纳米结构钴薄膜电极的制备及其异常红外性能研究

用循环伏安电沉积法在玻碳基底上制备纳米结构钴薄膜, 扫描电子显微镜研究结果表明, 纳米结构钴薄膜主要由平均粒径为150 nm的钴粒子组成, 同时还有为数不多的粒径在400~500 nm的钴粒子. 以CO为探针分子, 结合原位傅里叶变换红外反射光谱研究结果, 发现所制备的纳米结构钴薄膜具有异常红外效应. 吸附态CO发生异常红外吸收, 谱峰增强了26.2倍, 测得线型吸附态COL的Stark系数为77.5 cm-1·V-1.     

CeO2(111)和CeO2(100)的界面调控合成及在Pt(111)上的结构转变

氧化铈基催化材料在催化反应中存在显著的晶面效应,为了在分子尺度上理解其催化化学,需要可控合成具有明确表面结构的氧化铈.因此,我们研究了Pt(111)上氧化铈纳米结构和薄膜的生长.人们通常使用金属-氧化物之间的强相互作用来解释Pt/CeO_x催化剂上的催化过程,然而对于Pt与CeO_x之间的强相互作用仍旧缺乏原子尺度上的了解.我们的结果表明, Pt与氧化铈之间的相互作用可以影响氧化铈的表界面结构,这可能会进而影响Pt/CeO_x催化剂的性质.在Pt(111)上生长的氧化铈薄膜通常暴露CeO_2(111)表面.我们发现Pt(111)表面厚度在三层以内的氧化铈薄膜,其结构是高度动态且随着退火温度升高而变化的,这种动态结构变化可归因于Pt和氧化铈间的界面电子作用.当氧化铈薄膜的厚度增大到三层以上,其负载的氧化铈团簇开始表现出迥异于三层以下氧化铈纳米岛的优异的热稳定性,表明Pt与CeO_x之间的界面电子作用主要影响厚度在三层以内的氧化铈纳米结构.采用常规的反应沉积方法难以获得完全覆盖Pt(111)衬底的规整氧化铈薄膜,而我们通过采取一种两步的动力学限制生长方法,制备出了完全覆盖Pt(111)衬底的氧化铈薄膜.对于Pt(111)上厚度约为3-4层的氧化铈薄膜,在超高真空中于1000 K退火会导致氧化铈薄膜表面形成CeO_2(100)结构.这是因为高温还原促进了c-Ce_2O_3(100)缓冲层的形成,该缓冲层被Pt的界面电子转移以及相匹配的超晶格所稳定,并进一步成为顶层CeO_2(100)结构生长的模板.进一步在900 K的氧气中处理则可将薄膜CeO_2(100)表面完全转变为CeO_2(111)表面.因此, Pt(111)上氧化铈纳米岛和薄膜所展现的结构动态变化是由Pt-CeO_x界面作用与氧化铈层间作用相互竞争所决定.本研究提供了对氧化铈负载Pt催化剂的原子级理解,虽然Pt/CeO_2催化剂活性增强的原因常被简单归结于界面强相互作用,我们的研究在原子尺度上进一步表明Pt/CeO_2在还原条件下易形成界面Ce_2O_3层.此外,本研究提供了不同晶面二氧化铈模型催化剂的构筑方法,可将对氧化铈晶面效应和Pt/CeO_x催化剂的研究推进到分子尺度.     

层层组装法制备核壳SiO_2/Pt粒子及其CO电氧化和原位电化学FTIR光谱

采用层层组装法合成了核壳SiO2/Pt粒子,用电化学循环伏安法(CV)和原位电化学傅里叶变换红外(FTIR)光谱研究了SiO2/Pt粒子对CO分子的氧化和吸附行为.透射电子显微研究表明:包覆SiO2的Pt壳是由团聚的Pt纳米微粒构成,其平均厚度大约为26nm.CO在SiO2/Pt粒子修饰的玻碳(GC)电极上的主氧化峰为0.49V(vsSCE),表现出比本体Pt金属好的催化性能.电化学FTIR光谱研究发现:线性CO在SiO2/Pt粒子上的IR吸收带的方向发生倒反,而且在不同的研究电位下,每个吸收带劈裂为两个间隔约为14cm-1的吸收带,这种劈裂现象在饱和吸附CO的Pt金属表面上是很难观察到的.这些异常的红外吸收现象可能是由SiO2/Pt粒子的结构效应导致的.     

