【作者】 庄树新；

【导师】 黄可龙；

【作者基本信息】 中南大学 ， 应用化学， 2012， 博士

【摘要】 本论文以系统研究钙钛矿型双效氧电极的电化学性能为工作目的。选择La1-xCaxCoO3为研究对象,从La1-xCaxCoO3的B位Ca掺杂量入手,筛选出对氧还原和氧析出都具有高催化活性的La0.6Ca0.4CoO3作为双效氧电极的催化剂。为了进一步提高催化剂的催化活性和导电性,首次采用化学还原法将金属银包覆在La0.6Ca0.4CoO3催化剂表面,并将该二元催化剂应用于双效氧电极的研究,运用多种物理、化学的分析和测试手段及电化学研究方法,系统研究了银-La0.6Ca0.4CoO3二元催化中银含量对双功能氧电极电化学性能的影响。研究发现,与单元催化剂的La0.6Ca0.4CoO3双效氧电极相比,二元催化剂的银-La0.6Ca0.4CoO3双效氧电极具有更好的电化学性能,并且认为3wt.%载银量为最佳。首次采用改进的柠檬酸-硝酸盐自燃法制备出具有高比表面积的纳米多孔的La0.6Ca0.4CoO3催化剂,通过TG-DSC、XRD、SEM和粒径分布等测试手段确定了最佳的煅烧温度和造孔剂用量,并将其用于双效氧电极中。通过对该系列双效氧电极的阴极和阳极稳态极化曲线测试、恒电流测试和循环性能测试,发现纳米多孔的La0.6Ca0.4CoO3具有更好的催化活性,并将改善的电化学性能归咎于其高比表面积和新颖纳米多孔形貌采用电化学交流阻抗研究La0.6Ca0.4CoO3双效氧电极的电极过程,利用Z-view2.0软件对Nyquist曲线进行了非线性拟合并提出了相应的等效电路。拟合实验结果发现,双效氧电极过程主要是由高频区的多孔电极固有阻抗和低频区的电子转移与活性物质扩散电阻构成。同时,采用该等效电路研究了银-La0.6Ca0.4CoO3二元催化剂和高比表面积的纳米多孔La0.6Ca0.4CoO3催化剂的双效氧电极的电极过程。实验结果表明,纳米多孔La0.6Ca0.4CoO3和银-La0.6Ca0.4CoO3催化剂的引入不仅可以降低多孔电极的固有阻抗而且还可以提高催化剂对氧析出／还原的催化活性,从而提高了双效氧电极的电化学性能和循环性能。研究了高比表面积的纳米多孔Lal1-xCaxCoO3(0.2≤x≤0.5)钙钛矿型氧化物对H202电还原活性,使用循环伏安法和恒电流法,测试了La1-xCaxCoO3系列化合物对于过氧化氢的电催化还原性能。同时也检测了La1-xCaxCoO3化合物中La与Ca的比例及煅烧温度对其催化性能的影响。在La1-xCaxCoO3系列化合物中,650℃煅烧的La0.6Ca0.4CoO3展现出最佳的催化活性。首次将其应用于自制的铝-H2O2电池中,在含有0.4mol·dm-3H2O2的3.0mol·dm-3KOH的水溶液中,使用这种材料作为铝-H2O2半燃料电池的阴极催化剂,在150mA·cm-2电流密度下该电池的电压为1.34V,能量密度为201mWcm-2,发现这种新型的电池是一种很有潜力大功率的能源。更多还原

【Abstract】 In this dissertation, electrochemical performance of perovskite bi-functional oxygen electrodes are studied. Perovskite-type series of compounds La1-xCaxCoO3powders were synthesized by citrate-nitrate auto-combustion method and used as electrocatalyst for bi-functional oxygen electrodes. The influence of the ratio of La to Ca of La1-xCaxCoO3on their catalytic performance was investigated by polarization curves in alkaline electrolyte. Among these compounds, La0.6Ca0.4CoO3calcined at650℃exhibited the highest catalytic activity for oxygen reduction and evolution.In order to further improve the catalytic activities and electron conductivity of the perovskite-electrocatalyst, the La0.6Ca0.4CoO3powder were modified with silver by chemical reduction method. The silver-modified La0.6Ca0.4CoO3powder was used as binary electrocatalyst for bi-functional oxygen electrodes. By means of the physical and chemical examinations and electrochemical methods, the silver loading was found to have a significant impact on the electrode performance, which could facilitate or block the electrochemical processes of the gas diffusion electrodes. The binary catalyst electrodes exhibited higher electrocatalytic activities than that of the electrodes with only La0.6Ca0.4CoO3as the catalyst. The best performance was achieved when the silver loading was3.0wt.%.Well-dispersed nanoporous La0.6Ca0.4CoO3catalyst for bi-functional oxygen electrode was synthesized by a modified citrate-nitrate auto-combustion method using Vulcan XC-72R as a pore-forming material. The calcination temperature and the content of the pore-forming material were optimized by TG-DSC, XRD, particle size distribution and SEM analysis. Compared with the traditional citrate-nitrate auto-combustion method, the perovskite La0.6Ca0.4CoO3prepared by this modified technique illustrated higher electrocatalytic activity mainly due to the high surface area and the novel nanostructure, which would provide potential applications in metal-air batteries and fuel cells.The La0.6Ca0.4CoO3bifunctional oxygen electrode processes were investigated by electrochemical impedance spectroscopy (EIS). The overall impedance data were fitted by a complex non-linear least squares fitting program in Z-view2.0software. The impedance spectra were analyzed by an equivalent circuit containing an electrode intrinsic resistance at the high frequency and kinetic impedance through the porous electrode at the low frequency. Meanwhile, the equivalent circuit was used for studying the silver-modified La0.6Ca0.4CoO3binary electrocatalyst and the nanoporous Lao.6Cao.4Co03with high specific surface area how to improve their electrode processes. The EIS results confirmed that the silver-modified La0.6Ca0.4CoO3and the nanoporous La0.6Ca0.4CoO3with high specific surface area used as electrocatalysts for bi-functional electrode could reduce both intrinsic and kinetic impedance, indicating that their electrical conductivity and electrocatalytic activity were higher than the common La0.6Ca0.4CoO3catalyst.Well-dispersed nanoporous La1-xCaxCoO3were also synthesized by the modified a citrate-nitrate auto-combustion method. Their catalytic activities for hydrogen peroxide electroreduction in3.0mol·dm-3KOH at room temperature were first evaluated by cyclic voltammetry and galvanostatic measurement. The influence of annealing temperature and the ratio of La to Ca of La1-xCaxCoO3on their catalytic performance were investigated. Among the series of compounds, La0.6Ca0.4CoO3calcined at650℃exhibited the highest catalytical activity. An aluminum-hydrogen peroxide semi fuel cell using La0.6Ca0.4CoO3as cathode catalyst showed a peak power density of201mW·cm-2at150mA·cm-2and1.34V running on0.4mol·dm-3H2O2.更多还原