Linear Potential Sweep Research Articles

Single-Particle Spectroelectrochemistry: Revealing the Electrochemical Tuning Mechanism of Chemical Interface Damping in 1,2-Benzenedithiol-Adsorbed Single Gold Nanorods.

Chemical interface damping (CID) is a newly proposed plasmon damping pathway based on interfacial hot-electron transfer from metal to adsorbate molecules. However, achieving in situ tunability of CID in single gold nanorods (AuNRs) remains a considerable challenge. Here, we present the CID effect induced by benzene 1,2-dithiol (BDT) molecule adsorption on single AuNRs and the effective electrochemical tunability of CID in BDT-adsorbed AuNRs immobilized on an indium tin oxide (ITO) surface. Manipulations of the electrochemical potential alter the electron density of AuNRs, thereby influencing and tuning the localized surface plasmon resonance (LSPR) spectrum, with cathodic potential blueshifting and anodic potential redshifting. The strong adsorption of BDT on Au induced CID in single AuNRs. The potential-induced LSPR scattering spectra of BDT-adsorbed AuNRs for linear potential sweep showed a stable LSPR spectral response, irrespective of the concentrations of BDT molecules. Due to the involvement of two Au-S bonds, BDT molecules have a higher free adsorption energy and a lower desorption rate on the Au surface. This resulted in a stable LSPR spectral response for a linear electrochemical potential sweep. Furthermore, a constant anodic and cathodic potential application showed the tunability of the CID at the BDT-Au interface.

Optimized Fabrication of Carbon-Fiber Microbiosensors for Codetection of Glucose and Dopamine in Brain Tissue.

Dopamine (DA) signaling is critically important in striatal function, and this metabolically demanding process is fueled largely by glucose. However, DA and glucose are typically studied independently and, as such, the precise relationship between DA release and glucose availability remains unclear. Fast-scan cyclic voltammetry (FSCV) is commonly coupled with carbon-fiber microelectrodes to study DA transients. These microelectrodes can be modified with glucose oxidase (GOx) to generate microbiosensors capable of simultaneously quantifying real-time and physiologically relevant fluctuations of glucose, a nonelectrochemically active substrate, and DA, which is readily oxidized and reduced at the electrode surface. A chitosan hydrogel can be electrodeposited to entrap the oxidase enzyme on the sensor surface for stable, sensitive, and selective codetection of glucose and DA using FSCV. This strategy can also be used to entrap lactate oxidase on the carbon-fiber surface for codetection of lactate and DA. However, these custom probes are individually fabricated by hand, and performance is variable. This study characterizes the physical nature of the hydrogel and its effects on the acquired electrochemical data in the detection of glucose (2.6 mM) and DA (1 μM). The results demonstrate that the electrodeposition of the hydrogel membrane is improved using a linear potential sweep rather than a direct step to the target potential. Electrochemical impedance spectroscopy data relate information on the physical nature of the electrode/solution interface to the electrochemical performance of bare and enzyme-modified carbon-fiber microelectrodes. The electrodeposition waveform and scan rate were characterized for optimal membrane formation and performance. Finally, codetection of both DA/glucose and DA/lactate was demonstrated in intact rat striatum using probes fabricated according to the optimized protocol. Overall, this work improves the reliable fabrication of carbon-fiber microbiosensors for codetection of DA and important energetic substrates that are locally delivered to the recording site to meet metabolic demand.

Preparation of Spherical δ-MnO2 Nanoflowers by One-Step Coprecipitation Method as Electrode Material for Supercapacitor.

