| In response to the national call for"carbon peak"and"carbon neutralization",water metal-air batteries have become very promising energy conversion devices due to their advantages of high safety,high theoretical energy density,simple structure,low price and green environmental protection.Among them,aluminum has become the preferred material for metal-air batteries due to its rich reserves（4.23 billion tons of ore）and low cost（20000yuan/ton）.The severe polarization and hydrogen evolution corrosion on the negative electrode can be alleviated by changing plates and adding corrosion inhibitors,but the oxygen reduction reaction（ORR）on the air positive electrode has a slow kinetics due to complex four electron transfer and surface oxygen adsorption/activation,so it is very important to find an efficient ORR catalyst.Noble metal catalysts led by commercial Pt/C have excellent electrocatalytic performance,but the disadvantages of scarce Pt reserves,high price and poor electrochemical stability increase their application cost.Therefore,it is of great significance to design and develop non-metallic catalysts and non-noble metal catalysts with excellent performance.The serious harm of waste lithium-ion batteries to human body and the environment makes it imperative to recycle them.At present,people pay extensive attention to the recycling of metal elements.In fact,if each component is treated carefully,oxygen reduction catalysts with excellent electrochemical performance can be obtained.Through wet recovery,the main transition metal part can be designed and synthesized into transition metal oxygen reduction catalyst,and the leftover conductive agent and binder can be designed and synthesized into carbon based oxygen reduction catalyst.Therefore,based on the cathode material of waste lithium iron phosphate battery,carbon based ORR electrocatalyst was prepared by recycling conductive agent and binder,and its performance was compared with that of carbon based electrocatalyst derived from ZIF-67.At the same time,iron was recycled to prepare iron-based ORR electrocatalyst.The specific research contents and results are as follows:（1）The conductive agent and binder in the cathode material of waste lithium iron phosphate battery were recovered to prepare nitrogen doped carbon based ORR electrocatalyst,which was applied to aluminum-air battery.Taking the cathode material of waste lithium iron phosphate battery as the raw material,the NC-1000 catalyst obtained after 6 M hydrochloric acid treatment,6 times the supply of melamine as the precursor and 1000℃argon calcination as the dominant sample.Its the nitrogen doping content is 1.42%and it shows the structure of spherical carbon particles embedded in three-dimensional porous carbon.The half wave potential of NC-1000is 0.828 V（vs.RHE）and the Tafel slope is only 70.7 m V dec-1.The ORR reaction mechanism follows four electron transfer,the yield of hydrogen peroxide is less than 2%,and the half wave potential decreases by 20 m V after 5000 cycles of CV cycle,indicating that the ORR performance of NC-1000 is equivalent to that of Pt/C catalyst.The open circuit voltage of NC-1000 in aluminum air battery is 1.51 V,the maximum power density can reach141 m W cm-2 and the specific capacity can reach 1124.8 m A h g-1 when the current density is 20 m A cm-2.The discharge performance of NC-1000 is better than that of Pt/C catalyst when the current density is higher than 100 m A cm-2.The structure stability before and after discharge is good.（2）The bimetallic carbon based electrocatalyst derived from ZIF-67 was prepared and compared with NC-1000 in ORR performance and aluminum-air battery performance.Using 2-methylimidazole as nitrogen source,cobalt nitrate hexahydrate as cobalt source,manganese gluconate as manganese source and anhydrous methanol as solvent,the CM/NC-4 catalyst obtained through the synthesis of ZIF-67,the supply of manganese gluconate is 4 times that of ZIF-67,and argon atmosphere doping at 800℃is the dominant sample.Its the manganese doping content is 3.977%and it has three-dimensional porous structure and maintains the initial morphology of ZIF-67.The half wave potential of CM/NC-4 is 0.797 V（vs.RHE）and the Tafel slope is only 73.1 m V dec-1.The mechanism of ORR reaction is mainly four electron transfer,the yield of hydrogen peroxide is less than 20%,the half wave potential decreases by 3 m V after 5000 cycles of CV cycle,the current density retention rate is more than 90%after 10 hours of i-t test,indicating that the ORR performance of CM/NC-4 is inferior to NC-1000.The open circuit voltage of CM/NC-4 in aluminum-air battery is 1.57 V,slightly higher than that of NC-1000.It has a stable voltage platform at the current density of 1 m A cm-2 to 20 m A cm-2,and the discharge performance at the current density higher than 10 m A cm-2 is not as good as NC-1000.When the current density is 5 m A cm-2,the specific capacity of the battery is 797.7 m A h g-1,which is also less than NC-1000.（3）The iron element in the cathode of waste lithium iron phosphate battery was recovered to prepare iron oxide ORR electrocatalyst,which was applied to aluminum-air battery.The filtrate from dissolving the cathode material of waste Li Fe PO4 battery with hydrochloric acid was used as the raw liquid,the Fe2O3/foam nickel catalyst which was electrodeposited at a constant pressure of-1.0 V（vs.SCE）for 300 s and was calcined at 500℃for 2 h in air atmosphere was used as the dominant sample.Its crystalline particles are anchored on the surface of nickel foam substrate with certain ORR performance.The open circuit voltage of Fe2O3/foam nickel in aluminum-air battery is 1.40V.It has a stable voltage platform at the current density of 1 m A cm-2 to 20 m A cm-2.When the current density is 5 m A cm-2,the specific capacity of the battery is 628.4 m A h g-1.Its discharge performance is inferior to Pt/C.In conclusion,carbon based ORR electrocatalysts and iron oxide ORR electrocatalysts prepared by recycling waste lithium-ion batteries have broad application prospects in metal-air battery fields. |
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