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Aromaticity is a fundamental concept in chemistry. It is described by Hückel’s rule that states that a cyclic planar π-system is aromatic when it shares 4n+2 π-electrons and antiaromatic when it possesses 4n π-electrons. Antiaromatic compounds are predicted to exhibit remarkable charge transport properties and high redox activities. However, it has so far only been possible to measure compounds with reduced aromaticity but not antiaromatic species due to their energetic instability. Here, we address these issues by investigating the single-molecule charge transport properties of a genuinely antiaromatic compound, showing that antiaromaticity results in an order of magnitude increase in conductance compared with the aromatic counterpart. Single-molecule current–voltage measurements and ab initio transport calculations reveal that this results from a reduced energy gap and a frontier molecular resonance closer to the Fermi level in the antiaromatic species. The conductance of the antiaromatic complex is further modulated electrochemically, demonstrating its potential as a high-conductance transistor., Antiaromatic molecules are predicted to have unusual charge transport properties, but are notoriously unstable and reactive. Here, the authors successfully fabricate an antiaromatic molecular circuit, based on a macrocyclic complex, displaying much higher conductance than its aromatic counterpart.

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...

Pt-CeO(x) nanowire (NW)/C electrocatalysts for the improvement of oxygen reduction reaction (ORR) activity on Pt were prepared by a combined process involving precipitation and coimpregnation. A low, 5 wt % Pt-loaded CeO(x) NW/C electrocatalyst, pretreated by an optimized electrochemical conditioning process, exhibited high ORR activity over a commercially available 20 wt % Pt/C electrocatalyst although the ORR activity observed for a 5 wt % Pt-loaded CeO(x) nanoparticle (NP)/C was similar to that of 20 wt % Pt/C. To investigate the role of a CeO(x) NW promotor on the enhancement of ORR activity on Pt, the Pt-CeO(x) NW interface was characterized by using hard X-ray photoelectron spectroscopy (HXPS), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Microanalytical data obtained by these methods were discussed in relation to atomistic simulation performed on the interface structures. The combined techniques of HXPS, TEM-EELS, and atomistic simulation indicate that the Pt-CeO(x) NW interface in the electrocatalyst contains two different defect clusters: Frenkel defect clusters (i.e., 2Pt(i)(••) - 4O(i)″ - 4V(o)(••) - V(Ce)″″) formed in the surface around the Pt-CeO(x) NW interface and Schottky defect clusters (i.e., (Pt(Ce)″ - 2V(O)(••) - 2Ce(Ce)') and (Pt(Ce)″ - V(O)(••))) which appear in the bulk of the Pt-CeO(x) NW interface similarly to Pt-CeO(x) NP/C. It is concluded that the formation of both Frenkel defect clusters and Schottky defect clusters at the Pt-CeO(x) NW heterointerface contributes to the promotion of ORR activity and permits the use of lower Pt-loadings in these electrocatalysts.

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)

A bias application system for tracking electrochemical reactions by x-ray photoelectron spectroscopy (XPS) is constructed using a laboratory-based apparatus. A specialized sample holder and stage with three electrical terminals provide contacts to a potentio-galvanostat on the outside, allowing bias application to an electrochemical device in the analysis chamber under vacuum conditions. The application of a direct current bias voltage to the sample holder is confirmed using metal Au samples. The Au 4f peaks from the Au grounded to the analyzer are identical, while those from the Au insulated from the analyzer shift due to the applied bias voltage. Furthermore, galvanostatic lithiation/delithiation processes and in situ XPS measurements are performed on a Si thin-film electrode after transferring the sample into the XPS apparatus without exposure to open air using a newly developed transfer vessel. After the initial lithiation process, a Li 1s peak containing a lithium-silicide component appears, and the Si 2p peaks shift to a lower binding energy due to the lithiation of the Si electrode. After the subsequent delithiation process, the Si 2p peak from the lithium silicide partially shifts back to a higher binding energy. As a result, in situ XPS measurements of the lithiation/delithiation reactions are successfully performed using the developed system.

