【作者】 徐志花；

【导师】 张鉴清；

【作者基本信息】 浙江大学 ， 物理化学， 2006， 博士

【摘要】 高铁酸盐（Fe（Ⅵ））具有较高的氧化还原电位、较大的电化学理论容量、原料来源丰富，本身及放电产物对环境无污染，不仅可用作废水和生活用水中的处理剂及有机合成反应中的氧化剂，还可以用作超级铁电池中的正极材料。为了有效地利用有限的自然资源和保护自然环境，实现可持续发展，高铁酸盐（Fe（Ⅵ））的制备及应用引起了研究工作者的兴趣。在高铁酸盐（Fe（Ⅵ））的三种主要制备方法中，电化学方法以其对环境无污染和制备过程较简单易行等优点受到了关注。但在电化学制备过程中，在长时间和大电流电解的情况下，高铁酸盐生成的电流效率不是很高，进一步提高电化学合成高铁酸盐的电流效率是科学工作者们正在研究的热点。目前虽然高铁酸钾的稳定性最好，但其放电性能不够理想。其它具有较高理论容量的高铁酸盐如CaFeO₄等的电化学性能有待于研究。本论文首先概述了高铁（Ⅵ）酸盐的制备方法、纯度分析方法、物理化学性质、碱性溶液中铁电极的电化学行为以及高铁（Ⅵ）酸盐在氧化合成有机物、水处理和作化学电源等领域的应用。接着简要地介绍了本文的选题目的和意义及实验方案。在第三章中，研究了阳极材料、电流密度、温度等因素对电化学制备高铁酸钠的电流效率、浓度及Fe（Ⅵ）／Fe_tol．比值的影响。结果发现，铁丝网电极在不同电流密度、电解时间和温度的影响下，生成高铁酸钠的电流效率、浓度及Fe（Ⅵ）／Fe（tol．）比值的变化趋势与灰口铸铁和球墨铸铁电极相似。只是相较于后两种阳极，铁丝网电极在较小电流密度下，电流效率达最大。当铁丝网为阳极时，电解2h后，最高电流效率可达73.6％（j=1.02 mA／cm²），而球磨电极和灰口铸铁电极分别58.8％（j=8 mA／cm²）和61.7％（j=8 mA／cm²），这些差异可能与阳极的组成及结构有关。还研究了在溶液中添加各种阴离子对以铁丝网为阳极电解生成高铁酸钠的影响。发现在14 mol／dm³NaOH溶液中在添加PO₄^3-、SO₄^2-和SiO₃^2-等阴离子，在较低阴离子浓度和较低电解温度的条件下，可以在一定程度上改进高铁酸钠生成的电流效率。在第四章中，对超声波在14 mol／dm³ KOH溶液中辅助直接电合成K₂FeO₄固体的影响作了研究，并采用扫描电子显微镜（SEM）、X-射线衍射（XRD）和傅立叶红外吸收光谱（FTIR）等技术对超声波作用和无超声波作用直接电合成的K₂FeO₄的表面形貌和结构进行了表征。通过对超声波对纯铁电极电化学行为影响的研究表明，超声波能加快电极表面上的固体K₂FeO₄向本体溶液中的转移和延缓电极表面的钝化，还能减慢O₂析出的速度，这可能就是超声波作用能够提高固体K₂FeO₄生成的电流效率的原因。但同时超声波作用也能加快固体高铁酸钾的分解，所以需要选择合适的超声波功率，本实验中所用的超声波功率为14.6 W。在合适的超声波功率（14.6 W）和较小的电流密度（0.8 mA／cm²）下，电解6.84 h时，生成固体高铁酸钾的电流效率可达77.2％。在本章中还研究了不同的K⁺／（K⁺Na⁺）（[OH^-]=14 mol／dm³）比例对直接电化学制备固体高铁酸钾的影响。结果发现，在较低的温度下（60℃），电解2 h后，在9 mol／dm³ KOH+5 mol／dm³ NaOH溶液中生成固体高铁酸钾的电流效率可达64.9％；在14 mol／dm³ KOH溶液中，生成固体高铁酸钾的最大电流效率在70℃，约63.9％。在这两种溶液中制备的固体高铁酸钾有相似的表面形貌和红外吸收光谱特征。因此，可以通过优化K⁺／Na⁺的比值，在较低的温度下（≤65℃），直接制备K₂FeO₄固体。在第五章中，采用SEM、XRD、FTIR和BET等技术对比研究了间接和直接电解法制备的K₂FeO₄的表面形貌、结构和比表面积等性质，还采用恒流放电和电化学阻抗谱等电化学手段研究了这两种方法制备的K₂FeO₄电极的电化学性能。结果表明，这两种方法制备的K₂FeO₄具有相同的晶型结构，但晶体的生长取向存在差异，而且它们的表面形貌及比表面积也有差异。对这两种方法制备的K₂FeO₄电极的电化学行为的研究发现，在相同的放电条件下，间接电解合成法制备的K₂FeO₄具有较大的放电容量和较小的电极极化。在接下来的一章中对高铁酸钙的制备方法进行了探索，并采用元素分析仪、SEM、XRD、FTIR、热重（TG）和DSC等技术对其物理化学性质进行了表征和分析，结果表明，高铁酸钙可能以CaFeO₄·2H₂O形式存在，此时合成得到的最高纯度可达74.9％；较大量的三价铁化合物及结晶水是造成高铁酸钙的稳定性较差的重要原因。采用恒流放电对高铁酸钙的电化学性能进行了研究，结果表明，尽管高铁酸钙样品含有相对较大量的杂质，但在较大的放电电流和相对较低的温度（≤15℃）下，相对于高铁酸钾，高铁酸钙能表现出较好的放电性能。在最后一章中，采用SEM、和FTIR等手段表征了Ag₂FeO₄的表面形貌和结构，初步研究了Ag₂FeO₄电极在碱性溶液和非水溶剂中的电化学性能，结果表明，Ag₂FeO₄是由纳米或亚微米级粒子组成；在低温环境中具有较好的稳定性，随着温度的升高，分解速度增大得较快。在相同的条件下，与K₂FeO₄相比，在碱性溶液中，Ag₂FeO₄放电性能较差；在非水溶剂中，其电化学性能远远好于K₂FeO₄电极。更多还原

【Abstract】 The preparation and application of ferrate （VI） compounds, which could be used as strong oxidants in water treatment and organic synthesis, and cathodic materials in "super-iron" batteries, have got much attention in the world, due to their high redox potentials, large theoretic capacity, abundance of raw materials in nature and non-toxicity to the environment.In the main three preparation methods of ferrate （VI）, the electrochemical preparation is widely investigated recently, due