Design Synthesis And Electrocatalytic Performance Of SmMn₂O₅ Nanocrystals

With the rapid consumption of traditional energy fuels,exploring clean and renewable energy technologies has become a major problem that mankind face.Zinc-air batteries have the advantages of high safety and high theoretical energy density,and show great potential in practical applications.However,the cathode reaction of the zinc-air battery is limited by the slow oxygen reduction reaction（ORR）process.Pt-based catalysts was limited in large quantities for its exorbitant price.However,transition metal oxides have become one of the most popular oxygen reduction catalysts due to their low cost and good catalytic performance.Among them,manganese-based mullite has a complex crystal structure,excellent stability,richness,adjustability and other advantages.Therefore,we mainly takes SmMn₂O₅ as an example to design and synthesize it from three aspects and study its electrocatalytic performance.（1）We synthesized SmMn₂O₅ nanocrystals with manganese acetate as the manganese source,and synthesized SmMn₂O₅ with different crystallinity by controlling the hydrothermal reaction time.The effect of crystallinity on oxygen vacancies and catalytic performance was explored.Researches have shown that when the reaction conditions are 150℃for 3 h,the crystallinity of the sample is the worst.At this time,there are more oxygen vacancies and the half-wave potential is 0.76 V（vs.RHE）.We assembled a zinc-air battery and its measured power density is 119 m W cm^-2.（2）SmMn₂O₅/CNTs composites were synthesized by hydrothermal reaction after using manganese acetate as the manganese source and adding different amounts of carbon nanotubes to the precursor.The half-wave potential is 0.81 V（vs.RHE）with20 mg CNTs,which increases 170 m V compared to SmMn₂O₅.The sample was assembled with a zinc-air battery,and the corresponding power density is 125 m W cm^-2.After a 600-hour cycle test,the charge-discharge voltage difference changes by10 m V.（3）Using manganese acetate and manganese nitrate as manganese sources,different amounts of La were introduced during the reaction to synthesize Sm_1-xLa_xMn₂O₅ nanocrystals.In addition,the sample Sm_0.7La_0.3Mn₂O₅ synthesized with manganese acetate as the manganese source shows the best ORR activity with a half-wave potential of 0.83 V（vs.RHE）.At the same time,it was assembled with a zinc-air battery with a power density of 147 m W cm^-2,after 800 h after the cycle test,the charge-discharge voltage difference only changes 10 m V.The half-wave potential of the Sm_0.7La_0.3Mn₂O₅/Mn O₂ sample synthesized with manganese nitrate as the manganese source reached 0.85 V（vs.RHE）,and the air battery power density is 137m W cm^-2.After 800 h cycle testing,the charging and discharging platform changes 20m V,indicating that the sample has ultra-high stability.