【作者】 陈昀；

【导师】 王启东； 陈长聘； Cesar Sequeira；

【作者基本信息】 浙江大学 ， 材料学， 2002， 博士

【摘要】 燃料电池是继水力、火力和核能发电之后即将迅速发展的发电技术，具有大能量密度、高效率、低污染和低噪音等特有优势，应用或拟应用的范围涉及到国家安全和人们日常生活的各个方面，是可能对国民经济及产业结构产生重大影响的新型能源转换技术。论文系统综述了国内外燃料电池，尤其是低温型质子交换膜燃料电池（PEMFC）和碱性燃料电池（AFC）的发展历程、研究状况及目前存在的主要问题，并扼要归纳了迄今稀土系储氢电极合金研究的主要进展。在此基础上，本文确定了以储氢合金MlNi_3.65Co_0.85Al_0.3Mn_0.3为主要研究对象，从优化燃料电池阳极结构、提高储氢合金表面的电催化活性及延长工作寿命出发，采用结构与材料性能表征及电化学分析测试等手段，探索研究了储氢合金代Pt作为PEMFC和AFC阳极催化材料的本征特性、影响因素及发展前景。 论文工作首先从PEMFC的基础工艺入手，对影响PEMFC核心膜电极（MEA）的三个主要性能因素进行了系统研究并对Pt／C MEA制备技术进行了综合优化，为储氢合金的引入打好基础。研究发现，对电极催化层的质子交换膜（PEM）侧进行Nafion溶液浸渍处理可扩展MEA的三维反应区域，使离PEM表面较远的催化剂也能参与电极反应；浸渍电极与PEM进行热压结合可促进质子的传递；对电极厚度的控制则能明显提高MEA的交换电流密度。综合优化结果表明，经综合制备的优化的Pt／C MEA 0.5V放电电流密度达到483 mA·cm^-2。 详细研究了储氢合金Mli_3.65Co_0.85Al_0.3Mn_0.3代Pt作为PEMFC MEA 中的阳极电催化材料的电化学性能。结果发现，对合金进行球磨、表面处理及表面镀Pd等改性以及对阳极合金载量、粒度和添加造孔剂等进行优化均能有效提高MEA储氢合金阳极的电催化性能。实验材料中充氢球磨的合金具有最大的反应比表面积和最好的电催化活性，其放电电流密度和最大输出功率密度均比机械破碎合金高出1倍。材料与乙炔黑混合球磨可使电极反应三相界面扩大，从而改善储氢合金阳极催化层中电子的传导能力。表面热碱还原处 浙江大学博士学位论文理进一步提高了储氢合金的电催化活性和比表面积。上述表面改性处理可破坏储氢合金表面氧化层，同时因部分Mn、AI及其氧化物被腐蚀溶解，部分合金表面氧化物被还原及合金在部分氢化时形成的新鲜裂纹都是改善或提高储氢合金阳极MEA电化学性能的因素。 研究发现，以热碱还原处理和化学镀3 t％Pd的储氢合金制备的MEA呈现最佳的电化学性能。镀Pd后的表面对氢的离解吸附能力、电导能力均明显增强，尤其在欧姆极化和浓差极化阶段中其放电性能得到进一步提高。经综合优化的储氢合金阳极 MEA 0．5 V下放电电流密度达到了 168 a·Cm－＼0．2 V下放电电流可达 232．4 a．cm”‘，最大输出功率则达到 84 mw·cm“；40a·。m－入恒流放电 24 hrs后 MEA输出功率仍为 22石8 mw·cm－＼ 维持在起始输出功率(31．31 mw·cm’勺的 72．40(铸态合金阳极 MEA i作 8 hrs其输出功率则从起始值的 10．55 mw·。m”下降到0．lmw·cm勺，表明储氢合金阳极MEA已具备较好的氢阳极氧化催化能力和一定的工作寿命。电极工作温度和压力对电化学反应影响的研究表明，压力提高可明显促进电极的电化学反应；而温度则存在一最佳范围。对本实验合金而言，60℃时可获得最佳电催化性能，过低则电极反应速度慢，过高则合金不能形成相对稳定的催化吸氢相。 对不同改性处理的储氢合金MINi。。SC。。8。AI。｝Mn03在碱性三电极体系及作为AFC阳极电催化材料的电化学性能进行了系统地研究。结果表明，储氢合金经球磨、表面处理及表面镀Pd等改性后电催化活性均显著提高。由于处理后合金表面上形成了富Ni层和Pd层以及晶粒细化和表面积增大，合金电极表面电荷转移阻抗降低，交换电流密度从铸态的90．8 InA含‘提高到175．7hall，表观活化烩为由铸态的 19．12 kJ·mol”l下降到 14二0 kJ·mol＼但是，镀覆金属Pd对体相中氢向合金表面的扩散起一定阻碍作用，测出的扩散系数相对铸态合金有所降低。在对AFC储氢合金阳极的结构和组成进行的系统研究中发现，催化层中添加 2 t％乙炔黑＊～22 t％PTFE和 5 t％(NH止C。O。时，AFC储氢合金阳极具有最小的过电位和最佳的放电性能。优化后的AFC储氢合金阳极以 50 IlbA·cm－’电流密度放电时 AFC电极电位为 0866 V；电位为 0．5 V时放电电流密度最高可达 196．2 InA·。m”＼ 显示了良好的阳极催化能力。研究表明环境温度对AFC储氢合金阳极放电性能也有明显影响，工作温 一11一 浙江人学博士学位论文度为 40℃时，储氢合金阳极性能尤其是在大电流密度时性能最佳。在对 AFC储氢合金阳极在不同电流密度下的工作稳定性的研究中发现，随着电流密度的升高电极的衰退加速，在30℃和25 InA·cm”‘恒电流密度放电时200 hrs电位衰退率为 0．26 mV．hr’‘，表现出较好的工作稳定性。在 75 a．cm‘2放电更多还原

