【作者】 王耀琼；

【导师】 魏子栋；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2010， 博士

【摘要】 直接甲醇燃料电池（DMFC）和染料敏化太阳能电池（DSSC）作为清洁、无污染的氢能和太阳能的电转化设备之一而日益受到重视。但二者都因为寿命、成本和效率等问题而尚未得到实际应用。DMFC至今未能商业化的原因之一是,Pt或PtRu为催化阳极催化剂易被甲醇氧化的中间产物CO毒化而引起缓慢的甲醇氧化动力学。本文的第3章和第4章就上述问题进行了相关探讨:（1）甲醇在电氧化的过程会产生大量的COads,并毒化Pt催化剂,而磷钼酸(H₃PMo₁₂O₄₀,PMo₁₂)能够在Au的催化下选择性氧化CO（g）。基于此,在Pt和Au共生的铂金（Au/Pt）电极上,通过Au催化PMo12氧化甲醇氧化的毒性中间体CO,Pt催化甲醇脱氢,应能提高甲醇电氧化的催化活性和抗中毒性能。一种金属在另一种金属表面的欠电位沉积是可控制备这两种金属共生表面的有效方法。但欠电位沉积是因为基体材料的电子逸出功大于沉积金属的电子逸出功,即,较活泼的金属在较不活泼的金属基体上能够在比其平衡电位更正的电位下实现电化学沉积。Au不能在Pt表面发生欠电位沉积,但Cu能。为此,我们采用先在Pt电极表面欠电位沉积Cu,然后Au置换Cu的方法,在Pt电极上制备出了Au呈亚单层分布的铂金（Au/Pt）催化电极。结果表明:甲醇在Au/Pt电极上的电化学氧化在PMo12存在的情况下得到了明显的增强;相比Pt电极,在PMo12溶液中,甲醇在Au/Pt电极上氧化的起始电位负移了400 mV。研究认为,无论是吸附态的氢还是CO都可以在低电位下因Au的催化被PMo12氧化去除,使Pt重新释放出新鲜表面。而Pt表面生成能够氧化CO的含氧物质则需要更高的电位。此外,Pt对PMo12氧化CO无催化作用。（2）与TiO₂纳米颗粒相比,TiO2纳米管（TNTs）具更大的比表面积、对光更强的散射能力和更少的晶界数目,因此,TNTs在光照条件下能够产生更多的电子空穴对和有效的减少电子空穴对的复合,在光照情形下,TNTs更能有效地光解水产生强氧化性含氧物种·OH。基于强氧化性的含氧物种·OH非常有利于甲醇电氧化的毒性中间体CO的氧化去除的特点,我们采用电化学阳极氧化法在钛基底上制备了TiO₂纳米管阵列（TNTs/Ti）,并以此为载体,通过脉冲电沉积将Pt沉积在TNTs/Ti基体上,制得了Pt/TNTs/Ti催化电极,在光照条件下,研究了甲醇在Pt/TNTs/Ti电极上的电化学氧化。结果表明,TiO2纳米管阵列光生含氧物种·OH对毒性中间体CO强的氧化去除能力,使得甲醇在Pt/TNTs/Ti电极上恒电位下氧化时,没有出现传统的Pt或PtRu电极上甲醇恒电位下氧化时,电流随时间不断衰减的现象。以TNTs/Ti为载体的Pt/TNTs/Ti催化电极,在光照条件下,彻底地解决了Pt或PtRu电极上甲醇氧化中毒问题。对电极是DSSC的重要组成部分,其主要作用是催化电解质溶液中I3?从外电路接受电子还原为I?,提高还原反应的效率和减小还原反应的过电势,进而避免I3?不经外电路而直接从电池光阳极TiO₂导带中捕获电子还原为I?,达到提高DSSC的光电转化效率的目的。本文的第5章和第6章就如何获得高催化活性的DSSC对电极进行了相关探讨:（1）将Cu溅射在导电玻璃（FTO）上形成Cu/FTO电极,然后将其置于氯铂酸(H₂PtC_l6)溶液中,通过Pt对Cu的置换制得DSSC的Pt/FTO对电极。与热分解Pt盐制备的PY-Pt/FTO对电极相比,采用溅射-置换（SD）制备的SD-Pt/FTO对电极不仅很好的回避了直接溅射Pt昂贵的Pt靶材的问题,更主要的是克服了热解法获得的PY-Pt/FTO对电极,其Pt颗粒分散性差、FTO基体因受热电阻增大等缺点。结果表明,以SD-Pt/FTO为对电极DSSC的光电转化效率比以PY-Pt/FTO为对电极DSSC的提高了16.5 %。（2）相对FTO基底,DSSC对电极中金属基底的使用可以进一步降低电池的电阻和增强对光的二次反射,从而进一步提高DSSC的性能。基于此,通过Pt置换预先电沉积在Ti基底上的Cu而制得了DSSC的Pt/Ti对电极。实验结果表明:与传统的热分解法制备的Pt/FTO对电极相比,以Pt/Ti为对电极的DSSC比以Pt/FTO为对电极的DSSC的光电转化效率提高了20.8 %。更多还原

