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Most degradation compounds of TEGDME in lithium oxygen batteries were generated during charge and molecules generated during charge were decomposed during discharge.

Interfacial water plays an essential role in natural phenomena and scientific applications despite causing many economic losses. Therefore, its real monitoring is no question mandatory; however, suitable techniques are quite rare and/or with limitations.Moisture Sensor (MS) was used to detect the galvanic response current arising from the stacked interfacial water molecules between two dissimilar electrodes under controlled relative humidity (RH). Simultaneously, the frequency response was detected using QCM sensor as a quantitative tool. Bare and Hydrophilic (HP) sensor surfaces were used to examine the surface wettability. Moreover, sum frequency generation (SFG) was used to investigate the qualitative formation and the nature of stacked interfacial water molecules on bare and HP modified surfaces of quartz prism.Results revealed that, response current and frequency change were increased as the number of stacked water molecules increased. Correlating response current and frequency gave a clear quantitative estimation of stacked water molecules on the sensors' surfaces. Interfacial water molecules possessed strong H-bonding nature at the bare prism surface whereas, strong and weak H-bonding were existing at the HP/prism surface. Such findings provide feasible evaluation for the galvanic current source due to stacked interfacial water molecules at different levels of RH.

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.

CO2 emissions are a major factor that contributes to global warming and climate change. Therefore converting CO2 to useful chemicals that can be used for energy or industrial needs is essential. Electrochemical reactions (ECRs) with Pt electrodes have been extensively studied for CO2 reduction and have shown to heavily favor the hydrogen reduction reaction but there has been a dispute as to whether the addition of pyridine enhanced the production of organic compounds. In-situ use of Sum Frequency Generation spectroscopy during the ECR of CO2, shows that intermediates and products for organic product formation do not appear at the reaction interface and that pyridine most likely lays flat on the catalytic surface possibly blocking CO2 adsorption sites.

Rechargeable lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. Despite significant efforts by many research groups, LAB is still far from practical use and many problems must be overcome [1]. The first problem is associated with the use of air as it contains many components other than oxygen including N2, water, and CO2, which interfere battery reactions. Thus, most of the fundamental studies are not on LAB but on Lithium-oxygen battery (LOB), which uses pure oxygen as an active material. Even LOB has many serious problems, including low cyclability caused by (1) high charging overpotential, which induces degradation of positive electrode (carbon) and electrolyte solution, and (2) degradation/dendrite formation of negative Li metal electrode. To improve the cyclability, it is essential to clarify the mechanism of degradation of electrodes and electrolyte. Here we employed mass spectroscopy to follow products generation during charging so that we can clarify the degradation mechanisms of electrodes and electrolyte. Porous carbon sheet (KJCNT from KJ Specialty Paper), lithium metal (Honjo Metal), 1 M LiTFSI TEGDME (both from Sigma-Aldrich) solution, PE separator (W-Scope), and stainless steel mesh (Hohsen) were used as positive electrode, negative electrode, electrolyte, separator, and gas diffusion layer, respectively. Isotope exchanged TEGDME, i.e., 13CH3-TEGDME and CD3-TEGDME, which were synthesized in our laboratory, and 18O2 (Taiyo Nippon Sanso) were used for mass spectroscopy for precise products assignments. Details of set-up for mass analysis have been reported elsewhere [2]. We carried out online QMS (Quadrupole Mass Spectrometer) measurement for mass numbers of decomposition products between 12-90 during the potential sweep from OCP to 4.8 V (0.05 mV/s). Figure 1 shows the current and mass signals of m/z = 18 (H2O), 32 (O2), and 44 (CO2) as a function of potential. It is clear that current increased immediately as potential was scanned from OCP (~2.8 V ), reached a maximum at 3.3 V, decreased gradually, reached a minimum at 4.0 V, increased again to reach a maximum at 4.4 V, decreased to reach a minimum at 4.6 V and increased again. The potential dependence of O2 signal is very similar to that of current as the main battery reaction is Li2O2 → 2Li+ + O2 + 2e-. Two clear peaks were observed at around 3.3 V and 4.4V, showing the presence of two kinds of Li2O2 [3]. The H2O signal started to increase just after the 1st current/O2 peaks where the current efficiency for O2 generation current efficiency started to decrease, suggesting the H2O formation is related to the decrease of the current efficiency. The CO2 signal started to be significant at 4.1 V where current and the O2 signals started to increase again and reached a maximum at ca. 4.5 V, which is more positive than those of current and O2 signal but equal to H2O peak. Although current increased again significantly at potentials more positive than 4.65 V, no mass signals of O2, H2O and CO2 increased. Instead signals such as m/z = 15, 29, 31, 45, and 60, which are related to organic molecules derived from TEGDME, became significant. Figure 2 shows the online QMS results at 4.65 V. We can see that various mass signals such as 15, 29, etc. were observed at this potential. By careful analysis of the results with the assistance of isotopes 18O2, 13CH3-TEGDME, and CD3-TEGDME, presence of CH3OH, HCHO and other organic molecules with high vapor pressure originated from TEGDME were confirmed. Additionally, we detected molecules with low vapor pressure such as CH3O(CH2)2OH, CH3OCH2COCH3, etc., which were derived from TEGDME by GC/MS analysis of samples collected every 1hr. Based on the products detected by online QMS and GC/MS, possible degradation mechanism of electrolyte can be deduced. I will discuss the degradation mechanism of electrolyte based on the above results. [1] Liu T., et al. Current challenges and routes forward for nonaqueous lithium–air batteries. Chemical reviews, 2020, 120(14): 6558-6625. [2] Ue, M., et al. Material balance in the O2 electrode of Li–O2 cells with a porous carbon electrode and TEGDME-based electrolytes, RSC Advances, 2020, 10(70): 42971 - 42982. [3] Nishioka K, et al. Isotopic depth profiling of discharge products identifies reactive interfaces in an aprotic Li–O2 battery with a redox mediator. Journal of the American Chemical Society, 2021, 143(19): 7394-7401. Figure 1

