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ABSTRACT: Dissociative adsorption and electro-oxidation of CH3OH at Pd electrode in alkaline solution are investigated by using in situ infrared spectroscopy with both internal and external reflection modes. The former (ATR-SEIRAS) has a higher sensitivity of detecting surface species while the latter (IRAS) can easily detect dissolved species trapped in a thin-layer-structured electrolyte. Real-time ATR-SEIRAS measurement indicates CH3OH dissociates to COad species at Pd electrode accompanied with a "dip" at open circuit potential, while deuterium-replaced CH3OH cannot, suggesting that the breaking of C-H bond is the rate-limiting step for the dissociative adsorption of CH3OH. Potential dependent ATR-SEIRAS and IRAS measurements indicate that CH3OH is electro-oxidized to formate and/or (bi)carbonate, the relative concentrations of which depend on the potential applied. Specifically, at the potentials negative of ca. -0.15 V (vs. Ag/AgCl), formate is the predominant product, while (bi)carbonate (or CO2 in the thin layer structure of IRAS) is more favorable at potentials from -0.15 to 0.10 V. Further oxidation of the COad intermediate species arising from CH3OH dissociation is involved in forming (bi)carbonate at potentials above -0.15 V. While partial transformation from interfacial formate to (bi)carbonate may be justified, no bridge-bonded formate species can be detected over the potential range under investigation.
Langmuir 01/2013; · 4.19 Impact Factor
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ABSTRACT: Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO(2) production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.
Physical Chemistry Chemical Physics 11/2012; · 3.57 Impact Factor
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ABSTRACT: Aimed at searching for highly active and stable nano-scale Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt-PbO(x) nanocomposite (Pt-PbO(x) NC) catalyst with a mean size of 3.23 nm was synthesized through a simple wet chemistry method without using a surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstrated that the as-prepared Pt-PbO(x) NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation. For instance, Pt-PbO(x) NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram tests. The ratio of current densities per unit Pt mass on Pt-PbO(x) NC, nm-Pt and Pt black catalysts is 27.3 : 3.4 : 1 for the long-term (2 hours) chronoamperometric experiments measured at -0.4 V (vs. SCE). In situ FTIR spectroscopic studies revealed that the activity of breaking C-C bonds of ethanol of the Pt-PbO(x) NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation to CO(2) on the as-prepared Pt-PbO(x) NC catalyst.
Physical Chemistry Chemical Physics 11/2012; · 3.57 Impact Factor
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ABSTRACT: Porous MnO/C nanotubes are synthesized by a facile hydrothermal method followed by thermal annealing, and possess excellent cyclability and high rate capability as an anode for lithium ion batteries.
Chemical Communications 07/2012; 48(68):8502-4. · 6.17 Impact Factor
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ABSTRACT: A novel dicranopteris-like Fe-Sn-Sb-P composite was prepared, for the first time, by electrodeposition. The quaternary Fe-Sn-Sb-P alloy of multiphase displayed an excellent cycling performance as an anode of Li ion secondary batteries.
Chemical Communications 06/2012; 48(54):6854-6. · 6.17 Impact Factor
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ABSTRACT: A surface plasmon resonance (SPR) based biosensor for glucose is presented in which a thin gold film modified with polypyrrole
and glucose oxidase (PPy-GOx) acts as the sensor chip. It is based on SPR response to the change of refractive index of PPy-GOx
film by the enzymatic catalytic reaction. The co-electropolymerization of pyrrole and GOx was carried out under cyclic voltammetric
conditions, and simultaneously monitored by in-situ SPR. It has been revealed that the enzymatic reaction between GOx and
PPy in the presence of glucose can lead to distinct changes in the SPR signal. From the experiments, a linear relationship
was obtained in the range 1–100μmolL−1 between glucose concentration and the rate of redox transformation of PPy. The detection limit was 0.5μmolL−1 (S/N = 3) and recoveries were 95.2–102.7%.
KeywordsGlucose-Surface plasmon resonance-Electrochemical-Poly(pyrrole)
Microchimica Acta 04/2012; 169(3):269-275. · 3.03 Impact Factor
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ABSTRACT: The processes of extraction and insertion of lithium ions in LiCoO(2) cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO(2) changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L(-1) LiPF(6)-EC (ethylene carbonate) :DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol(-1), respectively.
