【作者】 韩家军；

【导师】 李宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2009， 博士

【摘要】 银是典型的氧还原催化剂之一。在碱性电解质中,银对氧还原具有很高的催化活性。而且,对过氧化物离子分解也是很好的催化剂。因此,银被认为是燃料电池和金属空气电池中比较理想的氧电极催化剂。银催化剂在制备和使用过程中,容易引起团聚问题,难以制备出粒径较小、在催化剂载体上分布均匀的银粒子。所以,银作为催化剂,关键在于尽可能提高银的比表面积,使银粒子均匀地散布在催化剂载体上。本文提出了Ag（Ⅰ）配位聚合物还原法制备Ag/C催化剂,并考察了催化剂的制备条件。同时探讨了Ag/C催化剂的催化活性和氧在Ag/C上的还原反应。并将Ag/C用作直接硼氢化钠燃料电池和锌-空气电池的催化剂,测试了氧电极的性能。采用溶液法,基于磺酸Ag（Ⅰ）配位化合物（[Ag（L）]）,分别以亚丁基二咪唑（bbi）、三苯基膦为配体（tpp）,合成了[Ag（L）（bbi）]和[Ag（tpp）₂（L）]·C₂H₃N两种配位聚合物。通过Rigaku RAXIS-RAPID日本理学单晶衍射仪,获得了[Ag（L）（bbi）]和[Ag（tpp）₂（L）]·C₂H₃N两种配位聚合物的晶体结构。经文献检索证明,[Ag（L）（bbi）]和[Ag（tpp）₂（L）]·C₂H₃N两种配位聚合物单晶均确系为新单晶。在探索合成条件中,考察了酸度、溶剂和时间对两种配位聚合物生成的影响。有关[Ag（L）（bbi）]和[Ag（tpp）₂（L）]·C₂H₃N两种配位聚合物的性质,分别进行了耐酸碱和耐温试验。应用[Ag（L）（bbi）]和[Ag（tpp）₂（L）]·C₂H₃N两种配位聚合物,以NaBH4为还原剂,通过Ag（Ⅰ）配位聚合物还原法,分别制备了Ag/C催化剂。经Ag/C催化剂电催化活性比较,选择了[Ag（L）（bbi）]配位聚合物作为研究对象。并考察了[Ag（L）（bbi）]配位聚合物粉末粒径对Ag/C催化剂电催化活性的影响,以及超声波振荡时间对Ag粒子在活性炭载体上分散程度的影响。通过X-射线光电子能谱（XPS）、X-射线衍射（XRD）和扫描电子显微镜（SEM）对Ag/C催化剂进行表征,结果表明,使用Ag（Ⅰ）配位聚合物还原法制备Ag/C催化剂,[Ag（L）（bbi）]配位聚合物中的一价Ag（Ⅰ）还原为金属Ag反应的还原度高;Ag（Ⅰ）配位聚合物还原法制备的Ag/C催化剂中Ag颗粒的平均粒径比Ag2O还原法制备的小;与Ag2O还原法相比,Ag（Ⅰ）配位聚合物还原法制备的Ag/C催化剂中,Ag的颗粒较小、形状规则。并讨论了Ag（Ⅰ）配位聚合物还原法制备的Ag/C催化剂的电催化活性比Ag2O还原法制备的Ag/C催化剂明显增强的原因。利用循环伏安法,在碱性电解质中,探讨了Ag/C催化剂中Ag颗粒粒径对氧还原路径的影响,考察了Ag颗粒粒径与氧还原反应所产生的过电位之间的关系。结果表明,在粒径较大的Ag颗粒上,氧还原反应以四电子路径进行;在粒径较小的Ag颗粒上,氧还原反应以四电子路径和二电子路径同时进行。通过旋转圆盘电极法,研究了氧在Ag/C催化剂上的还原动力学反应。实验研究揭示,在碱性电解质中,Ag颗粒的粒径越小,越有利于氧还原反应按二电子路径进行;Ag颗粒的粒径越大,越有利于氧还原反应按四电子路径进行。根据Koutecky-Levich方程,测定了氧还原动力学反应的电子数目和速率常数,获得了氧在Ag/C催化剂上按四电子路径和二电子路径进行还原反应的比例。使用Ag（Ⅰ）配位聚合物还原法制备的10wt% Ag/C作为氧电极催化剂,分别组装了流动碱性电解质直接硼氢化钠燃料电池和流动碱性电解质锌-空气电池。通过VEGA51365B型扫描电子显微镜观测了氧电极催化层的微观表面形貌;又采用HIROMX-5040RZ体视显微镜观测了氧电极和Au/C电极催化层的微观表面形态。对硼氢化钠燃料电池,考察了NaBH4燃料溶液浓度和流速的影响;通过电极极化曲线和电化学阻抗谱（EIS）,讨论了氧电极和Au/C电极的性能。对锌-空气电池,通过电极极化曲线,讨论了氧电极和锌电极的性能。结果表明,在硼氢化钠燃料电池和锌-空气电池中,阳极极化较小,受温度影响较小;氧电极极化较大,其极化随着温度的上升而降低。于不同温度下,分别测试了硼氢化钠燃料电池和锌-空气电池的功率密度,并同时测定了NaBH4燃料的电氧化效率。更多还原

