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Two-dimensional (2D) boron monosulfide (BS) nanosheets are predicted to have several stable phases and unique electronic structures, endowing them with interesting attributes, including superconducting, thermoelectric, and hydrogen storage properties. In this paper, we report the experimental realization of 2D BS nanosheets by the physical exfoliation of rhombohedral boron monosulfide (r-BS). Moreover, we demonstrate the facile separation of a mixture of 2D BS nanosheets and the r-BS powder in acetonitrile; the former were selectively separated as a dispersion in the supernatant, whereas the latter remained in the precipitate. In addition, density functional theory calculations reveal a clear dependence of the bandgap energy (Eg) on the number of layers of stacked BS nanosheets, where Eg for BS nanosheets is approximately 1.0 eV higher than that for r-BS. Atomic force microscopy, cathode luminescence, ultraviolet-visible absorption spectroscopy, and excitation emission matrix experiments revealed a consistent bandgap difference of approximately 1.0 eV between the BS nanosheets and r-BS. We also demonstrate the applications based on the properties that originated from the difference in the bandgap between r-BS and BS nanosheets using photoelectrochemical current switching. These results indicate that the nanosheet bandgap can be tuned to a desired value by controlling the number of stacked 2D BS nanosheets. Therefore, BS nanosheets are promising non-metal 2D materials for applications requiring bandgap control, such as electronics and photocatalysis.

Passivation of the n-InP(100) surface with sodium sulfide (Na2S) aqueous solution is analyzed by photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). The room-temperature PL intensity increases essentially even after short treatment with sulfide solution for 1 min. The enhancement in the room-temperature PL intensity after passivation decreases with the increase in the bulk doping level of the semiconductor. Time-resolved PL studies performed at liquid-nitrogen temperature indicate reduction in the surface recombination velocity. This improvement of the PL intensity occurs just after transformation of the native oxide layer consisting mainly of indium phosphates to the passivating layer consisting of indium sulfides and oxides. The surface bands in n-InP(100) remained nearly flat both before and after sulfide passivation.

The adsorption behavior of perfluorosulfonated ionomers (PFSIs) on a Pt(111) surface in various solvents is investigated by in situ atomic force microscopy (AFM) and discussed on the basis of aggregation of PFSIs in the liquid phase. The AFM images show that, in an aqueous solution of PFSI (0.1 wt % Nafion + 99.9 wt % water), PFSI aggregates with a lateral size of 20-200 nm adsorb on the Pt(111) surface. In a PFSI solution containing a small amount of 1-propanol (0.1 wt % Nafion + 99.5 wt % water + 0.4 wt % 1-propanol), however, slightly smaller aggregates adsorb on the Pt(111) surface. Such solvent-dependent sizes of adsorbed aggregates are in reasonable agreement with apparent hydrodynamic radii of PFSIs in the corresponding solutions determined by dynamic light scattering (DLS) while assuming the formation of spherical aggregation. Interestingly, a step-terrace structure characteristic to a clean Pt(111) surface is observed in a propanol-rich PFSI solution (0.1 wt % Nafion + 44.45 wt % water + 55.45 wt % 1-propanol) but X-ray photoelectron spectroscopy clearly indicates the existence of fluorocarbon species at the Pt(111) surface, suggesting the formation of a smooth adsorbed layer of PFSIs in a lying down configuration. Absence of any features assignable to aggregates in DLS data suggests well-dispersion of PFSIs in such propanol-rich solution without aggregations. Thus, the adsorbed structure of PFSIs at Pt surfaces can be controlled by tuning the composition of mixed solvent, which affects the aggregation of PFSI in the liquid phase.

Water molecules within a thin hydration layer, spontaneously generated on hydrophobic protein surfaces, are reported to form a poorly dynamic network structure. However, how such a water network affects the conformational change dynamics of polar groups has never been explored, although such polar groups play a critical role in protein-protein and protein-ligand interactions. In the present work, we utilized as model protein surfaces a series of self-assembled monolayers (SAMs) appended with polar (Fmoc) or ionic (FITC) fluorescent head groups that were tethered via a 1.5-nm-long flexible oligoether chain to a hydrophobic silicon wafer surface, which was densely covered with paraffinic chains. We found that, not only in deionized water but also in aqueous buffer, these oligoether-appended head groups at ambient temperatures both displayed an anomalously slow conformational change, which required ∼10 h to reach a thermodynamically equilibrated state. We suppose that these behaviors reflect the poorly dynamic and low-permittivity natures of the thin hydration layer.