Spherical δ-MnO2 nanoflower materials were synthesized via a facile one-step coprecipitation method through adjusting the molar ratio of KMnO4 to MnSO4. The influence of the molar ratio of the reactants on the crystal structure, morphology, and electrochemical performances was investigated. At a molar ratio of 3.3 for KMnO4 to MnSO4, the spherical δ-MnO2 nanoflowers composed of nanosheets with the highest specific surface area (228.0 m2 g-1) were obtained as electrode materials. In the conventional three-electrode system using 1 M Na2SO4 as an electrolyte, the specific capacitance of the spherical δ-MnO2 nanoflowers reached 172.3 F g-1 at a current density of 1 A g-1. Moreover, even after 5000 cycles at a current density of 5 A g-1, the GCD curves remained essentially unchanged, and the specific capacitance still retained 86.50% of the maximum value. The kinetics of the electrode reaction were preliminarily studied through the linear potential sweep technique to observe diffusion-controlled contribution toward total capacitance. For the spherical δ-MnO2 nanoflower electrode material, diffusion-controlled contribution accounted for 65.1% at low scan rates and still remained significant at high scan rates (100 mV s-1), indicating excellent utilization efficiency of the bulk phase. The as-fabricated asymmetric supercapacitor HFC-7//MnO2-3.3-ASC presented a prominent specific energy of 16.5 Wh kg-1 at the specific power of 450 W kg-1. Even when the specific power reached 9.0 kW kg-1, the energy density still retained 9.5 Wh kg-1.

(Invited) Towards Understanding of Initial Co-Intercalation of Solvated Lithium Ions Under Galvanic and Linear Sweeping Control via In-Situ/In-Operando Atomic Force Microscopy

The applications of lithium-ion batteries (LIBs) have rapidly embedded into almost every aspect of our life and society. In the LIB industry, a well-controlled and lengthy process is proceeded before the LIBs are brought into markets. The aim of this process is to form a “good” solid electrolyte interphase (SEI) on the graphite anode in a LIB to prevent continuous electrolyte decomposition and graphite exfoliation, which greatly influence the performance and cycle life of a LIB. The SEI formation process usually takes one or two weeks, is the major bottleneck and the most expensive component for mass production of LIBs. Efforts have been devoted to accelerating the SEI formation process by increasing charging rates or skipping the high state-of-charge region. However, the shortened SEI formation time usually comes with a large decrease in capacity retention of a LIB.[1-3] Improving our understanding on the structure and property evolution of SEI during the SEI formation process is urgently required for the development of faster formation protocols without sacrificing the high quality SEIs.[4-7]Aiming at better understanding of the initial stage of SEI formation process in LIB production, in-situ electrochemical atomic force microscopy (EC-AFM) has been employed to monitor the morphological evolution of the electrode materials in nano-scale levels. While different from most of the previous works, this work applied Galvanic constant current (CC) control to closely mimic the industrial SEI formation processes of different formation rates. For comparison, linear potential sweep (LS) controlled SEI formation of various potential sweeping rates, which is commonly applied in fundamental studies of SEI formation, was also performed in parallel. For the first time, it is revealed that the onset potentials for co-intercalation and electrochemical reduction of solvated lithium-ion complexes, the two competitive and/or sequential processes during SEI formation, vary as a function of potential sweeping rates. The onset potential for co-intercalation shifts positively as the potential changing rate increases, which is in high contrast to the onset potential of their electrochemical reduction. It has been well established that the onset potential of their electrochemical reduction is largely determined by the lowest unoccupied molecular orbital (LUMO) level of the solvent molecules in the solvated lithium ion complexes,[6] so that it may remain largely constant or shift negatively, due to electrode polarization.[2] As a result, the onset potential for co-intercalation becomes more positive than that of the electrochemical reduction as the potential sweeping rate increases. Our experimental results demonstrate that this relationship applies to both CC and LS-controlled SEI formation processes. However, the difference between these two onset potentials is much greater in CC than that of LS controlled processes, due to the associated faster potential changing rates at the beginning of CC controlled lithiation. The difference becomes even more prominent when high charging current is applied to shorten the SEI formation time and lower LIB production cost. This understanding combined with the clear visible evidence of different structural evolution under CC and LS controls should provide more practical guidance to develop protocols for faster formation of SEI with higher quality, which is intensively pursued in industry.[1] Lee, H. H.; Wang, Y. Y.; Wan, C. C.; Yang, M. H.; Wu, H. C.; Shieh, D. T., A fast formation process for lithium batteries. Journal of Power Sources 2004, 134 (1), 118-123.[2] Bhattacharya, S.; Alpas, A. T., Micromechanisms of solid electrolyte interphase formation on electrochemically cycled graphite electrodes in lithium-ion cells. Carbon 2012, 50 (15), 5359-5371.[3] An, S. J.; Li, J. L.; Du, Z. J.; Daniel, C.; Wood, D. L., Fast formation cycling for lithium ion batteries. Journal of Power Sources 2017, 342, 846-852.[4] Wang, L. N.; Menakath, A.; Han, F. D.; Wang, Y.; Zavalij, P. Y.; Gaskell, K. J.; Borodino, O.; Iuga, D.; Brown, S. P.; Wang, C. S.; Xu, K.; Eichhorn, B. W., Identifying the components of the solid-electrolyte interphase in Li-ion batteries. Nature Chemistry 2019, 11 (9), 789-796.[5] Cai, W. L.; Yao, Y. X.; Zhu, G. L.; Yan, C.; Jiang, L. L.; He, C. X.; Huang, J. Q.; Zhang, Q., A review on energy chemistry of fast-charging anodes. Chemical Society Reviews 2020, 49 (12), 3806-3833.[6] Xu, K., Nonaqueous liquid electrolytes for lithium-based rechargeable batteries. Chemical Reviews 2004, 104 (10), 4303-4417.[7] Xu, K., Electrolytes and Interphases in Li-Ion Batteries and Beyond. Chemical Reviews 2014, 114 (23), 11503-11618. Figure 1

