纳米金膜电极上CN~-吸附的电化学和原位红外反射光谱研究

应用循环伏安(CV)和原位红外反射光谱(in situFTIRS)研究碱性介质中氰(CN-)在纳米金膜电极(nm-Au/GC)上的吸附行为.结果显示,当研究电极电位低于0.0 V时,CN-可稳定吸附在nm-Au/GC电极表面,高于0.0 V,则发生氧化脱附.发现nm-Au/GC表面具有异常红外效应(AIREs),即吸附态CN-谱峰呈现出与本体Au电极不同的方向倒反、红外吸收增强(39.2倍)以及半峰宽增加的异常光谱特征.本研究将纳米薄膜材料的这一AIREs从过渡金属拓展到币族金属,进一步证明AIREs是迄今研究的金属及合金纳米材料的普遍特性.     

钴铂合金薄膜的循环伏安电沉积及其异常红外性能研究

运用循环伏安电沉积在玻碳基底上制得纳米结构钴铂合金薄膜,扫描电子显微镜和X-射线能量散射谱研究表明,钴铂薄膜主要由平均粒经为139 nm的纳米粒子组成,钴和铂的原子比为3:5. 以CO为探针分子,电化学原位FTIR反射光谱研究发现钴铂薄膜具有异常红外效应. 吸附态CO发生异常红外吸收,谱峰比本体钴和铂分别增强了34和43倍.     

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.     

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.     

电化学原位步进扫描时间分辨显微镜FTIR反射光谱

结合步进扫描傅立叶变换红外光谱仪和红外显微镜，建立了电化学原位步进扫描时间分辨显微镜FTIR反射光谱.采用微电极和利用纳米结构表面的异常红外效应，显著提高表面吸附物种的红外检测灵敏度和红外电极表面对极化电位的响应速度，使广泛应用的外反射型薄层红外电解池的时间常数(τ=R1Cd)从使用常规盘电极的约40 ms降低到0.65 ms.研究了酸性介质中CO在Pt电极上的吸附过程，谱图的时间分辨率达50 μs.     

纳米钯膜电极的制备、结构表征和特殊反应性能

用循环伏安方法制备纳米钯膜电极,运用扫描隧道显微镜和原位红外光谱等方法研究其结构和反应性能.STM图像表明,制备的纳米钯膜具有特殊的层状结构,纳米级厚度的层状晶体由直径6nm左右的Pd微晶聚集而成.发现当钯膜厚度为几个纳米时,CO的吸附表现出异常红外效应,即红外谱峰反向和红外吸收显著增强(增强因子可达42.6).纳米钯膜电极对氢的反应也具有特殊的性能,与氢向钯晶格扩散吸收过程相比较,氢吸脱附的表面过程成为主要反应.研究结果还指出,纳米钯膜电极的异常红外效应和对氢反应的特殊性能与钯膜厚度密切关联,并可归结为钯膜材料的纳米尺度效应.     

碱性介质中甘氨酸在Pt电极上解离吸附和氧化反应的原 …

运用原位红外反射光谱研究了碱性介质中甘氨酸在Ｐｔ电极上的解离吸附和氧化反应行为,并利用纳米Ｐｔ膜极的异常红外效应鉴定反应过程中生成的表现吸附物种。结果表明,甘氨酸在Ｐｔ电极上极易发生解离,生成强吸附于电极表面上的氰基负离子。     

纳米结构Pt膜方波电位法制备及特殊红外性能

运用方波电位法处理Pt微电极,制备一系列具有较高表面粗糙度的纳米结构薄膜.扫描隧道显微镜（STM）观察到薄膜由Pt金属岛组成,并测得所研制的薄膜虽然其平均厚度从58 nm 增加到139 nm,但Pt金属岛的平均尺度仅从102 nm增加到114 nm,而岛的平均高度也只在15～18 nm之间变化.以CO为探针分子,结合原位FTIR反射光谱研究,发现所制备的纳米结构薄膜上吸附态CO的红外吸收都给出类Fano光谱,初步归结为Pt金属岛的尺度效应.     

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.     

