Abnormal Infrared Effects Research Articles

Electric potential distribution near nanocone arrays on metal substrates

Based on the nanostructured surface model, where conical nanoparticle arrays grow out symmetrically from a plane metal substrate, a theoretical model of the local electric potential near nanocones is built when a uniform external electric field is applied. In terms of this model, the electric potential distribution near the nanocone arrays is obtained and given by a curved surface using a numerical computation method. The computational results show that the electric potential distribution near the nanocone arrays exhibit an obvious geometrical symmetry. These results could serve as a basis for explaining many abnormal phenomena, such as the abnormal infrared effects (AIREs) which are found on nanostructured metal surfaces, as well as a reference for investigating the applications of nanomaterials, such as nanoelectrodes and nanosensors.

Partial electrical potential distribution around nanospheres in metallic nanostructured films

In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals.

Studies on the anomalous IR properties of CoPt nanorods

One-dimensional CoPt nanorods were obtained through the galvanic displacement reaction and chemical reduction. The average diameter of the nanorods was measured to be about 166.3 nm and the length was mostly between 1.0 and 5.0 microm obtained from the scanning electron microscopy (SEM) measurement. The IR optical properties of the CoPt nanorods and bulk Pt were investigated by in situ FTIR reflection spectroscopy employing CO adsorption as probe reaction at the solid/gas interface. The results of in situ FTIR indicated that bulk Pt shows a normal IR optical property and the CoPt nanorods display abnormal infrared effects (AIREs). The authors can obtain the same results whether the CoPt nanorods were loaded on glassy carbon (GC) or Au substrates. These results demonstrated that the AIREs were generated mainly by CoPt nanorods and the influence of the substrate materials can be neglected. The study confirmed that one-dimensional CoPt nanorods show AIREs, and throw a new sense to comprehend the anomalous IR properties observed on low-dimensional nanomaterials.

Polarizability and abnormal infrared spectra of molecules adsorbed on metal nanostructured surfaces

Based on the experimental results of abnormal infrared effects (AIREs) for molecules adsorbed on transition-metal nanostructured surfaces, the interactions and the polarizability of the adsorbed molecules are analyzed theoretically. By numerical simulations, the normal absorption spectrum, the Fano-like bipolar spectrum and the anti-absorption spectrum of the adsorbed CO molecules are obtained respectively. The results show that the adsorbed molecules on a metal nanostructured surface can accumulate together dues to the effect of local external electric field, which leads to a change in imaginary part of the molecular polarizability within a certain range of frequency, and even a negative value may appear.

One-dimensional CoPt nanorods and their anomalous IR optical properties

One-dimensional (1D) CoPt nanorods were synthesized by a galvanic displacement reaction. The morphology of the nanomaterials was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the coexistence of Co and Pt in the 1D nanorods. Studies of cyclic voltammetry (CV) demonstrated that the 1D CoPt nanorods exhibit a better electrocatalytic property for CO oxidation than that of bulk Pt electrode does. In situ electrochemical FTIRS illustrated, for the first time, that the 1D CoPt nanorods display abnormal infrared effects (AIREs), which was previously revealed mainly on 2D film nanomaterials.

Synthesis, Electrocatalytic and Anomalous IR Properties of Hollow CoPt Chainlike Nanomaterials

Hollow CoPt chainlike nanomaterials were synthesized by a galvanic displacement reaction. The morphology, structure, and composition of the nanomaterials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron dispersive X-ray (EDX) analysis. It has found that the hollow CoPt chainlike nanoparticles supported on glassy carbon substrate (CoPt/GC) exhibited enhanced electrocatalytic activity toward methanol oxidation in comparison with commercial Pt/C catalyst (Johnson-Matthey, 20 wt% Pt). The studies demonstrated also that the hollow CoPt chainlike nanomaterials possess a superior electrocatalytic property for CO oxidation than that of Pt/C and bulk Pt. The IR properties of the CoPt nanomaterials were investigated by in situ FTIR reflection spectroscopy employing CO adsorption as probe reaction. It has revealed that the hollow CoPt chainlike nanomaterials present abnormal infrared effects (AIREs).

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.

Electrochemical preparation and abnormal infrared effects of nanostructured Ni thin film

Nanometer-scale thin film of Ni supported on glassy carbon (nm-Ni/GC) was prepared by electrochemical deposition through cyclic voltammetry (CV). The properties of nm-Ni/GC were studied by electrochemicalin situ FTIR reflection spectroscopy using CO adsorption as probe reaction. It has revealed that the nm-Ni/GC exhibits abnormal infrared effects (AIREs). The study has extended the investigation of the AIREs that we have discovered initially on nanostructured film materials of platinum group metals and alloys to nanostructured film materials of iron group metals.

