalysts.Density functional theory calculations show that atomically dispersed Fe-N₅ species on the catalyst surface can significantly reduce the energy barrier of the decisive step in the catalytic process,thereby increasing the oxygen reduction catalytic activity.A thermally driven strategy of metal atoms diffusing and trapped was innovatively proposed to develop free-standing integrated electrode materials containing both single-atom and nanosized active parts.Nanosized bimetallic oxides（Co Fe O_x）were anchored on nitrogen-doped flexible self-supporting hollow carbon fibre cloth.Metal atoms would migrate from the bimetallic oxides during high-temperature treatment.Such metal atoms could be trapped by nitrogen doping,resulting in a large number of atomically dispersed Co/Fe active sites.Thus,free-standing and flexible integrated electrode material enriched with single-atom and nanosized active parts was obtained.Due to its structure advantages and multi-component synergistic effect for oxygen reduction and oxygen evolution reactions,the obtained catalyst shows excellent electrocatalytic oxygen activity（ΔE=0.542 V）.When assembled into liquid-state and flexible solid-state zinc-air batteries,the peak power densities of 237.4 m W cm^-2 and 141.1 m W cm^-2 were obtained,respectively.Furthermore,the battery performance was almost not decayed after 1000 charge-discharge cycles.The self-supporting catalyst exhibits excellent catalytic activity and stability,illustrating its good practical value.