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This study aims to control the structure of MXene macrostructures using individually dispersed MWCNTs to allow for scalability for various energy-related applications.

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

Cyclo-dehydrogenation is of importance to induce the planarization of molecules on noble surfaces upon annealing. In contrast to a number of successful syntheses of polycyclic aromatic hydrocarbons by forming carbon-carbon bonds, it is still rare to conduct conjugation and cleavage of carbon-nitrogen bonds in molecules. Here, we present a systematic transformation of the C-N bonds in11,11,12,12-tetraphenyl-1,4,5,8-tetraazaanthraquinodimethane as well as three other derivatives on Au(111). With bond-resolved scanning tunneling microscopy, we discovered novel the "heterocyclic segregation" reaction of one pyrazine ring with two nitrogen atoms to form two quinoline rings with one nitrogen each. Density functional theory calculations showed that the intramolecular ring-forming and -opening of N-heterocycles are strongly affected by the initial hydrogen-substrate interaction.

Electrocatalytic activities for the oxygen reduction reaction (ORR) of Au electrodes modified by as prepared and size selected (0.45–1.0, 0.22–0.45, and 0.1–0.22 µm) h-BN nanosheet (BNNS), which is an insulator, were examined in O2 saturated 0.5M H2SO4 solution. The overpotential was reduced by all the BNNS modifications, and the smaller the size, the smaller the overpotential for ORR, i.e., the larger the ORR activity, in this size range. The overpotential was reduced by as much as ∼330 mV compared to a bare Au electrode by modifying the Au surface by the BNNS of the smallest size range (0.1–0.22 µm). The overpotential at this electrode was only 80 mV more than that at the Pt electrode. Both the rotation disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements showed that more than 80% of oxygen is reduced to water via the four-electron process at this electrode. These results strongly suggest and theoretical density functional theory calculations support that the ORR active sites are located at the edges of BNNS islands adsorbed on Au(111). The decrease in size of BNNS islands results in an effective increase in the number of the catalytically active sites and, hence, in the increase in the catalytic activity of the BNNS/Au(111) system for ORR.

Although the theoretical energy densities of lithium-oxygen batteries (LOBs) far exceed those of lithium-ion batteries, the practical values of the LOBs are usually much lower because of the use of...

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...

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.

Metalloporphyrins were immobilized at single crystalline gold surfaces of (111), (100), and (110) orientations via imidazole-terminated alkanethiols. This method enabled us to simultaneously contro...

A periodicity implemented scheme of natural bond orbital (NBO) theory and normal mode analysis has been employed to investigate the tendency of the chemical bond strength of aryl isocyanide molecules with different para-substituted groups adsorbed on the Pt(111) surface. The NC bond order shows a clear correspondence with the NC stretching frequency; both of them exhibit a "volcano-like" profile as a function of the Hammett constant of the para-substituted groups for isolated molecules. When a molecule is adsorbed on the Pt(111) surface, the NC stretching frequency variations are determined by the resultant effect of sigma donation and pi back-donation between the molecule and the surface. The present comprehensive and systematic computations clarify the electron donating and withdrawing effects of the substituted groups on the interaction between the aryl isocyanide molecule and the transition metal substrate.

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 ...

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.

By the electrochemical lithiation of a Si(100) single-crystal substrate, regular quadrangular pyramidal shaped three-layered structures on Si(100) were observed in scanning electron microscopic ima...

The basic knowledge in battery research bridging the gap between academia and industry was reviewed by the authors from both fields. In the first half, the importance of three technological parameters in practical batteries is shown, i.e., (1) cathode loading, (2) anode/cathode pairing, and (3) electrolyte amount. We explain these key parameters in detail by showing several examples of the current lithium-ion batteries and lithium metal batteries in the literature with the aim of circulation of this key technological knowledge into academia, especially in the field of materials science. In order to clarify the correlation between the three key parameters and the energy density, simulations are carried out using a 1 A h pouch cell for a lithium-ion battery, i.e. graphite/LiNi0.8Co0.1Mn0.1O2 (NCM811), and three types of lithium metal batteries (Li/NCM811, Li/S, and Li/O2). The resultant energy densities, when the three key parameters are varied, are compared for these systems. In the second half, we survey representative reports on fundamental battery science mainly provided by academia, which contributed to the advancement of modern battery knowledge. However, this knowledge is necessary to be brought to our society assessed by the technological criteria used in industry, which are shown in the first half. In addition to the above discussions, we provide a cell simulator to calculate practical energy densities, which can be found as an Excel file in the ESI, and therefore it is free to access.