Electrochemical preparation and abnormal infrared effects of nanostructured Ni thin film

Electrochemical preparation and abnormal infrared effects of nanostructured Ni thin film

IR Optical Properties of Pt Nanoparticles and Their Agglomerates Investigated by in Situ FTIRS Using CO as the Probe Molecule

Pt nanoparticles (Ptn) and their agglomerates (Ptnag) were synthesized by chemical reduction methods. The mean sizes of Ptn and Ptnag were determined to be respectively 3.4 and 400 nm using transmission electron microscopy (TEM). CO adsorption on electrodes made of the two kinds Pt nanomaterials was used as the probe reaction. Studies of cyclic voltammetry revealed that the current peak potential of COad oxidation on electrodes of Ptnag supported on glassy carbon (Ptnag/GC) has been shifted negatively by about 80 mV in comparison with that on a bulk Pt electrode. In situ electrochemical FTIRS results illustrated that Ptn/GC and Ptnag/GC exhibit different IR properties for CO adsorption. In comparison with CO adsorbed on bulk Pt, a phenomenon of enhanced IR absorption (EIRA) was observed on dispersed Pt nanoparticles (Ptn). IR absorption of COad on Ptn/GC is enhanced 31 times and the full width at half-maximum (FWHM) of the COL band is increased to 40 cm-1, which is 25 cm-1 larger than the value (15 cm-1) measured on a bulk Pt electrode. In contrast to the EIRA of CO adsorbed on dispersed Pt nanoparticles, the abnormal infrared effects (AIREs) were encountered for CO adsorbed on agglomerates of Pt nanoparticles, in which a strong interaction is presented between Ptn. The IR features of CO adsorbed on Ptnag/GC illustrated that, except for the IR absorption of COad being enhanced 9 times and the FWHM of the COL band being increased to 25 cm-1, the direction of the COad bands is inverted from absorption to antiabsorption. The results of the present paper demonstrated that the EIRA and the AIREs are closely related to the agglomerate states of Pt nanoparticles, and throw a light on the origin of the particular IR properties of nanomaterials.

Abnormal Infrared Effects of Nanostructured Rhodium Thin Films for CO Adsorption at Solid/Gas Interfaces

Nanometer-scale thin films of rhodium supported on glassy carbon (nm-Rh/GC) were prepared by electrochemical deposition using cyclic voltammetry. STM studies demonstrated that the Rh film is made of layered crystallites of an average size 230 nm (l) × 90 nm (w) × 10−30 nm (h). In situ FTIR spectroscopic investigations revealed, for the first time, that the nanostructured film exhibits abnormal infrared effects (AIREs) for CO adsorption at solid/gas interfaces. The AIREs are characterized by the inverting of the direction of IR bands of adsorbed CO (COad), an enhancement of IR absorption intensity, and an increase in the full width at half-maximum (fwhm) of the bands. The inversion of the direction of the absorption bands and the increase in the fwhm are observed in spectra of CO on nm-Rh/GC of different Rh film thicknesses; the enhancement of IR absorption depends strongly on the thickness of the Rh film. The maximum enhancement factor has been determined to be 10.38 for an Rh film thickness of 79 nm. The...

Comments on the paper by M.-S. Zheng and S.-G. Sun entitled ‘In situ FTIR spectroscopic studies of CO adsorption on electrodes with nanometer-scale thin films of ruthenium in sulfuric acid solutions’ [J. Electroanal. Chem. 500 (2001) 223

It has been claimed that so-called abnormal infrared effects (AIREs) occur in the infrared reflectance spectra of particulate metals deposited on both moderately reflecting (e.g. glassy carbon) and highly reflecting (e.g. smooth Pt) substrates upon chemisorption on the metal particles of IR-absorbing molecules, typically CO. These AIREs would be characterized by: (i) increase, instead of decrease, of the IR reflectance at the absorption frequency of the chemisorbed molecule, producing anti-absorption bands (band inversion) (ii) enhancement of the intensity of the IR bands of the chemisorbed molecule (iii) increase of the full width at half-maximum (FWHM) of the absorption band of the chemisorbed molecule. It is proved here that these results need not be assigned to any new abnormal effects, but, on the contrary, are well-known phenomena. (i) Band inversion is perfectly explained by Fresnel's reflectance equations. (ii) The intensity increase of the IR bands is due to SEIRA (surface enhanced infrared absorption), a phenomenon discovered in 1980, and due to the large electric field increase produced between metal particles dispersed in a matrix. (iii) The somewhat higher FWHM of CO adsorbed on particulate as compared with massive metals can well be accounted for by the sensitivity of this parameter to changes in adsorbent structure. In conclusion, no new abnormal effects have to be invoked in order to explain the reported behaviour of CO and other molecules adsorbed on particulate metals deposited on moderately reflecting substrates, a category which also includes highly reflecting metals covered by a suitable layer of metal particles.