Analysis of the Charging Current in Cyclic Voltammetry and Supercapacitor's Galvanostatic Charging Profile Based on a Constant-Phase Element.

We investigated the charging current in cyclic voltammetry and the galvanostatic charging/discharging behavior of a controversial constant-phase element (CPE) to describe an electrical double layer used only in electrochemical impedance spectroscopy. The linear potential sweep in the time domain was transformed into the frequency domain using a Fourier transform. The current phasor was estimated by Ohm’s law with the voltage phasor and a frequency-dependent CPE, followed by an inverse Fourier transform to determine the current in the time domain. For galvanostatic charging/discharging, the same procedure, apart from swapping the voltage signal with the current signal, was applied. The obtained cyclic voltammetry (CV) shows (1) a gradual increase in the charging current, (2) a higher charging current at a low scan rate, and (3) a deviation from the linear relationship between the charging current and the scan rate. For galvanostatic charging/discharging, the results demonstrate (1) curved charging/discharging behavior, (2) a higher voltage in the early stage, and (3) a lower voltage during longer charging periods. In contrast to a previous approach based on solving a differential equation with a simple RC circuit, our Fourier transform-based approach enables an analysis of electrochemical data with an arbitrary and complex circuit model such as a Randles equivalent circuit. The CPE model is more consistent with previous experimental results than a simple ideal capacitor, indicating a ubiquitous CPE in electrochemistry and a fair figure of merit for supercapacitors.

Morphology of ZnO Films Fabricated by Electrochemical Oxidation of Metallic Zn

Anodic oxide films of zinc oxide in an aqueous solution of K Cl (0.1 M; 0.5 M and 1 M) were obtained by electrochemical oxidation of zinc metal. Zinc electrode was used as anode and platinum plate as cathode. The study discusses the influence of the concentrations of K Cl solution and the voltage applied to the electrochemical cell on the morphology of the obtained anode films, as well as their thermodynamic stability. The analysis of volt-ampere curves of linear potential sweep and chronoamperometric dependences showed that oxidation in 0.1 M K Cl solution at a voltage of 7.5 V allows to obtain continuous stable defect-free Zn O films on metal zinc.

Genesis and Propagation of Fractal Structures During Photoelectrochemical Etching of n-Silicon

The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH4F (aqueous) have been investigated during either a linear potential sweep or a constant potential hold (E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments revealed the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. The etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiOxFy on the surface. The two-dimensional fractal dimension, Df,2D, of the patterns increased with etching time to a maximum observed value of Df,2D = 1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface.