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 X-ray photoelectron spectroscopy (XPS) requires a vacuum (Chap. 132 X-ray Photoelectron Spectroscopy), in situ electrochemical (EC-) XPS has been a long-standing dream not only for fundamental science, but also for a wide range of applications including fuel cells, rechargeable batteries, photocatalysts, and biological processes. In the present chapter, various in situ EC-XPS systems are introduced.

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.

The Mg doping efficiency is found to be drastically enhanced in the p-GaN films grown on the free-standing GaN substrates by metal organic chemical vapor deposition. The free hole concentrations are five and ten times higher in the lightly and heavily Mg-doped homoepitaxial p-GaN, respectively, than those in the p-GaN-on-GaN/sapphires grown and activated at the same conditions although the Mg incorporation concentrations {[Mg]} are much lower. The indication of the p-type conductivity in the photoluminescence spectra at room temperature in p-GaN-on-GaN substrates is found to be the dominant ultraviolet luminescence band located at around 3.26 eV. This behavior is different in the heteroepitaxial p-GaN, for which the fingerprint of the p-type conductivity is the emergence of blue luminescence bands at around 2.9 eV. The markedly enhanced activation efficiency is attributed to the suppression of self-compensation centers in the high-quality homoepitaxial films. The Mg-Ga-O disordered layer, which is typically observed on the surface of p-GaN-on-GaN/sapphires due to the Mg diffusion along edge-type dislocations, is also inhibited on the homoepitaxial p-GaN film, which is beneficial for the stable operation of the vertical-type metal-oxide-semiconductor field effect transistors.

Understanding of the adsorbed structure of ionomers on the Pt electrocatalyst and carbon support surfaces are very important to improve the cell performance of polymer electrolyte membrane fuel cells (PEMFCs). The effect of the solvent composition and temperature on the adsorbed structure of ionomers have been studied by using various techniques, such as 19F nuclear magnetic resonance (19F NMR) spectroscopy, cryogenic scanning electron microscopy (cryo-SEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), and electron spin resonance (ESR) techniques. However, it has not been fully clarified yet, due to the complexity of the system composed of a variety of ingredients including the Pt electrocatalyst, carbon support, ionomers, solvent and other contaminants. Thus, we have investigated the adsorbed structure of ionomers on the Pt(111) surface as a model of an electrocatalyst by using atomic force microscopy (AFM) at various solvent compositions. A droplet of aqueous solutions of Nafion was placed on Pt (111) surfaces mounted on the AFM sample holder. AFM measurements were performed with Acoustic AC mode AFM using Agilent 5500 AFM microscope (Agilent Technologies, USA) with a silicon nitride cantilever. The images were recorded over a period of ~30 minutes with a scanning area of 1 µm × 1 µm. In a 2 wt% aqueous solution of Nafion, relatively small aggregates of Nafion ionomers with a height of ~2-3 nm were observed at the Pt(111) surface. Amount of adsorption increased with time and, eventually, the surface was entirely covered by randomly oriented aggregates with a thickness of ~4 nm. In a 0.2 wt% aqueous solution, aggregates larger than those observed in the 2 wt% aqueous solution were imaged, suggesting that larger aggregates were formed in the lower concentration solution. Such a concentration-dependent adsorption behavior is further discussed on the basis of solvent composition and conformation of Nafion ionomers in liquid phase. References Masuda, H. Naohara, S. Takakusagi, P. R. Singh, K. Uosaki: Chemistry Letters, 38, 884 (2009). Masuda, S. Faridah, P. Singh, H. Naohara, K. Uosaki, Journal of Physical Chemistry C, 117, 15704 (2013). Masuda, K. Ikeda, K. Uosaki, Langmuir, 29, 2420 (2013).