Physical Chemistry Chemical Physics 02/2012; 14(8):2617-30. · 3.57 Impact Factor
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02/2012; , ISBN: 978-953-51-0077-5
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ABSTRACT: a b s t r a c t In this work, we proposed an improved wet-chemical method to synthesize Platinum (Pt) nanoparti-cles supported on the mesoporous carbon (FDU-15). A well-dispersed Pt precursor in FDU-15 was first received by using a CH 2 Cl 2 solvent process and a simple melt-diffusion strategy. After the Pt precur-sor was reduced by formic acid without surfactant, almost 100% Pt nanoparticles were confined in the channels of FDU-15 (denoted as Pt/FDU-15). Physical (XRD, HRTEM and BET) and electrochemical (Cyclic voltammetry, CO ad stripping and chronoamperometry) methods were used to investigate the proper-ties of Pt/FDU-15. Compared with the commercial catalyst Pt/C, the Pt/FDU-15 catalyst exhibits a much higher electrocatalytic activity toward CO and methanol oxidation. The origins of the high electrocatalytic activity of the Pt/FDU-15 were discussed.
Electrochimica Acta 02/2012; 67:127-132. · 3.83 Impact Factor
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ABSTRACT: With their ability to convert chemical energy of fuels directly into electrical power or reversibly store electrical energy, systems such as fuel cells and lithium ion batteries are of great importance in managing energy use. In these electrochemical energy conversion and storage (EECS) systems, controlled electrochemical redox reactions generate or store the electrical energy, ideally under conditions that avoid or kinetically suppress side reactions. A comprehensive understanding of electrode reactions is critical for the exploration and optimization of electrode materials and is therefore the key issue for developing advanced EECS systems. Based on its fingerprint and surface selection rules, electrochemical in-situ FTIR spectroscopy (in-situ FTIRS) can provide real-time information about the chemical nature of adsorbates and solution species as well as intermediate/product species involved in the electrochemical reactions. These unique features make this technique well-suited for insitu studies of EECS. In this Account, we review the characterization of electrode materials and the investigation of interfacial reaction processes involved in EECS systems by using state-of-the-art in-situ FTIR reflection technologies, primarily with an external configuration. We introduce the application of in-situ FTIRS to EECS systems and describe relevant technologies including in-situ microscope FTIRS, in-situ time-resolved FTIRS, and the combinatorial FTIRS approach. We focus first on the in-situ steady-state and time-resolved FTIRS studies on the electrooxidation of small organic molecules. Next, we review the characterization of electrocatalysts through the IR properties of nanomaterials, such as abnormal IR effects (AIREs) and surface enhanced infrared absorption (SEIRA). Finally, we introduce the application of in-situ FTIRS to demonstrate the decomposition of electrolyte and (de)lithiation processes involved in lithium ion batteries. The body of work summarized here has substantially advanced the knowledge of electrode processes and represents the forefront in studies of EECS at the molecular level.
Accounts of Chemical Research 01/2012; 45(4):485-94. · 21.64 Impact Factor
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ABSTRACT: Butylphenyl-functionalized Pt nanoparticles (Pt-BP) with an average core diameter of 2.93 ± 0.49 nm were synthesized by the co-reduction of butylphenyl diazonium salt and H(2)PtCl(4). Cyclic voltammetric studies of the Pt-BP nanoparticles showed a much less pronounced hysteresis between the oxidation currents of formic acid in the forward and reverse scans, as compared to that on naked Pt surfaces. Electrochemical in situ FTIR studies confirmed that no adsorbed CO, a poisoning intermediate, was generated on the Pt-BP nanoparticle surface. These results suggest that functionalization of the Pt nanoparticles by butylphenyl fragments effectively blocked the CO poisoning pathway, most probably through third-body effects, and hence led to an apparent improvement of the electrocatalytic activity in formic acid oxidation.
Physical Chemistry Chemical Physics 12/2011; 14(4):1412-7. · 3.57 Impact Factor
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ABSTRACT: 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.
Guang pu xue yu guang pu fen xi = Guang pu 10/2011; 31(10):2606-10. · 0.84 Impact Factor
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ABSTRACT: Tetrahexahedral Pt nanocrystals (THH Pt NCs) bounded by high-index facets possess a high density of active sites and display therefore a higher catalytic activity in comparison with those enclosed by low-index facets. In the current communication, we report, for the first time, the decoration of THH Pt NC surfaces by using Bi adatoms and have demonstrated that the catalytic activity of the Bi decorated THH Pt NCs toward HCOOH electrooxidation has been drastically enhanced in comparison with bare THH Pt NCs. It has also been revealed that the catalytic activity of Bi decorated THH Pt NCs for all coverages investigated always exhibits a higher catalytic activity that is about double that of Bi decorated Pt nanospheres. The study is of great importance regarding both fundamentals and applications.
