Electrode Surface Structure Research Articles

Electrochemical degradation of reactive brilliant red X-3B with the (CeO2/C)-β-PbO2-PTFE composite electrode

The (CeO2/C)-β-PbO2-PTFE composite electrodes modified by graphite powder, cerium oxide powder, polytetrafluoroethylene (PTFE) and the homemade β-PbO2 powder were prepared by the high pressure molding technique. The X-ray diffraction (XRD) was used to test the purity of the homemade β-PbO2 powder. The surface structure and electrical property of electrodes were characterized by using scanning electron microscopy (SEM) and the cyclic voltammetry curves (CV). Those images indicated that in electrolysis the (CeO2/C)-β-PbO2-PTFE composite electrodes had higher activity than the β-PbO2-PTFE electrodes, as good as the excellent catalytic performance. In the electrode system the composite electrodes were applied to treat reactive brilliant red (RBR) X-3B solution and we studied the degradation influence factors and the reaction mechanism. The results showed that the electrode system was well in treating RBR X-3B solution with the 20%(CeO2/C)-β-PbO2-PTFE composite electrodes at the initial 100 mg/L RBR X-3B concentration, Na2SO4 concentration of 0.35 mol/L, the constant current density of 30 mA/cm2 and electrolyte pH=2. After electrolytic time of 90 min, the maximum decolorization and chemical oxygen demand (COD) removal rates reached 88.92% and 54.54%. And the decolorization rate of RBR X-3B was in conformity with pseudo-first-order kinetics equation. The RBR X-3B degradation mechanism in the electrochemical oxidation system was used with LC-MS to analyze the possible intermediates and degradation pathway.

Tris(trimethylsilyl) borate as an electrolyte additive for high-voltage lithium-ion batteries using LiNi1/3Mn1/3Co1/3O2 cathode

The influence of tris(trimethylsilyl) borate (TMSB) as an electrolyte additive on lithium ion cells have been studied using Li/LiCo1/3Ni1/3Mn1/3O2 cells at a higher voltage, 4.7V versus Li/Li+. 1wt% TMSB can dramatically reduce the capacity fading that occurs during cycling at room temperature (RT) and elevated temperature (60°C). After 150 cycles at 1C rate (1C=278mAh/g), the capacity retention of Li/LiCo1/3Ni1/3Mn1/3O2 is up to near 72% in the electrolyte with TMSB added, while it is only about 35% in the baseline electrolyte. The electrochemical behaviors, the surface chemistry and structure of Li/LiCo1/3Ni1/3Mn1/3O2 cathode are characterized with charge/discharge test, linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), thermal gravimetric analyses (TGA), scanning electron microscope (SEM) and transmission electron microscopy (TEM). These analysis results reveal that the addition of TMSB is able to protectively modify the electrode CEI film in a manner that suppresses electrolyte decomposition and degradation of electrode surface structure, even though at both a higher voltage of 4.7V and an elevated temperature of 60°C.

Study on the Behavior of Halide Ions Contained in Ionic Liquids on Au(111) Electrode Surface

