【作者】 刘博；

【导师】 陈金华；

【作者基本信息】 湖南大学 ， 应用化学， 2009， 博士

【摘要】 为了解决当前世界面临的能源短缺和环境污染两大难题,直接液体燃料电池以其具有燃料来源广、能量转化率高、低污染、储存和运输方便等优点,在便携式电源、电动机车和野外电站等领域具有广阔的应用前景,已经得到了世界范围的关注和重视。但是,电极电催化剂的活性较低及高昂的价格仍是阻碍燃料电池商业化发展的关键问题之一。提高催化剂活性、降低贵金属用量是推动燃料电池商业化发展的重要途径。为了降低燃料电池常用催化剂的用量从而降低催化剂的成本,提高催化剂的电催化性能,本论文开展了用于乙醇氧化、甲酸氧化和氧还原的新型电催化剂探索研究。从添加辅助催化剂,制备新结构催化剂,更换新型载体等方面入手,改进了电催化剂的电催化性能,并通过傅里叶红外光谱（FTIR）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、能量散射光谱（EDS）、X射线衍射（XRD）、循环伏安法（CV）、线性扫描法（LSV）、计时-电流法、计时-电位法等分析测试技术,对催化剂的形貌、结构、电化学性质等进行了详细研究。（1）利用SiO₂在酸性介质中的稳定性,将SiO₂通过HF刻蚀后,采用化学还原法,制备了Pt/SiO₂纳米催化剂,在相同金属催化剂载量下,以石墨片为电极,用CV、计时-电流法、计时-电位法考察了Pt/SiO₂纳米催化剂与商业催化剂E-TEK Pt/C、E-TEK PtRu/C及自制的Pt纳米催化剂在酸性介质中对乙醇的电催化氧化性能。发现乙醇在Pt/SiO₂催化剂上的氧化峰电流值分别是E-TEK Pt/C、E-TEK PtRu/C和自制的Pt纳米催化剂的3.4倍、2倍和4.4倍。而且通过500圈连续循环伏安扫描研究了催化剂的长期稳定性,发现Pt/SiO₂纳米催化剂具有更好的抗中毒能力和长期循环稳定性。（2）采用简单研磨热分解法以碳纳米管为载体,制备了Pt-MgO-CNTs纳米催化剂,通过用CV、计时-电流法、计时-电位法详细考察了Pt-MgO-CNTs /石墨电极在碱性介质中对乙醇的电催化氧化性能。结果表明,在相等Pt负载量下,当Pt与MgO的加入质量比为4/1时,Pt-MgO-CNTs纳米催化剂对乙醇的电催化氧化具有最好的电催化活性。发现在经过500圈连续循环伏安扫描后,乙醇氧化的峰电流值只下降为最初的84.5%,远远优于Pt/CNTs催化剂的60%,说明Pt-MgO-CNTs催化剂具有很好的长期电化学稳定性。（3）利用碳纳米管的特殊结构,通过高锰酸钾与碳纳米管直接反应,制备了一维纳米结构的MnO₂-C复合催化剂,并通过CV和LSV方法考察了MnO₂-C复合催化剂在碱性介质中对氧还原的电催化活性,结果表明,碳纳米管:高锰酸钾:硝酸的质量比为20:1:4时,得到的MnO₂-C复合催化剂的氧还原电催化活性最好。计算得出氧在MnO₂-C/玻碳电极上电化学还原的电子数为3.4,接近于4,说明氧还原在该电极上的主要反应产物为H2O。（4）采用石墨烯（G）为催化剂载体,利用三苯基膦为石墨烯与Pt纳米粒子的中间连接体,经煅烧后,制备了Pt/G纳米催化剂,并通过CV和LSV考察了Pt/G纳米催化剂在酸性介质中对氧还原的电催化活性。结果发现,在相同Pt负载量下,在电位为0.6 V时,Pt/G/玻碳电极的的质量比活性达17.6 mA mg-1,是E-TEK Pt/C/玻碳电极（2.03 mA mg-1）的8倍。依据旋转环盘测试,得出氧在Pt/G/玻碳电极上电化学还原的电子数为3.94,说明氧还原在该电极上主要以四电子还原方式进行。（5）采用石墨烯为催化剂载体,制备了PtPd/G纳米催化剂,在0.5 M H2SO4+0.5 M HCOOH溶液中,考察了PtPd/G纳米催化剂对甲酸的电催化氧化性能。发现同碳纳米管做载体的催化剂相比,电位在0.35 V时,PtPd/G/玻碳电极的电流值为1.71 mA,大于Pt-Pd-CNTs/玻碳电极的电流值（1.29 mA）,说明PtPd/G纳米催化剂对甲酸电催化氧化的活性更好。经长期稳定性考察后发现,以石墨烯为载体的PtPd/G纳米催化剂具有更好的长期稳定性。（6）采用牺牲Co核化学还原法,制备了PtPd纳米空心球,并得到1-PtPd/CNTs纳米催化剂,在0.5 M H2SO4+0.5 M HCOOH溶液中,考察了1-PtPd/CNTs纳米催化剂对甲酸的电催化氧化性能。发现同通常制备的不具有空心球结构的2-PtPd/CNTs纳米催化剂相比,1-PtPd/CNTs纳米催化剂对甲酸的电催化氧化性能更高,长期稳定性更好。并且同商用催化剂相比,发现1-PtPd/CNTs纳米催化剂在0.35 V处出现的氧化锋电流值分别是E-TEK PtRu/C的5.0倍, E-TEK Pt/C的10.7倍,表明1-PtPd/CNTs纳米催化剂比商业催化剂E-TEK Pt/C和E-TEK PtRu/C的电催化氧化甲酸的性能更好。更多还原