【Abstract】 As an energy conversion device, fuel cell (FC) will play a key role in the future world energy field as the mandatory characteristics, for power plants will be high power density, high efficiency, low emission and low noise level. In this thesis, domestic and foreign literatures on FC systems, especially the low temperature FC systems, namely the proton exchange membrane fuel cells (PEMFC) and alkaline fuel cells (AFC), were exhaustively reviewed. The current technical development and existing problems of PEMFC and AFC were reviewed. The main characteristics and development of mischmetal-based hydrogen storage electrode alloys (HSA) were also reviewed and discussed. On the basis of the literature review, the possibility of substituting Pt/C with HSA MlNij esCoo gsA10 3Mn<).3 as the anode catalyst of PEMFC and AFC, was studied in this thesis. The potential of using HSA as the catalyst in FC anode is studied on the ground of the optimization of the structure of FC anode, the improvements of electrocatalytic activity and working stability of HSA using the material structure analysis, electrochemical analysis and anode performance tests.Before adopting a HSA as the PEMFC anode catalyst, three main factors that affect the performance of PEMFC membrane electrode assembly (MEA) using Pt/C as anode catalyst and the optimum preparation technology for MEA were investigated. The results showed that the three-phase reaction zone of MEA anode could be enlarged by impregnating the catalyst loaded electrode in the protonic conducting material Nafion. The process enlarged the catalytic zone in MEA. The most suitable temperature for the compression of the Nafion impregnated electrode with the PEM to optimize the proton transfer between the catalyst layer and PEM and also the most suitable thickness of catalyst layer to enhance the exchange current density of MEA were found through experimentation. By means of the optimized technology, the Pt/C MEA obtained the current density of 483 mA-cm-2 at 0.5 V of cell voltage.The electrochemical properties of PEMFC MEA using differently prepared HSA MlNi3 65Coo.85Alo.3Mno.3 alloy as the anode electrocatalyst instead of Pt/C were studied and developed. Both the modification of anode HSA including the ball-milling, immersing the alloy powder in a hot alkaline solution containing KBHj and surface chemical coating with Pd, and the modification of the structure of MEA anode including the composition of the anode material and the introduction of pore-forming substance to improve the electrocatalytic activity of MEA anode were all tested. Compared with the as-cast HSA, the ball-milled HSA in fy had a higher specific surface areas and better electrocatalytic activity. And HSA ball-milled with acetylene black enhanced the three-phase interfaceregion in the electrode and improved the electron transfer ability of the catalyst layer. As a result of immersion the alloy powder in a hot alkaline solution containing KBH4, the oxidation layer on the surface of the alloy was partly destroyed, some elements including Mn, Al and their oxides were dissolved, and some oxides such as the Ni oxide were reduced into metallic state which all led to an increase of the specific surface area and the electrocatalytic activity of the alloy.The experimental data indicated that the best electrochemical performance of the MEA experimented was obtained by using the HSA modified by immersing in a hot alkaline solution containing KBHt and then chemical coating with 3 wt% Pd. The MEA with the aforesaid modification showed an enhanced surface capability of hydrogen dissociation and adsorption, an improved electron transfer ability and an increased electrochemical activity, especially in the electrode reaction region of ohmic polarization and concentration polarization. After being optimized, the current density of the MEA with HSA anode reached 168 mA-cm-2 at 0.5 V and 232.4 mA-cm-2 at 0.2 V and its maximum output power density reached 84 mW-cm-2. After 24-hour working stability test on MEA at 40 mA-cm-2, the power更多还原