Hydrogen is the most important clean fuels in the future and production of hydrogen from water by solar energy is required. Photoelectrochemical (PEC) and photocatalytic decomposition of water has been studied for long time. Most serious problem of PEC production of hydrogen from water is that while semiconductor electrodes with small energy gap can absorb large fraction of solar energy but unstable, those with large energy gap are stable but can absorb only small fraction of solar energy. This can be solved by using semiconductor of small gap and separating the reaction site from the surface. We have constructed viologen molecular layer on hydrogen terminated Si(111) surface and then Pt complex was introduced within the molecular layer by ion-exchange reaction [1-3]. Significant decrease of overpotential for dark hydrogen evolution reaction (HER) at n-Si electrode was observed by this modification. Further improvement was achieved by constructing multi-viologen-Pt -layers. Viologen layers and Pt species act as electro relay and HER catalyst, respectively. Phoelectrochemical HER at p-Si(111) electrode is also accelerated by the modification with viologen-Pt layers. In situ XAFS study during HER showed that Pt complexes not Pt particles acted as HER catalysts, i.e., confined molecular catalysts, as schematically shown in the figure [3]. The decrease of white line intensity suggests the formation of a hydride complex as an intermediate of HER. The formation of Pt particles may have been inhibited since the complexes are separated by molecular layers. Confined molecular catalyst by viologen-Pt layers for HER was also constructed on indium tin oxide (ITO). While two redox peaks corresponding to viologen dication/ radical cation (V2+/V+•) and viologen radical cation/neutral form (V+•/V0) were observed in cyclic voltammogram (CV) of viologen monolayer modified ITO electrode without Pt complex, no redox peaks but large current due to HER was observed at viologen monolayer modified ITO electrode with Pt complex. Spectroelectrochemical measurements at constant potentials and during potential scan showed stable spectra corresponding to radical cation (V+•) and neutral form (V0) of viologen at potentials between V2+/V+• and V+•/V0 redox peaks and more negative than V+•/V0 redox peak, respectively, at an ITO electrode modified by viologen monolayer without a Pt complex but no absorption peaks corresponding to V+• or V0 at an ITO electrode modified by viologen monolayer with a Pt complex. Time-resolved spectroelectrochemical measurements, however, showed that V+• is formed upon the potentials step to the potentials more negative than V2+/ V+• redox potential and disappeared within ca. 1 ms at the ITO electrode modified by viologen monolayer with Pt complex, confirming that electron is transferred from ITO electrode to proton via viologen moiety and Pt complex [4]. By incorporating various metal complexes, not only HER but also CO2 reduction can be accelerated [5, 6] References [1] T. Masuda, K. Uosaki, Chem. Lett., 33 (2004) 788-789. [2] T. Masuda, K. Shimazu, K. Uosaki, J. Phys. Chem. C, 112 (2008) 10923-10930. [3] T. Masuda, H. Fukumitsu, S. Takakusagi, W.J. Chun, T. Kondo, K. Asakura, K. Uosaki, Adv. Mater., 24 (2012) 268-272. [4] C. Kurniawan, H. Noguchi, T. Masuda, K. Uosaki, Electrochem. Commun., 62 (2016) 56–59. [5] Y. Sun, T. Masuda, K. Uosaki, Chem. Lett., 41 (2012) 328-330. [6] T. Masuda, Y. Sun, H. Fukumitsu, H. Uehara, S. Takakusagi, W.-J. Chun, T. Kondo, K. Asakura, K. Uosaki, J. Phys. Chem. C, 120 (2016) 16200-16210. Figure 1

