Anodic Potential Limit Research Articles

Revealing the causes of degradation of an asymmetric ionic liquid supercapacitor with a composite polyaniline/carbon electrode

The extended window of electrochemical stability of ionic liquids and the high specific capacitance values of activated carbon (AC)/conductive polymer (polyaniline, Pani) composite materials are promising approaches to improve the performance of supercapacitors (SC).In this work, we studied the stability of an asymmetric AC//Pani-C cell with 1 M solution of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) in acetonitrile as an electrolyte. Pani-C (56 wt% of Pani) composite was prepared by oxidative polymerization of aniline in the presence of high surface area AC (SBET = 2300 m2‧g−1). Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission and scanning electron microscopies data confirmed the formation of Pani-C composite. Combination of cyclic voltammetry, galvanostatic charge/discharge method, and electrochemical impedance spectroscopy in 2- and 3-electrode cell configurations gave information about anodic (1 V vs. Ti) and cathodic (−1.8 V vs. Ti) potential limits of electrochemical stability, and potential of zero charge of Pani-C and AC.From these data, optimal mass ratio of Pani-C and AC electrodes was obtained for asymmetric SC assembly. It was found that after 500 charge/discharge cycles, the capacitance of the asymmetric AC//Pani-C SC decreased by 15% from 46.8 to 39.9 F·g−1 as a result of Pani-C degradation. The specific capacitance of AC remained virtually unchanged (decreased from 144 to 141 F·g−1), while that of Pani-C decreased by 8.7% from 230 to 210 F·g−1. Electrochemical measurements showed that degradation is accompanied by an increase in the working potential window of Pani-C (from 0.85 V to 0.97 V) and a shift in Emin…Emax working potentials from 0.15 … 1 to 0.52 … 1.49 V vs. Ti in the beginning and in the end of stability test, respectively. The last region is related to the potential for non-conductive pernigraniline formation (1.3 V vs. Ti). It was shown that the main reason of AC//Pani-C SC capacitance decay is a gradual increase in the operating potential window with a constantly shifts towards anodic values of positive Pani-C electrode, which resulted in accumulation of nonconductive polymer form that does not participate in charge accumulation.

Comparative Study of Guanidine-, Acetamidine- and Urea-Based Chloroaluminate Electrolytes for an Aluminum Battery.

Aluminum-based batteries are a promising alternative to lithium-ion as they are considered to be low-cost and more friendly to the environment. In addition, aluminum is abundant and evenly distributed across the globe. Many studies and Al battery prototypes use imidazolium chloroaluminate electrolytes because of their good rheological and electrochemical performance. However, these electrolytes are very expensive, and so cost is a barrier to industrial scale-up. A urea-based electrolyte, AlCl3:Urea, has been proposed as an alternative, but its performance is relatively poor because of its high viscosity and low conductivity. This type of electrolyte has become known as an ionic liquid analogue (ILA). In this contribution, we proposed two Lewis base salt precursors, namely, guanidine hydrochloride and acetamidine hydrochloride, as alternatives to the urea-based ILA. We present the study of three ILAs, AlCl3:Guanidine, AlCl3:Acetamidine, and AlCl3:Urea, examining their rheology, electrochemistry, NMR spectra, and coin-cell performance. The room temperature viscosities of both AlCl3:Guanidine (52.9 cP) and AlCl3:Acetamidine (76.0 cP) were significantly lower than those of the urea-based liquid (240.9 cP), and their conductivities were correspondingly higher. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) showed that all three electrolytes exhibit reversible deposition/dissolution of Al, but LSV indicated that AlCl3:Guanidine and AlCl3:Acetamidine ILAs have superior anodic stability compared to the AlCl3:Urea electrolyte, as evidenced by anodic potential limits of +2.23 V for both AlCl3:Guanidine and AlCl3:Acetamidine and +2.12 V for AlCl3:Urea. Coin-cell tests showed that both AlCl3:Guanidine and AlCl3:Acetamidine ILA exhibit a higher Coulombic efficiency (98 and 97%, respectively) than the AlCl3:Urea electrolyte system, which has an efficiency of 88% after 100 cycles at 60 mA g-1. Overall, we show that AlCl3:Guanidine and AlCl3:Acetamidine have superior performance when compared to AlCl3:Urea, while maintaining low economic cost. We consider these to be valuable alternative materials for Al-based battery systems, especially for commercial production.

