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For the development of lithium–air battery (LAB), which is one of the most promising next generation batteries, it is essential to understand the structure and properties of Li2O2, which is the dis...

The use of high-concentration electrolytes in lithium metal batteries enables the effective suppression of lithium dendrite growth at the lithium anode. The issue of the solvation structure at the ...

Increasing demands for the development of efficient electrochemical energy systems such as fuel cells and metal–air batteries have stimulated research interests in investigating the mechanistic pat...

As one of the major impurities in the organic electrolyte, HF can react with the alkali components in the solid electrolyte interphase (SEI), such as lithium alkoxide and lithium carbonate, to form more LiF-rich SEI. Here, the effects of HF on the lithiation behavior of the single crystal Si(111) anode were studied using scanning electron microscopy, soft X-ray emission spectroscopy, and windowless energy-dispersive X-ray spectroscopy. When the Li–Si alloy is formed in 1.0 M LiPF6 in the propylene carbonate solvent, it has a layered structure that contained the first layer of crystalline Li15Si4 (c-Li15Si4) alloy pyramids, the second layer of amorphous Li13Si4 (a-Li13Si4) alloy, and a third layer of Li-diffused LixSi alloy. When the more concentrated HF is in the electrolyte solution, less amount of the c-Li15Si4 alloy is formed in the first layer. It suggests that the Si lithiation can form only amorphous LixSi alloy relative to the components in the electrolytes. The study also explains why only amorphous LixSi alloy formation was observed in some previous studies.

Li–air battery has attracted much attention because of its very high theoretical energy density, but its actual performance is still very low. Most important reasons are the slow kinetics and low reversibility of electrodeposition/dissolution of Li–O2 species at the cathode. Thus, much effort has been devoted to understand the mechanisms of these processes but low reproducibility makes the full understanding of the mechanism difficult. Here we demonstrate that low reproducibility is caused by impurities in solution by showing how HF and H2O, major impurities, affect the potential dependent product distribution during discharge at Li–O2 cathode. HF causes significant mass increase as a result of the deposition of fluorine-containing species and H2O converts Li2O2 to proton containing side products such as H2O2, LiHO2, and LiOH and induces the solvent, DMSO, decomposition. These results demonstrate the importance of the impurity control in the operation of Li–air battery.

Potential-dependent double-resonance sum frequency generation (DR-SFG) spectroscopy is used to probe a 5σa electronic state of adsorbed CO on Pt thin layer modified Au surfaces in acid solution by showing an amplitude enhancement of atop CO peak due to a surface electronic resonance between visible light and the electronic transition from the Fermi level of Pt to the 5σa antibonding state of CO. The energy level of 5σa state of adsorbed CO on the Pt layer-modified Au electrodes is found to be different from that on bulk Pt electrodes and depend on the thickness of the Pt layer. The observed SFG results are tentatively explained by the shift in d-band energy of the electrode substrates, which could also be responsible for their different electrochemical characteristics toward CO oxidation.

Calcium ion (Ca2+)-induced functional expression of calmodulin (CaM), which is a signal transmitter in living cell, is known to be associated with its conformation change; however, it is difficult to correlate the conformational change and functional expression induced by Ca2+ reversibly as it is not easy to change the Ca2+ concentration while keeping the CaM concentration in solution. This can be done if CaM is immobilized on a solid surface while maintaining its function intact. Here CaM is immobilized on a self-assembled monolayer (SAM) of Ni-nitrilotriacetic acid (NTA) on a Au surface by histidine tag (His-tag) method. The conformational change of the immobilized CaM induced by the Ca2+ concentration change in solution was investigated using surface-enhanced infrared absorption spectroscopy (SEIRAS). The Ca2+-induced conformational change of CaM immobilized on the Au surface was followed by monitoring IR intensities at 1550 and 1645 cm–1, which originated from the Ca2+ binding site (EF hand) in CaM an...

To clarify the origin of the anomalous increase of the intensity of the sum frequency generation (SFG) peak corresponding to the stretching of preadsorbed CO on a Pt(111) electrode in H2SO4 solution prior to anodic oxidation CO, potential-dependent SFG measurements were carried out by using eight different visible-light energies (527∼635 nm). Anomalous SFG intensity peaks were observed at all visible light except at 527 nm, and the potential of the SFG peak shifted with the visible-light energy by 1 V/eV, showing that the origin of the anomalous increase of SFG intensity is not due to the potential-dependent geometric structure change of adsorbed CO suggested before but due to a resonance of visible and/or SF light with electronic transition from the Fermi level of Pt(111) to the 5σa antibonding state of adsorbed CO. The present work showed that SFG spectroscopy can probe not only the molecular structure but also the electronic structure of the electrochemical interface, which is difficult to be determine...

The adsorption of large biomolecules such as proteins is of high relevance in medicine; adsorbed proteins can initiate undesirable biological reactions such as blood coagulation or immune responses, which adversely affect the human body and the functioning of medical devices. Thus, the suppression of protein adsorption onto material surfaces is essential for medical and biomedical applications. Interfacial water molecules may play a key role in protein adsorption. In this context, in this study, we prepare various types of surfaces (hydrophobic, hydrophilic, anionic, cationic, and zwitterionic) using polymer brushes with different molecular structures. We analyze the adsorption of negatively and positively charged proteins using a quartz crystal microbalance (QCM) to quantitatively investigate protein adsorption onto the polymer brush surfaces. The structure of the interface between the polymer brushes and water media is investigated using sum frequency generation (SFG) spectroscopy. Our comparison of the...