In recent times, ionic liquids (IL) have been studied as alternatives to water and organic solvents because of their unique features, in particular, tunability and designability. The electrochemical window, viscosity, conductivity, and hydrophobicity of ILs can be tuned by altering their molecular structures. One of the applications of ILs is as an electrolyte solution for electrochemical devices. In the last decade, many researchers have investigated the electrochemical characteristics of ILs and the behavior of IL/electrode interfaces. On the other hand, the effect of impurity contained in ILs on electrode surface structure has not been well uncovered. Typical impurities are halide ions, alkaline metal ions, and water. It has been well known that the halide ions are adsorbed on metal electrode surface and affect electrochemical processes. Especially, chemically adsorbed halide ions are called “specific adsorption anions”. To understand the effect and the behavior of halide ions exist at electrode/ILs interfaces is important from both scientific and industrial point of views. In this study, the behavior of halide ions on the Au(111) electrode surface in two ionic liquids (IL), 1-buthyl-1-methylpyrrolidiniun bis(trifluoromethylsulfonyl)amide ([BMP]TFSA) and 1-buthyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([BMIM]TFSA), was investigated by monitoring the electrode surface structure. Potential dependences of the X-ray diffraction intensity, which originate from the Au(111)-(1 × 1) structure and the surface normal structure, were simultaneously measured with cyclic voltammograms. We considered the dependence of ion concentration and ion species. The electrolytes were prepared using [BMP]Cl, [BMP]Br, [BMP]I, [BMIM]Br, [BMP]TFSA, and [BMIM]TFSA. The electrolytes were dehydrated at 80 °C under vacuum for 24 h before use. A “drop cell” was used as the electrochemical cell. A working electrode was a Au(111) single crystal disk (Φ ≈ 5 mm). Surface X-ray scattering (SXS) experiments were conducted at BL14B1, SPring-8 using a κ-type diffractometer. A 30 keV X-ray was used to obtain a sufficient attenuation length in the drop cell arrangement. In [BMP]TFSA, cyclic voltammograms (CV) showed both halide ion species and their concentration dependence. In the ion species dependence, current values increased in the order of Cl-, Br-, and I-. The cathodic current peak position also shifted to negative potential in the same order. Further, the kinetics of surface reconstruction became faster as the concentration increased. On the other hand, the potential dependence of the surface (1 × 1) structure showed no common behavior. In [BMIM]TFSA, small dependence was observed in both CVs and surface structure. The results revealed that halide ions are co-adsorbed with ionic liquid molecules on electrode surfaces and they increase the mobility of surface atoms. In contrast, the Au(111) surface does not reconstruct to the (p × √3) structure even in the IL containing 200 mM Br−, suggesting that the interaction between halide ions and surface Au atoms is weaker than that between IL molecules and surface Au atoms, that is, the surface property is mainly governed by adsorbed IL molecules. Furthermore, compared with results measured in the two ILs, it was revealed that the effect of halide ions on the Au(111) electrode surface structure depends on the strength of the interaction between IL molecules and surface Au atoms.

Effect of KOH Treated Graphene in Green Monoliths of Pre-Carbonized Biomass Fibers on the Structure, Porosity and Capacitance of Supercapacitors Carbon Electrodes

Activated carbon monoliths (ACMs) electrodes for supercapacitor application were prepared from the green monoliths (GMs) containing KOH treated self-adhesive carbon grains (SACG) added with KOH treated graphene at its weight percentages of 0, 2, 4, 6, 8 and 10 %, respectively. The SACG were prepared from fibers of oil palm empty fruit bunches by a low carbonization temperature method. The ACMs were produced by the carbonization and activation of the GMs. The surface area, structure and specific capacitance of the ACMs electrodes were found affected by the graphene addition. The highest surface area of the ACMs electrode was observed for the addition of 6% graphene, which corresponds to the carbon turbostratic structure of the ACMs electrodes with the values of its crystallites interlayers spacing (d002 and d100) at 0.352 nm and 0.205 nm, and its crystallites stack-width (La) and stack-height (Lc) at 43.21 nm and 10.06 nm, respectively. The specific capacitance of the cell using this electrode was 112 F / g.

Structural and Electrical Characterization of Solution-Processed Electrodes for Piezoelectric Polymer Film Sensors

Solution-processable graphene and carbon nanotube-based electrode materials were used here to provide electrodes on flexible piezoelectric polyvinylidenefluoride sensors. Piezoelectric sensitivity measurements, image-based analysis, adhesion tests, and sheet resistance measurements were applied to these printable sensors to rigorously analyze their performance and structure. The printable sensors showed electrical performance similar to metallized sensors, whereas the adhesion of the solution-processed materials to the substrate is not as high as that of the evaporated metal films. This also affects the measured sensor sensitivity values. The measurements based on optical images were found to be a promising method to capture detailed information about the electrode surface structure.