【Abstract】 To solve the problems of energy shortage and environmental pollution in the world, the direct liquid fuel cell were paid much attention and investigated widely. They have wide applications in the portable equipment, electric car and field power etc. due to the low-pollution, abundant sources, high energy efficiency, the easy storage and transportation of the fuel. However, the low electrochemical activity and high cost of the electrocatalysts are still the key issues hindering the commercial application of fuel cell. Therefore, the improvement of the electrocatalytic activity of the electrocatalysts and the decrease of the loading mass of noble metals are the effective routes for the commercial application of fuel cells.In this dissertation, the assistant catalysts, new structure of classical catalysts and new catalyst supports in fuel cells have been developed and investigated. The micrographs, structure and properties of the catalysts applications have been investigated by Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, cyclic voltammetry （CV）, chronoamperometry and polarization method, etc. The main points in this dissertation are summarized as follows:（1） Based on the good stability of SiO₂ in acid solution, SiO₂, as the second catalyst, was introduced into the preparation of Pt catalyst for ethanol electrooxidation and the resulted catalyst was investigated by electrochemical methods. For the same loading mass of catalyst, the peak current of ethanol oxidation on the Pt/SiO₂/graphite electrode is about 3.4, 2 and 4.4 times as high as that on the E-TEK Pt/C/graphite, E-TEK PtRu/C/graphite and Pt/graphite electrodes, respectively. Moreover, Pt/SiO₂ catalyst shows excellent anti-poisoning ability and long-term cycle stability.（2） MgO was introduced in the anodic electrocatalyst system for ethanol oxidation in alkaline solution and the resulting Pt-MgO-CNTs/graphite electrode was investigated by electrochemical methods. For the same loading mass of platinum catalyst, the best electrocatalytic activity on Pt-MgO-CNTs/graphite electrode is obtained when the mass ratio between Pt and MgO is 1:4. And the better long-term cycle stability can be obtained at the Pt-MgO-CNTs/graphite electrode, as compared to the electrode without MgO. （3） Based on the special structure of CNTs, MnO₂-C hybrid catalyst with 1D nanostructure was prepared by the redox reaction between CNTs and KMnO4. And the electrocatalytic activity of the MnO₂-C/glassy carbon electrode for oxygen reduction reaction （ORR） in alkaline solutions was investigated by electrochemical methods. The results indicate that the MnO₂-C composite shows good electrochemical properties for ORR when the mass ratio of CNTs, KMnO4 and HNO3 is 20: 1: 4。The electron number （n） involved in the O₂ reduction was calculated to be 3.4, which is close to the theoretical value for four-electron-reduction of O₂.（4） With the organic molecule triphenylphosphine as the linker, Pt nanoparticles were assembled uniformly on the graphene sheets and used as the electrocatalyst for oxygen reduction reaction （ORR）. The electrocatalytic properties of the Pt/G catalyst for ORR have been evaluated by typical electrochemical methods. With the same Pt mass loading, the current of ORR at the Pt/G catalyst （70.4μA） was about 8 times as high as that at the Pt/C catalyst （8.1μA） at 0.6 V. The results indicate that the Pt/G catalyst has excellent electrocatalytic properties for ORR and the number of electrons involved in ORR is 3.94 based on the results from the rotating ring-disk electrode （RRDE） investigation.（5） Graphene was used as the catalyst support for catalytic oxidation of formic acid in acidic solution and investigated by electrochemical methods. The PtPd nanoparticles loaded on the surface of the graphene exhibit higher electrocatalytic activity for formic acid oxidation than the Pt catalyst supported on CNTs. With the equivalent loading mass of Pt, the current at 0.35 V on PtPd/G catalyst （1.71 mA） is higher than that of the PtPd/CNTs （1.29 mA）. The corresponding results imply that the electrochemical performance （high electrocatalytic activity, better long-term cycle stability） of PtPd nanoparticles for formic acid oxidation is improved by the new graphene support.（6） Carbon nanotubes supported PtPd hollow nanospheres have been prepared by a replacement reaction between sacrificial cobalt nanoparticles and PtCl62-, Pd2+ ions. The electrocatalytic properties of the PtPd hollow nanospheres have been investigated by typical electrochemical methods, respectively. The results indicate that the CNTs supported PtPd hollow nanospheres have excellent electrochemical properties for the electrooxidation of formic acid （high electrocatalytic activity and excellent stability） due to the high surface area resulted from the hollow nanosphere structure with porous shell. For the same loading mass of catalyst, the peak current of formic acid oxidation on the PtPd hollow nanospheres catalyst supported on the CNTs is about 5 and 10.7 times as high as that on the E-TEK PtRu/C and E-TEK Pt/C catalysts, respectively. Moreover, PtPd hollow nanospheres catalyst supported on CNTs showed excellent long-term cycle stability.更多还原