Organic nanoparticles whose size and rigidity are finely tuned by cross-linking the end groups of dendrimers

Dendrimers with molecular weights ranging from ca. 2700 to 11 000 and from 16 to 64 homoallyl ether end groups were cross-linked using the Grubbs ring-closing metathesis reaction. A combination of SEC, MALDI-TOF-MS, and AFM were used to characterize the cross-linked nanoparticles. The data suggest a significant decrease in volume with cross-linking and a concomitant increase in rigidity, both of which can be controlled independently with a fair degree of precision.     

Potential-dependent reorientation of thiocyanate on Au electrodes

Thiocyanate (SCN) adsorption on an Au electrode is examined using surface-enhanced Raman scattering (SERS) measurements, along with detailed density functional theory (DFT) calculations. Both the calculation and the spectroscopic measurements show that three different geometries are adopted by SCN adsorption in the potential region studied (0.0 V 相似文献   

Adsorption configuration and local ordering of silicotungstate anions on Ag(100) electrode surfaces

X-ray reflectivity, cyclic voltammetry, and scanning tunneling microscopy (STM) are used to examine the structure of alpha-SiW12O4(4-) or silicotungstic acid (STA) adsorbed on Ag(100) in acid solution. The voltammetry shows that STA passivates the Ag surface relative to electron transfer to a solution redox species. STM images reveal the formation of a series of lattice structures, one of which can be associated with a commensurate ( radical13x radical13)R33.69 degrees structural model. X-ray reflectivity measurements show uniquely that STA orients with its four-fold axis perpendicular to the Ag(100) surface and that the center of the STA molecule is 4.90 A above the top layer of the Ag substrate. Analysis of bond lengths leads to a footprint of STA on Ag(100), in which the four terminal O atoms are located near the hollow sites and have a Ag-O bond length of 2.06 A. This bond length is consistent with a strong covalent interaction between STA and the Ag surface.     

Materials science of the gel to fluid phase transition in a supported phospholipid bilayer

We report the results of in situ AFM measurements examining the phase transition of bilayers formed from the zwitterionic phospholipid, DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine, supported on mica. The images show that the fluid to gel phase transition process features substantial tearing of the bilayer due to the density change between the two phases. The gel to fluid transition is strongly affected by the resultant stress introduced into the gel phase, which changes the degree of cooperativity, the shape of developing fluid phase regions, and the course of the transition.     

Electrocatalysis of peroxide reduction by Au-stabilized, Fe-containing poly(vinylpyridine) films

We show that poly(vinylpyridine) (PVP) coated glassy carbon surfaces containing Fe(CN)6(3-) exhibit catalytic activity toward electroreduction of H2O2. While Fe(CN)6(3-) is catalytically inactive in solution phase, it exhibits catalytic activity upon incorporation into the PVP film, because film incorporation leads to an open coordination site in the otherwise inert Fe(CN)6(3-) molecule. However, this catalytic activity is quickly lost during H2O2 electroreduction due to leaching of the Fe species from the PVP film. The Fe catalyst in the PVP film could be stabilized by 1 order of magnitude in time by electrodeposition of small Au particles. Characterization of the film using scanning electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy shows that covalent attachment between the Au particle and the Fe-based catalyst is a likely mechanism for catalyst stabilization.     

Optimization of a permeation-based microfluidic direct formic acid fuel cell (DFAFC)

A design for a passive, air-breathing microfluidic fuel cell utilizing formic acid (FA) as a fuel is described and its performance characterized. The fuel cell integrates high surface area platinum (cathode) and palladium-platinum (anode) alloy electrodes within a PDMS microfluidic network that keeps them fully immersed in a liquid electrolyte. The polymer network that comprises the device also serves as a self-supporting membrane through which FA and oxygen are supplied to the alloy anode and cathode, respectively, by passive permeation from external sources. The cell is based on a planar form-factor and in its operation exploits FA concentration gradients that form across the PDMS membrane. These latter gradients allow the device to operate stably, producing a nearly constant limiting power density of ~0.2 mW/cm2, without driven laminar flow of fluids or the incorporation of an in-channel separator between the anodic and the cathodic compartments. The power output of this elementary device in air is subject to electrolyte mass transport impacts, which can be reduced for a given design rule by decreasing the internal ohmic resistance of the cell. The results suggest that operational stability can be improved by decreasing the kinetic losses imposed on the cathode side of the cell due to FA crossover and modalities for doing so, such as by increasing the efficiency of fuel capture at the anode.     

In situ EC-STM studies of MPS, SPS, and chloride on Cu100: structural studies of accelerators for dual damascene electrodeposition

Electrochemical, differential capacitance, and in situ electrochemical scanning tunneling microscopy (EC-STM) methods are used to examine the interaction of bis(3-sulfopropyl)-disulfide (SPS) and mercaptopropylsulfonic acid (MPS) with Cu(100) surfaces both in the absence and presence of chloride. Both electrochemical and differential capacitance results are weakly perturbed by the addition of either MPS or SPS in the potential region between -0.2 and -0.5 V versus Ag/AgCl relative to the additive-free case. EC-STM images obtained from solutions of MPS alone exhibit a c(2 x 2) adlattice whereas those from SPS alone yield only the (1 x 1) structure. In the presence of Cl-, both adsorbates evince only a c(2 x 2) adlattice on the Cu(100) surface. The desorption potential of these structure is identical to that found with Cl- alone. These results show that neither MPS nor SPS adsorbs strongly on Cu(100) in the presence of Cl-.     

In situ electrochemical X-ray absorption spectroscopy of oxygen reduction electrocatalysis with high oxygen flux

An in situ electrochemical X-ray absorption spectroscopy (XAS) cell has been fabricated that enables high oxygen flux to the working electrode by utilizing a thin poly(dimethylsiloxane) (PDMS) window. This cell design enables in situ XAS investigations of the oxygen reduction reaction (ORR) at high operating current densities greater than 1 mA in an oxygen-purged environment. When the cell was used to study the ORR for a Pt on carbon electrocatalyst, the data revealed a progressive evolution of the electronic structure of the metal clusters that is both potential-dependent and strongly current-dependent. The trends establish a direct correlation to d-state occupancies that directly tracks the character of the Pt-O bonding present.     

The Long‐Term Stability of KO2 in K‐O2 Batteries

The rechargeable K‐O₂ battery is recognized as a promising energy storage solution owing to its large energy density, low overpotential, and high coulombic efficiency based on the single‐electron redox chemistry of potassium superoxide. However, the reactivity and long‐term stability of potassium superoxide remains ambiguous in K‐O₂ batteries. Parasitic reactions are explored and the use of ion chromatography to quantify trace amounts of side products is demonstrated. Both quantitative titrations and differential electrochemical mass spectrometry confirm the highly reversible single‐electron transfer process, with 98 % capacity attributed to the formation and decomposition of KO₂. In contrast to the Na‐O₂ counterparts, remarkable shelf‐life is demonstrated for K‐O₂ batteries owing to the thermodynamic and kinetic stability of KO₂, which prevents the spontaneous disproportionation to peroxide. This work sheds light on the reversible electrochemical process of K⁺+e^?+O₂?KO₂.