Microscopein situ FTIRS studies of CO adsorption on an array of platinum microelectrodes

An array of platinum microelectrodes was designed and fabricated. The adsorption of CO on such a Pt microelectrode (μ-Pt) was investigated by employing microscopein situ FTIR spectroscopy. A nanostructured film is formed at the surface of μ-Pt (denoted as μ-Pt(R)) when it has been subjected to a treatment of fast potential cycling. Abnormal infrared effects (AIREs) were observed in CO adsorption on the surface of μ-Pt(R), consisting of the inversion of the IR bipolar CO band and the extensively enhanced IR adsorption of COad species.

Abnormal infrared effects of nanometer scale thin film material of PtPd alloy in CO adsorption

Nanometer scale thin film material of PtPd alloy supported on glassy carbon (nm-PtPd/GC) was prepared by the electrochemical codeposition method under cyclic voltammetric conditions. STM patterns demonstrated that the prepared thin films are composed of layered crystallites in elliptic form. Electrochemicalin situ FTIRS studies explored the abnormal infrared effects (AIREs) of nm-PtPd/GC for CO adsorption, which are (i) the remarkable enhancement of IR absorption, (ii) the inversion of COad band direction, and (iii) notable increase in the full width at half maximum (FWHM) of COad bands. The results demonstrated also that the enhancement factor of IR absorption varies with the thickness of PtPd alloy film and has reached a maximum value of 38.3 under the experimental conditions.

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 COad on nm-Ru/GC was significantly enhanced. Moreover, the direction of COad bands is inverted and the full width at half maximum of COad 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.

Abnormal infrared effects and electrocatalytic properties of nanometer scale thin film of PtRu alloys for CO adsorption and oxidation

Nanometer scale thin films of PtRu alloy supported on glassy carbon (nm-PtRu/GC) were prepared using electrochemical codeposition under cyclic voltammetric conditions. The composition of the PtRu alloy was altered by varying the concentration of Pt4+ and Ru3+ ions in the deposition solution. STM results demonstrated that the nm-PtRu film was composed of crystallites appearing in a layered hexagonal form. The nm-PtRu/GC exhibited a high catalytic activity for CO oxidation, consisting mainly in a negative shift of potential for COad oxidation. In situ FTIR spectroscopic studies revealed that the nm-PtRu/GC alloy electrodes of different surface composition exhibit abnormal infrared effects (AIREs) as observed on electrodes of nanometer scale thin films of transition metals. The AIREs observed on nm-PtRu/GC electrodes consist in the inversion of COad bands, the significant enhancement of IR absorption and an increase in the FWHM. Following the increase in Ru component in the nm-PtRu thin film the FWHM was increased progressively from 20 cm−1 on a nm-Pt/GC to 55 cm−1 on a nm-Ru/GC electrode, and the enhancement factor of IR absorption by COL was between 10.5 to 13.1. The present study has provided new understanding of the structure and properties of nanometer scale thin film PtRu alloy material, and highlights its potential for fuel cell applications.

In Situ FTIR Spectroscopic Studies of Adsorption of CO, SCN-, and Poly(o-phenylenediamine) on Electrodes of Nanometer Thin Films of Pt, Pd, and Rh: Abnormal Infrared Effects (AIREs)

Pt, Pd, and Rh films of a few nanometers in thickness supported on glassy carbon (GC) and other substrates were prepared by electrochemical voltammetry. STM patterns illustrated that the prepared thin films are composed of crystallites of layer structure and exhibit a low surface roughness. Studies of in situ FTIR spectroscopy on chemisorption of CO and SCN- and formation of a polymer of o-phenylenediamine (POPD) on electrodes of nanometer thin films have been conducted to explore the abnormal infrared effects (AIREs), which consist of two main characteristics: (1) inversion of IR bands; (2) the enhancement of IR absorption of adsorbates. The results demonstrated that the AIREs depend mainly on the structure and the chemical nature of nanometer thin films. In all cases of chemisorption on thin films of platinum-group metals supported on GC or supported on polymer-covered GC, the direction of IR bands of adsorbates is inverted in comparison with the direction of IR bands of the same adsorbates on correspo...

In situ FTIR spectroscopic studies of CO adsorption on electrodes of nanometer-thin layer of Pt-Ru and Pt-Pd surface alloys

CO adsorption on nanometer-thin layer of surface alloys of Pt-Ru and Pt-Pd prepared by electrochemical codeposition has been studied usingin situ FTIR spectroscopy. Abnormal infrared effects (AIREs) that consist of the enhancement of IR absorption by adsorbed CO on different surface sites and the inversion of IR band direction have been observed on the thin-layer prepared. The results also demonstrate the considerable significance of Pt-Ru and Pt-Pd surface alloys in electrocatalysis applications.