Theoretical Study Of New Porous Materials For Batteries And Electrocatalsts

The development of social economy requires increasing demand for energy.Searching for new energy resources as alternatives to fossil fuels and increasing energy untilization efficiency have become a topic of great relevance,which are expected to not only solve environmental problems such as carbon dioxide emissions,but also overcome the global energy crisis.Materials play a crucial role in energy storage and coverson processes.As energy storage devices,rechargeable batteries,can improve energy utilization efficiency.The electrode materials with low diffusion barriers and high storage capacity of lithium ions are essential for high-performance rechargeable LIBs.Additionally,materials with highly-efficient electrocatalytic activity,e.g.for hydrogen evolution reaction(HER)and oxygen evolution/reduction reaction(OER/ORR),are essential for energy conversion processes.The search for high performance electrocatalytic materials has become a topic of great relevance in the field of energy and materials.The potential of porous materials in energy storage and conversion are drawing increasing interest,due to their unique structure and excellent mechanical and photoelectric properties and so on,and becomes a hot topic in the field of energy materials.In this dissertation,using first-principles calculations within demsity-functional thoery(DFT),we have studied the M3N/MX3 porous structures,1,4,5,8-naphthalenete-tracarboxylic dianhydride(PNTCDA)and two-dimensional(2D)TM3(HITP)2 metal-organic frameworks(MOF)as electride(or anchoring)materials for alkali-metal-ion(or lithium-sulfur)batteries and electrocatalysts for HER,OER/ORR in energy conversion processes.The roles of lattice structure and electronic properties of these porous materials on the atomic/molecular adsorption,diffustion and catalytic activity revealed in the first-principles calculations offer theoretical guidance for the relevant experimental explorations.The main research contents and results are summerized as follows:1.M3N/MX3 is a class of porous material that has been widely synthesized in the experiment.Our theoretical research proved that a new class of porous materials as the electrode material for lithium ion batteries(LIBs).Taking advantage of the large voids,high lithium mobility and storage capacity can be achieved.Taking Cu3N as an example,the diffusion barrier of Li on the nanosheets experiences an energy barrier of about 0.09 eV,which is much lower than those of presently proposed electrode materials.The maximum Li capacity of Cu3N nanosheets can reach 1008 mA h g-1.This work opens an avenue for developing electrode materials for high performance LIBs.In addition,the similar structures with Cu3N,TiF3,having ferromagnetic half-metallic properties,Meanwhile,TiF3 crystal has stable ferromagnetism and half-metallicity under Li insertion.The TiF3 crystal has low Li diffusion barriers(0.16-0.37 eV)and moderate Li storage capacity(256 mA h g-1),which the parameters can be compared with common battery electrode materials.We introduce half-metal materials into traditional LIBs as electrode materials for spin batteries,the combination of the half-metal with LIBs may offer a promising solution for long-desired spin batteries in spintronics.2.Organic polymeric PNTCDA has distinctive advantages including low cost environmentally friendlliness and safety.We demonstrate that polymeric PNTCDA is an organic electrode material with the potential for Li,Na and K ion batteries.The unique enolization mechanism during the charging process in PNTCDA leads to a neglectable lattice contraction of only-1.68%for Li,-0.37%for Na,and-0.56%for K.Therefore,the volume during charging and discharging changes little,which improves the stability of the battery.In addition,the adsorption of AM ions(enolization process)is barrierless.The theoretical capacities are 366 mA h g-1(Li),366 mA h g-1(Na),and 183 mA h g-1(K),which are comparable to those of other well documented inorganic electrodes.In addition,PNTCDA can not only be used as the anode in Li-ion batteries and Na-ion batteries(NIBs),but also the cathode in K-ion batteries(KIBs).Combining with the environmentally friendly of PNTCDA and the polymerized structure is insoluble in water-based electrolytes,making it a potential versatile electrode material for alkali metal ion battery3.Lithium-sulfur(Li-S)batteries have been intensively concerned to fulfill the urgent demands of high capacity energy storage.However,its implementation has been impeded by multiple challenges,in particular,lithium polysulfides(LiPSs)are easily dissolved in the electrolyte and the "shuttle effect" between the electrodes,resulting in poor cycle stability.We have carried out theoretical research on the interaction between 2D MOF Cu3(HITP)2,and LiPSs.We calculated that Cu3(HITP)2 can not only effectively anchors LiPSs to suppress the shuttle effect,but also keeps their cyclic structures undecomposed.Meanwhile,low decomposition reaction barrier represents fast delithiation reaction kinetics.We also calculated the effects of the binding of LiPSs by changing the intermediate transition metals and the surrounding ligand environment.We found a descriptor based on the property of transition metal and surrounding ligand and establish a volcano plot between binding energy and this descriptor,which further provides the theoretical basis of transition metal or ligand design for the development of excellent anchoring material of Li-S battery.4.HER and OER are two important reactions in energy conversion.Highly-efficient electrocatalysts for HER,OER/ORR are essential in energy conversion processes.On the basis of first-principles calculations,we investigated the HER,OER/ORR electrocatalytic performance of porous materials:MX3(M=Ti,Sc,Nb,Ta,Mo,W,Re;X=F,O)and 2D TM3(HITP)2.Our calculations showed that TiF3 and WO3 can serve as efficient HER electrocatalysts with the overpotentials comparable to those of the platinum-based catalysts.For porous structures of MX3,we established a relationship between the surface adsorption ability of a material and its electronic structure.In addition,our calculations showed that the 2D MOF Cu3(HITP)2 which have been synthesized in recent experiments can serve as a bifunctional catalyst for overall water splitting,while Fe3(HITP)2,Co3(HITP)2 and Zn3(HITP)2 are promising for both OER and ORR in fuel cells and metal-air batteries.An efficient descriptor(AGo*-AGOH*)for the OER/ORR activity of these electrocatalysts was proposed to find the optimal catalyst in the volcano plot,which reveales the regulation law of the catalytic performance for 2D TM3(HITP)2.The tunable catalytic activity in the TM3(HITP)2 opens an avenue for design of multi-functional catalysts.