Preparation Of Ligand-modulated Fe Atom Dispersion Catalysts And Investigation Of ORR Performance

The fossil energy crisis and environmental pollution have driven the development of green and sustainable energy technologies,such as fuel cells and zinc-air batteries,which are favored for their greenness and high energy conversion efficiency.However,they suffer severely from the multielectron transfer process in the cathodic oxygen reduction reaction(ORR),which has hampered their performance greatly.Although Pt-based materials can accelerate ORR kinetics effectively,their shortage and high costs limit their commercial applications.Recently,carbon materials loaded with metal phthalocyanine or metal porphyrin have become promising candidates due to excellent performance,where after thermal decomposition,they result in single-atom catalysts(SACs)of metalnitrogen-carbon(M-N-C).Among them,iron-based catalysts exhibit outstanding ORR activity,and their microenvironment can be appropriately modulated to regulate their ORR activity through the influence on central metal’s electron structure.In this study,we utilized porous nitrogen-doped carbon from ZIF-8 and a ligand molecule to chelate Fe2+,resulting in the production of atomically dispersed Fe-N-C structure and Fe AC/Fe SA-N-C structure catalysts.We then investigated the ORR catalytic activity and performance of these catalysts in zinc-air batteries using an electrochemical workstation and battery testing system.Additionally,we analyzed the composition and source of activity of the catalysts through various physical characterization methods.The research findings are outlined below:1.Porous nitrogen-doped carbon derived from ZIF-8 was employed as a support to disperse Fe2+ using 2,2’-bipyridine as the ligand molecule for thermal decomposition preparation of Fe-N-C single-atom catalysts.The aggregation of Fe atoms appears at a lower temperature,while a large number of bright Fe single-atom spots were observed by aberration-corrected scanning transmission electron microscopy in the catalyst synthesized at higher temperatures,indicating successful preparation of single-atom catalysts containing Fe-N-C structures.Nitrogen isotherm adsorption/desorption tests showed that the catalyst synthesized at a higher temperature had a specific surface area of up to 1562.42 m2 g-1.In an alkaline solution,a half-wave potential of 0.907 V was achieved,and the zinc-air battery capacity assembled with this catalyst reached 783 m Ah g Zn-1,with power density of 173.64 m W cm-2.The charge-discharge cycle lasted almost 165 hours without significant decay,and the discharge voltage remained almost unchanged after continuous discharge for 190 hours.This single-atom catalyst exhibited excellent battery performance.2.A porous nitrogen-doped carbon supported by ZIF-8 and a 3,6-di(2-pyridyl)-1,2,4,5-tetrazine ligand dispersed Fe2+ were synthesized by pyrolysis to prepare the Fe AC/Fe SA-N-C catalyst.Numerous bright Fe atoms and clusters with close distances were observed under spherical aberration-corrected electron microscopy.Isothermal nitrogen adsorption-desorption testing results showed that the catalyst synthesized at higher pyrolysis temperatures had a specific surface area of 1144.95 m2 g-1 and contained a large number of mesopores.The prepared Fe AC/Fe SA-N-C exhibited excellent catalytic activity in alkaline solution,similar to Fe-N-C single-atom catalysts.The presence of clusters improved the corrosion resistance of the catalyst,resulting in superior stability.In a 12-hour timed current test,the current only decayed by 28%,and the half-wave potential reached 0.883 V.The zinc-air battery assembled with this catalyst achieved a specific capacity of 772 m Ah g Zn-1,and the discharge voltage only decayed by 8.13% after 145 cycles,indicating good performance.