Effect of lanthanum, cerium and other elements on the electrochemical corrosion properties of Pb–Ca–Sn–Al alloy in lead–acid batteries

The effects of different additives including selenium, silver, ytterbium, lanthanum, and samarium with a dosage of 0.02 wt.% ± 0.005 wt.% on the electrochemical behavior of Pb–Ca–Sn–Al alloy have been studied in sulfuric acid solutions. The electrochemical properties were evaluated by linear potential sweep (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Metallurgical microscope and scanning electron microscope (SEM) were employed to investigate the morphology-property relationships of the corrosion layer and corrosion section of Pb–Ca–Sn–Al alloys. It was found that the additives including Ag, La and Sm can to some extent refine the grain and regular grain boundary of Pb–Ca–Sn–Al alloy, which was confirmed by metallurgical microscope. The formation of a uniform and dense corrosion layer on the surface of these three alloys can effectively reduce the corrosion rate of the alloy. Furthermore, the growth of Pb (II) and PbO2 in corrosion layer on Pb–Ca–Sn–Al alloy is remarkably inhibited by adding Ag, La, and Sm as determined by the results of CV, EIS, and SEM. These experimental facts indicate that adding Ag, La and Sm can improve the corrosion resistance of the alloy.

Hybrid gel polymer electrolyte with good stability and its application in electrochromic device

Using propylene carbonate (PC) as solvent, a hybrid gel polymer electrolyte (GPE) based on poly(propyleneglycol) bis(2-aminopropyl ether) (2-APPG) and 3-isocyanatepropyltriethoxysilane (ICS) was successfully synthesized by sol–gel method. The result shows the hybrid gel polymer electrolyte with [O]/[Li] ratio of 22 has a high ionic conductivity, good thermal stability, as well as good electrochemical stability. The ionic conductivities reach as high as 1.43 × 10− 3 S cm− 1 at 30 °C and 3.36 × 10− 3 S cm− 1 at 100 °C, respectively. Nearly 0 weight loss was observed up to 100 °C. The electrochromic device is fabricated by using the hybrid gel polymer as electrolyte. The results demonstrate its high coloration efficiency (267.4 cm2 C− 1) and long cycle life (150 cycles with the linear potential sweep between − 3.5 and + 2.5 V), When the applying voltage is increased to as high as 5 V on the electrochromic device, a fast response is obtained (colored/bleached time are 13/19 s), which indicates its potential application under high voltage conditions.

Double Current Maxima Formed under Linear Potential Sweep Conditions in Acetic Acid Solutions at pH < 2.5

The kinetics of hydrogen evolution on a copper electrode in acetic acid solutions is studied by the method of linear potential sweep. At рН < 2.5, double current peaks are observed with the height directly proportional to both √v (v is the potential sweep rate) and the total concentration of proton donors and acceptors. Upon the transition from the copper electrode to the platinum electrode, the overpotential of this process considerably decreases, but the shape of current peaks remains unchanged. The analysis of kinetics of acetic acid dissociation points to the high degree of lability of this system, which allows the relationship between the surface concentrations of its components to be expressed through the corresponding equilibrium constants. At certain potentials, significant changes in the surface pH are observed, which favor the appearance of an additional current peak in the cathodic chronovoltammogram. The Tafel plots normalized with respect to the surface concentration of hydrogen ions allow the following values of kinetic parameters to be obtained: i0 ~ 0.3 nA/cm2 and αc = 0.75. Chronovoltamograms simulated with the use of these values demonstrate double maximums which adequately agree with experimental data.

Photoelectrocatalytic Degradation of 4-Chlorophenol by Using Decahedron BiVO4 as Catalyst and Pd and MnOx as Cocatalysts on Designed Facets

Decahedron BiVO4 with {040} dominant crystal facets was synthesized for BiVO4/FTO photoelectrodes, where the {040} facets improve the charge carrier mobility. The dechlorinating cocatalyst Pd and the oxidation cocatalyst MnOx (x = 1.5–2.0) were photodeposited selectively on the {040} and {110} facets, respectively, of the decahedron BiVO4. In the linear potential sweep data, the 0.5% mass ratio of the double-deposition precursor (0.5 wt% Pd/MnOx/BiVO4) electrode attained the highest photocurrent density (0.992 mA/cm2) under 450 nm light irradiation. The presence of cocatalysts of Pd and MnOx synergistically suppressed the radiative photocharge recombination and caused the redshift of the corresponding visible light to the highest wavelength of 543 nm. Notably, the decahedron BiVO4 with {040} exposed crystal facets exhibited significantly higher photocurrent than irregular BiVO4. Irradiation was the main exciting force of free charge, and the applied potential indispensably yielded additional hydroxyl radicals (·OH). This finding was confirmed by the 2.77 times higher degradation efficiency of 4-chlorophenol (4-CP) by photoelectrocatalysis than that by photocatalysis. The 4-CP decomposition and mineralization rates reached 96.5% and 91.9%, respectively. Hence, a photoelectrocatalytic system containing multifunctional BiVO4 for chlorophenol degradation was constructed.

