Prussian Blue Analogues Derived Materials Used In Oxygen Electrocatalysis Of Zn-Air Batteries

China is the second biggest oil-consuming country in the world,however,there are many risks in the oil supply security due to the complicated geopolitics.Moreover,greenhouse-gas emissions and air pollution associated with the combustion of fossil fuels are becoming more and more urgent.Developing clean and renewable energy is particularly important to guarantee the energy security in China.However,the disadvantage of clean energy is that it cannot provide stable energy source.Only with the help of energy storage and conversion technology can it enter the energy consumption market.Zn-air battery(ZAB)is a kind of low carbon and sustainable energy conversion and storage technology,which has been in the spotlight for years.One of the bottlenecks restricting its large-scale application is that the cost and performance of air electrode catalyst failed to meet the requirements of commercialization.Therefore,it is very vital to develop low cost and high activity air electrode catalysts.Prussian blue analogues(PBAs)can be used as precursor materials to prepare low-cost electrode materials with excellent structure and diverse components.The application of PBAs-derived electrocatalysts in ZAB to improve the performance of the battery and prolong the service life has attracted more and more attention.In this thesis,using PBAs as precursors,through hybridized with other materials,low temperature phosphorization or high temperature pyrolysis,four kind of electrocatalysts were prepared.There are hollow carbon nanoboxes,porous bimetal phosphides,CoFealloy cubes supported on N-doped carbon nanosheets and Co-Fe-Ru nanoparticles loaded on porous N-doped carbon sub-micro spheres.The structure-activity relationship between materials and catalysis(battery)performance was explored,providing new insights for the construction of electrode materials using PBAs as precursor.The following aspects of work were carried out in this thesis:(1)Polydopamine coated Zn-FePBA was adopted as precursor.Fe/Fe₃C nanoparticles encapsulated in hollow carbon nanobox(Fe/Fe₃C/HCNB)was prepared through pyrolysis of the precursor.The unique porous hollow structure could facilitate the mass transfer in the electrocatalysis.Compare with solid structure,the discharge performance of ZAB assembled by Fe/Fe₃C/HCNB was extremely promoted.Furthermore,the improved hydrophilicity of air electrode coated with Fe/Fe₃C/HCNB increased the active sites taking part in the electrocatalysis.Finally,the Fe/Fe₃C/HCNB based ZAB reached a high power density of 274 mW·cm^–2.(2)Although,construction of excellent structure can improve the performance of Fe/Fe₃C/HCNB,but the composition of the catalyst was not regulated.Therefore,Zn/Fe-CoPBA was used as precursor to realize simultaneously tuning the structure and composition.Porous cobalt and iron bimetallic phosphides(p-CoFeP)was synthesized through pyrolysis,phosphorization and etching of the precursor.More importantly,the synthesis method could make the electron transfer from Co,Feto P element easier,resulting OER benefited high-value metal elements.Finally,a porous cobalt-iron bimetallic phosphide OER electrocatalyst with excellent performance could be optimized by adjusting the addition amount of Zn.It only required overpotential of 280 mV to reach 10 mA·cm^–2.(3)Since the performance of ZAB assembled by the mixture of above two materials was unsatisfactory,bifunctional oxygen electrocatalyst was designed by hybridized two active species.The Fe-CoPBA were in-situ grow on the surface of N-doped carbon nanosheets.After pyrolysis,the CoFealloy cubes supported on N-doped carbon nanosheets(CoFe/FeNC)were established.CoFe/FeNC not only inherited the good catalytic activity of N-doped carbon nanosheets for ORR,but also showed a synergistic effect between the two active species in catalyzing OER.ZAB assembled by CoFe/FeNC reached a peak power density of 154.1 mW·cm^–2.The energy efficiency after 350 h cycling at 5 mA·cm^–2 was just decreased by 2%.(4)The discharge performance and the cycling stability at large current density of ZAB needed to be further improved.Thus,based the experience learned in the above chapter,Zn-CoPBA was first chosen as precursor.Then TA-Fe^?layer was formed on its surface.Next,Ru³⁺was introduced by chelation and finally Co-Fe-Ru nanoparticles encapsulated in porous N-doped carbon microspheres were prepared by annealing the Zn-CoPBA/TA-Fe^?/Ru³⁺precursor.The evaporation of Zn enhanced the porosity of carbon materials,which exposed more active sites of Co-Fe-Ru/PNCS and promoted the catalytic activity of ORR and OER.The introduction of Ru element increased the intrinsic activity and further reduced the overpotential of OER.Thus,the Co-Fe-Ru/PNCS-based ZAB showed a peak power density of 234.3 mW·cm^–2.In the cycling discharge/charge test,Ru element was oxidized to form Ru O₂,which was beneficial to OER.The charge voltage was reduced and therefore the corrosion degradation of the catalyst itself was eliminated effectively.As a result,the discharge/charge cycling test at 10 mA·cm^–2 of Co-Fe-Ru/PNCS-based ZAB reached the lifetime 150 h.