Lithium-ion batteries (LIBs) have been widely used for various applications including portable devices and electric vehicles. Improvement of the cyclability and capacity is an important challenge. In the manufacturing process, active materials, conductive additives and binders are mixed in a solvent at a certain ratio and the slurry is casted, dried and pressed on a metallic foil current collector to yield a composite film. The composite films are assembled together with an electrolyte solution and a separator in coin or laminate cells. The packing density and mechanical strength of each material are important parameters for the cell performance because the volume expansion and resulting mechanical stress may cause a destruction of the electrical connections between binders, current collectors and the active materials during the charge/discharge processes. Young's modulus is one of the most important mechanical properties because it is an indicator of the mechanical strain in a material under a certain amount of stress. Nanoindentation has been used to measure the Young's moduli of various materials. However, it has a few restrictions as follows: (i) sample surface has to be destructed in nanoindentation and (ii) it has a limited spatial resolution, typically a few micrometers, due to the size of the disruption. Although recent atomic force microscopy (AFM) techniques allow non-destructive and high-resolution Young's modulus mapping by measuring force curves at each point using relatively weak force of2-based positive and graphite-based negative composite electrodes before and after the charge-discharge cycles in a coin cell for a demonstration. Reference: H. Sakai, Y. Taniguchi, K. Uosaki, T. Masuda, “Quantitative cross-sectional mapping of nanomechanical properties of composite films for lithium ion batteries using bimodal mode atomic force microscopy”, 2019, 413, 29-33.

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.

Plasmonic metal nanostructures are expected to function as optical antennas that can promote photon–molecule interactions. Despite recent advancements in the field of plasmonics, it is still difficult to achieve plasmonic enhancement of the overall efficiency of photochemical reactions. Here, we compare the photocurrent generation efficiency with and without optical antennas on a same porphyrin-based molecular monolayer. The overall reaction efficiency is strongly affected by the electrochemical properties of the optical antennas. This result indicates that plasmonic enhancement of photoelectrochemical reactions must be considered with respect to both the electromagnetic design of optical antennas for the efficient capture of photon energy and electrochemical design for the suppression of undesirable reverse electron transfer.

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.

To understand how electrochemical processes proceed at electrode/electrolyte interfaces and to improve the efficiencies of these processes, it is essential to probe these processes in situ real time. Thus, the developments of in situ techniques have been carried out very intensively for a long time. Thanks to the technological advancement in electronics, optics, quantum beams, and nanomaterials, various in situ techniques, which are capable of determining molecular, geometric, and electronic structures at electrochemical interfaces, have been developed in the last several decades and they are applied to a wide range of electrochemical interfaces from both fundamental and practical points of view. Here, various in situ techniques are described with historical aspects, several key innovations related to the techniques, and a few examples for the techniques to be applied.

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.

Various interesting processes are taking place at solid–liquid interfaces, i.e., electrode–electrolyte interfaces, and therefore the electronic and geometric structures play crucial roles in those interfacial processes. X-ray absorption fine structure (XAFS) allows us to clarify not only the interfacial static structures but also the dynamic structural changes in situ and in real time, because x-rays can penetrate through the liquid phase without significant loss in intensity. In this chapter, applications of in situ XAFS to various electrode–electrolyte interfaces are briefly overviewed from the viewpoint of fundamental electrochemistry and several examples of in situ XAFS studies on electrocatalytic reactions are presented.

Conditions for electrochemical deposition of atomically flat, pseudomorphic Pt layer on Au(111) electrode surface were established based on electrochemical and in situ resonance surface X-ray scattering (RSXS) studies on potential dependence of Pt deposition. When Pt was deposited at relatively large overpotential, a three-dimensionally grown rough Pt layer was formed on a Au(111) surface. When the overpotential was very small, Pt nuclei was formed but did not grow any more. At appropriate overpotential between these two potentials, atomically flat, pseudomorphic Pt layer was grown with a layer-by-layer growth mode.

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.

Metal nanostructures have the potential to increase photon–molecule interaction efficiency due to their plasmonic antenna effect. However, plasmonic enhancement of the efficiency of photochemical reactions such as photosynthesis is rather difficult because excited molecules are easily quenched near the metal surface. Sphere–plane metal nanostructures have an advantage to reduce such undesirable contribution due to their controllability of metal–molecule interfaces. Here, structural tuning of optical antenna properties, which is indispensable for selective enhancement of photochemical reactions, is demonstrated as plasmonic enhancement of photoinduced electron transfer reactions on porphyrin-based monolayer systems using the sphere–plane nanoantennas. The efficiency of photocurrent generation was substantially enhanced in good agreement with the plasmonic resonance properties of the optical antenna. The contribution of the excited state quenching was also evaluated by comparing the enhancement factor of th...