Electrochemical processes in weakly acid solutions containing Cu(II)-glycine complexes

Rotating disc electrode (RDE) and linear potential sweep (LPS) voltammetry together with electrochemical quartz crystal microgravimetry (EQCM) were used for the investigation of cathodic processes in weakly acid solutions (pH 3–5) containing Cu(II)-glycine complexes and 0.3 M NaClO4 as a supporting electrolyte. The Cu2+ aqua-complex and monoligand complex CuL+ dominate in slightly acid Cu(II)-glycine solutions. Less than 1% of Cu(II) is converted to Cu(I) upon contact of solutions with a copper electrode. At pH > 4, the formation of surface layers containing Cu2O becomes possible.Due to the specific redistribution of species at the electrode surface, characteristic pre-waves appear on the RDE voltammograms, which are transformed into additional current peaks under LPS conditions. Using the model of mass transport of chemically interacting particles, changes in surface concentrations were estimated with further construction of linear Tafel plots normalized with respect to the surface concentration of the electrochemically active complex.The following values of kinetic parameters (the cathodic charge transfer coefficient, αc1, and the exchange current density, i01) were determined for the rate-determining step CuL+ + e → CuL: αc1 = 0.23 and i01 = 0.36 mA cm−2 (pH 3); αc1 = 0.44 and i01 = 0.14 mA cm−2 (pH 4). According to EQCM data, additional processes involving the formation of surface oxides arise at pH 5.

Experimental Study of PVD Cu/CVD Co Bilayer Dissolution for BEOL Cu Interconnect Applications

In this study, we characterize the anodic dissolution behavior of thin PVD Cu/CVD Co bilayer films using linear sweep amperometry in a potassium nitrate electrolyte. The Co and Cu dissolution peaks are well separated, enabling an assessment of the continuity of the Cu overlayers. Complete coverage of the Co film is attained at a PVD Cu overlayer nominal thickness of ~20 nm. Exposing the bilayer films to various wet solutions (as a “pretreat”) followed by a linear potential sweep allows measurement of the Co loss during pretreatment. The impact of a pretreat in Cu plating chemistries with different cupric ion concentrations and various organic additive packages is characterized on the Cu/Co bilayer stack. Electrical data are presented for 24 nm CD dual Damascene BEOL test structures for Cu plating chemistries with different Cu contents. The influence of the plating bath Cu concentration on yield is discussed with respect to the observed dependency of Co loss on the pretreat solution Cu content.

Influences of Saccharin on Electrochemical Behavior of Nickel Electrodeposition

Electrodeposition of Ni was performed in acid Watt's solutions. Saccharin concentrations were varied in order to analyze its influence on the electrochemical behaviors of Ni deposition. Investigations were conducted using CHI660D, by methods of linear potential sweep, cyclic voltammetry and A. C. Impedance. Results indicate that with the increase of saccharin concentration, the cathodic polarization, apparent activation energy and the electrochemical reaction resistance of Ni electrodeposition increase. The exchange current density decreases with the increase of saccharin concentration. The electrodeposition of Ni is a mixing process controlled by electrochemical polarization and concentration polarization. The change of saccharin concentration does not affect the electrodeposition mechanism of Ni. But there is an obvious inhibition and blocking effect of saccharin on nickel electrodeposition. When the concentration of saccharin is 4g/L, its adsorption capacity in electrode is close to saturation. The saccharin concentration should be less than 4g/L.