电化学原位扫描显微红外反射光谱及其对铂表面CO吸附的红外成象

利用Fourier变换红外光谱仪 ,红外显微镜和X Y扫描平台 ,通过设计和研制原位红外显微池和计算机接口及控制软件 ,建立了电化学原位扫描显微红外反射光谱 .研究工作显示 ,这一新的空间分辨原位红外反射光谱技术不仅可以获得固 /液界面环境中表面微区振动光谱的信息 ,还可以用于电极表面红外成象 .获得的CO在Pt多晶电极表面吸附性能的化学图象在 10 -2 cm尺度上给出电极表面微区反应性能的不均一性及其分布 .     

CoPt nanoparticles and their catalytic properties in electrooxidation of CO and CH(3)OH studied by in situ FTIRS

CoPt nanoparticles supported on a glassy carbon electrode (denoted as CoPt/GC) were prepared by galvanic replacement reaction between electrodeposited Co nanoparticles and K(2)PtCl(6) solution. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were both employed to characterize the CoPt nanoparticles. It was shown that the CoPt nanoparticles have irregular shapes and most of them exhibit a core-shell structure with a porous Co core and a shell of Pt tiny particles. The composition of the CoPt nanoparticles was analyzed by energy-dispersive X-ray spectroscopy (EDX), which depicts a Co : Pt ratio of ca. 21 : 79. Studies of cyclic voltammetry (CV) demonstrated that CoPt/GC possesses a much higher catalytic activity towards CO and methanol electrooxidation than a nanoscale Pt thin film electrode. In situ FTIR spectroscopic studies have revealed for the first time, that a CoPt nanoparticles electrode exhibits abnormal IR effects (AIREs) for IR absorption of CO adsorbed on it. In comparison with the IR features of CO adsorbed on a bulk Pt electrode, the direction of the IR bands of CO adsorbed on the CoPt/GC electrode is inverted completely, and the intensity of the IR bands has been enhanced up to 15.4 times. The AIREs is significant in detecting the adsorbed intermediate species involved in electrocatalytic reactions. The results demonstrated a reaction mechanism of CH(3)OH oxidation on CoPt/GC in alkaline solutions through evidencing CO(L), CO(M), HCOO(-), CO(3)(2-), HCO(3)(-) and CO(2) as intermediate and product species by in situ FTIRS.     

In situ FTIR spectroscopic studies of CO adsorption on electrodes with nanometer-scale thin films of ruthenium in sulfuric acid solutions

A nanometer-scale thin film of ruthenium supported on glassy carbon (nm-Ru/GC) was prepared by electrochemical deposition under cyclic voltammetric conditions. Scanning tunneling microscopy (STM) was used to investigate the structure and to measure the thickness of the thin film. It has been found that the Ru thin film is composed of layered Ru crystallites that appear in a hexagonal form with dimensions of about 250 nm and thickness around 30 nm. In situ FTIR spectroscopic studies demonstrated that such a nanostructured Ru thin film exhibits abnormal infrared effects (AIREs) for CO adsorption (G.Q. Lu et al., Langmuir 16 (2000) 778). In comparison with CO adsorbed on a massive Pt electrode, the IR absorption of CO_ad on nm-Ru/GC was significantly enhanced. Moreover, the direction of CO_ad bands is inverted and the full width at half maximum of CO_ad bands is increased. It has been revealed that the enhancement factor of IR absorption of CO adsorbed on nm-Ru/GC electrodes depends strongly on the thickness of the Ru film. An asymmetrical volcano relationship between the enhancement factor and the thickness of the Ru film has been obtained. The maximum value of the enhancement factor was measured as 25.5 on a nm-Ru/GC electrode of Ru film thickness around 86 nm. The present study has contributed to exploration of the particular properties of nanostructured Ru film material and to the origin of the abnormal infrared effects.     

Electrochemical preparation and structural characterization of Co thin films and their anomalous IR properties