In situ X-ray photoelectron spectroscopy is applied to electrochemical lithiation/delithiation processes of an amorphous Si electrode sputter-deposited on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte. After the first lithiation, a broad Li peak appears at the Si surface, and peaks corresponding to bulk Si and Si suboxide significantly shift to lower binding energy. The appearance of the Li peak and shift of the Si peaks confirm the formation of lithium-silicide and lithium-silicates due to the lithiation of Si and native suboxide. The composition of lithium-silicide is estimated to be Li3.44Si by quantitative analysis of electrochemical response and photoelectron spectra. Peak fitting analysis shows the formation of Li2O and Li2CO3 due to side reactions. Upon the following delithiation, the peak corresponding to Li3.44Si phase shifts back to higher binding energy to form Li0.15Si phase, while lithium-silicates, Li2O, and Li2CO3 remained as irreversible species. Thus, electrochemical reactions accompanied with lithiation/delithiation processes are successfully observed.

In this study, highly ordered anodic porous metal oxides of transition metals (W, Fe, Co, and Nb) were prepared by anodization combined with a pretexturing process. The formation of an array of dimples on the metal surface was achieved by dry etching using ordered anodic porous alumina as a mask. Subsequent anodization of the pretextured metals generated metal oxides (WO3, Fe2O3, Co3O4, and Nb2O4) with an ordered hole array structure because each dimple acted as a starting point for hole development. The hole periodicity of the resulting ordered anodic porous metal oxide could be controlled by changing the periodicity of the dimples formed on the substrate. Ordered anodic porous films obtained by this process could be used in various functional devices that require ordered hole array structures.

Interfacial phenomena of oxide cathode/sulfide electrolytes are crucial for the improvement of energy density and cycle stability of all-solid-state batteries. Thin-film batteries provide a simple reaction field for mechanistic studies. We fabricated a model film battery consisted of LiCoO2 cathode, LiNbO3 buffer layer, amorphous Li3PS4 electrolyte, and Li metal anode by physical vapor deposition. Structural changes at the cathode-side interface were investigated by in situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) using Ar etching. The LiCoO2 lattice showed a reversible change under high voltage operation with the upper cutoff voltage of 4.5 V. A cathode electrolyte interphase (CEI) layer was formed at the interface by decomposition of LiNbO3 and Li3PS4. The ionic and electronic conductivities of the CEI layer could be crucial to improve the reaction resistance and the cycle stability of the oxide cathode/sulfide electrolyte interface.

Nanoscale Young's modulus mapping of the cross-section of electrode composite films used in lithium ion batteries was carried out using bimodal atomic force microscopy. Clear difference in Young's modulus was observed between the particles of active materials and matrix of conductive additives/binders in the composites of LiCoO2-based positive and graphite-based negative electrodes. Interestingly, there were a few particles showing significantly reduced Young's modulus in the 100% state-of-charge positive electrode although such particles were not present in the pristine electrode.

Silicon-cobalt nanocomposites on NrGO, Si-Co/NrGO, were synthesized by the modified polyol method. Rice husk was used as the silicon source. The composites were primarily characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy equipped with energy dispersive spectroscopy. The small-sized particles of the silicon-cobalt product were effectively distributed on the NrGO. Finally, these anode materials were tested in lithium-ion batteries by haft-coin cell assembly. Electrochemical properties were measured and the result showed an initial capacity of 975 mAh g-1. This material is expected to be used as a high-performance anode, suitable for the next generation of anode materials in lithium-ion batteries.

Various important processes take place at solid/liquid interfaces. Understanding of structural changes accompanying with those interfacial processes is important not only for fundamental science but also for a wide range of applications, especially electrocatalysis. In the last several decades, a variety of microscopic and spectroscopic techniques have been developed to observe geometric/molecular/electronic structures at the solid/liquid interfaces in situ. However, techniques to probe the electronic structure of electrocatalysts are still limited because of the complexity of the experimental setup and the interpretation of results. Since the 1980s, our groups have developed and utilized various techniques which enable to investigate those structural changes under electrochemical potential control. In the present paper, our recent research progress on the electronic structure at solid/liquid interfaces, (1) in situ XAFS studies on molecular catalysts confined within molecular layers and electrocatalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells, (2) development of an in situ electrochemical XPS apparatus for the solid/liquid interfaces and (3) investigation of the electronic structure of metal surfaces modulated by adsorbed species by in situ DR-SFG is briefly reviewed.