This work figures out the material balance of the reactions occurring in the O2 electrode of a Li–O2 cell, where a Ketjenblack-based porous carbon electrode comes into contact with a tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte under more practical conditions of less electrolyte amount and high areal capacity. The ratio of electrolyte weight to cell capacity (E/C, g A h−1) is a good parameter to correlate with cycle life. Only 5 cycles were obtained at an areal capacity of 4 mA h cm−2 (E/C = 10) and a discharge/charge current density of 0.4 mA cm−2, which corresponds to the energy density of 170 W h kg−1 at a complete cell level. When the areal capacity was decreased to half (E/C = 20) by setting a current density at 0.2 mA cm−2, the cycle life was extended to 18 cycles. However, the total electric charge consumed for parasitic reactions was 35 and 59% at the first and the third cycle, respectively. This surprisingly large amount of parasitic reactions was suppressed by half using redox mediators at 0.4 mA cm−2 while keeping a similar cycle life. Based on by-product distribution, we will propose possible mechanisms of TEGDME decomposition and report a water breathing behavior, where H2O is produced during charge and consumed during discharge.

Catalytic activity of monometric metal macrocycles for oxygen reduction reaction (ORR) was investigated using rotating disk electrode voltammetry in acidic media. Iron(II) phthalocyanines (FePc) and cobalt(II) tetraphenylporphyrins (CoTPP) were immobilized on Au surfaces through molecular wires with different terminal groups of pyridine and isocyanide. The measured ORR behavior of FePc was largely influenced by the axial ligand while CoTPP promoted only the two-electron reaction regardless of the axial ligand. The FePc immobilized with pyridine was easily detached from the surface under the ORR condition, and was able to promote the four-electron reaction only under the high overpotential application. The FePc with isocyanide was more stable with the activity for the four-electron reaction, due to stronger electron donation to Fe central ions.

Although the market share for Li-ion batteries (LiBs) has continuously expanded, the limited theoretical energy density of conventional LiBs will no longer meet the advanced energy storage requirements. Lithium-air batteries (LABs) are potential candidates for next-generation rechargeable batteries because of their extremely high theoretical energy density. However, the reported values for the actual energy density of LABs are much lower than those for LiBs, mainly due to the excess amount of electrolyte in the cell. In the present review article, the practical energy density is estimated for the representative LABs reported in academia, and the critical factors for improving the energy density of LABs are summarized. The criteria for evaluating LABs in laboratory-based experiments are also proposed for accurately predicting the performance of practical cells in industry.

Photoelectrochemistry, semiconductor electrochemistry, and/or photocatalysis are of active research fields and thousands of papers are published in these fields annually. Many research groups are attracted in these subjects because of their potential importance in achieving carbon neutral society based on solar energy, a renewable energy. Although semiconductor electrochemistry had been studied systematically since 1950's and many reviews and books were published by early 1970's,1-7 research on photoelectrochemistry became very active in the late 1970's after the 1st oil crisis triggered by the paper by Fujishima and Honda,8 in which they suggested that solar energy may be directly converted to a chemical energy, hydrogen, by using semiconductor/aqueous electrolyte solution/metal cells.8 Research activities were high in 1980's and the ECS has organized symposia on photoelectrochemistry/semiconductor electrochemistry in the annual meetings many times with the publications of proceeding volumes.9-14 Many important developments were made in the 1970's and 1980's. Major target of the photoelectrochemistry/photocatalysis research changed from solar energy conversion to environmental issues12, 13 and activities gradually declined due to the lack of funding, particularly in the US. There must be reasons why photoelectrochemistry lost supports as solar energy conversion process in 1990's and it is a good time to look back what had been achieved, what were the problems, and are these problems solved by now. In this talk, I will try to sum up the results achieved by 1990's and compare them with current activities. References 1. M. Green, in Modem Aspects of Electrochemistry, No. 2. Ed. by J. O'M. Bockris, Butterworths, London, 343-407 (1959). 2. J. F. Dewald. in Semiconductors. ACS Monograph, No. 140, Ed. by N. B. Hannay, Reinhold, New York, 727-752 (1959). 3. H. Gerischer. in Adv. Electrochem. Electrochem. Eng., Vol. 1, Ed. by P. Delahay, lnterscience, New York, 139-232 (1961). 4. P. J. Holmes. Ed., The Electrochemistry of Semiconductors, Academic. London, 1962. 5. V. A. Myamlin and Yu. V. Pleskov, Electrochemistry of Semiconductors. Plenum, New York. 1967. 6. H. Gerischer, in Physical Chemistry: An Advanced Treatise, Vol. IXA. Ed. by H. Eyring. Academic. New York. 1970, Chap. 5. 7. S. R. Morrison, Prog. Surf. Sci., 1(1971) 105. 8. A. Fujishima and K. Honda, Nature, 238 (1972) 37. 9. PV 77-3, "Semiconductor Liquid-Junction Solar Cells", Ed. by A. Heller. 10. PV 82-3, "Photoelectrochemistry: Fundamental Processes and Measurement Techniques. Ed. by W. L. Wallace, A. J. Nojik, and S. K. Deb. 11. PV 88-14, "Photoelectrochemistry and Electrosynthesis on Semiconducting Materials", Ed. by D.S. Ginley, A. Nojik, N. Armstrong, K. Honda, A. Fujishima, T. Sakata, and T. Kawai. 12. PV 93-18, Environmental Aspects of Electrochemistry and Photoelectrochemistry'', Ed. by M. Tomkiewicz, H. Yoneyama, R. Haynes, and Y. Hori. 13. PV 94-19, "Water Purification by Photocatalytic, Photoelectrochemical, and Electrochemical Processes", Ed. by T. L. Rose, E. Rudd, 0. Murphy, and B. E. Conway. 14. PV 97-20, "Photoelectrochemistry", Ed. by K. Rajeshwar, L. M. Peter, A. Fujishima, D. Meissner, and M. Tomkiewicz.