Journal of the American Chemical Society 08/2011; 133(33):12930-3. · 9.91 Impact Factor
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ABSTRACT: The oxidation of adsorbed CO on Pt single crystal electrodes has been studied in alkaline media. The surfaces used in this study were the Pt(111) electrode and vicinal stepped and kinked surfaces with (111) terraces. The kinked surfaces have either (110) steps broken by (100) kinks or (100) steps broken by (110) kinks and different kink densities. The voltammetric profiles for the CO stripping on those electrodes show peaks corresponding to the oxidation of CO on the (111) terraces, on the (100) steps/kinks and on the (110) steps/kinks at very distinctive potentials. Additionally, the stripping voltammograms always present a prewave. The analysis of the results with the different stepped and kinked surfaces indicates that the presence of the prewave is not associated with defects or kinks in the electrode surface. Also, the clear separation of the CO stripping process in different peak contributions indicates that the mobility of CO on the surface is very low. Using partial CO stripping experiments and studies at different pH, it has been proposed that the low mobility is a consequence of the negative absolute potential at which the adlayers are formed in alkaline media. Also, the surface diffusion coefficient for CO in these media has been estimated from the dependence of the stripping charge of the peaks with the scan rate of the voltammetry.
Physical Chemistry Chemical Physics 08/2011; 13(37):16762-71. · 3.57 Impact Factor
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ABSTRACT: The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO(2) and SnO(2), as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).
Chemical Society Reviews 07/2011; 40(7):4167-85. · 28.76 Impact Factor
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ABSTRACT: In this work, surface modification at atomic level was applied to study the reactivity of step sites on platinum single crystal surfaces. Stepped platinum single crystal electrodes with (1 1 1) terraces separated by monoatomic step sites with different symmetry were decorated with irreversibly adsorbed adatoms, without blocking the terrace sites, and characterized in 0.1 M HClO4 solution. The kinetics of CO oxidation on the different platinum single crystal planes as well as on the step decorated surfaces has been studied using chronoamperometry. The apparent rate constants, which were determined by fitting the experimental data to a mean-field model, decrease after the steps of platinum single crystal electrodes have been blocked by the adatoms. This behavior indicates that steps are active sites for CO oxidation. Tafel slopes measured from the potential dependence of the apparent rate constants of CO oxidation were similar in all cases. This result demonstrates that the electrochemical oxidation of t
Electrochimica Acta 07/2011; 56(17):5993-6000. · 3.83 Impact Factor
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ABSTRACT: The first lithium-ion insertion and extraction processes of a graphite electrode at different potentials were studied by electrochemical impedance spectroscopy (EIS). The results revealed that, below the potential of 0.65 V during the first lithiation, three semicircles were observed in the Nyquist plots; namely, two semicircles appeared in the middle-frequency region. This new phenomenon has been investigated through the detailed analysis of the change of kinetic parameters obtained from simulating the experimental EIS data for lithium-ion insertion and extraction in graphite as a function of potential. It has been found that the two semicircles in the middle-frequency region were strongly potential-dependent, and they were both attributed to the charge-transfer process. Evidence was presented (supported by model calculation) that the two semicircles observed in the middle-frequency region originated from the nonhomogeneous, multilayered porous microstructure of the graphite electrode, which resulted from a parallel combination of impedance response of the thinner parts and thicker parts of the electrode.
04/2011;
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ABSTRACT: The characterization of electrode processes induced by lithiation/delithiation of Sn−Ni alloy films electroplated on a copper substrate is presented. Galvanostatic discharge/charge measurements were combined with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS shows the buildup of a solid electrolyte interphase (SEI) layer formed by reductive decomposition of the electrolyte at the surface of the Sn−Ni anode during the first discharge. The SEI layer is constituted of a mixture of Li2CO3, ROCO2Li, Li2C2O4, and/or ROLi whose balance is not markedly modified upon cycling. ToF-SIMS depth profiling evidences an incomplete initial alloying process of lithium ion with Sn and the resulting partition of the Sn−Ni layer alloy into a fully lithiated outer part and a partially lithiated inner layer during the first discharge. After the first cycle, the volume expansion/shrink associated with the alloying/dealloying reaction, also evidenced by ToF-SIMS, irreversibly cracks and divides the Sn−Ni alloy into island-like morphology with gaps filled by the SEI layer. Multicycling (tested up to 9 cycles) amplifies the division of the Sn−Ni alloy layer and the related penetration of the SEI layer as indicated by the increase of trapped lithium and chlorine but with no apparent loss of active material or drop of capacity.
03/2011;
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ABSTRACT: A cold-welding strategy is proposed to rapidly join together Au nanoparticles (AuNPs) into two-dimensional continuous structures for enhancing the electrooxidation of carbon monoxide by injecting a mixture of ethanol and tolulene into the bottom of a AuNP solution.
Chemical Communications 03/2011; 47(15):4481-3. · 6.17 Impact Factor
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ABSTRACT: A Pt nanoparticle netlike-assembly (Pt-NNA) synthesized through a facile hydrothermal method, with high specific surface area and large overall size, exhibits much higher durability and 2.9 times higher mass activity for oxygen reduction reaction than commercial Pt black catalyst.
Chemical Communications 02/2011; 47(12):3407-9. · 6.17 Impact Factor