Determining the atomic structure across electrolyte–electrode interfaces with a sufficient temporal resolution is crucial to understanding how electrochemical reactions proceed. Surface X-ray diffraction is a well-established method for determining interface structures at the atomic scale. However, existing measurement methods are often incapable of quantifying time-dependent structural changes during electrochemical processes because acquiring a diffraction rod profile sufficient for structure determination usually takes a longer time than the rate of the structural changes. This report demonstrates that the wavelength-dispersive method, which can acquire a range of the diffraction rod profile at once, is capable of the time-resolved analysis of electrochemical dynamics on a time scale of seconds and less, using electrochemical reactions on Pt(111) electrode surface as examples. In the case of the electrochemical oxidation of methanol, the quantitative analysis of the transient vertical displacement of t...

Room temperature (RT) bistable switching materials continue to fascinate the scientists since they can be utilized for a new class of molecular-based switches or memories. While the spin crossover (SCO) compound is categorized into these attractive materials, designing of a SCO system showing desirable bistability (i.e., wide hysteresis loop spanning RT) in a rational way is still a very challenging issue. We report herein a new family of neutral molecular iron(II) complexes showing hysteretic SCO in a wide range of switching temperatures (239–409 K) and hysteresis widths (1–31 K) spanning RT. These materials were obtained as single crystals of two solvent-free compounds [FeII(ptm2-dmpn)(NCS)2] (1; ptm2-dmpn = N,N′-bis[(1-phenyl-1H-1,2,3-triazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine) and [FeII(p-ttm2-dmpn)(NCS)2] (2; p-ttm2-dmpn = N,N′-bis[(1-p-tolyl-1H-1,2,3-triazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine), and two solvatomorphs [FeII(p-ttm2-etpn)(NCS)2]·solvent (p-ttm2-etpn = N,N′-bis[...

Organic molecular layers with viologen moieties as electron transfer mediators were constructed on hydrogen-terminated Si(111) surfaces, and metal catalysts for multielectron transfer reactions were incorporated into the molecular layers by immersing the viologen-modified Si(111) electrodes in aqueous solutions containing various metal complexes (K2PdCl4, NaAuCl4, and K2PtCl4). Significant enhancements were achieved for CO2 reduction at the Au-modified Si(111) electrode and for both hydrogen evolution reaction (HER) and CO2 reduction at the Pd-modified Si(111) electrode. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis showed that Au complexes were spontaneously reduced to metal nanoparticles during the metal insertion, and therefore, actual catalysts for CO2 reduction at the Au-modified Si(111) electrode were Au metal nanoparticles. In contrast, Pd complexes were inserted into the molecular layers and partly reduced during HER and CO2 reduction. Pd complexes and ...

Potential-dependent structures and potential-induced structure changes of the Pt(111) electrode in perchloric and sulfuric acid electrolyte solutions were investigated in the potential region between the underpotential deposition (UPD) of hydrogen (0.05 V vs RHE) and surface oxide formation (0.95 V) by in situ surface X-ray scattering (SXS) using the electrolyte thickness controllable spectroelectrochemical cell. In both solutions, the interfacial structures, including not only the surface arrangements of the adsorbates but also the Pt(111) surface atomic arrangements at various potentials, were accurately determined and compared with those previously reported in the literature. Several differences and new results when compared to the previously reported results were found by in situ potential-dependent structure measurements as follows: at 0.90 V, while oxygen species, such as an adsorbed hydroxyl group (OHad), H2O, and/or H3O+ with a total coverage of 1 monolayer (ML), are adsorbed on the atop site of t...