The selectivity rules of sum frequency generation spectroscopy were exploited to determine propyl chain order during the time-dependent oscillatory adsorption of propyltrimethoxysilane (PTMS) and Langmuir-type growth of propyldimethylmethoxysilane (PDMMS). During the early stages of film growth, molecular packing density determines the extent of propyl chain defects within both films with high surface coverage resulting in a film with fewer defects. Following this, an ordered monolayer-like film stabilizes on the Al2O3 substrate for both silanes. Although this result is intuitive for the Langmuir-type growth of PDMMS, the stabilization of molecular ordering despite the continuing oscillation in PTMS surface coverage indicates the presence of a stable monolayer, while it is the oligomerized PTMS dendrimers which continue to desorb and readsorb to the substrate. We also reveal for the first time, the formation of a physisorbed bilayer during the self-assembly process of PTMS. The presence of this ordered, physisorbed bilayer on top of the covalently bound PTMS film plays a key role in the process of the molecular self-assembly mechanism and is proposed to enable further condensation of the covalently bound film.

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 Li

Among the various fuel cell electrocatalysts studied for the cathodic oxygen reduction reaction and anodic fuel oxidation reaction, platinum-based materials have attracted much attention over the past decade because of their high activity for both reactions. However, Pt-based catalysts suffer from several problems, such as their high cost, low abundance, and low long-term stability. Bimetallic Pt-based nanostructures with a core–shell structure have been considered as candidate cathode catalysts for polymer electrolyte fuel cells. In this study, a Pt/Pd/C catalyst was successfully synthesized by the hydrogen-sacrificial protection method to improve the performance of a membrane electrode assembly. Furthermore, on the basis of electrochemical spectroscopic findings, it was shown that control of the surface structure is an effective strategy to improve the cell performance of the Pt/Pd/C catalyst.

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.

Gold is known to be a poor electrocatalyst for oxygen reduction reaction (ORR) in acidic solution as oxygen is reduced to H2O2 by 2-electron process with high overpotential at a Au electrode. We found that the overpotential for ORR is decreased by the modification of the Au electrode with boron nitride nanosheet (BNNS), an insulator, but ORR still proceeds by 2-electron process. We have recently demonstrated that the decoration of BNNS by gold nanoparticles (AuNPs: 5–30 nm) opens a 4-electron ORR route to water, although only ca. 50% of oxygen is reduced to water. Here, we report that more than 80% of oxygen is reduced to water at the Au electrode modified by BNNS decorated with AuNPs of small size (ca. 5 nm) with narrow size distribution. Furthermore, the ORR overpotential is much less than that at the Au electrode modified by BNNS decorated with AuNPs of random size (5–30 nm) by 100–120 mV and is only 100 mV more than that at a Pt electrode.