Available and Cheap Methodology for Accurate Onset Potential and Tafel Slope Determination of Earth-Abundant Water Oxidation Electrocatalysts

To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behaviour the determination of the onset potential and Tafel slope in each studied electrolyte are key parameters.[1] Nevertheless, this evaluation becomes particularly problematic for first-transition metal catalysts as well as by the use of electroactive collectors whose redox peaks overlap the onset potential and hinder the correct determination of Tafel slope.[2] A usual solution to solve this problem is the in-situ determination of generated oxygen by mass spectrometry.[3]However, this in-situ determination is very expensive and only available in few laboratories. To overcome these limitations, coulovoltammetric response obtained from cyclic voltammetry allow a quantitative separation in the same potential range of the charge consumed by reversible (redox peak) reactions and the charge consumed by the irreversible reaction: the oxygen release. Accordingly, by means of quantifying the irreversible charges for different anodic potential limits is possible the unambiguous determination of both, the onset potential and the Tafel slope values isolating the catalyst redox contributions. To demonstrate the use of this technique, the onset potential and the Tafel slope for three benchmark electrocatalysts based on first-transition metal: a layered double hydroxide, a Prussian blue analogue and a β-Layered hydroxide were determined.[4] This study evidence the potential of coulovoltammetry as a straightforward and powerful tool for the investigation of electrocatalytic performances.

Temperature-Dependent Electrochemical Stability Window of Bis(trifluoromethanesulfonyl)imide and Bis(fluorosulfonyl)imide Anion Based Ionic Liquids.

The electrochemical stability of 22 commercially available hydrophobic ionic liquids was measured at different temperatures (288.15, 298.15, 313.15, 333.15 and 358.15 K), to systematically investigate ionic liquids towards electrolytes for supercapacitors in harsh weather conditions. Bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)imide anions in combination with 1-Butyl-1-methylpyrrolidinium, 1-Ethyl-3-methylimidazolium, N-Ethyl-N, N-dimethyl-N(2methoxyethyl)ammonium, 1-Methyl-1-(2-methoxyethyl)pyrrolidinium, N-Pentyl-N-methylpyrrolidinium, N, N-Diethyl-N-methyl-N-propylammonium, N, N-Dimethyl-N-ethyl-N-benzyl ammonium, N, N-Dimethyl-N-Ethyl-N-phenylethylammonium, N-Butyl-N-methylpiperidinium, 1-Methyl-1-propylpiperidinium, N-Tributyl-N-methylammonium, N-Trimethyl-N-butylammonium, N-Trimethyl-N-butylammonium, N-Trimethyl-N-propylammonium, N-Propyl-N-methylpyrrolidinium cations were selected for the study. Linear regression with a numerical model was used in combination with voltammetry experiments to deduce the temperature sensitivity of both anodic and cathodic potential limits (defining the electrochemical stability window), in addition to extrapolating results to 283.15 and 363.15 K. We evaluated the influence of the cations, anions, and the presence of functional groups on the observed electrochemical stability window which ranged from 4.1 to 6.1 V.

Combined Electrochemical, Ellipsometric and Microgravimetric Study of Ion Permeable Polydopamine Films

The facile deposition of polydopamine on virtually any material and its recognized adhesive properties justify its extensive application in the biomedical field. However, these films are heterogeneous, poorly conductive and impermeable to many small molecules and ions, limiting their use in electrochemical applications. Hereby, we have potentiodynamically grown polydopamine films on gold using an anodic potential limit of 1.1 V, higher than the typically used values (0.5−0.8 V), aiming at preparing thick and permeable films. The mass increment during the electropolymerization of dopamine undergoes an abrupt change upon the 20th potential cycle, forming a more porous coating, compared to the polymer grown up to 0.8 V. By modelling in situ ellipsometric data, the abrupt phenomenon could be related to a temporary and local loss of polymer adherence to the surface, with the creation of a very porous layer, that is fulfilled in the subsequent cycles with new polymer fibers. Consequently, drastic topographic changes are depicted in polymers grown with 20 and 100 cycles, by atomic force microscopy. Films prepared with 100 cycles are thicker, more electroactive and more permeable to ionic species, than thinner films, unraveling their potential as adhesive matrices in electrochemical transduction devices.