Li metal batteries are revived as the next-generation batteries beyond Li-ion batteries. The Li metal anode can be paired with intercalation-type cathodes LiMO2 and conversion-type cathodes such as sulfur and oxygen. Then, energy densities of Li/LiMO2 and Li/S,O2 batteries can reach 400 Whkg−1 and more than 500 Whkg−1, respectively, which surpass that of the state-of-the-art LIB (280 Whkg−1). However, replacing the intercalation-type graphite anode with the Li metal anode suffers from low coulombic efficiency during repeated Li plating/stripping processes, which leads to short cycle lifetime and potential safety problems. The key solution is to construct a stable and uniform solid electrolyte interphase with high Li+ transport and high elastic strength on the Li metal anode. This review summarizes recent progress in improving the solid electrolyte interphase by tailoring liquid electrolytes, a classical but the most convenient and cost-effective strategy.

The influence of pre-coating Li7La3Zr2O12 (LLZ) with Au on the charge transfer resistance (Rint) at the interface of LLZ and lithium (Li) is examined by AC impedance spectroscopy using a three-electrode system. The Au diffuses into Li after physical contact with Li, and the open-circuit potential reaches approximately 0 mV (vs. Li/Li+) accompanied by a decrease in Rint. During the Li dissolution/deposition cycles, the electrode potential changes with 0 mV as the central potential, indicating that Li metal dissolution/deposition on Li metal proceeds predominantly at the interface. Rint increases and decreases during Li dissolution and deposition, respectively, regardless of the presence or absence of the Au coating; however, the increase in Rint during Li dissolution is suppressed at the Li/Au-coated LLZ (Au-LLZ) interface. The decreased Rint is considered to be due to an increase in the effective contact area at the electrode/LLZ interface, which is achieved by pre-coating Au onto the LLZ surface.

Nano-structured silicon anodes are attractive alternatives to graphite in lithium-ion batteries; however, despite recent progress in nano-engineered composites, its use remains limited. One of the issues, particularly in silicon-dominated anodes, is the poor Coulombic efficiency of lithium–silicon processes. Previous studies have shown that repeating the amorphous–crystalline hysteretic lithium–silicon phase transformations can abruptly improve irreversibility and eventually minimize cumulative irreversible lithium consumption in exchange of certain parasitic capacity sacrifice. Here, we reveal mechanism behind the phenomenon that the single phase transformation spontaneously and pseudo-topologically transforms nano-structured silicon into quantum-scale frameworks without gravimetric loss. The way it forms is clearly distinct from ever explored formation mechanism of porous nano-structures such as (electro)chemical etching, Kirkendall voiding, and percolation theory. Further, we implanted the structural transformation feature into lithium-ion full cells, largely redesigning the conventional one, by modulating cathode/anode capacity loading balance and prelithiation dose in the anode to embed the unique feature in the cells. We show that the cell preferentially triggers the efficient irreversibility-depletion phenomenon upon cycling and consequently outperforms conventional silicon-based cells.

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.

Kinetics of platinum monolayer formation via the redox replacement of underpotentially deposited copper on a Au(111) electrode surface by a platinum tetrachloride complex (PtCl42–) was studied by voltammetry, X-ray photoelectron spectroscopy (XPS), electrochemical quartz crystal microbalance (QCM), energy-dispersive spectroscopy (EDS), and scanning tunneling microscopy (STM). The Pt 4f7/2 peak intensities of XPS and voltammetric responses of H adsorption/desorption increased as the incubation time increased in PtCl42– solutions. The resonance frequency of the Cu/Au QCM in 0.05 M H2SO4 solution was observed to quickly decrease within 1 min when it contacted with PtCl42– solutions, and then it remained unchanged for hours. EDS data showed that Cu was not found at high PtCl42– solutions. Ex situ STM images revealed a largely uncovered Au(111) surface with mountain-like Pt nanoparticles at a replacement time of 10 min, and mostly covered Au(111) one with plain-like Pt nanoparticles of 4 h. The average size of...