Size and lattice constant of thiol self-assembled monolayer (SAM)-modified gold nanoclusters (GNCs) assembled on Au(111) surfaces after each electrochemical treatment were investigated using grazing incidence x-ray diffraction (GIXRD). When the potential was swept between 0 and 1.3 V (vs. Ag/AgCl), the size and lattice constant of GNCs slightly decreased due to the oxidative desorption of the SAMs. As the number of potential cycles increased, the size of GNCs started to increase due to the aggregation, while the lattice constant continued to decrease due to further desorption of the SAMs from the GNCs. After most of the SAMs were removed from the GNCs, the size and lattice constant monotonically increased with the number of potential cycles. The size dependent lattice constant change was observed when GNCs were smaller than ~35 Å. Keywords: Gold nanoclusters (GNCs), Size dependence of lattice constant of GNCs, Grazing incidence x-ray diffraction (GIXRD), Self-assembled monolayer (SAM)

Passivation of n-InP(1 0 0) surface with an aqueous sodium sulfide solution was investigated by photoluminescence and x-ray photoelectron spectroscopy techniques. It was found that even a brief treatment for 1 min turns out to be enough for an essential enhancement of the photoluminescence intensity, which comes amid etching off the surface indium phosphate layer and formation of In–S and In–OH surface chemical bonds. A longer sulfide treatment results in a smaller photoluminescence enhancement due to formation of indium oxide, in addition to In–S and In–OH bonds. Both native-oxide-covered and sulfide-treated n-InP(1 0 0) surfaces have almost no band bending. The enhancement of photoluminescence intensity after sulfide treatment can be explained by modification of the surface states spectrum due to the transformation of the surface chemical bonds.

Si is an attractive anode material for next-generation lithium batteries including all-solid-state batteries because it has a high theoretical capacity density (4200 mAh g-1). However, Si suffers from the irreversible capacity loss related to the severe volume expansion/shrinkage during the lithiation/delithiation processes. In liquid-type batteries, the main cause of the capacity loss is the continuous formation/decomposition of the solid electrolyte interphase (SEI) on the Si anodes [1]. However, the capacity loss of the Si anode is also regarded as a serious issue even in all-solid-state batteries without using electrolyte solution. Thus, a fundamental understanding of the lithiation/delithiation reactions of the Si anode is important to solve the problem. X-ray photoelectron spectroscopy (XPS) enables us to analyze the elemental composition, oxidation states, and electronic structure of the sample surface. In situelectrochemical XPS, which can measure the same position of a sample under the operational condition for batteries, allows a stepwise analysis of the reactions without interference from variation and inhomogeneity of samples [2]. Here, lithiation/delithiation reactions of an amorphous Si electrode in a thin-film cell is investigated by using an XPS apparatus equipped with an applying voltage system [3]. The amorphous Si with a thickness of about 100 nm is formed on the Li6.6La3Zr1.6Ta0. 4O12 (LLZT) sheet by radio-frequency magnetron sputtering, and the Cu is further coated on the sputtered Si layer by DC sputtering. During the Cu deposition, a stainless-steel stencil mask is used to yield an uncoated amorphous Si part with a diameter of about 2 mm as an analytical region for the XPS measurements. The Li metal layer is thermally deposited on the other side of LLZT. After the thin-film cell with the final structure of [Cu/Si(100 nm)/LLZT(500 µm)/Li metal(1.3 µm)] is connected to the sample holder in an Ar-filled glove box, it is transferred to the XPS apparatus by using a vacuum suitcase to prevent from exposing to open air. The cell is cycled between 0.01 and 1.2 V at 0.02C (1.245 µA) in UHV chamber of the XPS apparatus. The Si surface is observed by XPS before/after the lithiation/delithiation processes. The galvanostatic potential profiles show that the capacity for the first lithiation and delithiation processes is 3160 and 2977 mAh g-1, respectively. A broad Li 1s peak appears after the first lithiation process, confirming the Li insertion to the Si electrode. According to the peak fitting, the Li 1s peak is composed of lithium-silicide (LixSi), Li2O, and Li2CO3. The Li2O and Li2CO3 are possibly formed by the reaction of the lithium-silicide surface with a trace amount of residual gas from the vacuum chamber and LLZT. The Li2O and Li2CO3 contribute to the irreversible capacity loss because these components remain even after the subsequent delithiation process. In the Si 2p region, peaks originated from bulk Si (Si0) at 99.1 eV and Si suboxide (SiOx) at 101.9 eV are shifted to lower binding energy side. These peak shifts indicate the formation of lithium-silicide (LixSi) and lithium-silicate (Li4SiO4) due to the insertion of Li ions to each layer. Based on the calculation using the peak intensities and known physical parameters, it is proposed that the Si electrode has a surface structure of [Li2O (2.5 nm)/Li4SiO4 (0.9 nm)/LixSi] at this state. In addition, the composition of the LixSi is estimated to be Li3.27Si from the charge integration and the thickness of each layer. After the subsequent delithiation process, the Li4SiO4 peak remains in the same position. In contrast to the immobility of the Li4SiO4 peak, the LixSi peak is shifted back to the higher binding energy side, but it does not completely return to the original position of the Si0 peak. The composition of the lithium-silicide phase at this state is estimated to be Li0.14Si. Therefore, Li trapped in Li0.14Si and formation of Li4SiO4, Li2O, and Li2CO3 contribute to the irreversible capacity loss of the Si electrode. References: [1] Y. Xu, K. Wood, J. Coyle, C. Engtrakul, G. Teeter, C. Stoldt, A. Burrell, A. Zakutayev, J. Phys. Chem. C, 123 (2019) 13219-13224. [2] X.H. Wu, C. Villevieille, P. Novak, M. El Kazzi, J. Mater. Chem. A, 8 (2020) 5138-5146. [3] R. Endo, T. Ohnishi, K. Takada, T. Masuda, submitted (2020).

