Preparation Of Vanadium Single-atom And Sodium Single-atom Catalysts Embedded In Carbon Matrix For Oxygen Reduction Reaction

In recent years,with the increasing population and industrialization,people’s demand for energy is continually growing.Excessive consumption of fossil energy has caused serious environmental pollution.It’s our top priority to find clean alternative energy and achieve efficient energy conversion.Because fuel cells can convert chemical energy into electrical energy,like zinc-air batteries and proton exchange membrane batteries(PEFCs)et al,which have been employed in a wide range of electric equipment.The inert oxygen reduction reaction is the cathode of the above device,so the use of electrocatalysts could promote the reaction process.Therefore,high-activity catalysts play a vital role in energy conversion efficiency.Currently,platinum-based catalysts take up the mainstream position,but their scarcity,high cost and instability limit its extensive applications.Therefore,the approach to design high-efficiency noble metal-free catalysts is particularly important.In electrocatalysis,single-atom catalysts have become an emerging frontier due to their high activity,high selectivity and high stability.It is defined as single atoms dispersed on supports,with the smallest metal size and the largest utilization efficiency.Generally,the active center is a transition metal(such as Fe,Co,Ni,Cu,and Zn).By combining with dopants(N,O,S,B,and P,etc.)to regulate electronic structure of metal center,single-atom catalyst exhibits fascinating activity for oxygen reduction reactions,which is considered to be ideal candidates to replace precious metal catalysts.Here we prepare precursors by selecting appropriate organic ligands and metal salts,and finally obtain high-activity single-atom catalysts by serval pyrolysis and acid leaching processes.The specific work is as follows:1.The current reports on single-atom catalysts mainly focus on transition metal(Fe,Co,Mn,Zn,etc.)binding with nitrogen(Me-N),and d-band center of the metal is regulated by the N element.Virtually,the investigation found that vanadium coenzyme factors(V-HPOs)in algae involve in the redox reaction of halogen compounds by controlling various oxygen-containing species.Inspired by this,this paper designs and prepares vanadium single-atom catalysts with N and O co-coordination.In this paper,glycine was used as the organic ligand to react with ammonium metavanadate metal,and the metal-organic complex was obtained.Then,the monodisperse vanadium-based catalyst embedded on the carbon substrate was got by further several high-temperature pyrolysis and acid leaching.The vanadium single-atom catalyst exhibits high electrocatalytic oxygen reduction activity and zinc-air battery performance.In 0.1 M KOH solution,its half-wave potential reaches 865mV,surpassing the commercial Pt/C,and there is no degradation in performance after 5000 cycles of cycling voltage.In the zinc-air batteries,the power density reaches 180mW/cm2 and exhibits good stability.In addition,the catalyst also has good acid activity(half-wave potential 710mV)and excellent stability.Via XANES,IR,XPS,HAADF-STEM and other characterizations,we confirmed the configuration the catalyst is VN1O4.By means of density functional theory calculations,it reveals the activity of the catalyst originates from the unique VN1O4 structure.2.Currently,single-atom catalysts mainly focus on transition metal elements,and there are few reports on main group metals.Because the outermost layer of sodium has only one S electron,the valence of sodium is single,which helps to alleviate the Fenton effect.In this paper,glycine with carboxyl and amino groups is used to react with sodium compound,introducing N and O heteroatoms into the precursor.Na single-atom catalyst supported on carbon substrate demonstrates high electrocatalytic oxygen reduction activity.The half-wave potential of the catalyst reaches 81 OmV under alkaline conditions,comparable to commercial 20%Pt/C.After 8000 CV cycles,the catalyst activity shows no decline.In addition,the catalyst exhibits excellent tolerance to methanol,and has great application prospects in energy conversion devices in the future.