Recent developments on the modification of graphite electrodes with nanoparticles

The surface structure of common graphite electrodes are suitable for electrochemical detection of various analytes due to their favorable properties such as good conductivity and resistance to environmental and chemical hazards. Also this material is cheap and available. Modifying the surface of electrode improves their ability for various determinations. Modifying graphite electrodes with nanoparticles has attracted lots of attention due to their unique characteristics. In this article we review applications of modified graphite electrodes with nanomaterials.

Direct electrochemical hydrogenation of toluene at Pt electrodes in a microemulsion electrolyte solution

In the present study, we demonstrated a new concept for the direct electrochemical hydrogenation of toluene using an acidic microemulsion electrolyte with active Pt electrodes to pave the way for efficient methylcyclohexane mass production. We have achieved a Faradaic efficiency of 80% for the toluene/methylcyclohexane conversion at a Pt black electrode, under galvanostatic conditions and in a one-compartment cell. The reaction rate and selectivity of the toluene reduction were found to depend strongly on the surface structure of the Pt electrodes.

Structure and Li+ ion transport in a mixed carbonate/LiPF6 electrolyte near graphite electrode surfaces: a molecular dynamics study.

Electrolyte and electrode materials used in lithium-ion batteries have been studied separately to a great extent, however the structural and dynamical properties of the electrolyte-electrode interface still remain largely unexplored despite its critical role in governing battery performance. Using molecular dynamics simulations, we examine the structural reorganization of solvent molecules (cyclic ethylene carbonate : linear dimethyl carbonate 1 : 1 molar ratio doped with 1 M LiPF6) in the vicinity of graphite electrodes with varying surface charge densities (σ). The interfacial structure is found to be sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. We also evaluated the potential difference across the electrolyte-electrode interface, which exhibits a nearly linear variation with respect to σ up until the onset of Li+ ion accumulation onto the graphite edges from the electrolyte. In addition, well-tempered metadynamics simulations are employed to predict the free-energy barriers to Li+ ion transport through the relatively dense interfacial layer, along with analysis of the Li+ solvation sheath structure. Quantitative analysis of the molecular arrangements at the electrolyte-electrode interface will help better understand and describe electrolyte decomposition, especially in the early stages of solid-electrolyte-interphase (SEI) formation. Moreover, the computational framework presented in this work offers a means to explore the effects of solvent composition, electrode surface modification, and operating temperature on the interfacial structure and properties, which may further assist in efforts to engineer the electrolyte-electrode interface leading to a SEI layer that optimizes battery performance.

Improving the Cycling Performance of the Layered Ni-Rich Oxide Cathode by Introducing Low-Content Li2MnO3

The layered Ni-rich oxide LiNi0.8Co0.1Mn0.1O2 cathode has been significantly attractive due to its large reversible capacity (∼200mAhg−1). However, the inherent poor cycling stability of the Ni-based cathode materials is always a serious issue for restricting its commercialization. In this paper, we introduced Li2MnO3 as an electrochemical inactive component in Ni-rich oxide LiNi0.8Co0.1Mn0.1O2 to stabilize its structure. The modified LiNi0.8Co0.1Mn0.1O2 composites with low-content Li2MnO3 were prepared by a solid-state reaction process. The results from XRD structure refinement and SAED confirm that Li2MnO3 phase exists homogeneously in the composites. The modified LiNi0.8Co0.1Mn0.1O2 composites with inactive Li2MnO3 show much better cycling stability and stable average discharge voltage compared with the pristine one when charged to 4.5V. Especially, the modified LiNi0.8Co0.1Mn0.1O2 composite with 10% Li2MnO3 (LNCMO-1090) delivers a reversible capacity of 207mAhg−1 and keeps 155mAhg−1 after 100 cycles at 20mAg−1 (0.1C), corresponding to a capacity retention of 75%, while LiNi0.8Co0.1Mn0.1O2 could only maintain a capacity of 128mAhg−1 with a capacity retention of 59% after 100 cycles. The improved cycling performance of the Li2MnO3-containing electrode could be attributed to the stabilized effect of Li2MnO3 on the electrode surface structure, as evidenced by the lower charge-transfer resistance.