Spectroelectrochemical measurements at indium tin oxide (ITO) electrode modified with viologen monolayer showed two redox peaks corresponding to viologen dication/radical cation (V2+/V+·) and viologen radical cation/neutral form (V+·/V0) in cyclic voltammogram (CV), and stable spectra corresponding to radical cation (V+·) and neutral form (V0) of viologen at potentials between V2+/V+· and V+·/V0 redox peaks and those more negative than V+·/V0 redox peak, respectively. On the other hand, at viologen monolayer modified ITO electrode with Pt complex confined within the monolayer by ion exchange reaction, no redox peaks but large current due to hydrogen evolution reaction (HER) were observed in CV and no absorption peaks corresponding to V+· or V0 were observed in the UV/visible spectra obtained during the potential scan. Time-resolved spectroelectrochemical measurements, however, showed that V+· is formed upon the potential step to the potentials more negative than V2+/V+· redox potential and disappeared within ca. 1 ms, showing that electron is transferred from ITO electrode to proton to form hydrogen via viologen moiety and Pt complex. Keywords: Spectroelectrochemistry, Viologen monolayer, Confined molecular catalyst, Hydrogen evolution reaction

Ions' response to hydrophobic surfaces The strength of interactions between ions depends on their solvation environment. Schellman postulated in the 1950s that when aqueous solvated ions approached a hydrophobic surface (such as a parts of a protein surface), interactions between ions would be enhanced. Chen et al. experimentally tested this theory by studying the dissociation of organic ions bonded by salt bridges after the addition of acid. The ion pairs were held by tethers at different distances from hydrophobic surfaces. The salt bridge was stronger when it was closer to the hydrophobic surface. Science , this issue p. 555

Although lead-halide perovskite-based solar cells hold the promise of a breakthrough in the production of next-generation photovoltaic devices, anomalous hysteresis in current–voltage curves and inadequate stability remain as major challenges. Here, we demonstrate the production of low-temperature solution-processed perovskite solar cells (ITO/PEDOT:PSS/perovskite/PC61BM/Ca/Ag) with hysteresis-free current–voltage characteristics, excellent photostability, and high reproducibility via the inclusion of methyl ammonium chloride (MACl) using the interdiffusion method. The best-performing devices exhibited a power conversion efficiency of over 12%. Our devices showed promising stability by maintaining more than 90% of their initial performance over long periods of time at ambient conditions with encapsulation using common techniques, as well as no obvious degradation after 2 h of continuous light exposure. We statistically compared fabrication processes using the interdiffusion method with or without MACl by creating a histogram of over 120 devices for each method. The results clearly indicated that including MACl gave better reproducibility and a higher average efficiency of 9.5%, as well as improved device stabilities.

The photoelectrochemical (PEC) carbon dioxide reduction process stands out as a promising avenue for the conversion of solar energy into chemical feedstocks, among various methods available for carbon dioxide mitigation. Semiconductors derived from cheap and abundant elements are interesting candidates for catalysis. Whether employed as intrinsic semiconductors or hybridized with metallic cocatalysts, biocatalysts, and metal molecular complexes, semiconductor photocathodes exhibit good performance and low overpotential during carbon dioxide reduction. Apart from focusing on carbon dioxide reduction materials and chemistry, PEC cells towards standalone devices that use photohybrid electrodes or solar cells have also been a hot topic in recent research. An overview of the state-of-the-art progress in PEC carbon dioxide reduction is presented and a deep understanding of the catalysts of carbon dioxide reduction is also given.

