【作者】 梁镇海；

【导师】 孙彦平；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2007， 博士

【摘要】 在电化学应用技术中，耐酸阳极材料的选择和制备一直是电化学工业的难题之一，高性能的阳极材料应当具有导电性能好、耐氧化、耐腐蚀、使用寿命长、催化活性高和成本低等优点。在强酸性溶液中，由于酸的腐蚀性和阳极氧析出的强氧化性，致使阳极材料的选择很困难。因此选择合适的耐酸性阳极材料将是一个非常有实际意义的课题。有关耐酸性阳极材料的选择，阀金属钛是目前国内外公认的最佳基体材料。钛具有密度小、机械强度高、耐腐蚀、导电性好和廉价等优点。非贵金属半导体氧化物PbO₂、SnO₂、MnO₂等具有较好耐腐蚀性和较高的电催化活性，适用于做阳极材料的活性层。因此，钛基氧化物（Ti／MO₂）在环境污染物去除、电化学合成等工业生产中是广泛应用的阳极材料之一。但该类电极存在的明显问题是：①由于阳极放出活性氧，扩散到基体表面形成TiO₂绝缘体使电极导电能力降低；②钛基体与表面活性层的结合力差，特别是当TiO₂绝缘体生成后，基体与活性层的机械结合力减弱，致使表面活性层脱落，在强腐蚀性的酸性溶液中尤其严重。本文认为加入氧化物（SnO₂、Sb₂O₄、MnO₂等）形成固溶体氧化物中间层可增强钛基体和活性层（MnO₂、SnO₂和PbO₂）之间的粘结力和导电性，同时也可增加阳极的机械强度和耐腐蚀性能，这可有效解决以上问题。本文首先采用了热分解、电沉积等方法及其组合技术制备出具有多元非贵金属氧化物中间层的电极，对氧化物中间层及活性层进行了表征，同时探讨了掺杂半导体氧化物固溶体的形成机制，主要研究了多元氧化物中间层形成的匹配固溶体在电极中的作用，探讨了晶体构型等因素对固溶体形成的影响和固溶体中间层形成过程中产生的晶体缺陷、氧空位对电极导电性能的影响，并考察了上述电极的使用寿命和电催化性能。其次将分形几何理论引入钛基氧化物电极体系，探讨了氧化物电极表面的分形维数和电催化性能之间的关系。最后将该类电极应用于含酚有机废水处理及电解还原偏硼酸钠制备硼氢化钠体系，考察了该类氧化物电极的电催化等综合性能，为耐酸阳极的工业化提供理论依据。主要研究内容及结论如下：1．选择金属钛为基体，非贵金属半导体氧化物（SnO₂、Sb₂O₄、MnO₂等）为中间过渡层材料，MnO₂、SnO₂和PbO₂为活性层，采用热分解、电沉积和溶胶-凝胶及其组合技术制备了具有多元氧化物中间过渡层的Ti／PbO₂、Ti／MnO₂及Ti／SnO₂阳极，利用SEM、XRD、XPS等技术对上述电极表面形貌、结构物相、组成价态进行了表征；采用快速寿命法考察了氧化物电极在1.0 mol／L H₂SO₄溶液中4A／cm²下的预期使用寿命。同时探讨了电极在酸性溶液中的电催化性能。研究结果表明：①用溶胶凝胶法制备出了纳米级的一元锑掺杂的Ti／SnO₂电极，最佳烧结温度为600℃，SbCl₃最佳掺入量为4％。加速寿命实验表明电极使用寿命较长，动力学测试表明该电极是一种高析氧过电位的电极材料，同时探讨了Ti／SnO₂+Sb₂O₄电极在酸性溶液中的析氧机理。②用热分解和电沉积法分别制备出具有多元氧化物中间层的Ti／PbO₂电极，该电极的活性层（Pb₃O₄和β-PbO₂）成菜花蘑菇状，其表面积大催化活性优良。稀土铈、钇掺杂的三元中间层的PbO₂电极寿命较长，电催化性能良好，该类电极在酸性溶液中的使用寿命和放氧动力学参数比单质铅电极优越。③用热分解法制备出具有不同多元中间层的Ti／MnO₂电极，该电极的活性层是β-MnO₂，该电极在酸性溶液中放氧特性优良，a、b值普遍比贵金属的小，i₀值较大，过电位小，其中Ti／SnO₂+RuO₂+MnO₂／MnO₂电极的析氧是SN₁反应机理，电极的析氧活化能（8KJ／mol）比PtO₂（60.67KJ／mol）和Pt／MnO₂（18.83KJ／mol）电极均低，是酸性溶液中低析氧过电位的理想材料。④具有二元SnO₂+Sb₂O₄固溶体中间层的Ti／MO₂阳极是用于酸性溶液中不同析氧体系的较理想的阳极材料。Ti／SnO₂+Sb₂O₄／MnO₂、Ti／SnO₂+Sb₂O₄／PbO₂和Ti／SnO₂+Sb₂O₄阳极在1.0mol／L H₂SO₄中的析氧起始电位依次增大，分别为1.701V、1.860V和1.918V，因此Ti／SnO₂+Sb₂O₄／PbO₂和Ti／SnO₂+Sb₂O₄阳极在酸性溶液中析氧电位较高，适用于阳极氧化的电化学体系；Ti／SnO₂+Sb₂O₄／MnO₂有较低的析氧电位，比较适合于阳极析氧的电化学体系。⑤一元Sb₂O₄中间层、二元SnO₂+Sb₂O₄中间层、三元SnO₂+Sb₂O₄+MO₂（M=Ru、Mn）中间层分别是Ti／SnO₂、Ti／PbO₂和Ti／MnO₂电极中较匹配的中间层材料。其中，二元SnO₂+Sb₂O₄（56％Sb₂O₃和44％Sb₂O₅）中间层能与相同晶体构型的铅锰活性层及二氧化钛形成良好的匹配固溶体，该固溶体生长过程的活化能较低（约13.965kJ／mol），形成的固溶体中间层表面晶粒均匀细小、结合紧密无裂缝，可有效阻止新生态氧原子的扩散，减少二氧化钛绝缘层的形成，从而延长电极的使用寿命。其作为中间层的Ti／SnO₂+Sb₂O₄／PbO₂、Ti／SnO₂+Sb₂O₄+MO₂（M=Ru、Mn）／MnO₂和Ti／SnO₂+Sb₂O₄阳极在工业电流密度（1000A／m²）下的预期使用寿命可分别达到15.7y、10.6y及4.6y。同时固溶体在形成过程中产生的晶体缺陷、氧空位增强了电极的导电性能，具有该固溶体中间层的Ti／PbO₂在相同电流密度下比单纯的用Pb作阳极节约电能17％，因此电极的综合性能明显提高。2．电极表面的粗糙程度是影响电极性能的一个重要因素。本文根据分形几何理论首次采用盒维数法计算了钛基氧化物电极表面的分形维数，并用该维数定量描述电极表面的粗糙程度。同时利用不同扫描速度下的循环伏安图形，根据扫描速度与峰电流的双对数关系测定了氧化物电极的分形维数。最后探讨了氧化物电极的分形维数和电催化性能之间的关系。将分形几何理论与电极材料的电催化性能相关联，为深入研究电催化剂提供了一条新的思路。研究结果表明：具有固溶体中间层的钛基氧化物电极是一类多孔三维电极，其分形维数介于2～3之间。由盒维数方法计算的钛基氧化物电极表面的分形维数大小顺序为：Ti／RuO₂＞Ti／MnO₂＞Ti／PbO₂，析氧电催化性能也按照同样的顺序呈现一定的规律。采用循环伏安方法测定的分形维数是Ti／PbO₂电极的较高，这与该电极的表面形貌相吻合，此两类方法各有其特点，都可以用来构建电极的表面形态和电化学性能之间的关系。3．