Electropolymerization and Electrochemical Performance of Nickel Schiff Base Complexes on Reduced Graphene Oxide(RGO) Support for Supercapacitors

Supercapacitors have a high power capability and relatively large energy density compared to the conventional capacitors. Conducting polymers have been shown as promising electrode materials because of their high conductivity and fast redox activity. N,N_-ethylenebis(salicylideneaminato) nickel(II), (Ni(salen)), which is the archetype of Schiff base metal complexes, was easily synthesized onto the surface of reduced graphene oxide(RGO) by the route of linear potential sweep. Growth parameters such as the apparent surface coverage and the doping level were investigated to confirm the effects of supports on the Ni(salen) polymerization.SEM, TEM, Raman, and XPS analyses show that the poly(Ni(salen)/RGO composite prepared from this approach,at the same time it exhibited an excellent electrocapacitive performance with a high specific capacitance over 260 F g-1 Fig.1 (a) Polymerization Q varies with polymerization time at different voltages ; (b) GCD curves of MWCNTs and the composites at a current density of 1.0 mA cm2 under the voltage range of 0 V to 1.2 V. Reference 1 Kim, M., Lee, C., & Jang, J. (2014). Fabrication of Highly Flexible, Scalable, and High‐Performance Supercapacitors Using Polyaniline/Reduced Graphene Oxide Film with Enhanced Electrical Conductivity and Crystallinity.Advanced Functional Materials, 24(17), 2489-2499. 2. Salanne, M., Rotenberg, B., Naoi, K., Kaneko, K., Taberna, P. L., Grey, C. P., ... & Simon, P. (2016). Efficient storage mechanisms for building better supercapacitors. Nature Energy, 1, 16070. Acknowledgement This work is financially supported by the National Natural Science Foundation of China (No. 51372021). Figure 1

Electrodeposition preparation of Ni–Fe alloy foil

In this study, the electrodeposition of a nickel (Ni)–iron (Fe) alloy foil was thoroughly investigated. Linear potential sweep and cyclic voltammetry method were used to investigate the electrochemical behaviour of the nickel–iron alloy foil. In addition, single-factor experimental studies were combined with an orthogonal test analysis to obtain optimum experimental conditions. Scanning electron microscopy and X-ray diffraction were used to investigate the surface morphology and the crystalline structure of the nickel–iron alloy foil. The obtained nickel–iron alloy foil was a face-centred cubic crystal with a bright and smooth surface, in which no pinholes or cracks appeared. The average hardness value, electrical resistivity, maximum permeability, saturation magnetic flux density (B s) and residual magnetism (B r) of the obtained nickel–iron foil were 280 HV, 38–41 μΩ cm, 0·172 mH/m, 1·093 T and 0·0088 T, respectively. Lastly, the obtained nickel–iron foil displayed good soft magnetic properties, toughness and low residual stress.

Anodic Oxidation of Carbon and Electrolyte with Different Conducting Salts in High-Voltage Lithium-Ion Batteries Studied By Online Electrochemical Mass Spectrometry