Photoexcited hole transfer to MnOx cocatalysts on SrTiO3 photoelectrodes was examined under controlled potential conditions during UV irradiation using in situ Mn K-edge X-ray absorption fine structure (XAFS) spectroscopy. The absorption edges of spectra were found to shift to higher energies during irradiation, indicating that MnOx cocatalysts were oxidized by the migration of photoexcited holes accompanied by a positive potential shift of the MnOx cocatalysts. This oxidation process was promoted by the application of a positive applied potential, suggesting that the photoexcited hole transfer was enhanced by upward band bending at the cocatalyst–photoelectrode interface. Structural changes of the MnOx cocatalyst were found to depend on the UV photon intensity; thus, the observations of photoexcited electron transfer by XAFS are associated with the photoelectrochemical activity during water splitting.

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.

X-ray photoelectron spectroscopy (XPS), which intrinsically requires vacuum, was used to characterize chemical species in a liquid using laboratory XPS apparatus equipped with a conventional Al-K alpha source and an environmental cell with an ultra-thin silicon nitride membrane as a quasi-transparent window for the transmission of X-rays and photoelectrons. Aqueous solutions of cesium chloride at different concentrations were encapsulated in the cells, and the membrane in contact with the solution was irradiated with X-rays to collect the photoelectrons emitted from the chemical species in a liquid through the membrane. Cs 4d photoelectron peaks were observed, and the peak intensity increased proportionally with the concentration. Thus, the quantitative analysis of solution species by this method is demonstrated. Published under license by AIP Publishing.

Potential dependent adsorption of oxygen on a gold electrode surface was proved by electrochemical quartz crystal microbalance. The adsorption of oxygen was started to be observed at potentials more positive than the potential where ORR started to take place and the amount of adsorbed oxygen increased and reached the saturated value as potential became more negative. The critical potentials, at which oxygen adsorption was started to be observed, were dependent on anions in solution. The adsorption of oxygen started at more positive potential in perchlorate solution than in sulfate solution, showing the inhibition of the adsorption of oxygen by strongly adsorbed sulfate anion. Keywords: Au electrode, Oxygen adsorption, Electrochemical quartz crystal microbalance

Potential-dependent adsorption/desorption behavior of perfluorosulfonated ionomer (PFSI) on a platinum electrode was investigated by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), and electrochemical atomic force microscope (EC-AFM) in a Nafion, that is, PFSI, dispersed aqueous solution without any other electrolyte. PFSI adsorbed on the platinum surface in the potential region between 0.1 and 0.8 V versus Ag/AgCl and desorbed from the surface at 1.1 V where place-exchanged Pt oxide was formed. Once platinum oxide was reduced, PFSI readsorbed on the surface. These processes took place reversibly.

The structure of the perfluorosulfonated ionomer (PFSI)/Pt(111) interface in a membrane electrode assembly (MEA)-like configuration of a polymer electrolyte membrane (PEM) fuel cell, that is, a vacuum evaporated Pt layer/PEM(Nafion membrane)/PFSI(adhesion Nafion layer)/Pt(111) single crystal, and its bias-induced change were investigated by surface X-ray scattering measurement at an atomic level. Crystal truncation rod measurement shows that PFSI adsorbed on the Pt(111)-(1 × 1) surface without bias. When the Pt(111) electrode was positively biased to form Pt oxide, the PFSI layer was detached from the Pt surface and oxygen atoms penetrated into the Pt lattice.

Potential-dependent adsorption/desorption behavior of perfluorosulfonated ionomer (PFSI) on a gold electrode was investigated by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), and electrochemical atomic force microscopy (EC-AFM) in a Nafion (i.e., PFSI) dispersed aqueous solution without any other electrolyte. It was found that PFSI serves as an electrolyte and that electrochemical measurements can be performed in this solution without any significant IR drop. PFSI molecules were adsorbed on the Au surface in the lying-down configuration in the potential range between 0 and 0.45 V, the amount of adsorbed PFSI increased when the potential was made more positive than 0.75 V, and the adsorbed PFSI fully desorbed from the surface at potentials more positive than 1.4 V where gold oxide was formed. Once the gold oxide had been reduced, PFSI readsorbed on the surface, albeit slowly. PFSI desorbed from the surface as the potential was made more negative than 0 V. These processes took place reversibly.