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.

There is no clear consensus on the exact compounds that are generated during the room temperature lithiation of Si, which may include amorphous LixSi or a crystalline Li15Si4 alloy. Here, the lithiation behavior of a single-crystal Si(1 1 1) anode was studied using scanning electron microscopy (SEM), soft X-ray emission spectroscopy (SEXS), and windowless energy dispersive X-ray spectroscopy (EDS). A Li-Si alloy generated electrochemically via potentiostatic lithiation was found to have a layered structure that contained the 1st layer of crystalline Li15Si4 (c-Li15Si4) alloy pyramids, the 2nd layer of amorphous Li13Si4 (a-Li13Si4) alloy, and the 3rd layer of Li-diffused LixSi alloy. A maximum cathodic current appeared during this process, and both the c-Li15Si4 and Li-diffused LixSi alloys were observed to grow during the initial lithiation and to maintain almost constant thicknesses prior to reaching the maximum current, while the 2nd layer began to grow after the maximum current. Comparing the experimental and theoretical currents showed that the lithiation of crystalline Si is diffusion-controlled. The low Li diffusion coefficients in the bulk LixSi alloy and bulk Si evidently result in a low current density during Si lithiation.

In situ broad band sum frequency generation (SFG) spectroscopy was applied to clarify the oxidation mechanism of adsorbed CO on Pt(1 1 1) electrode in alkaline solution in comparison with that in acidic solution. A single SFG peak due to CO adsorbed on-top site of Pt(1 1 1) was observed in the region of 1950 – 2150 cm−1. While oxidation of adsorbed CO proceeded in a nucleation-growth mode via Langmuir–Hinshelwood (L-H) mechanism by reacting with adsorbed OH in the main peak region in 0.1 M HClO4 solution, adsorbed CO was oxidized in a random oxidation model via Eley-Rideal (E-R) mechanism by reacting with OH− in the solution in the pre-peak region in 0.1 M NaOH solution. The main anodic peak was still observed even after the SFG peak due to on-top CO was totally disappeared by anodic oxidation in the pre-peak region, showing there existed SFG inactive adsorbed CO, although its structure was not clear.

Electrochemical cyclic voltammetry and potential dependent double resonance sum frequency generation (DR-SFG) spectroscopy were performed on CO adsorbed on polycrystalline Pt and Pt(111) electrodes in H 2 SO 4 solution to examine the effect of substrate on the electronic structure of CO. The dependence of SFG intensity on potential and visible energy for atop CO band was observed on both polycrystalline and single crystalline Pt electrodes. Enhancement of the SFG intensity was determined to be a direct result of a surface electronic resonance of the visible/SF light with the electronic transition from Fermi level of Pt to the 5σ a anti-bonding state of adsorbed CO, in agreement with previous results. Interestingly, when compared to the Pt(111) electrode, the distribution width of the intensity enhancement region on polycrystalline Pt is broader than on Pt(111). This suggests that the energy distribution of the 5σ a state of CO on polycrystalline Pt surface is broader than that on Pt(111) due to the complex surface structure of the polycrystalline Pt electrode.

In vivo, cells are immersed in an extracellular solution that contains a variety of bioactive substances including ions and water. Classical electrophysiological analyses of epithelial cells in the stomach and small intestine have revealed that within a distance of several hundred micrometers above their apical plasma membrane, lies an extracellular layer that shows ion concentration gradients undetectable in the bulk phase. This “unstirred layer”, which contains stagnant solutes, may also exist between the bulk extracellular solution and membranes of other cells in an organism and may show different properties. On the other hand, an earlier study using a bacterial planar membrane indicated that H+ released from a transporter migrates in the horizontal direction along the membrane surface much faster than it diffuses vertically toward the extracellular space. This result implies that between the membrane surface and unstirred layer, there is a “nanointerface” that has unique ionic dynamics. Advanced technologies have revealed that the nanointerface on artificial membranes possibly harbors a highly ordered assembly of water molecules. In general, hydrogen bonds are involved in formation of the ordered water structure and can mediate rapid transfer of H+ between neighboring molecules. This description may match the phenomenon on the bacterial membrane. A recent study has suggested that water molecules in the nanointerface regulate the gating of K+ channels. Here, the region comprising the unstirred layer and nanointerface is defined as the interphase between the plasma membrane and bulk extracellular solution (iMES). This article briefly describes the physicochemical properties of ions and water in the iMES and their physiological significance. We also describe the methodologies that are currently used or will be applicable to the interphase research.