High-voltage structural evolution and its kinetic consequences for the Na4MnV(PO4)3 sodium-ion battery cathode material

The recently demonstrated possibility of high-voltage extraction of more than 2 Na ions per Na4MnV(PO4)3 formula unit is considered as a possible way to increase the specific energy of this material, which would open up prospects for its application in sodium-ion batteries. However, for the Na4MnV(PO4)3 material and for a wide group of related NASICON-structured materials, high-voltage Na extraction was demonstrated to lead to a rapid decrease in capacity and a sharp increase in hysteresis between the charge and discharge curves. In this work, we use electrochemical and structural analysis to elucidate the reasons for the degradation observed after deep desodiation of Na4MnV(PO4)3. X-ray diffraction analysis of the electrodes after cycling demonstrates that a phase transformation is initiated when the anodic potential limit exceeds 3.8 V, which results in the formation of distorted NASICON-type phases and gradual amorphization. X-ray absorption spectroscopy studies suggest that the observed detrimental phase transitions might be triggered by the changes in the local environment of oxidized vanadium, which destabilize the structure. We thus demonstrate that the degradation of the Na4MnV(PO4)3 material is of thermodynamic origin, with its consequences being reflected in a dramatically decreased de/intercalation rates and a rapid deterioration in the material performance.

Improving the onset potential and Tafel slope determination of earth-abundant water oxidation electrocatalysts

To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behavior the determination of the onset potential in each studied electrolyte is a key parameter. Nevertheless, this evaluation becomes particularly problematic for first-transition metal catalysts as well as by the use of electroactive collectors (e.g. Ni foams) whose redox peaks overlap the onset potential. A usual solution to detect the onset potential requires the availability of in-situ mass spectrometric determination of the generated oxygen. In this work, we present fast and easier available cyclic voltammetry and coulovoltammetric responses to determine the onset potentials of three benchmark electrocatalysts: a layered double hydroxide, a Prussian blue analogue and a β-Layered hydroxide. Cyclic coulovoltammetric responses allow, as we demonstrate here, a quantitative separation in the same potential range of the charge consumed by reversible (redox) reactions and the charge consumed by the irreversible reaction: the oxygen release. Quantifying the irreversible charges (that correspond to the OER) for different anodic potential limits permits the unambiguous determination of both, the onset potential and the Tafel slope values without the catalyst redox contributions. As far as we know, this is the first time that this fast, available and cheap methodology has been applied for the OER determination. Thus, coulovoltammetry arises as a friendly and powerful tool for the investigation of electrocatalytic performances.

Physicochemical and electrochemical properties of the (fluorosulfonyl)(trifluoromethylsulfonyl)amide ionic liquid for Na secondary batteries

In this study, thermal, physical, and electrochemical properties of the ionic liquid electrolyte system, Na[FTA]-[C3C1pyrr][FTA], (FTA‒ = (fluorosulfonyl) (trifluoromethylsulfonyl)amide and C3C1pyrr+ = N-methyl-N-propylpyrrolidinium) have been investigated for Na secondary batteries. The asymmetric FTA‒ structure provides a wide liquid-phase temperature range, especially at low x(Na[FTA]) (x(Na[FTA]) = molar fraction of Na[FTA]) and low temperature range. Glass transition at 170–209 K is the only observed thermal behavior in the x(Na[FTA]) of 0.0–0.4. Temperature dependence of viscosity and ionic conductivity obeys the Vogel‒Tammann‒Fulcher equation, and the correlation between molar conductivity and viscosity follows the fractional Walden rule. The anodic potential limits are above 5 V vs. Na+/Na at 298 and 363 K. The noticeable effects of x(Na[FTA]) are observed in the electrochemical performance of Na metal and hard carbon electrodes. In both cases, a moderate concentration, x(Na[FTA]) of 0.2–0.3, enables favorable charge-discharge behavior. At 363 K, the discharge capacities of the hard carbon electrode at x(Na[FTA]) of 0.3 are 260 and 236 mAh g−1 at the current densities of 20 and 200 mA g−1, respectively. The optimum cycling performance occurs at x(Na[FTA]) = 0.3, providing satisfactory capacity retention and high average Coulombic efficiency.

Propionitrile as a single organic solvent for high voltage electric double-layer capacitors

This study investigates the novel use of propionitrile (PN) as the single organic solvent for high-voltage carbon/carbon capacitors. Quaternary ammonium salts spiro-(1,1ʹ)-bipyrrolidinium tetrafluoroborate (SBPBF4) and 1,1-dimethylpyrrolidinium tetrafluoroborate (DMPBF4) dissolved in acetonitrile (AN) and propionitrile (PN) are compared. PN-based electrolytes exhibit a large and symmetric electrochemical stability, an exceptional anodic potential limit, good ionic conductivity, and low viscosity, allowing EDLCs to operate at 3.5 V even with a high current density (2.5 A g−1). Moreover, PN-based electrolytes can suppress the anodic dissolution of the Al current collector at a high potential. These advantages help in the realization of EDLCs with excellent cycling stabilities at high voltages. As a result, at 3.5 V, EDLCs with PN-based electrolytes exhibit the highest energy and power density of 49.3 Wh kg−1 and 22.9 kW kg−1, respectively. Therefore, the electrolyte systems reported here could be a promising electrolyte candidate to replace currently commercialized electrolytes for practical applications.