to its simple processe and non-pollution. However, the problem is that the current efficiency of ferrate （VI） electrosynthesis is not very high. So far, solid K₂FeO₄ is found to be the most stable in all investigated ferrate （VI） compounds, but its discharge performance is not very ideal. Hence it is interesting to probe alternate ferrate （VI） salts with high intrinsic capacity, such as CaFeO₄.In this dissertation, the preparation and the purity analysis, the physicochemical properties of ferrate （VI）, and the electrochemical behavior of iron electrode in alkaline solutions, as well as the application in water treatment, organic synthesis and super-iron batteries were firstly reviewed. Then, the goal and ideas of our work were introduced.In the third chapter of this dissertation, the influences of anode materials, current density, temperature on the current efficiency, concentration of produced ferrate （VI）, and the ratio of Fe （VI） /Fe_tol. were investigated. It was found that the variation trend of the related parameters in the ferrate （VI） electrosynthesis using iron wire gauze was similar to those using grey cast iron or nodular cast iron. Compared with the two latter anodes, the iron wire gauze anode presented the highest current efficiency at relatively small current density. After 2 h electrolysis, the current efficiency of ferrate （VI） electrosynthesis was 73.6% when current density was 1.02 mA/cm² using the iron wire gauze, while it was 58.8% and 61.7% using grey cast iron and nodular cast iron, respectively, when the current density was 8 mA/cm². The differences were presumably related to the composition and structure of the anodes. The influences of the addition of different anions in 14 mol/dm³ NaOH on the ferrate （VI） electrosynthesis were also investigated using iron wire gauze anode. The results showed that at the conditions of lower concentration of anions, such as, PO₄^3-, SO₄^2- and SiO₃^2-, etc. and lower temperatures, the current efficiency of ferrate （VI） electrosynthesis increased to some extent.In the fourth chapter, the effects of ultrasound on the direct electrosynthesis of solid K₂FeO₄ and the anodic behaviors of pure iron were investigated, and the physical properties of the samples were characterized by means of XRD, FTIR and SEM. The experimental results showed that the existence of ultrasound could decrease the formation potential of ferrate （VI） and the passivation extent of iron anode, as well as O₂ evolution rate, which led to higher current efficiency for the direct electrosynthesis of solid ferrate （VI） at 65℃in 14 mol/dm³ KOH solution. It was also found that in the experimental scope the suitable ultrasonic power was 14.6 W. The largest current efficiency under 14.6 W of the