Optimization of electrocatalytic properties of NiMoCo foam electrode for water electrolysis by post-treatment processing

Hydrogen is a potential alternative to fossil fuels in coping with the increased global energy demand, and water electrolysis is an attractive approach for H2 production. Nickel–molybdenum–cobalt (NiMoCo) foam electrodes used for water electrolysis were prepared by the electrodeposition method, and the influence of heat treatments on the surface structure of NiMoCo foam electrodes, mechanical properties, and electrochemical performance of the synthesized electrodes was investigated in order to optimize the post-treatment processes. The residual carbon in the surface of the electrode was removed by decarbonization in the atmospheric condition. The carbon content decreases to lower than 200 × 10−6 when the temperature exceeds 500 °C. Next, the material is reduced in hydrogen atmosphere from 500 to 1100 °C to remove the surface oxides. As the temperature increases, the surface molybdenum content increases significantly between 500 and 800 °C, the surface grains become coarser, and the tensile strength and elongation increase as well. The lowest polarization overpotential is obtained at 800 °C. Below 800 °C, the electrode is only partially reduced and some black oxide zones are observed on the electrode surface, which leads to the higher polarization overpotential. The samples heat-treated at the temperatures of higher than 800 °C show better strength and toughness as well as brighter appearance. However, the surface particle coarsening leads to a decrease in the specific surface area and a higher overpotential.

Laser Battery with Outstanding Liquid Electrolyte Wetting and Performance

The performance of lithium-ion batteries (LIB) can be negatively affected by poor liquid electrolyte wetting of electrode and separator materials causing insufficient cell reliability, reduced safety, and poor electrochemical performance at high charging and discharging rates (C-rate). These drawbacks become even more substantial for large electrode areas and with an increase in electrode thickness. Within the electrolyte filling process, homogeneous wetting of electrode and separator layers is strongly requested to guarantee maximal capacity and optimal performance under challenging operation. To accelerate and homogenize the electrolyte wetting of electrode materials, cost-efficient laser-structuring processes have been recently developed. It could be shown that micro-capillary structures can be easily formed into electrodes resulting in improved electrolyte wetting (Figure 1). In order to test the improvement in wetting of laser-structured electrodes with liquid electrolyte, lithium nickel manganese cobalt oxide (NMC) cathodes were tape-casted, laser-structured, and incorporated into pouch cells vs. graphite anodes with a cell size of 5 x 5 cm2. The assembled cells were electrochemically cycled immediately after the process steps electrolyte filling, vacuuming, and final sealing to investigate the microstructures ability for electrolyte transport in the electrode. By carrying out C-rate dependent cycling it could be shown that pouch cells incorporating laser-structured electrodes exhibited about 80 % of initial discharge capacity at 2C/2C charging/discharging rate while capacity retention of about 50 % was examined for cells with unstructured electrodes. Furthermore, the long-term cycling stability was investigated for pouch cells with unstructured and laser-structured standard electrodes at 1C/1C charging/discharging rate. Also, cells with structured electrodes exhibited > 80 % of initial discharge capacity for cycle numbers > 1000 while cells with unstructured electrodes failed for cycle numbers < 200. This improvement in cycling stability was attributed to drastically accelerated electrolyte wetting in the electrodes as well as to improved interfacial reactions kinetics provided by laser-generated electrode surface structures. In order to investigate the impact of change in surface topography onto the cycling behavior, Electrochemical Impedance Spectroscopy (EIS) was carried out. EIS spectra were analyzed within C-rate dependent and long-term cycling. In addition to electrode wetting, many efforts have been undertaken to also enhance the wettability of separators by applying ceramic coatings to polymeric base materials. To further accelerate the electrolyte wetting speed, we investigated a rather new technological approach for ultrafast femtosecond laser patterning of surface-coated separators. Micro-channel structures could be formed into the thin film coating of the separators resulting in improved wetting properties. In frame of post-mortem studies, Laser-Induced Breakdown Spectroscopy (LIBS) of electrode materials is performed in order to compare “Laser-Batteries” and standard lithium-ion cells after same cycling age. LIBS is a new approach for a rapid post-mortem analysis and it enables a fast chemical mapping of electrode materials to qualitatively investigate the evaluation of degradation mechanisms in LIB´s. Finally, these laser-based processes for electrodes and separators are under intense investigation for process up-scale from laboratory-scale to industrial roll-to-roll processes with respect to processing speed, electrode area, process compatibility, and processing costs. The outstanding advantages of high-capacity “Laser-Batteries” with laser-structured electrodes and separators have to be transferred to the industrial process. Advantages which result from superwicking of laser-modified battery materials are significantly reduced cell storage time-spans, enhanced cycling life-time, and improved high C-rate behavior due to enhanced interfacial reaction kinetics. Figure 1