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.

It is demonstrated that resonance surface X-ray scattering (RSXS), in which incident X-ray energy close to the Pt LIII absorption edge (11.55 keV) is used, is very useful for the determination of the structure of electrodeposited Pt thin layers on a Au(1 1 1) surface. This technique was applied to characterize the structure of electrodeposited Pt layers on Au(1 1 1) substrates prepared under two extreme conditions, which are known to provide rough and atomically flat layers. Detailed structural information was obtained by RSXS measurements and it was confirmed that the structures of the Pt layers were as reported. Pt atoms of the atomically flat monolayer were found to be situated at the threefold hollow cubic closest packing (ccp) sites of the Au(1 1 1)-(1 × 1) surface.

In recent years, five-axis controlled machine tool attracts attention from the increase in demand for improvement of productivity. Five-axis controlled machine tool which is added two axes for rotating and tilting to three translational axes, and can give arbitrary tool attitudes for a workpiece.

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.

Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface. We developed a series of ionic head groups-appended self-assembled monolayers with C2, C6, C8, and C12 space-filling alkyl chains, which capture a dendritic guest via the formation of multiple salt bridges. The guest release upon protonolysis is progressively suppressed when its distance from the background hydrophobe changes from 1.2 (C2) to 0.2 (C12) nanometers, with an increase in salt bridge strength of ~3.9 kilocalories per mole.

A photoemission microspectroscopy of 30 meV energy resolution and 0.3 μm lateral resolution has been applied to observe crystalline domains formed on a polycrystalline copper plate. Surface images based on the Shockley state specific to the (1 1 1) surface clearly showed many crystalline islands composed of the (1 1 1) surface. Similarly, surface images based on the unoccupied image-potential state were measured by employing two-photon photoemission spectroscopy. The high-energy resolution spectroscopy provides insight on the nm-scale surface morphology. The Shockley state was observed even on a poorly crystallized area, while the image-potential state was observed only on an area where mean (1 1 1) terrace length is sufficiently long.

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...

Pt-CeOx/C (1.5 ≤ x ≤ 2) electro-catalyst is one of the most promising cathode materials for use in polymer membrane electrolyte fuel cells. To clarify the microstructure of Pt-CeOx heterointerface, we prepared Pt-loaded CeOx thin film on conductive SrTiO3 single crystal substrate by using a stepwise process of pulse laser deposition method for the preparation of epitaxial growth CeOx film followed by an impregnation method which loaded the Pt particles on the CeOx film. The electrochemistry observed for the Pt-loaded CeOx thin film on the conductive single crystal substrate was examined by using cyclic voltammetry in 0.5 M H2SO4 aqueous solution, and a cross-sectional image of the aforementioned Pt-CeOx thin film electrode was observed using a transmission electron microscope. The electrochemistry observed for Pt-CeOx thin film electrode clearly showed the promotion effect of CeOx. Also, the microanalysis indicated that unique, large clusters that consisted of C-type rare-earth-like structures were formed in the Pt-CeOx interface by a strong interaction between Pt and CeOx. The present combination analysis of the electrochemistry, microanalysis, and atomistic simulation indicates that the large clusters (i.e., 12 (PtCe''-Vo(••)) + 2 (PtCe''-2Vo(••)-2CeCe')) that were formed into the Pt-CeOx interface promoted the charge transfer between Pt surface and CeOx, suggesting that the oxygen reduction reaction activity on Pt can be maximized by fabrication of C-type rare-earth-like structure that consists of the aforementioned large clusters in the Pt-CeOx interfaces.

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