Recently, many research activities have been devoted to the development of near 5 V cathode materials, e.g. the LiMn1.5Ni0.5O4 spinel, in order to raise the energy density of lithium-ion batteries and to allow for longer driving ranges of battery electric vehicles.1 However, the enhanced degradation of carbon and electrolyte by the use of these high-voltage cathodes could not be mitigated so far. It was demonstrated recently by On-line Electrochemical Mass Spectrometry (OEMS),2 that the anodic oxidation of conductive carbon, carbon coatings, and electrolyte at ≈5.0 V can be substantial at high temperature and in the presence of trace water, posing significant challenges for the implementation of 5 V cathode materials.3,4 While these studies were done with LiClO4 as conducting salt in order to study the effect of H2O addition on oxidation without side reactions of salt and water, e.g. HF formation, we want to investigate now to which extent the lithium salt can influence gas generation at high voltage. We employ our newly developed two-compartment cell in which anode and cathode compartments are separated by a Li+-ion conducting solid electrolyte (Ohara glass) laminated with aluminum and polypropylene foil, so that the gas evolution from degradation processes at high voltage can be studied selectively for the positive electrode without cross-diffusion of reaction products and gas generation from the counter-electrode, thereby enabling a more detailed analysis of the decomposition pathways.5 This is a major advance over conventional cells, where the gases come from both electrodes, and thus do not allow a deconvolution of the simultaneously occurring reactions from anode and cathode. Furthermore, OEMS is used to compare three types of lithium salts in terms of their influence on the anodic stability (close to 5 V) of electrolyte and conductive carbon in the battery cell. These are the commercially used salt LiPF6, the sulfur- and nitrogen-containing LiTFSI, and the fluorine-free and oxygen-containing compound LiClO4. The salts are mixed with ethylene carbonate (EC) at a concentration of 1.5 M, so that linear carbonates like EMC or DMC which have a much higher vapor pressure than EC can be avoided, allowing for precise signal quantification in OEMS.3 The comparison of the salts will be done on the basis of the CO/CO2 gas evolution monitored by OEMS at various temperatures between 25 and 60°C. We employ a fully 13C-labeled carbon electrode to deconvolute the CO/CO2 evolution from electrolyte oxidation (12C) from that of the conductive carbon oxidation (13C). We quantify our OEMS results using a calibration gas, and give both, quantitative and mechanistic insights into the effect of the conducting salt on gas evolution in high-voltage lithium-ion batteries. By quantification of both CO/CO2 isotopes we determine the molar oxidation rate and the weight loss of electrolyte and carbon due to anodic oxidation. In summary, this study elucidates to which extent the lithium salt can influence gas generation at high voltage and might allow to deduce design principles for the synthesis of novel electrolyte salts. Figure 1 shows in the upper panel the current-potential profiles of 13C-carbon//lithium half-cells with the three different conducting salts at 1.5 M in EC upon a linear potential sweep from OCV to 5.5 V vs. Li/Li+. The corresponding evolution of both isotopes of CO2 (solid lines) and CO (dotted lines) for the electrolyte oxidation and the 13C-carbon oxidation are shown in the middle panel and the lower panel, respectively. References O. Gröger et al., J. Electrochem. Soc., 162, A2605 (2015).N. Tsiouvaras et al., J. Electrochem. Soc., 160, A471 (2013).M. Metzger et al., J. Electrochem. Soc., 162, A1123 (2015).M. Metzger et al., J. Electrochem. Soc., 162, A1227 (2015).M. Metzger et al., J. Electrochem. Soc., 163, A798 (2016). Acknowledgement The authors gratefully acknowledge BASF SE for financial support of this research through the framework of its Scientific Network on Electrochemistry and Batteries. Figure 1. Carbon and electrolyte oxidation upon linear potential sweep from OCV to 5.5 V vs. Li/Li+ at 0.1 mV/s with a 13C-carbon working-electrode and a metallic lithium counter-electrode for an EC-based electrolyte with 1.5 M LiClO4, LiPF6, or LiTFSI, respectively. (a) Current-potential profile, (b) 12CO/12CO2 from electrolyte oxidation, (c) 13CO/13CO2 from carbon oxidation. Figure 1

Evaluation of manganese dioxide deposition on lead-based electrowinning anodes

In this study, the initial stages of the MnO2 electrodeposition on different lead-based electrowinning anodes (Pb–MnO2 and PbAg) in sulfuric acid electrolyte solutions were investigated. The MnO2 deposition and its preliminary effects on the oxidation of the anodes were studied using electrochemical techniques including potentiostatic polarization and linear potential sweep voltammetry. The potentiostatic polarizations were accompanied by chemical analysis of the electrolyte to investigate the manganese oxidation rates on the anodes. Scanning electron microscopy (SEM) was employed to characterize the deposited MnO2 layers. The presence of MnO2 particles on the Pb–MnO2 composite anode contributed to the deposition of a very uniform, dense, and stable MnO2 layer. The effects of the MnO2 composite particles in the composite anode on the current distribution, Mn3+ disproportionation rate and Mn2+ oxidation rate, were proposed as the possible causes of the observed properties of the MnO2 layer on this anode. The MnO2 layer on the Pb–MnO2 anode grew quickly during the initial stages. This layer became smoother over the course of polarization. Although the oxidation of the anodes was hindered by the deposited MnO2 layer, this effect was more significant on the composite anode than the conventional PbAg anode. This was attributed to different properties of the MnO2 layers deposited on these anodes.

