【作者】 王雅琼；

【导师】 陆路德；

【作者基本信息】 南京理工大学 ， 化学工程与技术， 2009， 博士

【摘要】 电化学技术是利用电化学基本原理实现物质化学转化的技术,其应用涵盖了化学电源、电镀、电冶金、无机和有机电合成、电化学水处理、材料的腐蚀与防护、纳米材料的制备等诸多领域。电极作为实现电化学过程必不可少的材料,其结构和性能不仅影响电化学过程的速率、选择性、能耗等,甚至决定着整个电化学过程的成败。因此,电极材料的制备及其结构性能研究,尤其是耐酸阳极材料的研究和开发是电化学技术应用中值得关注的重要问题。本文采用聚合物前驱体法制备了Ti/Sb-SnO₂膜,并通过对Ti/Sb-SnO₂表面进行修饰制备了Ti/Sb-SnO₂/PbO₂和Ti/Sb-SnO₂/MnO_x电极,用X-射线衍射、扫描电镜、循环伏安、加速寿命实验等方法测定了电极的结晶结构、表面形貌、电化学活性表面积以及电化学孔隙率等,对电极的微观结构及电化学性能进行了分析表征,研究了金属氧化物电极的化学组成及制备方法对电极结构和性能的影响,并将不同的电极材料用于苯酚的电化学氧化降解及C,的电化学氧化过程。主要研究内容和研究结果如下:1.聚合物前驱体法制备的Sb-SnO₂中间层的结构及其对电极性能的影响聚合物前驱体法是制备纳米材料的方法之一,近年来该方法也被用来制备金属氧化物电极,但将聚合物前驱体用于制备Ti/Sb-SnO₂膜,系统研究Ti/Sb-SnO₂膜的结构以及对多层金属氧化物电极性能的影响还未见报道。本文将聚合物前驱体用于钛基多层金属氧化物电极中间层Sb-SnO₂的制备,研究了聚合物前驱体法制备的Sb-SnO₂膜的结构和性能。研究结果表明,与不加中间层的Ti/PbO₂电极相比,加入用聚合物前驱体法制备的Sb-SnO₂中间层后,Ti/Sb-SnO₂/PbO₂电极的电催化性能及电极寿命明显提高。与传统的小分子醇类前驱体相比,聚合物前驱体法制备的Sb-SnO₂结晶度高,表面均匀致密。在加速寿命实验条件下(60℃,1.0 mol·L^-1H₂SO₄,4.0 A·cm^-2),以Sb-SnO₂为中间层的Ti/Sb-SnO₂/PbO₂电极的寿命达29.8小时,分别是传统的小分子醇类前驱体乙醇的2.1倍,乙二醇的4.3倍,正丁醇的4.8倍。聚合物前驱体能使Ti/Sb-SnO₂/PbO₂电极的性能明显改善主要是由于聚合物前驱体能均匀稳定地分散金属离子,而且聚合物前驱体还具有良好的流动性和粘性,克服了小分子醇类前驱体粘度低,在金属基体上附着性差,沉积效率低等问题。因此,聚合物前驱体法制得的氧化物膜结晶完善,其致密的氧化物膜不仅自身内应力小,不易脱落,而且也有利于减缓电解液向金属基体的渗入生成钝化膜,从而提高了电极的寿命。2.PbO₂电极活性层的制备方法对电极结构和性能的影响分别采用热分解法、电沉积法和铅基电化学阳极氧化法制备了铅氧化物电极,探讨了铅氧化物电极活性层的制备方法对电极结晶结构及表面形貌的影响,研究了不同制备方法下电极的电化学活性表面积及电化学孔隙率。研究结果表明,电极的制备方法对PbO₂活性层的结构和性能有显著的影响。将Pb（NO₃）溶液涂覆于钛基体上热分解直接得到的是以Pb₃O₄为主的铅氧化物,Pb₃O₄在电解液中经阳极氧化后才转化为β-PbO₂。Pb（NO₃）溶液阳极电沉积法以及硫酸介质中铅基电化学阳极氧化法则可直接制得以β-PbO₂为主要成分的PbO₂电极。虽然三种方法都可以制得PbO₂活性层,但由于制备方法不同,其微观结构有很大的差异,因此电极的电催化活性也不同。PbO₂电极的总伏安电荷和电化学孔隙率反映了电极析氧电化学活化表面积的大小和分布,热分解法制备的PbO₂电极总伏安电荷为57.1 C·cm^-2、铅基电化学阳极氧化法为20.1C·cm^-2,电沉积法仅7.5 C·cm^-2;对应的电化学孔隙率分别为97.4%、90.5%、82.7%。电沉积法制备的PbO₂电极的伏安电荷和电化学孔隙率都是三者中最低,主要与其紧密堆砌的块状结构以及较大的晶粒尺寸有关。加速寿命实验条件下,不同方法制备的电极在电解过程中的槽电压及电极的微观结构的研究表明,无论是热分解法还是电沉积法,电解过程中槽电压都有一个较长的稳定期,失活过程则相对较短。电极失活后,XRD谱图及能谱图上都有明显的钛基体的峰,而活性层和中间层金属的相应特征峰强度则明显下降甚至消失,表明电极失活源自氧化物层的脱落。与热分解法相比,电沉积法制得的紧密堆砌的PbO₂块状结构虽然降低了它的电催化活性,但却有利于提高电极的稳定性和寿命。在相同的加速寿命实验条件下,电沉积法制备的Ti/Sb-SnO₂/PbO₂电极的稳定期达86小时,其加速寿命达89.8小时,是热分解法的3倍以上。3.非贵金属氧化物电极的制备及结构与性能研究贵金属氧化物电极由于其成本高而使工业化应用受到限制。因此,本文分别对三种非贵金属氧化物电极（Ti/Sb-SnO₂、Ti/Sb-SnO₂/PbO₂和Ti/Sb-SnO₂/MnO_x）的制备以及结构性能进行了研究。Ti/Sb-SnO₂电极的制备采用了聚合物前驱体法,然后用热分解法对Ti/Sb-SnO₂电极表面进行修饰制备了含Sb-SnO₂中间层的Ti/Sb-SnO₂/PbO₂和Ti/Sb-SnO₂/MnO_x电极,研究了电极的制备条件对其微观结构和性能的影响,并以硫酸溶液为介质,研究了电极的析氧催化活性。研究结果表明,电极的制备条件显著影响电极的微观结构,从而影响电极的电催化性能及寿命。所研究的三种电极在硫酸介质中析氧电势由高到低依次是Ti/Sb-SnO₂、Ti/Sb-SnO₂/PbO₂、Ti/Sb-SnO₂/MnO_x;相同电极电势下的析氧速率也是Ti/Sb-SnO₂电极最大,Ti/Sb-SnO₂/MnO_x则最小。