将溶胶凝胶法制备的钛基二氧化锡电极用于含酚废水处理，考察了锑掺杂量和电极的焙烧温度等因素对含酚废水处理效果的影响，计算了在该电极上苯酚氧化的动力学参数和活化能；采用热分解和电沉积组合技术制备了具有多元氧化物过渡层的钛基二氧化铅电极并用于处理含酚废水体系，研究了其动力学规律，考察了各种因素对废水处理效率的影响；同时考察了Ti／MnO₂和不锈钢／MnO₂电极在光电催化条件下苯酚的降解转化率。结果表明：具有固溶体氧化物中间层的Ti／SnO₂+Sb₂O₄、Ti／SnO₂+Sb₂O₃+MnO₂／PbO₂和Ti／SnO₂+MnO₂+RuO₂／MnO₂（光电）阳极用于含酚废水深度处理，苯酚降解率可分别达到96.5％、95.8％和91.5％；Ti／SnO₂+Sb₂O₄、Ti／SnO₂、Ti／SnO₂+Sb₂O₃+MnO₂／PbO₂和Ti／PbO₂电极上苯酚氧化的电流效率分别为73.5％、66.0％、62.0％和54.9％，用于含酚废水深度处理，消耗的电能依次增大。可见具有固溶体氧化物中间层的Ti／SnO₂+Sb₂O₄电极是深度处理含酚废水较好的电极材料。4．将上述具有多元氧化物固溶体中间层的电极（Ti／SnO₂+Sb₂O₄／PbO₂、Ti／SnO₂+Sb₂O₄／MnO₂及Ti／SnO₂+Sb₂O₄）和Ti／Sn等阴极应用于偏硼酸钠制备硼氢化钠的原位硼循环体系。首次将NaBO₂电解还原（充电）成硼氢化物，硼氢化物在放氢时再（放电）产生副产物偏硼酸钠，从而实现硼的原位循环利用。同时首次建立了镍电极开路电位测定微量硼氢根浓度(10^-5-10^-3mol／L)方法，测量相对标准偏差为2.22％，回收率为98.43％。最后初步提出了电解偏硼酸钠制备硼氢化钠电化学反应机理的动力学规律。综上所述，多元匹配的氧化物固溶体中间层对钛基氧化物电极的综合性能起了关键作用。中间层的加入使基体和活性层形成良好的匹配固溶体，该固溶体不仅增加了其导电性，而且增强了与基体和活性层之间的结合力，使得上述氧化物电极在酸性溶液中的使用寿命增加，电催化性能得到改善。尤其，二元SnO₂+Sb₂O₄是一种较好的中间层材料。更多还原

【Abstract】 The selection and preparation of acid-proof anodic materials are always achallenge in the electrochemical applications. A high performance anodicmaterials should have following characteristics: high electrical conduction,good electrocatalytic properties, long service life, corrosion resistance,availability, as well as low cost etc., but due to the strong oxidizability relatedto oxygen evolution and the corrosiveness of acid to anode, the selection ofanodic material used in sulfuric acid electrolyte is more difficult than thatused in mild condition, and it is also of high practical significance in industry.Valve metal titanium, having high mechanical strength, low density,corrosion resistance, good conductivity and low-cost, is recognized as themost suitable substrate among all the acid-proof materials, non-precioussemiconductor oxides （SnO₂, Sb₂O₄, MnO₂, etc.） are appropriate to be theactivated layer of anodes, because they have not only good electrocatalyticproperties, but also good corrosion resistance. So titanium anodes （Ti/MO₂）are very well-known in the electrochemical industry, their applications allowa long and stable operation in several important industrial fields, such as theelectrochemical synthesis and the degradation of pollutant. However, thedisadvantage is that the evolving oxygen diffuses into the substrate to formtitanium dioxide-an insulator-can cause a reduction of conductivity andweakens the binding of activated layer to the substrate, the former will detach from the titanium support, especially in a strong acid electrolyte. View fromabove, addition of oxides （SnO₂, Sb₂O₄, MnO₂, etc.） as an intermediate layerinterposed between substrate and activated layer, all form of a solid solution,provides a way to improve corrosion resistance, binding force andconductivity. Thereby problems arising from above are prevented.This paper presents an investigation on performance of Ti/MO₂ electrode.First, a novel anode with intermediate layers