铂纳米粒子和锰卟啉修饰的聚苯胺新材料的制备及表征

借助循环伏安电化学聚合制备了聚苯胺(PANi)/MnT1239卟啉复合材料,再利用还原恒电位沉积法负载铂纳米粒子(Pt NP),最终制备了聚苯胺/MnT1239卟啉/铂纳米粒子复合材料.电沉积铂之后聚苯胺/MnT1239卟啉材料发生明显样貌变化,棒状结构平均直径从90 nm增加到200 nm,材料具有较大的表面积,空间可负载性好.铂纳米粒子平均尺寸在20 nm,附着均匀,氧化峰电流在0.2 V处达到7.4 mA,电化学性能优良.     

枝晶状Pt 薄膜的制备及其特殊红外效应

采用方波电位, 在10×10^-3 mol·L^-1 K₂PtCl₆+3×10^-4 mol·L^-1 PbAc₂+0.5 mol·L^-1 HClO₄溶液中, 于本体Pt 电极上电沉积制备出枝晶状Pt 薄膜. 随着沉积时间的增加, 枝晶长度逐渐由400 nm增加到900 nm, 且枝晶上的小晶粒(~10 nm大小)变得密集. 根据循环伏安(CV)曲线中氢吸脱附电量可得出Pt 薄膜具有中等粗糙度(C_r=9-36), 且电极表面的粗糙度随着沉积时间增加而增大. 观察到Pt 薄膜上吸附态CO的原位红外光谱具有明显的增强吸收效应, 当沉积时间为6 min 时所制得的枝晶Pt 电极的红外增强效应最大. CO呈现多种谱峰形状, 随着沉积时间的增加, 谱峰形状依次为左高右低的双极峰(类Fano 红外效应), 单极向下(表面增强红外吸收), 左高右低的双极峰, 单极向上(异常红外效应), 左低右高的双极峰和单极向下. 这表明纳米材料薄膜所呈现出的特殊红外性能, 与纳米材料的尺度和聚集状态等密切相关. 所制备的枝晶状Pt 薄膜有望为深入认识纳米材料的特殊红外性能提供一个良好的模型材料.     

团聚铂纳米粒子电极在甲醇氧化中的电催化特性

用H2还原法并以Nafion作为稳定剂合成团聚的Pt纳米粒子，附载于玻碳表面制备电催化剂.透射电子显微镜（TEM）和扫描电子显微镜（SEM）表征结果指出,团聚Pt纳米粒子的平均尺寸约为400 nm.运用电化学循环伏安法(CV)和原位傅立叶变换红外反射光谱（in situ FTIRS）研究甲醇的氧化过程，发现团聚Pt纳米粒子电极具有较高的电催化活性.原位FTIRS研究结果检测到甲醇在所制备的电催化剂上氧化的中间体为线型吸附态CO物种，其红外吸收给出异常红外效应的光谱特征.     

Pd微电极阵列表面纳米薄膜的方波电位制备及其特殊的红外性能

制备了单根可寻址Pd微电极阵列,运用方波电位法对阵列上每根Pd微电极处理不同时间,诱导生成一系列不同纳米结构的Pd薄膜.以CO为探针分子,结合原位显微傅里叶变换红外反射光谱进行表面组合电化学研究,一次性地获得CO吸附在不同纳米结构Pd薄膜上的红外光谱.观察到随方波电位法处理时间的逐步增加,桥式吸附态CO的红外光谱峰从正常吸收光谱到类Fano光谱,再到异常红外光谱的转变过程.结合扫描电子显微镜观察纳米薄膜的形貌,发现不同红外光谱特征都对应着特定的纳米结构.     