ultrasonic power and small electrolysis current （0.8 mA/cm²） reached to 77.2% after 6.84 h electrolysis.In this chapter, the influences of different ratio of K⁺/（K⁺ + Na⁺ ） （[OH^-]=14 mol/dm³） on the direct electrosynthesis solid K₂FeO₄ were also investigated. The results showed that, at lower temperatures（60℃）, the apparent current efficiency of electrosynthesis solid potassium ferrate （VI） could reach 64.9 % in 9 mol/dm³ KOH + 5 mol/dm³ NaOH solution after 2 h electrolysis, while it went to its maximal value, about 63.9% at 70℃in 14 mol/dm³ KOH. The solid potassium ferrate （VI） samples prepared from the two solutions exhibited similar SEM and infrared absorptions. Therefore, solid K₂FeO₄ could be obtained at lower temperature （≤65℃） through optimizing the ratio of K⁺/Na⁺.In the fifth chapter of this dissertation, K₂FeO₄ powders were synthesized by the ex-situ and in-situ electrochemical methods, respectively, and characterized by IR, SEM, XRD and BET. Their electrochemical performances were investigated by means of galvanostatic discharge and electrochemical impedance spectroscopy （EIS）. The results of physical characterization showed that the two samples had similar structural features, but the orientation growth of the crystals, their surface morphologies and specific surface areas were different. The results of discharge experiments indicated that the ex-situ electrosythesized K₂FeO₄ electrode had much larger discharge capacity and lower electrode polarization （that is, smaller Rt value） than the in-situ electrosynthesized K₂FeO₄ electrode.In the following chapter, calcium ferrate （VI） powders prepared from potassium ferrate （VI）, were characterized by titration analysis, elemental analyzer, SEM, XRD, IR, TG and DSC. The results showed that the synthesized sample mainly consists of calcium ferrate （VI）, and calcium ferrate （VI） may exist as CaFeO₄·2H₂O with a highest obtained purity of 74.9%. The relatively higher Fe （III） impurity and crystalloid water might be responsible for the poor stability of the calcium ferrate （VI） sample. The results of galvanostatic discharge experiments indicated that the calcium ferrate （VI） sample displays better intrinsic rate discharge capability and larger discharge capacity at lower temperatures （≤15℃）.In the last part of this dissertation, Ag₂FeO₄ was characterized by SEM and FTIR, and its electrochemical performances were investigated by constant current discharge. The results showed that, Ag₂FeO₄ consisted of nano or submicron particles; with the temperature increasing, Ag₂FeO₄ decomposed quicker. At the same discharge conditions, the discharge performance of Ag₂FeO₄ was worse than that of K₂FeO₄ in the alkaline solution, but it was far better in the non-aqueous solution.更多还原