of multiple non-noble metaloxides was prepared by thermal decomposition, sol-gel and the combinationtechnology, the intermediate layers and activated layer were characterized,mechanism of formation of oxide solid solution was discussed, the role ofmatched solid solution in anode was proposed, the effect of crystal structure,crystal defect and oxygen vacancy on the formation and conduction of solidsolution was researched, the service life and catalytic properties of anodeswere also tested. Then the fractal geometry theory was introduced into thefield of titanium oxide electrodes, the correlation between surface fractaldimension and the electrocatalytic performance was proposed. Finally, theseanodes were applied into phenol wastewater treatment and the electrolyticreduction of sodium metaborate to sodium borohydride. The contents andconclusions are as follows:1. The metal titanium and non-noble metal semiconductor oxides （SnO₂,Sb₂O₄, MnO₂, etc.） were singled out as the substrate and the intermediatelayer respectively, the oxides （MnO₂, SnO₂ and PbO₂） are chosen as the activelayers, Ti/PbO₂, Ti/MnO₂ and Ti/SnO₂ anodes with multiple intermediatelayers were prepared by thermal decomposition, electrodepositing, sol-gel andcombination technology, above electrodes morphology, crystal phase, surfacecomposition and valence state were characterized by means of SEM, XRDand XPS, the anticipated service lives of electrodes were measured using accelerated life test in 1.0mol/L H₂SO₄ solution at a current density of 4A/cm².The electrocatalytic properties of electrodes have also been studied. Theresults are as follow:①The nanometer-sized Ti/SnO₂ electrode was prepared by sol-geltechnique. The optimum doping concentration of antimony is 4% and the bestsintering temperature is 600℃. The service life is prolonged, determined bythe accelerated lifetime test, the over potential for oxygen-evolution is highbased on the kinetics test. The mechanism of the oxygen evolution reaction onthe anode was also proposed.②The Ti/PbO₂ anode with multiple intermediate layers was prepared bythermal decomposition and electrodepositing technology, the mushroomshaped activated layer （Pb₃O₄andβ-PbO₂）, possessed a high surface area, leadto a good electrocatalytic property. When the rare earth elements Ce and Ywere doped into the intermediate layer, the service life, kinetic parameters ofoxygen evolution and electrocatalytic property of Ti/PbO₂ in acidic solutionwere better than lead anode.③A novel Ti/MnO₂ anode with different multiple intermediate layers andactivated layer （β-MnO₂） was prepared by thermal decomposition. The resultsindicated that the kinetic parameters a, b and overpotential are smaller thanprecious metal, the i₀ is bigger than precious metals, The activation energy ofoxygen evolution reaction on Ti/MnO₂ anode （8KJ/mol） is lower thanPtO₂（60.67KJ/mol） and Pt/MnO₂（18.83KJ/mol）, the substitution mechanismof oxygen evolution is SN₁. Among all the anodes with different intermediatelayers, the Ti/SnO₂+RuO₂+MnO₂/MnO₂ appears to be an ideal material foroxygen-evolution in acid solution due to its lower overpotential.