【作者】 李晶；

【导师】 王峰；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2011， 硕士

【摘要】 氯碱工业是通过电解制备烧碱及氯气的高能耗产业,因而开发低能耗的食盐电解技术越来越受到人们关注。其中,采用气体扩散电极的氧还原反应来替代离子膜法中的活性阴极的析氢反应,可降低理论分解电压,从而大幅度降低能耗,因而具有广阔的应用前景。尽管气体扩散电极在离子膜法食盐电解技术上取得很大进展,但是由于其在高碱、高温、高氧等恶劣工况条件下工作,对气体扩散电极的基体结构、贵金属催化剂、碳载体等都可能造成不同程度的腐蚀,使电极稳定性下降、性能衰减,因而制约着其商业化的应用。本论文针对在食盐电解工作环境下的碳基银纳米粒子复合气体扩散电极的电催化稳定性及耐久性进行了系统的研究评价。首先从电极催化材料入手,研究了电极催化剂银纳米粒子及不同碳载体在加速腐蚀的情况下的稳定性及其腐蚀机理；并考察了电极本体结构在腐蚀介质及不稳定工况条件下的稳定性及腐蚀机理；最后初步评估小型电极的使用寿命。这对延长电极使用寿命、降低电极生产成本等具有重要意义。首先通过对阳极加速腐蚀,随着极化电压的增大,银颗粒逐渐转变为薄膜态Ag20、块状Ag20、及钝化态AgO；但是活性极化的不同阳极电位加速腐蚀下,电极均保持了较好的耐久性。通过对常用炭黑载体Vulcan XC-72、其石墨化炭黑GCB及其酸化炭黑进行了阳极腐蚀分析。经过石墨化处理后的炭黑载体具有较高的导电性,且在阳极氧化过程中的氧化程度最低,因而耐腐蚀性能最好。通过对电极进行失重浸泡,Ag/C电极在长时间浸泡过程表面亲水性能越来越强。红外分析得出浸泡之后增加了更多-COO和-C=O的官能团。极化曲线测试发现氧还原极限扩散电流密度略有减小。阻抗显示浸泡过后氧还原的容抗弧增大,电荷转移电阻增大,从而使氧还原效率下降。通过模拟多次停车逆电不稳定工况,发现电极催化层被严重刻蚀,电极催化层颗粒粒径也发生了明显增大,使电极稳定性明显下降,极大的减小了电极的结构寿命。通过氧气浓度的变化,对电极进行结构失效寿命评价,拟合结果达到了5.1年。并且通过对电极进行电催化剂寿命失活稳定性测试,电催化剂寿命失活的年数为5.4年。表明电催化剂耐高温高碱高氧的稳定性及耐久性表现良好。更多还原

【Abstract】 Chlor-alkali industry is a high-energy-consumption industry which produces chorine and sodium hydroxide by brine electrolysis, therefore, more and more attention is paid to the development of low-energy-consumption technology in brine electrolysis. Although much progress has been made in the gas diffusion electrode in ion-exchange membrane brine electrolysis, there are many factors restrict the commercial application. The operating conditions of gas diffusion electrode is with high alkaline concentration, high temperature and high oxygen concentration, which may cause different degrees of corrosion on the matrix structure, precious metal catalysts, carbon support.This thesis aims to systematically study and evaluate the electro catalytic stability and durability of Ag/C gas diffusion electrode in the operating condition of brine electrolysis. First, the the stability and corrosion mechanism of Ag/C electrocatalytic materials was studied, consisting of the stability and corrosion mechanism of silver nanoparticles and carbon support in accelerated corrosion situation; then, the stability and corrosion mechanism of Ag/C electrode in corrosive medium and unstable operating conditions was also involved. At last, the lifetime of miniature Ag/C electrode was preliminary evaluated. This has the significant meaning in prolonging the lifetime and reducing cost of electrode.At first, after the accelerated anodic corrosion of electrode, we can conclude silver transfer into Ag2O film, Ag2O bulk, passivation film of AgO gradually with the increase of anodic potential, and the durability of electrode is well in different anodic potential. Then, we studied the anodic corrosion of carbon black, such as Vulcan XC-72, graphite carbon black and acidifying Vulcan XC-72 and acidifying graphite carbon black. We can make the conclusion that the corrosion resistance of graphite carbon black is well. The reason is graphite carbon black has high conductivity and it has low oxidation degree in the anodic oxidation.According to the experiment of weight loss in NaOH solution, we can find that the hydrophilic of electrode become more stronger as time goes on after dipping in NaOH solution. FT-IR result shows there are much more-COO and -C=O organic functional groups, which are in the ester or epoxide. Polarization curve shows the limited diffusion current density of oxygen reduction decrease slightly. EIS indicates radius of condensance arc increases, which means charge transfer resistance increases and oxygen reduction efficiency decreases. Simulating the unstable operating condition of brine electrolysis -repeatedly shutting down make the current reverse. We can find that the catalytic layer of electrode is serious etched, particle size also obviously increases, the stability obviously decreases, making the structure life greatly reduced.Using changes of oxygen concentration, we evaluate the structure lifetime of electrode and the fitting result is about 5.1 years. And we test the decay rate of electrocatalyst, which shows the failure life is 5.4 years. This indicates the stability and durability of electrocatalyt is well in the operating conditions of high alkaline concentration, high temperature and high oxygen concentration.更多还原