【作者】 彭红建；

【导师】 谢佑卿；

【作者基本信息】 中南大学 ， 材料物理与化学， 2007， 博士

【摘要】 质子交换膜燃料电池（PEMFC）具有高能量密度、运行温度低和稳定性能好等优点,在航天领域、潜艇、电动车、飞船等领域具有广泛的应用前景,但由于催化材料价格昂贵,制约其商品化,本文在系统合金科学理论（SSA）框架的指导下,运用纯单质系统理论系统研究了金属Pt、Ru和Pd的的电子结构,物理性质和热力学性质随温度的变化,和特征晶体理论对Pt-Ru合金系进行了系统研究,为电催化剂在SSA框架指导下设计提供完整的数据资料。本文主要对金属Pt、Ru和Pd和Pt-Ru合金系进行了以下几个方面的研究:（1）以MATLAB（MATrix LABoratory）为工具,对单原子状态自洽法的算法进行研究;（2）应用纯单质系统理论中的单原子（OA）方法和能带理论中单电子（OE）方法,即第一原理（FP）方法分别计算了金属Pt、Ru和Pd的fcc,hcp,bcc和liquid初态特征晶体电子结构,并相互进行比较,分析金属Pt、Ru和Pd的电子结构与晶体结构的关系,及金属Pt的电子结构与电阻率和化学活性的关系;（3）应用纯单质系统理论,计算了金属Pt、Ru和Pd的物理性质和热力学性质随温度的变化,得到OK至熔点T_m的温度范围内纯金属单质的完整信息,并与SGTE数据库的结果、FP方法的计算结果及JANAF实验数据进行了比较;（4）应用特征晶体理论对Pt-Ru合金系进行系统分析,选择Pt-Ru合金系的体积和能量相互作用方程,确定Pt-Ru合金系的特征原子序列和特征晶体序列的基本信息;（5）开拓系统合金科学框架应用于催化材料设计,揭示电催化剂的电子结构与催化活性的关系,并对其进行结构表征,为电催化剂的设计指明了方向;（6）应用特征原子排列设计和特征晶体相加定律研究了Pt-Ru合金催化剂的催化性能和稳定性,并拟定其成分的配比方案;（7）以金属Ni为例,阐明OA方法与FP方法的差异,并探讨金属Ni,Pd,Pt的电子结构与物理性质的差异的原因。本文着重研究了电子结构—晶体结构—物理性质和热力学性质及催化性能之间的内在联系,取得了以下几个方面的创新成果:（1）运用数值功能运算极强的MATLAB为工具,能快速、准确地确定金属晶体的电子结构,进一步完善了单原子状态自洽法;（2）用OA方法和FP方法分别计算了金属Pt、Ru和Pd的fcc,hcp,bcc和liquid态的电子结构,并相互进行了比较,金属Pt的计算结果符合较好,而金属Ru、Pd的结果相差较大;分析了金属Pt、Ru和Pd的电子结构与晶体结构的关系,及金属Pt的电子结构与电阻率和化学活性的关系,由于s_f电子最少,所以电阻率最大,也是化学活性最低的原因;（3）计算了金属Pt、Ru和Pd从OK到熔点温度T_m的物理性质（包括势能曲线、热膨胀系数、体弹性模量、晶格振动能、晶格常数和单键半径）,和热力学性质（包括恒容和恒压比热、熵、焓和Gibbs能等）,与FP方法计算结果、SGTE数据库和JANAF实验数据都符合较好。（4）应用特征晶体理论对Pt-Ru合金系进行系统分析,选择了第九方程为Pt-Ru合金系的体积和能量相互作用方程,确定了Pt-Ru合金系的特征原子序列和特征晶体序列的基本信息;（5）开拓了系统合金科学框架应用于催化材料的设计,近似地用体相的电子结构来代替表面Pt原子的电子结构,揭示了电子结构与催化活性的关系,主要是由于Pt原子聚合时,有0.5个d电子转化为s电子,增加了d空穴,对催化活性有利;及FP方法计算的态密度和能带结构解释了催化活性,并与XRD表征的结果一致;合金元素的加入,增加了Pt的d空穴,晶格常数也随之减小,对催化活性有利,为电催化剂的设计指明了方向;（6）应用特征原子排列设计和特征晶体相加定律研究了Pt-Ru合金催化剂的催化活性、稳定性及成分配比,计算了Pt-Ru有序合金中Pt和Ru原子个数之比分别为3:1,1:1和1:3的势能和晶格常数,并分析了组元Pt的组态变化,即ψ₄^Pt→ψ₈^Pt→ψ₁₂^Pt;计算了无序合金的性质和组元Pt的电子结构,随着Ru含量的增加,势能降低,稳定性升高,晶格常数减小,Pt的d带空穴增加,使催化活性增强,但随着Ru含量超过50%后,d空穴增加得非常缓慢,催化活性增加不大。综合考虑稳定性、d空穴增加的快慢、成本及抗CO的能力,确定Pt-Ru合金催化剂成分的最佳配比约为1:1;（7）以金属Ni为例,阐明了OA方法与FP方法的差异,并探讨了金属Ni,Pd,Pt的电子结构与物理性质的差异,除了电子结构的影响外,还有4f电子的屏蔽作用。更多还原

