Theoretical Investigation Of Two-dimensional And Alloy Materials In Battery Application

In order to meet the increasing energy demand,while reducing the dependence on fossil fuels and reducing the environmental pollution,it is urgent for human beings to develop cost-effective and environment-friendly energy storage equipment.Lithium batteries(LiBs)is one of the advanced energy storage systems which can meet the above performance indexes and have sufficient technical maturity.Because of the low limit energy density,even if lithium ion batteries are developed to the best of their performance,they can not meet human energy needs.Among the numerous energy storage devices,lithium-sulfur(Li-S)batteries,an upgraded generation of lithium ions,can break through the energy limitation of lithium batteries and achieve even higher capacity theoretically.On the other hand,fuel cell,a kind of equipment which can directly convert chemical energy into electric energy,has been paid more and more attention.Because of the high efficiency and no heat consumption,fuel cell is considered to be the "ultimate energy".With first principles calculation,this thesis discussed the application potential of binary alloy materials and two-dimensional materials in the above two kinds of batteries.Based on different modification strategies in catalyst,we explored the insight into improving performance of catalytic activity.In chapter 3,we studied the application of Ni-Fe,Co-Fe alloy materials in lithiumsulfur batteries according to the alloying and concentration effects in the material modification strategy.And then,the improved performances were discussed with the analysis of electronic properties.Corresponding results indicated the strong binding energy between Fe and polysulfides.Although this strong binding energy can effectively inhibit the shuttle effect of poly sulfide in solution,it also hinders the lithiation process of polysulfide,which makes the current density of the battery decrease obviously.The addition of Co and Ni can effectively reduce the binding energy of polysulfide.The electronic structure analysis shows that,with the filling of electrons in d band,doping of Co and Ni can decrease the d band center,leading to the decreasing of adsorption energy.In chapter 4,we explored the potential application of two-dimensional TMD materials MoS2 in oxygen reduction reactions.According to the concentration effect in the material modification strategy,the influence of different concentration P doping on the catalytic performance is discussed.DFT calculation results show that the structure with a P doping concentration of 5.5%is more stable than 3.7%of that structure.Meanwhile,P doped MoS2 shows different ORR catalytic activity under different doping concentrations.The active sites increase with the increasing of doping concentration.In that case,oxygen can be adsorbed and dissociated stably.While developing new energy batteries,efficient hydrogen preparation is equally important.Compared with the traditional hydrogen production from fossil fuel cracking,electro-powered hydrogen production through electrochemical reaction is more environmentally friendly and sustainable.Therefore,in Chapter 5,we propose a set of catalyst design schemes for electrochemical decomposition of water.This part discussed the size effect and surface boundary effect on HER catalytic activity by comparing Cu based nanoparticles with different sizes.Mx@Cus5-x(x=1,13 and M=Fe,Ru and Os)core-shell nanoparticles were designed.After that,we discussed the stability and electronic properties cording to DFT calculation for each particles.The result shows that the size effect and the boundary effect act on the adsorption of hydrogen on the surface of the cluster at the same time and form a competitive relationship.The W doped RuO2 solid solution was also used as the OER catalyst for electrolytic water to explore the effect of alloying effect on the catalytic performance of RuO2 in oxygen evolution reaction.Results indicated that alloying results in additional active sites on the surface.Under acidic conditions,different H+concentrations induce different OER catalytic activity on the surface of binary alloy oxides.