Controlling Surface Oxygen Concentration of a Nanocarbon Film Electrode for Improvement of Target Analytes.

A nanocarbon film consisting of nanocrystallites with mixed sp2 and sp3 bonds formed by unbalanced magnetron sputtering, was studied with respect to changes in the characteristics caused by the surface oxygen concentration. An electrochemical pretreatment (ECP) was conducted to change the surface oxygen concentration of the nanocarbon film. X-ray photoelectron spectroscopy (XPS) measurements revealed that nanocarbon films with different amounts of surface oxygen could be prepared. In addition, we observed no significant increase of surface roughness (Ra) at the angstrom level after ECP, owing to a stable structure containing 40% of sp3 bonds. The electrode characteristics, including the potential window, and electrochemical properties for some redox species, such as Ru(NH3)63+/2+, Fe(CN)63-/4- and some biomolecules, were investigated. The anodic potential limit became wider and ΔEp of Fe(CN)63-/4- became smaller at the treated nanocarbon film electrode than those of the as-deposited nanocarbon film electrode. Based on these results, we realized to measure uridylic acid (UMP) and inosine triphosphate (ITP) with a high oxidation potential by direct oxidation, which was difficult to measure at the as-deposited nanocarbon film electrode.

Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen Reduction Reaction Catalyst.

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mgPt-1 at 0.9 VRHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mgPt-1 at 0.9 Vcell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core-shell catalysts.

Hunting ionic liquids with large electrochemical potential windows

Ionic liquids (ILs) with large electrochemical potential windows (EPWs) are ideally suited to improve the energy and power density of electrical devices for energy storage. However, guidelines are scarcely available for the selection or systematic screening of ILs for practical applications. Here, we present theoretical predictions for the EPW of thousands of cation‐anion pairs based on a long‐range corrected hybrid density functional theory. The cathodic and anodic potential limits were estimated from the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of individual cations and anions. The approximate method predicts EPWs in reasonable agreement with existing experimental data for several commonly used ionic systems and can be used as a screening tool for a large library of ILs. Five most stable anions, with the cathode stability in the order of B[CN]4 > PF6 > BF4 > BOB>NTf2, have been identified. These anions provide the largest EPWs when they are paired with conventional organic cations. The cation stability is reduced upon elongation of the alkyl chain length or branching of the molecular backbone. © 2018 American Institute of Chemical Engineers AIChE J, 65: 804–810, 2019

Atomic Layer-Deposited Molybdenum Oxide/Carbon Nanotube Hybrid Electrodes: The Influence of Crystal Structure on Lithium-Ion Capacitor Performance.

Merging of supercapacitors and batteries promises the creation of electrochemical energy storage devices that combine high specific energy, power, and cycling stability. For that purpose, lithium-ion capacitors (LICs) that store energy by lithiation reactions at the negative electrode and double-layer formation at the positive electrode are currently investigated. In this study, we explore the suitability of molybdenum oxide as a negative electrode material in LICs for the first time. Molybdenum oxide-carbon nanotube hybrid materials were synthesized via atomic layer deposition, and different crystal structures and morphologies were obtained by post-deposition annealing. These model materials are first structurally characterized and electrochemically evaluated in half-cells. Benchmarking in LIC full-cells revealed the influences of crystal structure, half-cell capacity, and rate handling on the actual device level performance metrics. The energy efficiency, specific energy, and power are mainly influenced by the overpotential and kinetics of the lithiation reaction during charging. Optimized LIC cells show a maximum specific energy of about 70 W·h·kg-1 and a high specific power of 4 kW·kg-1 at 34 W·h·kg-1. The longevity of the LIC cells is drastically increased without significantly reducing the energy by preventing a deep cell discharge, hindering the negative electrode from crossing its anodic potential limit.