Mesoporous Carbon Cathode in a Li-O2 Battery: Effect on Li2O2 Product Morphology and Recharge Potential

One of the major challenges of lithium-oxygen (Li-O2) battery is high recharging overpotential, which is responsible for low stability of both non-aqueous electrolyte and carbon electrode, leading to serious side reactions. The fundamental reason for the high overpotential is very poor conductivity of solid Li2O2 as a discharge product, which requires further energy to be electrochemically decomposed (Li2O2→2Li+ + O2 + 2e–). Interestingly, the crystallinity and morphology of the Li2O2 profoundly influence on its conductivity, thus affecting the charging overpotential.1,2 The amorphous Li2O2 has much higher ionic and electronic conductivities compared to the crystalline Li2O2.1 In addition, the small size of Li2O2 with large contact area to the carbon electrode can aid in its smooth decomposition at low charging potential.2 Such type of Li2O2, which has been clearly observed in the presence of some solid-state metal/metal oxide promoters,3,4 is possibly attributable to the high O2 adsorption affinity of the promoters. Unlike these reports, we herein present the unique structure of Li2O2 using a promoter-free mesoporous carbon electrode, which greatly lowers the recharge potential. The mesoporous carbon of CMK-3 consisting of cylindrical-shaped pores with a pore diameter of ~3.5 nm was employed to the cathode (positive electrode) in the Li-O2 cell using 0.5 M LiTFSI in TEGDME. Strikingly, the CMK-3 based Li-O2 cell shows a very low recharge potential below 3.5 V until ~75% of recharge process. The pivotal reason for the decreased overpotential may be associated with an amorphous and flake-shaped Li2O2 vertically formed on the surface of CMK-3 during discharge, which are almost completely decomposed at the low recharge potential. This result is very distinguished from other carbon electrodes such as ketjen black (KB) carbon particle, multi-walled carbon nanotube (MWCNT) and LPC-80 consisting of spherical pores with a diameter of ~80 nm, where higher recharge potentials shown can be correlated with typical structure of spherical and thick Li2O2 particles. We propose that the surface structure of mesoporous carbon electrode is key to implant the Li2O2 flake while the effect of cylindrical pores within the CMK-3 may be negligible when considering low capacity (~1100 mAh/gcarbon) associated with a high surface area (~1500 m2/g). A detailed morphological and electrochemical analysis will be discussed in the presentation. References (1) Tian, F.; Radin, M. D.; Siegel, D. J. Chem. Mater. 2014, 26, 2952-2959. (2) Dunst, A.; Epp, V.; Hanzu, I.; Freunberger, S.; Wilkening, M. Energy Environ. Sci. 2014, 7, 2739-2752. (3) Yilmaz, E.; Yogi, C.; Yamanaka, K.; Ohta, T.; Byon, H. R. Nano Lett. 2013, 13, 4679-4684. (4) Xu, J. J.; Wang, Z. L.; Xu, D.; Zhang, L. L.; Zhang, X. B. Nat. Commun. 2013, 4, 2438-2447. Figure 1