A series of electroactive composites containing cobalt nanoclusters and N-doped graphite-like carbon is obtained by catalytic chemical vapour deposition (CCVD) using Mg–Co–Al layered double hydroxides and acetonitrile. The influence of synthesis temperature, e.g. 600, 700 and 800 °C on their physicochemical properties is examined by means of X-ray diffraction, elemental analysis, thermal analysis, nitrogen sorption, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. N-doped graphite-like carbon in the catalysts shows various morphologies. The composite prepared at 600 °C contains plate-like particles, whereas those synthesized at 700 and 800 °C, contain not only plate-like particles but also multi-walled carbon nanotubes. The concentration of nitrogen uniformly incorporated in the carbon framework is ca. 2 wt %. The electrocatalytic properties of the catalysts for oxygen reduction reaction (ORR) are evaluated in alkaline media by cyclic voltammetry and rotating disk electrode (RDE) measurement. The composites are proved to have the ability to reduce oxygen according to 2-electron pathway.

In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L3 and Ce L3 edges of the Pt–CeOx/C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L3 edge of the conventional Pt/C catalyst in oxygen-saturated H2SO4 solution to clarify the role of CeOx in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt–CeOx nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeOx layer, of which Ce3+ was oxidized to Ce4+ instead of Pt at the Pt oxide formation potential.

Charge transport processes at the interface of n-GaAs (100) with an aqueous HCl solution are studied by electrochemical impedance spectroscopy. It is found that when open-circuit potential and anodic potentials are applied to the semiconductor the impedance spectra contain two capacitive semicircles corresponding to the capacitances of the space charge layer and surface states. In the case of open-circuit potential, semiconductor band bending at the interface with the solution is about 0.7 eV and the density of occupied surface states in the dark and under daylight conditions is 1.6 and 2.8 × 1012 cm2 eV−1, respectively. When cathode potentials are applied to GaAs, hydrogen evolution begins at the semiconductor/electrolyte interface and an additional inductive loop appears in the impedance spectra. At the same time, the density of occupied surface states increases considerably both due to a straightening of the semiconductor bands and to the appearance of As-H bonds. Thus, charge transport through the n-GaAs (100)/aqueous HCl solution interface is always mediated by semiconductor surface states.

Pt on ceria (CeOx) particles supported on carbon black (CB) were synthesized using the combined process of hot precipitation and impregnation methods. During 30 cycles of cyclic voltammetry pre-treatment in the potential ranging from −0.2 to 1.3 V (V vs. Ag/AgCl), it was observed that a small amount of CeOx, which consisted of the interface region between Pt and CeOx, remained on Pt particles. Other free CeOx particles were dissolved into H2SO4 aqueous solution. To develop the Pt-CeOx/CB catalyst, the surface chemical states, the net chemical composition, morphology and electrochemical behavior in H2SO4 aqueous solution were characterized. Our microanalysis and electrochemical analysis indicate that the active CeO2 with high specific surface area provides the continuous amorphous cerium oxide (Ce3+ ,C e 4+) layer with pores on the surface of Pt particles. It is concluded that the amorphous cerium oxide layer on Pt inhibits the oxidation of Pt surface and contributes to enhancement of the activity on Pt cathode. The single cell performance was also improved using the Pt-CeOx/CB cathode. Based on all data, it is expected that the design based on characterization of the interface between Pt and small amount of amorphous cerium oxide layer could help in preparation of more active Pt catalyst.

We report that the addition of amino acids to the amyloid peptide dramatically affected the structure and the rate of formation of amyloid fibrils. The attachment of three lysines to Aβ(10-35) gave the formation of remarkably long fibrils, while three glutamates resulted in a faster formation rate of the fibrils.

