导电聚苯胺和聚苯胺复合阳极材料的制备及电化学性能研究

【作者】 黄惠；

【导师】 郭忠诚；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2009， 博士

【摘要】 在湿法炼锌工业中,高浓度H28O4电解液体系使得Zn电积过程一直采用铅基合金阳极。但铅基合金阳极析氧过电位高,增加无用电耗约占Zn电积总能耗的30%,同时存在抗蠕变性能差以及Pb被腐蚀进入电解液并降低电Zn品质等问题。针对上述问题,Ti基电催化涂层阳极尽管可有效降低阳极过电位,但较短寿命与高昂成本使其难以取代铅基合金阳极。因此,开发新型节能阳极仍是湿法炼Zn领域的重要课题。本文在整合了有机化学、材料学、有色冶金和电化学等学科基础上,提出聚苯胺基节能阳极的概念。在保持铅银合金阳极优势的同时,降低阳极析氧过电位,减少阳极腐蚀并提高Zn品质。论文研究开发了导电聚苯胺、聚苯胺/二氧化钛(PANI/TiO2)和聚苯胺/碳化钨(PANI/WC)复合材料的制备技术,探讨了聚苯胺的聚合机理、导电机理、掺杂机理以及聚苯胺复合材料的复合机理,并探索出较佳工艺条件；建立了聚苯胺基阳极成型工艺,系统研究了聚苯胺基阳极的抗氧化性和电化学行为；深入研究了PANI/WC阳极在ZnSO4-Mn2+-H2SO4体系中析氧电位、槽电压、阳极寿命、电流效率、电能消耗、Mn2+的行为和阴极Zn品质；在此基础上,进一步与工业用Pb-Ag(1.0%)阳极比较。并利用FTIR、UV-vis、Raman、XRD、SEM、TEM、XPS、EDS、激光粒度分析和热分析等手段对材料的结构物相、表面形貌、氧化程度、掺杂程度、成分、粒径大小和热稳定性进行分析。采用阳极极化曲线、塔菲尔曲线、交流阻抗和循环伏安等电化学手段在酸性体系和碱性体系中分析了电极的动力学参数。研究结果如下：(1)开发了导电聚苯胺和聚苯胺复合材料的制备技术,建立了聚苯胺基阳极的成型工艺,制备了尺寸为70mm×50mm×5mm的聚苯胺基电极。(2)苯胺聚合是以头-尾连接的形式进行,且中间产物是高氧化态聚苯胺而后又逐渐转变成中间氧化态聚苯胺；质子化优先发生在分子链的亚胺氮原子上,质子酸发生离解,生成的H+转移到聚苯胺分子链上,使聚苯胺链中亚胺基团上的氮原子发生质子化反应,质子化反应使聚苯胺链上掺杂段的价带出现空穴,即P型掺杂;在导电聚苯胺分子中,无论是内分子链与分子链之间,还是分子与分子之间,变程跳跃导电和隧穿导电是同时存在的,是互相竞争的。(3)TiO2或WC与聚苯胺之间不是简单的混合而是存在着一定的相互作用；聚苯胺复合材料的环境稳定性和热稳定性均比纯聚苯胺的好；在高温下氧化,材料的主体结构未发生变化,表现出较好的抗氧化性,其中PANI/WC的抗氧化性最好。(4) PANI/WC复合材料中WC粒子中的C与PANI产生了化学键的作用,其导电能力是PANI的电子导电和W原子导电共同作用的结果；而PANI/TiO2复合材料中PANI分子链上的阳离子自由基生成的对阴离子受到TiO2中的O离子的置换,致使原来相临的两个对阴离子被O离子置换走,其导电能力是pn结形式的空穴和电子两种载流子参与导电。(5)系统研究了聚苯胺基电极的电化学行为,揭示了聚苯胺基电极的电化学行为与特征。结果表明,聚苯胺基电极在硫酸体系中的耐蚀性最好,在碱性体系中次之,在盐酸体系中耐蚀性最差。在硫酸体系中PANI/WC耐蚀性最好并且具有较好的催化活性。PANI/WC电极在硫酸体系电积锌工业中具有良好的应用前景。(6)采用尺寸为70mm×50mm×5mm的聚苯胺基阳极进行电解试验。结果表明,与工业用Pb-Ag(1.0%)阳极相比,电流密度为500A/m2时,聚苯胺基阳极析氧电位都明显降低了200～475mV。槽电压和电能消耗都有很大程度的降低；并且阴极Zn无铅污染；特别是PANI/WC阳极最为突出,槽电压降低到2.87V,电流效率提高到92.4%,电积1吨锌可节约电能为16.24%。另外,电解液中Mn2+本身的贫化发生了明显的变化,即Pb-Ag(1.0%)阳极对应电解后电解液Mn2+贫化比较明显,其贫化量为0.673g,而以聚苯胺基阳极的电解后电解液Mn2+贫化量为0.187～0.236g,聚苯胺基阳极有利于减少阳极泥的生成。(7)系统研究了不同电流密度下PANI/WC阳极的电化学行为,揭示了电流密度对槽电压、电流效率和阴极Zn品质的影响。当电流密度为250A/m2时电积锌在(101)晶面择优取向生长；电流密度增加到2000 A/m2时电积锌转变为在(002)晶面择优取向生长,同时对锌的表面形貌也有很大的影响。(8)PANI/WC阳极在电解过程中,失效的主要原因一方面是包覆在WC表面的聚苯胺逐渐脱落,使得WC裸露出来,从而阳极的导电性减弱;另一方面是阳极表面逐渐出现裂纹,最终甚至出现裂缝,使得整个阳极导电发生断路,从而失去导电性。更多还原