4.电极材料对苯酚电化学氧化降解及Cr³⁺电化学氧化过程的影响苯酚电化学氧化降解属于有机物的电化学氧化,而酸性介质中Cr³⁺电化学氧化再生Cr₂O₇^2-则是典型的无机阳离子的电化学氧化过程。本文以这两种典型的电化学氧化过程为研究体系,研究探讨了不同化学组成、不同制备方法制得的电极材料对电化学反应过程的影响。结果表明,三种非贵金属氧化物电极,即Ti/Sb-SnO₂、Ti/Sb-SnO₂/PbO₂和Ti/Sb-SnO₂/MnO_x电极,都可以使苯酚氧化降解,但反应速率明显不同。Ti/Sb-SnO₂电极最快,在25℃下其表观反应速率常数为6.66×10^-2min^-1,分别是Ti/Sb-SnO₂/PbO₂和Ti/Sb-SnO₂/MnO_x电极的2.7倍及4.7倍。但是,在电化学氧化Cr³⁺时发现,Ti/Sb-SnO₂电极的反应速率明显低于Ti/Sb-SnO₂/PbO₂电极,25℃下其表观反应速率常数仅为Ti/Sb-SnO₂/PbO₂的约1/4;而Ti/Sb-SnO₂/MnO_x电极则不能用于Cr³⁺的电化学氧化。无论是在苯酚溶液还是在Cr³⁺的硫酸溶液中,三种电极的析氧电势由高到低的顺序均为Ti/Sb-SnO₂、Ti/Sb-SnO₂/PbO₂、Ti/Sb-SnO₂/MnO_x,但是在不同的电化学过程中其电催化活性的顺序却不相同,表明阳极材料对电化学氧化过程的影响不仅与电极材料自身的性质有关,还与电化学反应过程的特性有关,其影响规律还有待于进一步研究。更多还原

【Abstract】 Electrochemical technology is used in many fields,such as chemical power, electroplating,electrometallurgy,inorganic and organic electrosynthesis,corrosion protection,waste water treatment,nano-materials preparation,etc.The electrode materials are obviously the heart of any electrochemical process,which can affect the reaction products,the process efficiency,the energy consumption and feasibility.Therefore,the study and development of electrode materials,especially the anodes used in acidic solution, is of significance in industrial electrochemical technology.The study was mainly focused on the DSAs（Dimensionally Stable Anodes）,which consisted of the base of Ti,the intermediate layers of Sb-doped SnO₂ and active coatings. The intermediate layers of Sb-doped SnO₂ were prepared by a polymeric precursor method （PPM）.Three kinds of active coating,the oxides of Pb or Sn or Mn,were prepared,and the microstructure and characteristics were also investigated.Three different deposition methods were employed to prepare PbO₂ active coatings.With these electrodes as anodes, the electrocatalysis characteristics was researched for three different electrochemical processes,the oxygen evolution reaction in acidic media,the electrochemical oxidation of phenol and the electrochemical oxidation of Cr³⁺to Cr₂O₇^2-,respectively.The effects of the composition and preparation conditions of the coatings on the microstructure and surface morphology were investigated by XRD and SEM.Electrocatalytic activity of the coatings was characterized by cyclic voltammetry and active area of electrodes.The study of anode stability was performed under galvanostatic condition(4.0A·cm^-2or 2.0 A·cm^-2)at 60℃and 1.0 mol·L^-1in aqueous H₂SO₄.The PbO₂ coatings were prepared by three