In Situ Coherent Surface x-Ray Scattering Study of the Au (111) Surface Dynamics in Electrolytes: The Effect of Surface Reconstruction and Chloride Adsorption

It has long been conceived that in equilibrium electrode surfaces in contact with electrolytes remain highly dynamic, exhibiting steady processes such as detachment and adsorption of surface atoms. Importantly, some of those microstate fluctuations play an essential role on formation of surface structure and composition, and ultimately affect the functionality of electrodes. Surface-sensitive techniques, like STM and surface x-ray scattering (SXS), have become invaluable to unraveling electrode surface structures under changing electrochemical environments. Measurements on surface dynamics, however, remain challenging for electrochemical systems [[1]]. In this talk, we will report on the study of Au (111) surface dynamics by coherent surface x-ray scattering (CSXS). A brief introduction will be given for implementation of CSXS and ISXS for electrochemical studies. Time-resolved capability of CSXS will be highlighted. To elucidate factors that could influence surface dynamics, Au (111) electrode surfaces are systemically tailored by varying electrochemical conditions. Phase transition in Au (111) electrode surface had been well characterized by SXS, with structural changes that were shown to be both dependent on potentials and solution chemistry [[2]]. A sharp drop in x-ray scattering intensity around 0.12 V, shown in Fig. 1 (black curve), marks phase transition from (p x√3) to (1x1), which then can be reconstructed back to form a (p x√3) structure in a reverse potential scan. A similar potential dependence is found with increasing chloride concentration as shown in Fig. 1 (red curve). Careful comparison of the hysteresis loops, presented in Fig. 1, additionally reveals that chloride concentration influences the kinetics of phase transition in Au (111) surfaces. In additional to structural details, we have also attained some preliminary results on the dynamics of Au (111) surfaces from CSXS experiments. In the present work, surface dynamics are quantified in terms of correlation time, a parameter that describes the temporal separation between two configurations that are no longer resemble each other due to microstate fluctuations. Correlation time in relation to surface structure will be shown and discussed as a function of applied potential and chloride concentration. A comprehensive analysis on surface dynamics will be performed to help establish its relations with surface structure and solution chemistry. [1] M. Pierce, V. Komanicky, A. Barbour, D. C. Hennessy, C. Zhu, A. Sandy, H. You, Phys. Rev. B 86, 085410 (2012). [2] J. Wang, B.M. Ocko, A. J. Davenport, H. S. Isaacs, Phys. Rev. B 46 10321 (1992). Figure 1

Relationship between the Origin of Constant-Phase Element Behavior in Electrochemical Impedance Spectroscopy and Electrode Surface Structure

We address two major and open questions on the ubiquitous and controversial constant-phase element (CPE) behavior in the electrochemical impedance spectroscopy (EIS) response of electric double layers (EDLs) and its relationship with surface properties. The first one concerns the physicochemical origin of this anomalous behavior, whereas the second one deals with the physical meaning of the CPE capacitance obtained from impedance data. For that purpose we have analyzed the EIS response of a well-controlled electrochemical reaction taking place on a surface electrode that was progressively modified by electrodissolution. A complete characterization of the surface structure was obtained by means of scanning with-light interferometry and X-ray diffraction and from a previous analysis based on atomic force microscopy. With regard to the first question, our results show direct evidence supporting the hypothesis that CPE behavior results from energetic rather than geometric heterogeneity (roughness). Regarding ...