【Abstract】 The anode of lead-based alloy is always used in industrial production of zinc owing to high concentration of H2SO4 in the electrolyte. However, there are several problems on the lead-based anode such as high oxygen evolution overpotential which can increase the energy consumption about 30% of the total energy consumption, low corrosion resistance and decrease of zinc quality due to lead dissolution in the electrolyte. Although titanium-based electro-catalytic coating anode can effectively reduce the oxygen evolution potential, it still cannot replace the lead-based anode due to its short life and high cost. Therefore, it still is an important subject to develop new energy-saving anode in the zinc hydrometallurgy.The concept of polyaniline (PANI)-based anode was put forward by the author based on the knowledge of organic chemistry, materials, non-ferrous metal and electrochemistry. PANI-based anode can reduce the anodic overvoltage, lower the anode corrosion rate and improve the product Zn quality while maintaining the advantages of Pb-Ag alloy anode. In this paper, the equipment and technics of PANI and PANI composite materials were developed, the polymerizing mechanism, conducting mechanism and doping mechanism of PANI and compositing mechanism of PANI/TiO2 and PANI/WC composite materials were studied systematically through exploring their synthesis conditions, and the optimal preparation condition under which the resultant PANI/WC had the highest conductivity was obtained. The equipment and technics of PANI-based anodes were developed, the electrochemical properties and anti-oxidation nature of PANI-base anodes were evaluated systematically。The cell voltage, current efficiency, anode life and zinc quality were discussed using PANI-based anodes in ZnSO4-Mn2+-H2SO4 system. Based on that, further with the industrial Pb-Ag (1.0%) compared with PANI-based anode.The microstructure, crystal phase, morphology, oxidation degree, doping level surface composition, particles size and thermal stability of synthesized materials were characterized by means of FTIR,UV-vis, Raman, XRD, SEM, TEM,XPS,EDS,laser grain size analysis and thermal analysis and so on. The electrochemical properties of anodes had also been studied by linear sweep voltammetry, A.C. impedance, Tafel plot and cyclic voltammetry. The main results are as following: (1) The equipment and technology of conductive PANI and PANI/composite materials were designed and developed. The forming process of PANI-based anodes was established and PANI-based anodes with dimension of 70mm×50mm×5mm are prepared.(2) Aniline polymerization was head-to-tail structure. Even intermediate products were higher oxidation states, and then turned to be emeraldine base gradually. Quinine-imine (-N=) was priorly protonated in doping reaction process. Pronton acid was ionized form H+, and H+ transfer in polyaniline molecule chain, and then the positive charge was distributed periodically along the molecular chain according to the inner-chain charge transfer. After protonated reaction, valence band of the doping segment polyaniline appeared hole (p model doping). In conductive polyaniline molecule, no matter among the chains or among the molecule, variable-range hopping and tunneling conductive existed at the same time and competed with each other.(3) WC or TiO2 particles and PANI molecular chains were not simply blended or mixed up, and a strong interaction existed at the interface of WC or TiO2 and PANI. Addition of TiO2 or WC could improve the conductivity composites. The environment and thermal stability of the composites were higher than that of the pure PANI. At a high temperature oxidation, the main structure of materials didn’t change, so they displayed a better anti-oxidation nature. Anyway, the anti-oxidation nature of PANI/WC anodes was best.(4) In the PANI/WC composites, chemical bonds were formed the WC particles and the PANI. The conductivity of the PANI/WC composites was the collaboration effect of the electronic conduction of the PANI and the conduction of free electrons. While in the PANI/TiO2 composites, the adjacent anion produced by the radical cation on the PANI molecule chain were replaced the 0 ions in the TiO2, its conductivity was the result of the participation of the hole and electron by the form of pn junction in the conduction process。(5) The electrochemical behavior of PANI-based anodes was studied systematically and electrochemical characteristics of PANI-based anodes were revealed. Results showed that the corrosion resistance of PANI-based anodes was best in sulfuric acid system and was worst in hydrochloric acid system. In sulfuric acid system, the corrosion resistance and catalytic activity of PANI/WC were best. In a word, PANI/WC anode has a good application prospects in sulfuric electrowinning zinc in the industry.(6) The PANI-based anodes with dimension of 70mm×50mm×5mm were tested in simulation electrolysis experiment and the anodes were found to perform well in industrial electrolysis conditions. The results showed that the anodic potential was decreased about 200-475mV at the current density of 500A/m2 compared with the Pb-Ag(1%) anode. The specific energy consumption was smaller than that of Pb-Ag (1%) anode and the lower material costs. Zinc deposits obtained had not Pb pollution. For the most prominent PANI/WC anode, the cell voltage was about 2.87V, current efficiency was about 92.4%, energy savings of electrowinning 1 ton zinc was about 16.4%. The current efficiency for PANI-based anodes was almost same as that of Pb-Ag (1%) anode which was 91%-93% while the PANI-based anodes were beneficial for reducing anode slime because the phenomenon of Mn2+ dilution was less obvious.(7) In order to illustrate effect of current density on PANI/WC anode, cell potential, current efficiency and the quality of cathode zinc were studied systematically at different current densities. Current density had great effect on the orientation of zinc crystals in electrowinning zinc. When the current density was 250A/m2, the zinc was superior to develop on the crystal face of (101), while to develop on the crystal face of (002) when the current density turned to 2000A/m. At the same time, current density also had effect on the surface morphology of deposited zin.(8) In the process of electrolysis, the PANI covered on the surface of the WC was peeled off gradually, which resulted in the decline of the conductivity of the PANI/WC anode. In addition, the cracks and even the crevices were emerged on the surface of the PANI/WC anode, appeared gradually on anodes made the cutting-out of the entire electrode conduct system, and finally lost conductivity.更多还原