酸性溶液中过渡金属及合金纳米薄膜电极的异常红外效应研究

以循环伏安方法在玻碳载体上制备纳米级厚度的过渡金属 (Pt,Pd ,Rh ,Ru)和合金 (PtPd ,PtRu)薄膜电极 ,并运用原位FTIR反射光谱研究了CO的吸附过程 .发现所制备的纳米薄膜电极均具有异常红外效应 ,即与本体金属电极相比较 ,吸附在纳米薄膜电极上的CO分子的红外吸收被显著增强 ,并且红外谱峰方向倒反 .本文的结果进一步证明异常红外效应是一种新的、普遍的现象 ,主要取决于过渡金属或合金膜的结构和厚度 .对异常红外效应的深入认识 ,不仅将推动红外反射光谱及界面电化学理论的发展 ,而且将在表面和界面分析中得到广泛应用 .     

原子层沉积制备掺氮碳膜修饰的 Pt/CNTs 实现甲醇高效电催化氧化

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

原子层沉积制备掺氮碳膜修饰的Pt/CNTs实现甲醇高效电催化氧化（英文）

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注.贵金属Pt是甲醇燃料电池阳极催化剂不可缺少的活性组分,但Pt价格昂贵,易与CO等中间体强相互作用而中毒失活,从而限制了甲醇燃料电池的广泛应用.因此,如何提高Pt的利用率成为一个关键问题.研究表明,在碳材料载体中掺杂氮元素,改变了载体本身的表面结构和电子性质,有利于Pt颗粒的成核和生长,可获得尺寸小、分布均匀的Pt纳米颗粒,能显著提升催化反应活性和Pt利用率.然而,传统的氮掺杂方法需要在高温、高压及氨气条件下进行,增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术,能够在原子级别精确控制膜的厚度,既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰.本课题组利用原子层沉积技术优势,首先在碳纳米管表面沉积了直径2 nm左右的Pt纳米颗粒,然后在Pt纳米颗粒外表面超薄修饰聚酰亚胺膜,通过后处理得到多孔掺氮碳膜修饰的Pt/CNTs催化剂.碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制.结果表明,适当厚度的碳膜修饰Pt/CNTs催化剂可显著提升其甲醇电氧化性能,电流密度可达商业20%Pt/C的2.7倍,催化剂稳定性也显著改善.然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现,超薄修饰碳膜后催化剂活性表面积有所降低,这是由于碳膜的覆盖导致表面Pt原子数减少.修饰前后催化剂颗粒尺度变化不大,推测催化剂活性的提高与形成了有利于催化反应的Pt-碳膜界面有关.然而,当碳膜修饰层过厚时,会导致反应物分子难以扩散到Pt颗粒表面,使催化剂活性降低.预吸附单层CO溶出实验结果表明,多孔掺氮碳膜超薄修饰Pt/CNTs催化剂后,CO氧化峰的起始电位和峰值电位都向低电位处偏移,这表明Pt表面吸附的CO在较低电位下即可被氧化,CO更容易从Pt表面移除,从而提高了催化剂的抗CO毒化能力.X射线光电子能谱实验结果进一步表明,经多孔掺氮碳膜修饰后,Pt的4f电子向高结合能处偏移,表明Pt原子周围的电子密度减小,从而弱化了Pt对CO吸附的σ-π键反馈作用,即减弱了Pt原子对CO的吸附,这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

Synthesis of nanostructured films from template electrodeposition technique

In this report, the use of a simple and versatile technique of templated electrodeposition through colloidal templates to produce nanostructured films of Pt and Au with regular submicron spherical holes arranged in a hexagonal close-packed structure is described. The templates were produced by self assembly of a monodispersed suspension of polystyrene spheres on gold substrates using capillary forces. The self assembly process was modified through the chemical modification of the gold substrate with cysteamine thiol. Films of Pt and Au were prepared by electrochemical deposition through the template. The electrochemical deposition charge and the current time curve were used to control the film height with a precision of approximately 10 nm. The colour of the nanostructured films changed as the film thickness was changed. On the other hand, high surface area of the nanostructured Pt film on top of the gold substrate was calculated using electrochemical cyclic voltammogram. About 55 roughness factor was obtained. SAXS measurements showed strong scattering at low angles indicating the presence of a well-ordered mesostructure.     