④The Ti/MO₂ anode with dual SnO₂+Sb₂O₄ intermediate layers is anoptimum material used for oxygen evolution in acidic solution. The initial potentials of Ti/SnO₂+Sb₂O₄/MnO₂, Ti/SnO₂+Sb₂O₄/PbO₂ and Ti/SnO₂+Sb₂O₄ anodefor oxygen evolution in 1.0mol/L H₂SO₄ solution are 1.701V, 1.860V and1.918V respectively. So the Ti/SnO₂ and Ti/PbO₂ electrodes are applicable inthe system of anodic oxidation, the Ti/MnO₂ anode is applicable in thesystem of anodic oxygen evolution.⑤The single Sb₂O₄, the dual SnO₂+Sb₂O₄ and the multipleSnO₂+Sb₂O₄+MO₂（M=Ru、Mn） are appropriate oxide intermediate layers forTi/SnO₂, Ti/PbO₂ and Ti/MnO₂ anodes respectively. Due to the same crystalstructure, the SnO₂+Sb₂O₄ （56% Sb₂O₃ and 44% Sb₂O₅） intermediate layercan form a matched solid solution with lead, manganese coatings and titaniumdioxide, activation energy is low （13.965KJ/mol） during the formation, tinyand closely grains were uniformly distributed on the solid solution surfacewithout cracked structure, thereby effectively preventing oxygenated speciestransport toward the titanium substrate to form titanium dioxide insulatinglayer and extending anode service life. The anticipated service lives ofTi/SnO₂+Sb₂O₄/PbO₂, Ti/SnO₂+Sb₂O₄/MnO₂ and Ti/SnO₂+Sb₂O₄ anodes canreach 15.7y, 10.6y and 4.6y respectively in an industrial current density（1000A/m²）. Meanwhile the conductivities of these anodes were alsoimproved because of the generation of oxygen vacancy and crystal defectsduring the formation of solid solution. Compared to a lead electrode, theconsumption of electricity by Ti/SnO₂+Sb₂O₄/PbO₂ electrode is 17% lower inthe same condition.2. Geometric factors are usually recognized to govern catalysis ofelectrode. The fractal geometry theory was firstly introduced to describe theanode surface irregularity quantitatively in this article, and the fractaldimensions of the oxide electrode surface were determined by means of boxdimension law and cyclic-voltammetry based on the correlation between different scan rate and peak current. Meanwhile the relationship betweenfractal dimension and electrocatalysis performance of oxide electrode wasalso investigated. The combination of fractal geometry theory and theelectrode electrocatalysis performance has provided a new method to theresearch of electrocatalysis. The results indicated that oxide electrode withmultiple transitional layers is porous and three-dimensional, the fractaldimension ranges from 2 to 3, the electrocatalysis performance of oxygenevolution on anode is related to surface fractal dimension, e.g., theelectrocatalytic