Biphenyl-2,2'-diylbis(10-methyl-9-methyleneacridan)-type electron donor 1, which has two tethered cyclic disulfide units at the 6,6'-positions, was designed and synthesized as the first member of a dynamic redox (dyrex) system that can form molecular layers on a Au(111) electrode. Upon the two-electron (2e) oxidation of 1, persistent dicationic dye 22+ was generated with the formation of a new C-C bond, which is reversibly cleaved upon 2e reduction to regenerate 1 (dyrex behavior). Similar dyrex interconversion occurs in the molecular layer on gold. The chemical identities of 1/Au and electrochemically generated 22+/Au were unambiguously determined by in situ IR spectral measurement under the attenuated total reflection mode. In situ scanning tunneling microscopy (STM) was conducted under electrochemical conditions to examine the surface structure of 1 adsorbed on a Au(111) electrode. Although no long-range ordered morphology was found in the STM image of 1, an in situ STM study of the potential-induced dyrex reaction of 1 to 22+ showed that the grained spots in the image became slightly brighter.

Overpotential for oxygen reduction reaction (ORR) at Au electrode is reported to be reduced by 0.27 V by the modification with boron nitride nanosheet (BNNS) but oxygen is reduced only to H2O2 by 2-electron process at Au electrode. Here we demonstrate that the decoration of BNNS with gold nanoparticles (AuNP) not only reduces the overpotential for ORR further by ca. 50 mV, but also opens a 4-electron reduction route to water. Both rotating disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements show that more than 50% of oxygen is reduced to water via 4-electron process at Au–BNNS/Au electrode while less than 20 and 10% of oxygen are reduced to water at the BNNS/Au and bare Au electrodes, respectively. Theoretical analysis of free energy profiles for ORR at the BN monolayer with and without Au8 cluster placed on Au(111) shows significant stabilization of adsorbed oxygen atom by the Au8 cluster, opening a 4-electron reduction pathway. Keywords: Fuel cell, Boron nitride, Oxygen reduction reaction, Gold nanoparticle, Gold electrode

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...

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

Pt–Ru/SnO2/C catalysts were prepared by a rapid quenching method. The structure and morphology of Pt–Ru particles in Pt–Ru/SnO2/C are controlled to obtain the same Pt–Ru particle as that in a commercial Pt–Ru catalyst. The Pt–Ru/SnO2/C and commercial Pt–Ru catalysts were characterized by X-ray diffraction and scanning transmission electron microscopy. Electrochemical activities were evaluated by CO stripping voltammetry, single cell tests, in situ infrared reflection–absorption spectroscopy (IRRAS) and surface-enhanced infrared absorption spectroscopy (SEIRAS). The Pt–Ru/SnO2/C catalyst showed the same structure, morphology and catalytic activity for hydrogen oxidation reaction (HOR) in the absence of CO as those of a Pt–Ru/C catalyst. Both the activity for electrochemical CO oxidation and Pt–CO bond strength were quantitatively evaluated. The addition of SnO2 decreased the Pt–CO bond strength with maintained HOR activity to enhance CO tolerance.

Since the surface is buried in liquid, electrochemical surface science is complicated. Therefore, one cannot benefit from the electron-based techniques mainly used in ultra-high vacuum (UHV) to study the structure and composition of surfaces since the mean free path of the electrons in dense media, i.e., water, is rather limited.

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...