methods including thermal decomposition of Pb（NO₃）solution,anodic electrodeposition of Pb（NO₃）solution and electrochemical oxidation of Pb in H₂SO₄ solution.The three electrodes prepared by different methods have an even greater difference in the microstructure and surface morphology,which results in the difference in composition,oxygen evolution potential and electrochemical active surfaces.For the thermal decomposition method,Pb₃O₄ is obtained,which could be transformedβ-PbO₂ after undergoing electrochemical oxidation as an anode.The electrochemical active surface of the three electrodes lies in the order Ti/Sb-SnO₂/PbO₂ prepared by thermal decomposition＞Pb/PbO₂＞Ti/Sb-SnO₂/PbO₂ prepared by electrodeposition.The larger the electrochemical active surface is,the better the electrocatalytic performance is.A polymeric precursor method（PPM）is widely used to prepare nano-particles.The main advantages of preparing oxide particles by this method are low grain size and possibility of making low-level doped material.The PPM was hired to prepare the coatings of Sb-doped SnO₂ as the intermediate layers of Ti-based metal-oxide electrodes. The results show that the Sb-SnO₂ intermediate layers bright significant improvement in the electrochemical characteristics and the lifetime of the PbO₂ anodes.Comparing with other traditional precursor solvents（ethanol,n-butyl alcohol and ethylene glycol）,the Sb-SnO₂ intermediate layers prepared by PPM assume high crystallinity and close microstructure,so the lifetime of the anodes with the Sb-SnO₂ intermediate layers prepared by PPM is enhanced.Three kinds of metal-oxide electrode,Ti/Sb-SnO₂/PbO₂,Ti/Sb-SnO₂/MnO_x and Ti/Sb-SnO₂,were prepared by thermal decomposition,in which Sb-dosed SnO₂ coatings were obtained by the polymeric precursor method.These electrodes were used as anodes in the process of electrochemical oxidation of phenol.The results show that the three kinds of electrode perform considerably difference.The best result is obtained with the Ti/Sb-SnO₂ anode,following by the Ti/Sb-SnO₂/PbO₂ anode and then the Ti/Sb-SnO₂/MnO_x anode, although complete phenol removal is achieved by all of the anodes.In the process of the electrochemical oxidation of Cr³⁺,Cr³⁺could be readily oxided at the Ti/Sb-SnO₂/PbO₂ anode;however,its oxidation is considerably slower at the Ti/Sb-SnO₂ anode and at the Ti/Sb-SnO₂/MnO_x anode without catalytic function.更多还原