Manganese-based Crystalline Porous Materials Are Used To Study The Performance Of Li-CO₂ Batteries

Environmental problems caused by fossil fuels are becoming more and more serious.CO₂from conventional combustion is the main cause of the greenhouse effect.Therefore,it is more important now than ever to develop renewable and clean energy technologies.Li-CO₂batteries are emerging energy storage devices that can not only captured CO₂and the corresponding redox reaction between Li anode and CO₂cathode,but also proposed for space exploration.However,several difficulties have limited the application of this technology,including a high charge overpotential,low recyclability,poor rate capability,and relatively low energy density.The development of CO₂-Li₂CO₃reversible conversion catalyst with high activity and efficiency is an important way to achieve the practical application of Li-CO₂batteries.Crystalline porous materials with high porosity,easy to functionalize modification,clear crystal structure and other advantages is conducive to the adsorption of CO₂molecules.It has a broad prospect in the design of catalysts for Li-CO₂batteries.Unfortunately,the current crystalline porous materials were limited in poor electrical conductivity and less exposure of catalytic sites which greatly limits the application of this kind of materials in Li-CO₂batteries.Therefore,how to design an efficient crystalline porous materials-based catalyst to improve the capacity and cycle capacity of Li-CO₂batteries is an important problem.Based on the research of our group,we concentrated on the preparation of crystalline porous materials-based composites and their performances in Li-CO₂batteries.From the point of view of material design structure,combined with theoretical calculation,we have carried out the following research:（1）A porphyrin-based covalent organic framework（COF-366-Mn）synthesized via the covalent connection between the terephthalaldehyde ligand and catalytically active tetrakis（4-aminophenyl）-porphinato manganese（II）（TAPP-Mn）has been designed as an efficient cathode catalyst according to the demand of high-performance Li-CO₂batteries.The as-designed COF-366-Mn cathode catalyst with abundant single-metal catalytic sites and uniform microporous channels.Uniform microporous channels in COF ensure efficient electron transport,efficient CO₂adsorption capacity and fast Li⁺transport performance.Combined with the catalytic action of Mn-porphyrin sites on CO₂reduction and Li₂CO₃decomposition,the goal of reducing overpotentials（1.49 V at 100 m A/g）and improving the performance of the batteries（180 cycles at 500 m A/g）was achieved.（2）A series of 2D-MOF nanosheets were obtained by simple ultrasonic exfoliating method,such as 2D-Mn-MOF,2D-Co-MOF and 2D-Ni-MOF.Their batteries performance was studied as cathode catalysts for Li-CO₂batteries.2D-Mn-MOF cathode catalyst has high capacity（22122 m Ah/g at 200 m A/g）,low overpotential（1.53 V at 100 m A/g）,cyclic ability（100 cycles at 500 m A/g）and full charge ability after deep discharge（100%）.Compared with three-dimensional Mn-MOF,the excellent performance of two-dimensional Mn-MOF may be attributed to its more exposed active sites and more uniform deposition of Li₂CO₃.However,2D-Co-MOF and 2D-Ni-MOF materials show high overpotential（1.98 V and 1.99 V at 100 m A/g）and poor cyclic performance（90 cycles and 88 cycles at 500 m A/g）.This study broadens the application range of two-dimensional MOF and has guiding significance for the material design of Li-CO₂batteries in the future.（3）DQTP-COF synthesized via the covalent connection between the 2,6-diaminoanthraquinone and 2,4,6-triformylphloroglucinol has been designed as an efficient cathode catalyst.A series of large-scale and ultrathin Mn O₂/DQTP-COF-NS hybrid materials have been successfully prepared through a KMn O₄based chemical exfoliation method.In this process of exfoliating,Mn O₂nanoparticles transformed by KMn O₄can be uniformly loaded on nanosheets and inhibit agglomeration.By regulating the amount of KMn O₄,a series of ultrathin Mn O₂/DQTP-COF-NS with tunable Mn O₂loading and thickness have been produced.These materials have excellent catalytic performance（120 cycles at 1000 m A/g）.Moreover,the CO₂activation mechanism has been discussed by DFT calculations.This work paves a new way in exploring porous crystalline materials as efficient cathode catalysts for Li-CO₂batteries.