Study of anomalous infrared properties of nanomaterials through effective medium theory

Effective medium theory is introduced into a three-layer model to study the anomalous IR properties of nanostructured Pt films. A composite system is set up for the nanostructured film together with adsorbates and water around it. The anomalous IR spectral features, which exhibit a transition from enhanced (or normal) IR absorption to Fano-type bipolar line shape and, finally, to enhanced anomalous IR absorption (the abnormal infrared effects) along with the change in structure and size of nanomaterials, as observed through experiments for CO molecule adsorption, are elucidated by an increase in the volume fraction of metal in the composite system and the effective thickness of the composite system. The theoretical simulation results illustrate that the spectral line shape of IR absorption depends strongly on the volume fraction of metal, while the intensity of the IR band is directly proportional to the effective thickness. This study has revealed, through a physical optical aspect of interaction of CO molecules with nanostructured metal films, one of the possible origins of anomalous IR properties and has shed light on interpreting the peculiar properties of nanomaterials.     

In situ STM studies of electrochemical growth of nanostructured Ni films and their anomalous IR properties

We have extended the study of anomalous IR properties, which were initially discovered on nanostructured films of platinum group metals and alloys, to nanostructured films of nickel, a member of the iron group triad, and broadened the fundamental knowledge on this subject. Nanostructured thin films of nickel supported on glassy carbon [nm-Ni/GC(n)] were prepared by electrochemical deposition under cyclic voltammetric conditions, and the thickness of films was altered systematically by varying the number (n) of potential cycling within a defined potential range for electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) was employed to monitor the electrochemical growth of nanostructured Ni films. These in situ STM images illustrated that, along the increase of the film thickness, Ni films have undergone a transformation from layer structure to island structure and finally to lumpish arris structure. Investigations by in situ FTIR spectroscopy employing adsorbed CO as the probe revealed that these nanostructures of Ni films yield abnormal IR features, Fano-like IR features, and normal IR features, respectively. The IR bands of CO adsorbed on Ni thin films of a layer structure were inverted in their direction and enhanced in their intensity up to 15.5 times on an nm-Ni/GC(4) electrode. The Fano-like IR features, which are defined as a bipolar band with its negative-going peak on the low wavenumber side and its positive-going peak on the high wavenumber side, are observed for the first time on Ni thin films of an island nanostructure, i.e., at the nm-Ni/GC(16) electrode. IR features changed to normal absorption in CO adsorbed on the nm-Ni/GC(25) electrode, i.e., that with lumpish arris nanostructured Ni film of a larger thickness.     

Anomalous IR properties of nanostructured films created by square wave potential on an array of Pt microelectrodes: an in situ microscope FTIRS study of CO adsorption

Thin films of different nanostructures on an array of nine Pt microelectrodes were prepared by applying a square wave potential treatment for different times (tau). It has been measured from the cyclic voltammetric studies that the relative surface roughness of the films was increased slightly and reached a maximal value of about 2.5. SEM studies demonstrated that with the increase of tau, the growth of island-shaped Pt crystallites on the films led to the formation of plumelike crystallites that can reach about 2-3.5 microm in length when tau exceeded 70 min. In situ microscope FTIR reflection spectroscopic studies illuminated that CO adsorbed on the array yielded different anomalous IR features. With the increase of tau, the direction of the CO L band (linearly bonded CO) was transformed from the negative-going direction (normal IR adsorption) to bipolar (Fano-like spectral line shape) and finally to the positive-going direction (abnormal IR adsorption). The intensity of the CO L band was enhanced significantly and a maximal enhancement factor of about 33 was measured when tau was 40 min; the center of the CO L band and the Stark tuning rate also showed regular changes. This study demonstrated that specific nanostructures of Pt thin films can be prepared through a square wave potential treatment for different times and revealed the intrinsic relationship between anomalous IR properties and surface nanostructures of the thin films.     