【Abstract】 The proton exchange membrane fuel cell（PEMFC）is a highly attractive power source for mobile and stationary applications due to its high power density at lower temperatures and its compact design.At present,the electrocatalyst costs of PEMFC is of high cost that hinder the commercialization of PEMFC.In this paper,we systematically study the electronic structure,physical properties and thermodynamic properties as a function of temperature.And we adopt the characteristic crystal of theory to systematically research on Pt-Ru alloy system.That supply electrocatalyst with complete datum for scientific designation in the light of SSA framework.In this paper,the following researches on Pt,Ru and Pd metals and Pt-Ru alloy system have been performed:（1）By means of MATLAB（MATrix LABoratory）, algorithms of single-atom self-consistency method was studied;（2）The electronic structure of Pt,Ru and Pd metals with fcc,hcp,bcc and liquid structure were calculated by using one-atom（OA）method in theory of pure element and one-electron （OE）method that is called first-principle（FP）method.The results were compared each other.The relationship between the crystal structure and electronic structure of Pt, Ru and Pd metals has been analysed.The relationship between the resistivity and chemical activity and the electronic structure of Pt metal has also been analysed.（3） To adopt the theory of pure elements to calculate physical properties and thermodynamic properties as a function of temperature of Pt,Ru and Pd metals,and to get integrate information in the range of OK to melting points Tm.These results were compared with the results of SGTE data,the calculation results by the first principle method and JANAF experimental value.（4）Pt-Ru alloy system was systematically studied by characteristic crystal theory.The atomic volume interacting function and energy interacting function between atoms in Pt-Ru alloy system were determined.The basic information of characteristic atom sequences and characteristic crystal sequence in Pt-Ru alloy system were obtained.（5）We further develop the application of the framework of systematic science of alloys.We brought to light the relationship between the catalytic activity and electronic structure of electrocatalyst, and characterized the structure of electrocatalyst.This will point out the direction of electrocatalyst designation.（6）We apply characteristic atom arranging designing technique and additive law of characteristic crystal to study the catalytic performance and stability of Pt-Ru alloy catalyst,and determine the program about their gradient. （7）We delude the difference between OA method and FP method such as Ni metal and discuss the relationship between the electronic structure and physical properties of Ni,Pd and Pt metal.In this paper,we focused on the research of the relationship among the electronic structure,crystal structure,physical properties,thermodynamic properties and catalytic performance,the results of this paper show that（1）The MATLAB（MATrix LABoratory）software aggregated the strongest value calculation as a tool.The electronic structure of crystal can be determined fast and accurately and consummate single-atom self-consistency method further;（2）The electronic structure of Pt,Ru and Pd metals with fcc,hcp,bcc and liquid structure by OA method and FP method.The results were compared with each other.The result of Pt metal is good agreement with each other,but the results of Ru,Pd metals have great difference.The relationship between the crystal structure and electronic structure of Pt,Ru and Pd metals has been analysed.The relationship between the resistivity and chemical activity and the electronic structure of Pt metal has also been analysed.Due to the least s_f electron,the electricity resistance of Pt is biggest,and the chemical activity is the lowest.（3）To adopt the theory of pure elements to calculate physical properties including potential energy curve,thermal linear expansion coefficient,bulk modulus,vibrating energies of lattice,lattice constants and single bond radius and thermodynamic properties including isometric and isobaric heat capacity,enthalpy,entropy and Gibbs energy as a function of temperature of Pt,Ru and Pd metals in the range of OK to melting points Tm.These results were good agreement with the results of SGTE data,the calculation results by first principle method and JANAF experimental value;（4）Pt-Ru alloy system was systematically studied by characteristic crystal theory.The ninth atomic volume interacting function and ninth energy interacting function between atoms in Pt-Ru alloy system were determined.The basic information of characteristic atom sequences and characteristic crystal sequences of Pt-Ru alloy system were obtained. （5）We open up the application of the framework of systematic science of alloys to designation in catalytic material.The electronic structure of phase is approximately substituted to that on the surface.We brought to light the relationship between the catalytic activity and electronic structure of electrocatalyst,When Pt atoms get together,there are 0.5 d electrons transform into s electrons,the number of d-electrons decreases,so increase d-orbital vacancy.It is advantageous to catalytic reaction. Density of state and energy band structure were also used to interpret the catalytic activity by FP method.The result is agreement with the result is characterized by XRD.After addition of another metal,the d electrons of Pt metal transfer to another metal,empty d-orbitals of Pt atom increase,and the lattice constant of alloy decreases, so it is more advantageous to catalytic reaction.This will point out the right direction of electrocatalyst designation.（6）We apply characteristic atom arranging designing technique and additive law of characteristic crystal to study the stability,catalytic performance and gradient composition of Pt-Ru alloy catalyst.The potential energies and lattice constants of Pt-Ru ordered alloy that the ratio of Pt to Ru is respectively 3:1,1:1 and1:3 were calculated.The configuration of component-Pt also had great change which isψ₄^Pt→ψ₈^Pt→ψ₁₂^Pt.The properties of Pt-Ru disordered alloy and the electronic structure of component-Pt were calculated.As the content of Ru increasing, the potential energies decreases,the stability increase,the lattice constants decrease, and the d-orbital vacancy enlarged,this is advantageous to reaction.But the percentage of Ru surpasses 50%,the d-orbital vacancy enlarged very slowly,this lead to have little influence on reaction.We conclude that the most proper ratio of Pt to Ru is 1:1 from stability,the d-orbital vacancy enlarging value,cost and carbon monoxide tolerant capacity.（7）We delude the difference between OA method and FP method such as Ni metal and discuss the relationship between the electronic structure and physical properties of Ni,Pd and Pt metals,main cause is shield effect of 4f electrons besides influence on electronic structure.更多还原