A silane coupling agent having a zwitterionic end group was covalently bound to a semi-cylindrical fused silica prism for sum-frequency generation (SFG) analyses and to a flat glass for estimating biological affinity. It was found that total intensity of the -derived from water in contact with a positively or negatively charged SAM-modified surface and a bare silica prism. These results indicated that water molecules in the vicinity of the zwitterionic SAM-modified surface are not strongly oriented in comparison with those of lopsidedly charged SAMs and bare silica. Moreover, the zwitterionic SAM surface suppressed non-specific adsorption of bovine serum albumin in contrast to the significant adsorption to lopsidedly charged SAMs and the bare cover glass. On the other hand, fibroblasts gradually adhered to the SAM surfaces and extended regardless of the electrical charge of the SAM, though the number of cells that adhered to the zwitterionic SAM was the smallest. The results strongly suggested that the charge neutralization of a solid material surface is very important for anti-biofouling properties.

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...

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

Novel intermetallic TaPt3 nanoparticles (NPs) are materialized, which exhibit much higher catalytic performance than state-of-the-art Pt3Sn NPs for electrooxidation of ethanol. In situ infrared-reflection-absorption spectroscopy (IRRAS) elucidates that the TaPt3 NPs cleave the C–C bond in ethanol at lower potentials than Pt NPs, efficiently promoting complete conversion of ethanol to CO2. Single-cell tests demonstrate the feasibility of the TaPt3 NPs as a practical energy-extraction catalyst for ethanol fuels, with more than two times higher output currents than Pt-based cells at high discharge currents.

Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI

Many important processes such as electrochemical reactions, biological processes, and corrosion are taking place at solid/liquid interfaces. To precisely understand the mechanism of these processes at solid/liquid interfaces, information on structures of molecules at electrode/electrolyte interface including short-lived intermediates and solvent at the interface is essential. The determination of the interfacial structures of the intermediate and solvent is, however, difficult by conventional surface vibrational techniques because the number of molecules at the interfaces is far smaller than those of bulk molecules.

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 electrocatalytic activities of various types of h-BN, i.e., spin coated BN nanotubes (BNNTs) and BN nanosheets (BNNSs) and sputter deposited BN, on Au electrodes as well as those of BNNS modified glassy carbon (GC) and Pt electrodes for the oxygen reduction reaction (ORR) were examined in O2 saturated 0.5 M H2SO4 solution based on the theoretical prediction that monolayered BN on a metal substrate may act as an electrocatalyst for ORR even though bulk BN is an insulator with a wide band gap. The overpotential for ORR at Au electrodes was reduced by ca. 100, ca. 270, and ca. 150 mV by spin coating of the dispersion of BNNT and liquid exfoliated BNNS, and sputter deposition of BN, respectively, proving the theoretical prediction. On the other hand, no change in the overpotential was observed at the glassy carbon electrode with BNNS modification and the overpotential even increased at the Pt electrode, suggesting that the interaction between BN and Au plays an important role in BN becoming ORR active.

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

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

The ultrafast carrier dynamics of GaAs(1 0 0) surfaces passivated with different sulfide solutions is studied by time-resolved measurements of infrared absorption using the femtosecond visible-pump infrared-probe technique. After passivation of n-GaAs(1 0 0) surface with the solution of ammonium sulfide in 2-propanol the three-fold decrease of the surface recombination velocity is observed. The treatment of the n-GaAs(1 0 0) surface with the aqueous sulfide solution has a smaller impact on the surface recombination velocity. The different effect of aqueous and alcoholic sulfide solutions on the efficiency of surface passivation is caused by the different mechanisms of charge transfer at the semiconductor/solution interfaces.

Humidity-dependent water structures at the interfaces between perfluorosulfonate ionomer (PFSI = Nafion) thin film and Pt and HOPG were determined at room temperature by using sum frequency generation (SFG) spectroscopy. At low relative humidity (RH) condition, a peak centered around 3600 cm−1 corresponding to water molecules interacting with sulfonic acid group in proton channel at PFSI surface was observed at both interfaces. However, while this peak increased with RH at PFSI/Pt interface, that at PFSI/HOPG did not increase. These results suggest that the structure of water molecules, especially the water molecules at the proton channel of PFSI surface, is strongly affected by the interaction of PFSI with Pt and HOPG. Keywords: Fuel cell, PEM, Perfluorosulfonated ionomer, Interfacial water, Sum frequency generation spectroscopy