The role of an inhibiting additive in selective copper (Cu) deposition was investigated using linear sweep and cyclic voltammetry and in situ SERS. Both the normalized SERS peak intensity of Basic Red 12 and the Cu deposition current showed hysteresis. These results indicate that Basic Red 12 desorbs or decomposes on the surface during electrodeposition of Cu. Therefore the concentration of Basic Red 12 on the patterned area decreases more than that on the flat area. This inhomogeneity of concentration leads to the preferential growth of Cu on the patterned area. Keywords: Anisotropic deposition, Selective deposition, Copper electroplating, Overburden, Copper interconnects

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

Lithium-air battery (LAB) is considered to be one of the most promising energy storage devices because of its large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use. Here we employed X-ray CT to monitor the structural development of laminated cell of lithium air batteries without dismantling the cells. The results are compared with those of SEM/EDS and FIB-SEM/EDS analyses, which were carried out after dismantling the cells. Figure 1 shows XCT images of cross section and slice of laminated cell of lithium air battery after several discharge/charge cycles. Each component is well resolved. Figure 2 shows XCT images of cross section of laminated cell of lithium air battery (a) as prepared, and after (b) one, and (c) ten discharge/charge cycles. It is clear lithium became porous even just after one cycle. The porous layer became much thicker after 10 cycles. For detailed understanding of the structure of the porous layer of lithium, the cells were dismantled and were subject to SEM/EDS and FIB-SEM/EDS analyses. Degradation of lithium layer was much less significant if the anode and cathode were separated by solid electrolyte (Ohara). Detailed results and advantages of XCT will discussed. 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

This work figures out the material balance of the reactions occurring in the O

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.

Nitridated carbon (NC) catalysts have attracted considerable interest as promising Pt-free alternatives to standard Pt/C catalysts in the oxygen reduction reaction (ORR). Aiming at a better understanding of the microscopic reaction mechanism and of the nature of the reaction-limiting step, we have investigated the ORR kinetics and in particular the kinetic isotope effects (KIEs) therein for three different NC catalysts with different nitrogen contents. The measurements were performed using ordinary and deuterated water electrolytes, under both alkaline and acidic solutions. From an analysis of the ORR kinetics on the most active NC-I catalyst, including the kH/kD ratio and the transfer coefficients, and from density functional theory (DFT) based computations, we derive that the initial proton-coupled electron transfer (PCET), whose process is to form OOH* from O2*, acts as the potential-determining step (PDS) under acidic conditions and the initial electron transfer, whose process is to form (O2•–)* from ...

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.

Because of its exceptional lithium storage capacity, silicon is considered as a promising candidate for anode material in lithium-ion batteries (LIBs). In the present work, we demonstrate that methods of soft X-ray emission spectroscopy can be used as a powerful tool for the comprehensive analysis of the electronic and structural properties of lithium silicides LixSi forming in LIB’s anode upon Si lithiation. On the basis of density functional theory and molecular dynamics simulations, it is shown that the coordination number of Si atoms in LixSi decreases with an increase in Li concentration both for the crystalline and amorphous phases. In amorphous a-LixSi alloys, Si tends to cluster, forming Si–Si covalent bonds even at the high lithium concentration. It is demonstrated that the Si-L2,3 emission bands of the crystalline and amorphous LixSi alloys show different spectral dependencies, reflecting the process of disintegration of Si–Si network into Si clusters and chains of the different sizes upon Si li...

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.

Dynamic changes in the charge-transfer resistance at a Li/Li 7 La 3 Zr 2 O 12 (LLZ) interface during lithium (Li) dissolution/deposition cycles are investigated with an alternative current (AC) impedance technique in a three-electrode system. The resistance respectively increases and decreases during electrodissolution and electrodeposition of Li. The resistance does not return to the initial value after one cycle of Li dissolution and deposition, which indicates that the change in resistance during dissolution is larger than that during deposition. Furthermore, the resistance is almost constant when Li deposition proceeds without prior Li dissolution. The respective increase and decrease in the interfacial resistance during Li dissolution and deposition is most likely due to the formation and disappearance of voids at the Li/LLZ interface, and the voids formation during Li dissolution is suggested to be a critical factor that influences the interfacial resistance.

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.