An organic monolayer with diarylethene and viologen moieties as a photochromic and an electroactive group, respectively, was constructed on a hydrogen-terminated Si(111) surface by sequential surface reactions. Photoswitching behaviour of electron transfer from the Si electrode to viologen moiety, larger and smaller current after UV and visible irradiation, respectively, was observed. This photoswitching behaviour can be explained by a change in molecular conductivity of diarylethene moiety, which separates Si surface and viologen moiety, as a result of ring closing and opening induced by UV and visible irradiation, respectively.

Organic molecular layers with viologen moiety (i.e., electron acceptor) were constructed on a hydrogen-terminated Si(111) surface via a Si−C bond. Electrochemical characteristics after each synthetic process were measured, and electron mediation capability of the viologen moiety was demonstrated. Incorporation of platinum particles on the viologen-modified Si(111) surface was proved to enhance the hydrogen evolution reaction (HER) rate. Further improvement of the HER rate was achieved by the modification with viologen/Pt multilayers. Photoelectrochemical HER at the p-Si(111) electrode was also significantly accelerated by the modification with mono- and multiviologen/Pt layers.

The lateral resolution of our laser-based microspot photoemission spectrometer [Surf. Sci. 507–510 (2002) 434] has been improved to 0.3 μm by focusing VUV light of 140 nm wavelength (8.9 eV photon energy). The VUV light is generated by frequency tripling a second-harmonic output of a regeneratively amplified titanium:sapphire laser of 250 kHz repetition rate, and is focused on a sample surface by a Schwarzschild objective of 0.29 NA. Time-of-flight (TOF) photoelectron spectra of energy resolution better than 40 meV are accumulated for 0.4 s during scanning the sample position by 0.1 μm/step. Measurement on a Ta-striped Si sample revealed that the lateral resolution is 0.3 μm, which is very close to the diffraction-limited spot diameter. The present microspectrometer is characterized with the simultaneous realization of the diffraction-limited lateral resolution and the high-energy resolution, which is close to the Fourier transform of the pulse width of the laser light (100 fs).

Photoelectrochemical carbon dioxide reduction was carried out at a p-type Si(111) electrode modified with a viologen molecular layer and [AuCl4]− or [PdCl4]2−. It was proven that the reduction reac...

A novel photoemission microspectrometer based on focused VUV coherent radiation is presented for simultaneous realization of

An organic monolayer with a thiol group at its end was formed on a hydrogen-terminated (H–) Si(111) surface via Si–C covalent bond by hydrosilylation. PtCl42− complex ions were then immobilized on ...

A metal–organic monolayer–semiconductor junction, exhibiting a diode behaviour, was constructed on a hydrogen-terminated n-type Si(111) by sequential surface reactions of (1) formation of an organic monolayer with a thiol terminal group, (2) platinum deposition onto the thiol group via adsorption of a platinum complex followed by chemical reduction, and finally (3) continuous Ag layer formation by electroless deposition. Rectifying behaviour was observed at this interface.

The Mn-oxide/Nb:SrTiO3 photoelectrode for oxygen evolution reaction was investigated by in situ Mn K-edge XAFS spectroscopy under UV irradiation. The oxidization of the Mn oxide was observed via photoexcited carrier transfer, which results in the positive potential shift of the Mn oxide cocatalyst toward oxygen evolution reaction.

We have applied photoemission microspectroscopy to copper phthalocyanine film grown on a polycrystalline copper with a lateral resolution of 0.3μm and an energy resolution of 30meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2eV depending on the sample positions, while the work functions were 4.3 and 4.5eV for the respective positions. The band was intense when the binding energy was low. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.

A single-crystal silicon surface was modified with a bisoxazoline-Pd molecular layer and utilized as a highly efficient (catalyst turnover number up to 780,000, 110 degrees C, 72 h) and recyclable catalyst in the aerobic oxidation of benzylic alcohols.

We have studied electron transport through single redox molecules, perylene tetracarboxylic diimides, covalently bound to two gold electrodes via different linker groups, as a function of electrochemical gate voltage and temperature in different solvents. The conductance of these molecules is sensitive to the linker groups because of different electronic coupling strengths between the molecules and electrodes. The current through each of the molecules can be controlled reversibly over 2-3 orders of magnitude with the gate and reaches a peak near the redox potential of the molecules. The similarity in the gate effect of these molecules indicates that they share the same transport mechanism. The temperature dependence measurement indicates that the electron transport is a thermally activated process. Both the gate effect and temperature dependence can be qualitatively described by a two-step sequential electron-transfer process.