【Abstract】 Silver is one of the typical catalysts of oxygen reduction. Ag has a reasonably high catalytic activity for O2 reduction in alkaline electrolyte. Furthermore, it is a good catalyst for perhydroxyl ion decomposition. Therefore, Ag is known as the ideal catalyst in the fuel cell and metal-air battery. Ag particles are easy to accumulate into larger particles in the process of preparation and usage, and therefore it is difficult to prepare finer and well-dispersed Ag particles on the carrier of catalysts. So the key to Ag as the catalysts lies in raising the specific surface area of Ag as far as possible and making Ag particles dispersed evenly onto the carrier of catalysts. In the present study, the Ag（Ⅰ） coordination polymer reduction method was introduced to prepare Ag/C catalysts, and the preparing condition of the catalysts was examined. The Ag/C catalytic activity and the reduction reaction of O2 on Ag/C were explored. The performance of the oxygen electrode was measured using Ag/C as catalysts for the direct sodium borohydride fuel cell and the zinc-air batteryBased on Ag（Ⅰ） sulfonate complexes （[Ag（L）]）, the coordination polymers of [Ag（L）（bbi）] and [Ag（tpp）₂（L）]·C₂H₃N have been synthetized using 1,1′-（butane-1,4-diyl）- diimidazole（bbi） and triphenylphosphine（tpp） as ligands by the conventional solution method. The crystal structures of [Ag（L）（bbi）] and [Ag（tpp）₂（L）]·C₂H₃N coordination polymers were obtained on a Rigaku RAXIS-RAPID diffractometer. The literature retrieval proved that the [Ag（L）（bbi）] and [Ag（tpp）₂（L）]·C₂H₃N coordination polymers were the new single crystals. The effects of acidity, solvent and time on the growth of the two coordination polymers were examined in the exploration of synthesis conditions. The tests for acid- and base-resistance and temperature-resistance were carried out on the properties of [Ag（L）（bbi）] and [Ag（tpp）₂（L）]·C₂H₃N coordination polymers.Ag/C catalysts were prepared by the Ag（Ⅰ） coordination polymer reduction method through [Ag（L）（bbi）] and [Ag（tpp）₂（L）]·C₂H₃N coordination polymers using NaBH4 as the reductant. The coordination polymer of [Ag（L）（bbi）] was selected as the object of study by comparing the electrocatalytic activity of Ag/C catalysts. The effects of the particle sizes of [Ag（L）（bbi）] powders on the electrocatalytic activity of Ag/C catalysts and the ultrasonic vibration time on the dispersity on Ag particles on the carrier were examined. By characterizing Ag/C catalysts throuhg X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）, the result showed that the reduction degree of Ag（Ⅰ） ions in [Ag（L）（bbi）] coordination polymer was high preparing Ag/C catalysts by the Ag（Ⅰ） coordination polymer reduction method, and the average particle size of Ag in Ag/C catalysts prepared by the Ag（Ⅰ） coordination polymer reduction method was smaller than that of Ag in Ag/C catalysts prepared by the Ag2O reduction method, and that the size of Ag particle in Ag/C catalysts prepared by the Ag（Ⅰ） coordination polymer reduction method was smaller and regular in shape compared with Ag/C catalysts prepared by the Ag2O reduction method. The cause of the significant enhancement of electrocatalytic activity was discussed for Ag/C catalysts prepared by the Ag（Ⅰ） coordination polymer reduction method compared with Ag/C catalysts prepared by the Ag2O reduction method.The effect of the particle size of Ag in Ag/C catalysts was investigated on the pathway of oxygen reduction in alkaline electrolyte using the cyclic voltammetry. The relationship was examined between the Ag particle size and the overpotential of the oxygen reduction reaction. The result indicated that the oxygen reduction reaction proceeded by the four-electron pathway mechanism on larger Ag particles, and proceeded by the four-electron pathway and the two-electron pathway, simultaneously, on finer Ag particles. The kinetics of oxygen reduction reaction was studied on Ag/C catalysts in alkaline electrolyte through the rotating disk electrode method. The experimental results showed that the finer Ag particles were beneficial to the oxygen reduction reaction proceeding by the two-electron pathway, and the larger Ag particles were beneficial to the oxygen reduction reaction proceeding by the four-electron pathway in alkaline electrolyte. According to the Koutecky-Levich equation, the electron number and the rate constant of the oxygen reduction reaction were determined, and the ratios of the oxygen reduction reaction of the four-electron pathway and the two-electron pathway were obtained on Ag/C catalysts.The direct sodium borohydride fuel cell and zinc-air battery with flowing alkaline electrolyte were assembled using 10wt%Ag/C prepared by the Ag（Ⅰ） coordination polymer reduction method as catalysts of the oxygen electrodes. The morphology of the catalyst layer of the oxygen electrode was observed by a VEGA51365B scanning electron microscopy（SEM）, and the surface morphologies of the catalyst layers of the oxygen electrode and the Au/C electrode were observed by a HIROMX—5040RZ stereomicroscopy. The effects of the concentration and flow rate of NaBH4 solution were examined for the sodium borohydride fuel cell, and the performances of the oxygen electrode and Au/C electrode were discussed through the polarization curves of electrodes and electrochemical impedance spectroscopies（EIS）. The performances of the oxygen electrode and zinc electrode were discussed for the zinc-air battery through the polarization curves of electrodes. The results indicated that the polarizations of the anodes are smaller and less effected by the temperature, and the polarizations of the oxygen electrode are larger and declines with rising temperature in the sodium borohydride fuel cell and zinc-air battery. The power densities of the sodium borohydride fuel cell and zinc-air battery were measured at different temperatures, and the electro-oxidation efficiency of the NaBH4 fuel was determined.更多还原