Preparation Of Carbon-based Electrocatalyst And Their Application In Zinc-air Battery

With the rapid development of the economy,the rapid consumption of energy and the deterioration of the environment have become the obstacles restricting the progress of human society,urgently needing new energy technologies.As a new battery technology integrating energy storage and energy conversion technology,Zinc-air batteries（ZABs）can be used as the power source of electric vehicles and as the storage energy of the battery.However,ZABs is limited by the slow oxygen reduction reaction and oxygen evolution reaction at the air cathode,like fuel cells.At present,Pt-based,Ir-based,and Ru-based noble metal catalysts are used commercially to solve the slow oxygen reaction.However,the high price and scarce reserves of precious metals seriously restrict the commercialization of ZABs,and catalytic technology has become a bottleneck of ZABs technology.So,it is the only way for ZABs industrialization to develop efficient and low-cost bifunctional catalysts to replace noble metal catalysts.Among many catalysts,nitrogen-doped carbon-based catalysts have become the research focus of bifunctional catalysts because of their excellent electrocatalytic activity and lasting stability.At the same time,as the element with the greatest electronegativity,fluorine has three lone pairs of electrons.Using fluorine to modify the nitrogen-doped carbon-based catalyst can change the density of electron clouds on adjacent carbon and improve its electrocatalytic activity better.Therefore,nitrogen and fluorine co-doped carbon-based catalysts are highly likely to replace noble metal catalysts as air electrode catalysts for ZABs.In this paper,melamine/dicyandiamide as a nitrogen-doped carbon framework,through high fluorine polyvinylidene fluoride（PVDF）/polytetrafluoroethylene（PTFE）modified carbon framework,prepared a series of transition metal-doped carbon-based catalyst,and its in-depth study,the main contents are as follows:（1）A series of N and F co-doped carbon-based catalysts MPFe_xCu_y containing Fe-Cu bimetal were prepared using Melamine and PVDF as precursors,referred the Fe/Cu bimetal center of cytochrome C oxidase（Cc O）as reference.XRD and rotary disk analysis show that the optimum carbonization temperature is 850℃.At the same time,when the ratio of iron to copper was 1:1,the catalyst showed good ORR activity in acidic electrolytes.ZABs can maintain a stable discharge of 110 h at a current of 10 m A cm^-2,which is higher than 80 h at commercial Pt/C.（2）Further study on the bi-functional catalytic activity of N and F co-doped carbon-based catalysts.Due to the wide sources,low price,non-toxic and harmless,and excellent electrocatalytic performance of iron and nickel,we synthesized the DPT-Fe_xNi_y series of bi-functional catalysts by Fe Ni bimetal doped dicyandiamide and PTFE mixture.Because the Fe_0.64Ni_0.36 intermetallic compound formed when the ratio of Fe to Ni is 2:1,the DPT-Fe₂Ni₁catalyst has the strongest bifunctional catalytic performance（ΔE=0.733V）,which is superior to commercial Pt/C+Ru O₂ mixed catalyst 26 m V.Furthermore,DPT-Fe₂Ni₁ as ZABs air electrode catalyst has excellent charge-discharge stability and peak power density of 349.2 m W cm^-2.（3）Finally,to explore the effect of FeCoNi tri-metal on the performance of N and F co-doped carbon-based catalyst,we calcined melamine,PTFE,and metal salt to generate MPT-Fe_xCo_yNi_z series catalyst by the one-pot method.It was found by rotary disk analysis that both double-doped Fe Co and triple-doped FeCoNi could increase the proportion of four-electron pathways in the ORR catalytic process,and the yield of H₂O₂ was lower than that of single-doped Fe catalyst.Meanwhile,MPT-Fe₁Co₁Ni₁ synthesized with FeCoNi atomic ratio of 1:1:1 has the best bifunctional activityΔE=0.719V.ZABs assembled with MPT-Fe₁Co₁Ni₁ as the cathode catalyst shows a peak power density of 385.7 m W cm^-2 and the charge-discharge stability of 300 cycles.However,the mechanism of the effect of FeCoNi tri-metal on the bifunctional activity of the catalyst is still unclear.