Voltammetric study of PrF3:Sr2+ and NdF3:Ba2+ solid electrolytes

Studies of single crystals of nonstoichiometric fluorides of PrF3:Sr2+ and NdF3:Ba2+ in contact with a Pt electrode were carried out using the method of voltammetry with a linear potential sweep, chronoamperometry, and cyclic voltammetry. The reaction of gaseous oxygen reduction (GOR) at the PrF3:Sr2+/Pt interface was accompanied by appearance of mobile oxygen forms. The catalytic activity of PrF3:Sr2+ with respect to gaseous oxygen, same as CeF3:Sr2+, can be explained by variable valency of praseodymium and cerium fluoride, which creates opportunities for using them in oxygen and oxygen-containing gas sensors. The GOR reaction at the NdF3:Ba2+/Pt interface appeared as a result of anodic polarization. After charging at E = 3.2 V, the NdF3:Ba2+ single crystal was successfully used for fluorination of Sb and Ag. NdF3:Ba2+ is most promising in devices based on reactions with participation of mobile fluoride ion in solid electrolytes, particularly, for generation of gaseous fluorine.

Methanol Oxidation on Pd-Ru/C Nanocatalysts: Role of Electronic Properties and FTIR Studies

In this work, methanol oxidation in alkaline solution was studied on carbon-supported Pd-Ru nanocatalysts of nominal Pd:Ru atomic composition 1:1. The synthesis of the catalysts involved the preparation of nanoparticles in colloidal state by a modified polyol method using two reducers. The nanoparticles were separated from the reaction medium and thoroughly cleaned by a sequence of centrifugation and redispersion steps. After that, the particles were supported on high surface area carbon powder (Vulcan XC-72, Cabot). The total metal load was 20 wt%. The carbon-supported catalyst obtained was repeatedly washed with dilute solution of KOH in ethanol, dilute solution of H2SO4, and hot water. After filtration, the catalyst was dried at 80o C. One sample of Pd/C prepared by the same method was used as reference material. Portions of the as-prepared Pd-Ru/C sample were thermally treated at 200 and 400oC during 4 hours in argon, aiming to verify if the degree of alloying could be increased. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) in solutions devoid of alcohol was used to evaluate the general electrochemical behavior. The CV curves showed a quite thick double layer region indicating the presence of Ru species. The electrocatalytic activities towards methanol oxidation were studied by linear potential sweeps and chronoamperometry. Oxidation of adsorbed CO was also measured. The charges of CO stripping curves allowed determining the Pd electrochemically active areas that were used for calculating current densities. It was observed that the catalytic activity was slightly improved after heat treatment at 200oC, while the treatment at higher temperature had a detrimental effect. Measurements of X-ray absorption spectroscopy were carried out around the Pd L3 edge (3173 eV) in order to evaluate the relevance of electronic effects. Despite the fact that these experiments could only be made in high vacuum conditions, it was found that current densities of methanol oxidation measured at 0.5 V vs RHE can be correlated with the Pd 4d band vacancy. It was observed that the methanol oxidation current density increases as the Pd 4d band vacancy becomes larger, in a way similar to what was observed for methanol oxidation in acid solution on Pt-Ru catalysts [1,2]. In situ Fourier transform infrared spectroscopy (in situ FTIR) experiments were performed in order to determine the distribution of reaction products as a function of the applied potential. In a general manner, data showed the formation of formate and the presence of small amounts of adsorbed CO between 0.3 and 0.7 V. The formation of CO2was only observed above 0.7 V as result of the acidification of the thin layer of solution in contact with the catalyst that is caused by the production of protons during methanol oxidation. Acknowledgments Thanks are due to the Brazilian Agencies FAPESP (2014/12255-6; 2013/50206-4; 2013/01822-4) and CNPq (407143/2013-0) for financial support and fellowships. Thanks are also due to the Brazilian Synchrotron Light Laboratory (LNLS) for assisting XAS measurements.