Pt-Ru合金薄膜的电沉积制备及其电化学表面增强红外吸收光谱

在1mmol·L-1H2PtCl6+1mmol·L-1RuCl3+0.1mol·L-1H2SO4镀液中采用电沉积法在化学镀金膜的红外窗口Si反射面上制备Pt50Ru50合金电极.利用原子力显微镜(AFM)可以观察到制备的Pt50Ru50合金电极形貌呈现出100-200nm大小的颗粒.常规电化学分析方法得出该电极具有典型的合金特征,对CO和CH3OH具有很好的催化氧化作用.应用电化学现场衰减全反射表面增强红外光谱法(ATR-SEIRAS)可以观察到该电极上Pt位和Ru位上CO的振动谱峰,且表现出Pt-Ru二元金属良好的协同催化性能.     

利用原位红外光谱与微分电化学质谱联用技术研究在Pt以及PtRu电极上发生的甲醇氧化反应

利用电化学衰减全反射原位傅里叶变换红外光谱与微分电化学质谱联用技术,在流动电解池环境以及恒电位条件下研究了Pt电极和Pt电极通过表面电沉积Ru形成的PtRu电极（PtxRuy）上发生的甲醇氧化反应（反应电解质溶液为0.1 mol/L HClO4＋0.5 mol/L MeOH）. 在0.3-0.6 V（参比电极为可逆氢参比）实验用到的所有电极上,CO是唯一能从红外光谱观察到的与甲醇相关的表面吸附物;在Pt0.56Ru0.44电极上可以观察到CO吸附在Ru原子形成的岛上和CO线式吸附在Pt电极表面红外波段,而其他电极上只能观察到Pt表面上线式吸附的CO;甲醇氧化活性按Pt0.73Ru0.27〉Pt0.56Ru0.44〉Pt0.83Ru0.17〉Pt的顺序递减;在0.5V时,甲醇在Pt0.73Ru0.27电极上的氧化反应的CO2电流效率达到了50%.     

Probing the interface in vapor-deposited bimetallic Pd-Au and Pt-Au films by CO adsorption from the liquid phase

Bimetallic Pd-Au and Pt-Au and monometallic Pd, Pt, and Au films were prepared by physical vapor deposition. The resulting surfaces were characterized by means of XPS, AFM, and CO adsorption from the liquid phase (CH2Cl2) monitored by ATR-IR spectroscopy. CO adsorption combined with ATR-IR proved to be a very sensitive method for probing the degree of interdiffusion occurring at the interfaces whose properties were altered by variation of the Pd and Pt film thickness from 0.2 to 2 nm. Because no CO adsorption was observed on Au, the evaporation of Pt-group metals on Au allowed us to study the effect of dilution on the adsorption properties of the surfaces. At equivalent Pd film thickness, the evaporation of Au reduced the amount of adsorbed CO and caused the formation of 2-fold bridging CO, which was almost absent in monometallic surfaces. Additionally, the average particle size on Pd-Au surfaces was smaller than that on monometallic Pd surfaces. The results indicate that a Pd/Au diffuse interface is formed that affects the Pd particle size even more drastically than the simple decrease in Pd film thickness in monometallic surfaces. Pt-Au surfaces were less sensitive to CO adsorption, indicating that the two metals do not mix to a significant extent. The difference in the interfacial behavior of Pd and Pt in the bimetallic gold films is traced to the largely different Pd-Au and Pt-Au miscibility gaps.