First-Principles Study Of Materials For Electrochemical Energy Storage And Conversion

Electrochemical energy storage and conversion has drawn increasing interest in past decades due to its wide applications in daily life,including batteries,supercapacitors and electrocatalysis,etc.The performance of electrochemical devices is significantly determined by electrode materials.In this thesis,designing new electrode materials is carried out by using first-principles simulations,supported by experiments,to give insight of interfacial phenomena and processes in electrochemical energy storage and conversion materials.The main contents are briefly summarized in the following.The first chapter introduces the fundamental of density functional theory and the knowledge of electrochemical energy storage and conversion;ways to design electrode materials by theoretical simulations are also proposed.The first half presents the development of density functional theory,several descriptions of exchange-correlation energy,and some commonly used density functional theory simulation softwares.Also,the practical ways to calculate various physical and chemical properties of materials and to study chemical reaction processes by using density functional theory are discussed.In the second half,a brief introduction to the basic concepts of electrochemical energy storage and conversion is given,mainly focusing on the mechanisms of electrochemical reactions and on how to use density functional theory to study the key issues in the corresponding reaction.The second chapter provides research on several interfacial phenomena and processes in lithium ion batteries.The first section is devoted to the lithium storage mechanism on single-layer graphene.We point out that the lithium storage capacity of single-layer graphene can be higher than previous reports by forming a super-dense close-packed multi-layer lithium stacking.In addition,the adsorption of lithium makes it easier to form defects on graphene.In the second section,a two-dimensional boron silicide is proposed as a novel negative electrode for lithium ion battery.Through theoretical simulations,the lithium adsorption and diffusion behavior on such material are investigated.Furthermore,the relationship between the lithium storage capacities,the averaged electrode potentials and the boron-silicon ratios are predicted.In the third section,the lithium storage capability of nitrogen-doped activated fullerene is studied.Combined with simulation and experiments,the effects of nitrogen doping and material curvature factors on lithium adsorption are discussed.The third chapter contains the design of electrode materials for hydrogen evolution electrocatalytic(HER)reaction.The first section discusses the synergistic modulation of nitrogen-doped carbons by molybdenum dioxide and nickel to boost up HER performance.It is considered that the active site is the carbon atom directly bonded to the nitrogen atom.Due to the synergistic modulation of the metal/metal oxide at lower layer,the strength of anti-bonding between the adsorbed hydrogen atom and the doped nitrogen atom is weakened,and the strength of bonding between hydrogen atom and carbon atom in the same hexagonal ring is enhanced,thus the hydrogen adsorption is more favored.The second section discusses the interfacial effect between molybdenum dioxide and nickel to enhance HER performance.The catalytic active site is at the oxygen atom near the interface.It is proposed that the hydrogen evolution mechanism lies in the charge enhancement effect at the interface and the orbital modulation effect of 2p orbital on the oxygen atom.The fourth chapter proposes the design of electrode material in the oxygen evolution electrocatalytic reaction(OER)and discusses the OER reaction mechanism of NiOOH.The Gibbs free energy diagram in OER reaction is studied.It is pointed out that the unsaturated coverage of surface hydroxyl groups is the key to boost up the OER activity of NiOOH.The fifth chapter summarizes all the works and prospects several future research topics.