The 2015 Colin G. Fink Summer Research Fellowship -- Summary Report: Crystal Orientation Effects on the Oxygen Evolution Reaction on Iridium Oxide

1The electrochemical behavior of metal catalysts is strongly dependent on the structure of the electrode material. 2,3 Therefore a deeper understanding of the relation between the electrode surface structure, in terms of crystal orientation, and its corresponding OER activity, is required in order to find the optimum form of iridium oxide catalysts with enhanced catalytic activity and stability. In this project, a polycrystalline iridium (p-Ir) wire (250 μm dia) was subjected to annealing and electrochemical etching to increase grain size and make the grain

On the Specific Adsorption of 7-methylguanine on Au(111) Surfaces for the Electroanalytical Sensing of Methylation Levels

The electrochemical determination of 7-methylguanine (7-mG) may result of interest because its presence can serve as probe of cytosine methylation of which is known as the most relevant epigenetic modification of DNA. This work explores the electrochemical response of 7-mG on different gold surfaces, both poly and single crystalline surfaces (Au (110), Au (111) and Au (100)). The results show that the adsorption-desorption process of the 7-mG is sensitive to the surface structure of the gold electrodes. Particularly, 7-mG adsorption-desorption profile on a Au (111) electrode exhibits some specific contributions which are found sensitive to the 7-mG concentration and, thereby could allow its quantification. These results may shed light on the future development of an electrochemical sensor for the diagnosis of the methylation degree in DNA.

In-situ electrochemical coating of Ag nanoparticles onto graphite electrode with enhanced performance for Li-ion batteries

The effects of silver hexafluorophosphate (AgPF6) as an electrolyte additive on the electrochemical behaviors of graphite anode are systematically studied by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The surface structure and composition of graphite electrode after electrochemical cycles are investigated through scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. It is found that Ag nanoparticles derived from electrochemical reduction of Ag+ are homogenously distributed on the graphite surface. Significant improvements on the discharge capacity, rate behavior, and low-temperature performance of graphite electrode are obtained. The reasons are associated with the decreased resistances of solid-electrolyte interface and charge-transfer process, which improve the electrode kinetics for Li+ intercalation/deintercalation.

The influence of surface crystallography on the interfacial behaviour of tetrabutylammonium cations at Au(1 0 0) and Au(1 1 1) electrodes

The impact of the structure of electrode surface on the behaviour of tetrabutylammonium cations on gold (100) and (111) electrodes has been studied using the cyclic voltammetry and differential capacity measurements. The adsorption features of these cations were found to be structure sensitive and resemble those of simple organic molecules rather than those of ions. It was also suggested that adsorption of anions from supporting electrolyte lifts the reconstruction which is modified by the tetrabutylammonium cations on the surface.

Invited: Surface Modification of Positive Electrode and its Effect to Bulk

Improvement technique of the life of Li-ion batteries has been intensively studied. Modification of the surface of positive electrode material including coating is effective to this purpose. In that process, it is very important to compare the bulk and surface structure of the positive electrode with/without surface modification to understand this effect.For basic information concerning the effect of surface modification, authors have applied Transmission Electron Microscopy (TEM) to visualize the structural distribution inside the positive electrode particles after degradation [1]. As a model material, we synthesized sub-micron size particle of positive electrode such as LiCoO2 by Pechini sol-gel method [2, 3] that could provide the suitable sample for TEM observation without damages from sample preparation like ion-milling or FIB. Analytical TEM measurements by scanning transmission microscopy (STEM) with electron energy-loss spectroscopy (EELS) equipped with monochromator were applied. Li-K EELS peak around 62 eV was clearly found and this peak intensity changed with Li charge-discharge state. The EELS mapping from the spectrum imaging method using this Li-K region spectra showed a distribution of Li in the particle or among particles during the charge discharge cycle. We discuss precisely the change of chemical states at the surface and Li ion distribution inside particles of positive electrode material with/without surface modification using Si, Zr, Al, Mg oxide during charge-discharge cycle.