Nanometer scale cobalt thin films of different structures and thicknesses supported on glassy carbon were prepared by electrochemical deposition under cyclic voltammetric conditions (denoted nm-Co/GC(n)). The thickness of Co thin films was altered systematically by varying the number (n) of potential cycling within a defined potential range in electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) and ex situ scanning electron microscopy (SEM) were employed to characterize the surface structure of Co thin films. It has been illustrated that the Co thin films were uniformly composed of Co nanoparticles, whose structure and size varied with increasing n. The structure of nanoparticles inside the Co thin films underwent a transition from bearded nanoparticles to multiform nanoparticles and finally to hexagonal nanosheets, accompanying with an increase of average size. In situ FTIR reflection spectroscopic studies employing CO adsorption as probe reaction revealed that the Co thin films all exhibited anomalous IR properties; that is, along with their different nanostructures they presented abnormal IR effects, Fano-like IR effects, and surface-enhanced IR absorption effects. CO adsorbed on Co thin films dominated by bearded nanoparticles yielded abnormal IR absorption bands; that is, the direction of the bands is inverted completely, with enhanced intensity in comparison with those of CO adsorbed on a bulk Co electrode. The enhancement of abnormal IR absorption has reached a maximal value of 26.2 on the nm-Co/GC(2) electrode. Fano-like IR features, which describe the bipolar IR bands with their positive-going peak on the low wavenumbers side, were observed in cases of CO adsorbed on Co thin films composed mainly of multiform nanoparticles, typically on the nm-Co/GC(8) electrode. IR features were finally changed into surface-enhanced IR absorption as CO adsorbed on the nm-Co/GC(30) electrode, on which the Co thin film is dominated by Co hexagonal nanosheets.     

Abnormal IR effects of Pt nanostructured surfaces upon CO chemisorption due to interaction and electron-hole damping

The abnormal IR effects (AIREs) characterized by a positive-going peak of platinum (Pt) nanostructured surface generated in a square-wave potential treatment upon CO molecule chemisorption was observed and analyzed with a consideration of the interparticle interaction and electron-hole damping between nanoislands and CO molecules. A theoretical simulation shows that the islanded nanostructured Pt surfaces, which gives rise to interparticle interaction, coupling with electron-hole mechanism, may contribute to the origins of positive-going peak (AIREs) observed by in situ Fourier transformation IR (FTIR) experiments.     

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.     

碱性介质中甘氨酸在纳米金膜电极上的吸附和氧化

运用原位红外反射光谱（in situ FTIRS）和电化学石英晶体微天平（EQCM）在分子水平上研究了碱性介质中甘氨酸在纳米金膜电极上的解离吸附和氧化过程.结果表明,甘氨酸在很低的电位下（－0.8 V, vs SCE）就可发生解离吸附.其解离产物氰基(CN－)与电极表面存在较强的化学吸附作用，形成AuCN－物种(红外吸收谱峰位于2100 cm－1附近).吸附在纳米金膜表面的CN－给出红外吸收显著增强、红外谱峰方向倒反和半峰宽增加的异常红外效应特征.吸附态CN－在低电位抑制H2O和OH－的吸附，当电位高于0.2 V可氧化产生OCN－；进一步升高电位到0.3 V则形成.溶液相物种OCN－和对应的红外吸收峰分别为2169 cm－1和2145 cm－1.实验结果指出，金以的形式溶解是导致电极表面质量显著减少的主要原因.     

Comparison of electron injection dynamics from re-bipyridyl complexes to TiO2 nanocrystalline thin films in different solvent environments

Factors that control photoinduced interfacial electron transfer (ET) between molecular adsorbates and semiconductor nanoparticles have been intensely investigated in recent years. In this work, the solvent dependence of interfacial ET was studied by comparing ET rates in dye sensitized TiO2 nanocrystalline films in different solvent environments. Photoinduced ET rates from Re(LA)(CO)3Cl [LA=dcbpy=4,4'-dicarboxy-2,2'-bipyridine] (ReC1A) to TiO2 nanocrystalline thin films in air, pH buffer, MeOH, EtOH, and DMF were measured by femtosecond transient IR spectroscopy. The ET rates in these solvent environments were noticeably different. However, differences between the rates in pH buffer and nonaqueous solvents (MeOH, EtOH, and DMF) were much smaller than the values expected from much more negative TiO2 conduction band-edge positions in the latter solvents under anhydrous conditions. It was suggested that the presence of adsorbed water, which was evident in FTIR spectra, lowered the band edge of TiO2 in these solvents and reduced the rate differences. The important effect of adsorbed water was verified by comparing two samples of Re(LP)(CO)3Cl [LP=2,2'-bipyridine-4,4'-bis-CH2PO(OH)2] sensitized TiO2 in DMF, in which the presence of a trace amount of water was found to significantly increase the injection rate.