【Abstract】 Direct methanol fuel cell （DMFC） and dye-sensitized solar cell （DSSC） are two kinds of device which directly transform chemical energy and solar energy into electric power, respectively, and attracting more and more interest from the world. However, there is a series of problems for the two devices, such as short service life, high cost and low efficiency, blocking them from the practical application.One of problems blocking DMFC from the practical application is the slow kinetics of methanol electro-oxidation due to CO poisoning to the Pt or PtRu anodic catalysts, resulting in a serious decline in the performance of DMFC. How to effectively remove of CO poison was intensively studied in the chapter 3 and 4 of this thesis. The main results obtained are as follows:（1） COads, an intermediate in the methanol electro-oxidation on Pt-based catalysts, has been thought a primary cause slowing down the kinetics of methanol electro-oxidation. On the basis of the understanding, that is, CO（g） can be oxidized by PMo₁₂ under catalysis of Au, the methanol electro-oxidation was investigated on sub-monolayer Au modified Pt electrode （Au/Pt） in participation of PMo₁₂ to improve the catalytic and anti-poison ability of Pt catalyst. Generally, the sub-monolayer metal is obtained by underpotential deposition （UPD）. The occurrence of UPD is in that the electron work function of the substrate metal is greater than that of the deposited metal, ie, the more active metal can be electrochemically deposited on the less active substrate metal at the more positive potential in contrast to the equilibrium potential predicted by the Nernst equation for bulk deposition. Thus, UPD of Au on Pt surface can not occurs to form the sub-monolayer Au, but Cu can. The Au/Pt electrode was prepared by chemically displacing underpotentially-deposited Cu on Pt surface in HAuCl4 solution. The results showed that the methanol electro-oxidation on Pt electrode was markedly enhanced in presence of PMo₁₂ and Au. The onset potential of methanol oxidation shifts 400 mV toward the negative direction on Au/Pt electrode with PMo₁₂ in comparison with Pt electrode with PMo₁₂. It is supposed that adsorbed hydrogen and intermediate CO from the methanol dehydrogenation and oxidation were electro-catalytically oxidized by oxidant state of PMo₁₂ with the aid of Au catalysis.（2） In comparison with TiO₂ nanoparticles （TNPs）, TiO₂ nanotubes （TNTs） have a larger surface area, a more effective scattering and absorption of light and less detrimental grain boundaries. TNTs can therefore generate more electron-hole pairs and effectively lessen the electron-hole recombining under illumination. Therefore TNTs can more effectively produce strong oxiding oxygen-containing species ?OH from water under illumination. We expected that CO, the poisoning intermediate of methanol electro-oxidation, can be effectively removed by strong oxiding oxygen-containing species ?OH produced on TNTs under illumination. On the basis of this perception, a Pt/TNTs/Ti electrode was prepared by electrochemically depositing Pt using the modulated pulse current method onto TNTs/Ti substrate, and then the methanol electro-oxidation was investigated on such an electrode under illumination. The results show that the performance and anti-poison ability of the Pt/TNTs/Ti electrode for methanol electro-oxidation under illumination is remarkably enhanced. CO poisoning is no longer a problem during methanol electro-oxidation with the Pt/TNTs/Ti electrode under illumination. The main role of a counter electrode in a DSSC, is to catalyze the reduction I3? by electrons through the outside circuit from the anode to I? instead of by electrons directly from the conduct bands of TiO₂ produced by illumination. How to fabricate an effective counter Pt electrode was intensively studied in the chapters 5 and 6 of this thesis. The main results obtained are as follows:（1） A Pt/FTO counter electrode of the dye-sensitized solar cells （DSSC） was prepared by sputtering （Cu）– displacement （Pt） method （SD） on a conductive glass （FTO） substrates （SD-Pt/FTO）. In contrast to PY-Pt/FTO counter electrode prepared by pyrolysis （PY） of Pt salts, SD-Pt/FTO counter electrode not only avoids the expensive Pt target with Pt direct sputtering but also overcomes the poor dispersion of Pt particles and the increased electric resistance of FTO substrate caused by pyrolysis. The results show the photoelectric conversion efficiency of DSSC with SD-Pt/FTO counter electrode increases by 16.5 % relative to that with PY-Pt/FTO counter electrode.（2） To lower electric resistance and improve reflecting ability of Ti substrate compared with that of commonly used FTO glass substrate, Ti sheet rather than FTO glass served as the counter electrode substrate was investigated. A Pt/Ti counter electrode of DSSC was prepared by displacing electrodeposited Cu deposits on a Ti sheet in H2PtCl6 solution. The photocurrent density–volt （J–V） curves show that the photoelectric conversion efficiency of DSSC with the Pt/Ti counter electrode reaches 7.61 %, increased by 20.8 % relative to that with the Pt/FTO counter electrode.更多还原