Boron nitride (BN), which is an insulator with a wide band gap, supported on Au is theoretically suggested and experimentally proved to act as an electrocatalyst for oxygen reduction reaction (ORR). Density-functional theory calculations show that the band gap of a free h-BN monolayer is 4.6 eV but a slight protrusion of the unoccupied BN states toward the Fermi level is observed if BN is supported on Au(111) due to the BN-Au interaction. A theoretically predicted metastable configuration of O2 on h-BN/Au(111), which can serve as precursors for ORR, and free energy diagrams for ORR on h-BN/Au(111) via two- and four-electron pathways show that ORR to H2O2 is possible at this electrode. It is experimentally proved that overpotential for ORR at the gold electrode is significantly reduced by depositing BN nanosheets. No such effect is observed at the glassy carbon electrode, demonstrating the importance of BN-substrate interaction for h-BN to act as the ORR electrocatalyst. A possible role of the edge of the BN islands for ORR is also discussed.

The formation process and structure of a self-assembled monolayer (SAM) of lipoic-acid-terminated polyproline on a gold surface in aqueous solution were investigated by several techniques. The amount of polyproline molecules on the gold surface was determined from the area of the reductive desorption peak, and orientation and thickness of the polyproline SAM were determined in situ by attenuated total reflection infrared (ATR-IR) spectroscopy and ellipsometry. The kinetics of the polyproline SAM formation process were discussed on the basis of these results. The in situ IR study confirmed that the conformation of the polyproline SAM was changed by changing the solvent from water to methanol and methanol to water, as is the case for polyproline dissolved in solution.

The conformation of self-assembled monolayers (SAMs) buried at metal-semiconductor interfaces plays a crucial role in the functioning of the molecular junctions thus formed. We have studied by vibrational sum frequency generation (SFG) spectroscopy the influence of deposited gold films on the molecular orientation of a series of n-alkyl monolayers that are covalently bonded to silicon(111) via Si-C linkages (≡Si-CnH_[2n+1],n = 10, 12, 14, and 18). The SFG spectra indicate that the gold contacts (overlayers) introduce significant gauche defects within the initially highly oriented alkyl chains. The methyl tilt angles of the buried n-alkyl monolayers depend on the gold deposition method (vacuum evaporation vs sputtering) and the alkyl chain length. These observations are supported by solid-state electrical measurements.

Nucleic acids possess charged phosphate groups in their backbones, which require counterions to reduce the repulsive Coulombic interactions between the strands. Herein we report how different mono- and divalent metal cations influence the molecular orientations of DNA molecules on silicon surfaces upon immobilization and hybridization. Our sum frequency generation (SFG) spectroscopy studies demonstrated that the degree of conformational variation of DNA self-assembled monolayers on silicon depends on the type of metal cations present. The molecular orientation change of immobilized single-stranded oligonucleotides correlates with DNA-cation affinity (Mg(2+)Ca(2+)K(+) approximately Na(+)): metal cations with the strongest affinity disrupt the structure of the underlying linker monolayer the most. Upon hybridization the trend is reversed, which is attributed to the greater ability of divalent cations to mask the negative charges on the DNA backbone. These findings provide useful information for the construction of more sensitive DNA biosensors, particularly the optimization of on-chip hybridization performance.

The reaction dynamics of trans-2-butene adsorbed to acidic hydroxyl groups on the surface of ferrierite zeolite is examined by time-resolved spectroscopy using a tunable infrared picosecond pulse laser system. The transient absorption spectra measured by a two-color pump−probe technique at 188−243 K reveal bleaching and hot bands of the OD stretching mode 2 ps after excitation. This vibrationally excited state relaxes within 20 ps at 188 K, while the bleaching band includes a long-lifetime component that lasts for more than 100 ps at 243 K. Thus, the OD (isotope-exchanged hydroxy groups) stretching band does not entirely recover in this period and is mirrored by an analogous weakening of the CH bending band of the adsorbed trans-2-butene. Simultaneously, three new bands in CH stretching region were observed at 3045, 3095, and 3130 cm-1. This result suggests the presence of a short-lived intermediate formed by reaction between the acidic hydroxyl groups and adsorbed trans-2-butene.

We have investigated olefins adsorbed on Bronsted acidic hydroxyl groups (OD) of DM20 zeolite by transient infrared absorption spectra after excitation of the OD stretching mode using picosecond infrared lasers. The olefins studied were ethylene, deuterated ethylene, propylene, and isobutene, and only isobutene was adsorbed on OD at its methyl group while the other olefins were adsorbed at their double bonds. For all the olefins except isobutene, simple vibrational relaxation of the v = 1 state was observed and the lifetimes were 2−4 ps. These lifetimes are an order faster than that of isolated OD. For isobutene, a long lifetime component lasting more than 500 ps was observed in addition to vibrational relaxation of 2 ps. The transient absorption spectra for isobutene-adsorbed zeolite at various time delays and frequencies indicated the existence of a short-lived species and a slow desorption process compared with vibrational relaxation.

Picosecond infrared-infrared pump−probe experiments in the OD stretching region were carried out on dehydrated and multilayer water-adsorbed γ-Al2O3. For the dehydrated γ-Al2O3, transient bands assigned to the bleaching and hot bands of the OD stretching mode of isolated surface hydroxyl groups were observed, and the population lifetime (T1) of the vibrational excited state (v = 1) of the mode was 200 ± 10 ps at 293 K. The characteristic temperature dependence of T1 is indicative of a seven-phonon process. For the water-adsorbed γ-Al2O3, the transient bleaching and transient hot bands with a lifetime of 10−12 ps were observed by excitation of the absorption peak at 2630 cm-1. In addition to these bands, weak transient bands were observed in the low-frequency region. These results are considered evidence of the existence of isolated water molecules on the γ-Al2O3 surface. Pure dephasing is also discussed based on the bandwidth of the observed transient bands.