Dissolution of Platinum Single Crystal Surfaces under Potential Cycling in Sulfuric Acid Solution

Pt dissolution is one of the most important topics in Polymer Electrolyte Fuel Cell (PEFC) field because of the origin of the Pt nanoparticle growth, which results in a cell performance loss of PEFC.1 Recent reports showed a submonolayer of Pt dissolution occurs under potential cycling conditions simulating the PEFC operation in acidic environments.2Surface structural controls of Pt nanoparticles against Pt dissolution under potential cycling are a key point to improve the corrosion resistance of Pt surface. We investigated the effect of crystal orientations on the dissolution of Pt surface using Pt(100), Pt(110), and Pt(111) single crystal electrode. Commercial Pt(100), Pt(110) and Pt(111) single crystal electrodes were used as the specimen. The specimens were polished down to 0.25 mm diamond paste, annealed with an oxygen-hydrogen burner for 2 h, and cooled in a stream of Ar gas, prior to the electrochemical measurements. Cyclic voltammetry (CV) at single crystal surfaces was conducted for 100 cycles to examine Pt dissolution. The potential range of CV was from 0.5 to 1.0, 1.2, and 1.4 V. 0.5 M H2SO4solution at 298 K open to air was used as the electrolyte. After 100 cycles of CV, the solutions were analyzed with ICP-MS for the quantification of amount of dissolved Pt. The surface morphology of Pt single crystal electrodes was observed by electrochemical STM measurements. Figure 1 shows STM images of Pt(100), Pt(110), and Pt(111) single crystal surfaces after the anealing, and the cross section height profiles along the white arrows. The surfaces of Pt(100), Pt(110), and Pt(111) single crystal electrodes were composed of atomic height steps and smooth terraces. The saw-like step structures were observed at Pt(100) and Pt(110) surface. In addition, Pt(110) surface was relatively roughened. CVs at Pt(100), Pt(110), Pt(111) single crystal, and polycrystalline Pt surfaces were shown in Fig. 2. The voltammograms of single crystal electrodes exhibited characteristic hydrogen adsorption/desorption peaks between 0.05 and 0.4 V. These peaks were not sharp because of a exposure in air atmosphere during the setup of electrochemical measurements but similar to those reported in the literatures.3This demonstrates well-controlled surface structures of single crystal electrodes were obtained. Figure 3 shows the amount of Pt ions dissolved from single crystal surfaces under 100 cycles of CV in 0.5 M H2SO4solution. The horizontal axis means the upper potential limit of CV. The dissolved amount at Pt(100) and Pt(110) surfaces was almost the same, and increased with rising the upper potential limit. Pt(111) surface hardly dissolved at potentials below 1.2 V, and the amount of dissolution at this surface in the potential range of 0.5–1.4 V was about a half of that at Pt(100) and Pt(110) surfaces. This result indicates Pt(111) surface has the highest corrosion resistance among the three single crystal electrodes examined.1. Y. Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, E. F. Holby, and D. Morgan, Top Catal, 46, 285 (2007).2. Y. Sugawara, T. Okayasu, A. P. Yadav, A. Nishikata, and T. Tsuru, J. Electrochem. Soc., 159(11), F779 (2012).3. N. M. Marković, and P. N. Ross, Surf. Sci. Rep., 45, 117(2002).Caption list:Figure 1 STM images of Pt(100), Pt(110), and Pt(111) single crystal surfaces after the anealing treatment.Figure 2 CVs at Pt(100), Pt(110), Pt(111) single crystal, and polycrystalline Pt surfaces at 10 mVs-1 in 0.5 M H2SO4solution.Figure 3 Amount of Pt ions dissolved from single crystal surfaces as a function of the upper potential limit of CVs. The CVs were carried out for 100 cycles at 10 mVs-1 in 0.5 M H2SO4 solution.