activity of Ti/RuO₂ anode with a higher box dimension isbetter than Ti/MnO₂ and Ti/PbO₂ anodes. However, the fractal dimension ofTi/PbO₂ calculated from cyclic-voltammetry method is greater than others,which coincides well with the irregularities of surface layer. Both twomethods have their own merits, can construct the relation between surfacemorphology and catalytic activity.3.The performance of Ti/SnO₂ prepared by sol-gel method wasinvestigated in the application of phenol contained wastewater treatment.Impacts of doping antimony and calcinations temperature on phenoldegradation were studied; kinetic parameters and activated energy of phenoldegradation were measured. A same investigation applied to theTi/SnO₂+Sb₂O₄+MnO₂/PbO₂ electrode prepared by thermal decompositionand electrodepositing. Photoelectrocatalytic degeneration of phenol on theTi/MnO₂ and stainless steel/MnO₂ electrode were conducted and the removalrates were also compared. The results indicated that Ti/SnO₂+Sb₂O₄,Ti/SnO₂+Sb₂O₄/PbO₂ and Ti/SnO₂+Sb₂O₄/MnO₂ anodes are applicable tophenol contained wastewater treatment, the removal rates are 96.5%, 95.8%,and 91.5% respectively. The current efficiencies for Ti/SnO₂+Sb₂O₄, Ti/SnO₂,Ti/SnO₂+Sb₂O₄+MnO₂/PbO₂ and Ti/PbO₂ in the same condition are 73.5%, 66.0%, 62.0%, and 54.9% respectively. So the Ti/SnO₂+Sb₂O₄ with solidsolution intermediate layer is an ideal anodic materials used for phenolcontained wastewater treatment.4 Ti/SnO₂+Sb₂O₄/PbO₂, Ti/SnO₂+Sb₂O₄/MnO₂, Ti/SnO₂+Sb₂O₄ anodesand Ti/Sn cathode were applied into the realization of electrochemicalreduction sodium metaborate to sodium borohydride, i.e., the NaBO₂ wasconverted directly into borohydride by electrochemical reduction （charge）, theborohydride produced by-product sodium metaborate again （discharge） whenhydrogen evolution occurs, thus in situ boron circulation was carried out. Thequantitative relationship between nickel electrode opening potential andborohydride concentration (10^-5-10^-3mol/L) was first established in this article,the relatively standard deviation is 2.22%, and the recovery ratio is 98.43%.Kinetics law of electrochemical reduction sodium metaborate to sodiumborohydride was also preliminary proposed.Summarizing the points above, we can make a conclusion that multipleintermediate layers of solid solution play an important role in the performanceof titanium based oxide anodes. Because the addition of oxides asintermediate layer can form matched solid solution, not only the anodeconductivity is improved, but also the binding force between the substrate andactivated layer is strengthened. So the service life of anode is prolonged inacid solution and their electrocatalytic ability is improved. Among all theintermediate layers mentioned above, the dual SnO₂+Sb₂O₄ is recognized asthe best in anodes.更多还原