Electrochemical Oxidation of Methanol and Ethanol on Electrodeposited Pd and PdNi-Coated Electrodes

Electrodeposited PdNi and Pd samples were tested for methanol and ethanol oxidation reaction (MOR and EOR) in alkaline solution using cyclic voltammetry (CV) and chronoamperometric (CA) measurements. Among the CVs for the MOR, all alloy samples showed higher current densities than pure Pd. Also the peak current densities for MOR of PdNi coatings are 5 to 8 times higher than that obtained on Pd coating depending on composition. Based on the ratio of the forward peak current to the backward peak current the tolerance of the catalysts to accumulation of carbonaceous species is determined. Besides this ratio increased with extending the anodic potential limit. The most tolerant catalyst is found to be Pd0.74Ni0.28 in methanol oxidation. Comparative study of methanol and ethanol electrooxidation in the alkaline media reveals that Pd0.74Ni0.26 alloy has a higher catalytic activity, as well as a better tolerance to accumulation of carbonaceous species.

(Invited) Role of Stress Induced By Anion Incorporation in Formation of Porous Anodic Alumina Films

Procedures to grow porous anodic alumina films with ordered and controllable arrangements of nanoscale pores have led to extensive research on PAA films as functional materials. Experiments and calculations show that transport in the oxide is assisted by plastic flow driven by mechanical stress (1-3). Pores initiate as the result of a morphological instability at the oxide-solution interface of the initially formed barrier oxide (4). Stress distribution measurements revealed high near-surface compressive stress levels, which may be associated with locally elevated concentrations of incorporated electrolyte anions. The instability leading to pore formation may be influenced by flow driven by anion incorporation-induced stress (5). Direct evidence for anion-induced stress in aluminum oxide was sought through stress measurements during open-circuit immersion of Al in phosphoric and sulfuric acids. The stress is compared with elastic anion incorporation-induced stress calculated from X-ray photoelectron spectroscopy (XPS) measurements of film composition. Al sheet samples of 99.998% purity were exposed at open circuit in either 0.4 M H3PO4 or 0.4 M H2SO4 solutions. In situ stress measurements during acid dissolution were carried out by phase-shifting curvature interferometry (6). According to the thin-film Stoney approximation, the detected sample curvature changes are directly related to the surface force change per sample width. The force per width is the biaxial in-plane stress integrated through the sample thickness. XPS was performed with a K-alpha instrument (Thermo Scientific) (7). The relative concentrations of P, S, Al, and O in the oxide were determined from areas of P2s, S2s, Al2p, O1s peaks. The oxide thickness and the anion concentration per area were determined from the relative areas of the Al2p peak contributions from oxide and metal. Fig. 1 shows that upon immersion of Al in both acids, force per width increased abruptly in the compressive direction to 2 min, and then relaxed slowly to constant levels. The initial compressive increases are not due to mechanical disturbances, as they significantly exceed the stress change in distilled water. The hypothetical anion incorporation-induced stress was calculated from the anion concentration per area by assuming that all the detected anions are absorbed within the oxide. The elastic force per width accompanying incorporation is then FwA = -(2/9) W A EoxNA /(1 - n ox ) where WA is the anion molar volume, Eox and n ox the elastic modulus and Poisson's ratio of alumina, and NA the per-area anion concentration from XPS. Fig. 1 shows that for dissolution in H2SO4, FwA is in excellent agreement with the measured force at all times. For H3PO4, agreement during the initial compressive increase is found but thereafter phosphate adsorption causes the calculation to diverge. Fig. 1 is strong evidence that anion incorporation in alumina films induces compressive stress. The stress of ~ 2 GPa inferred from the figure are comparable to near-surface stress levels measured earlier in anodic films (5). Additionally, we discuss evidence for anion-incorporated surface layers in anodic alumina from high-voltage cyclic voltammetry (CV) experiments (8). At high scan rates, the current-voltage dependence in the cathodic-direction scan reveals the conduction characteristics of the anodic film. By varying the anodic potential limit of CV, the dependences of conduction on both film thickness and electric field are assessed. High-resistivity surface layers are revealed in anodic films formed in phosphoric, sulfuric and oxalic acids. An instability mechanism for anodic alumina is described in which both the high resistivity and elevated stress level of the anion-containing near-surface layer play important roles. ACKNOWLEDGMENT Financial support was provided by JFE Steel Corporation and China Scholarship Council. REFERENCES 1. S. J. Garcia-Vergara, et al., Electrochim. Acta. 52, 681 (2006). 2. J. E. Houser, K. R. Hebert, Nature Mater. 8, 415 (2009). 3. J. Oh, C. V. Thompson, Electrochim. Acta, 56, 4044 (2011). 4. P. Mishra, K. R. Hebert, Electrochim. Acta, 222, 1186-1190 (2016). 5. Ö. Ö. Çapraz, et al., Electrochim. Acta 167, 404-411 (2015). 6. Ö. Ö. Çapraz, K. R. Hebert, P. Shrotriya, J. Electrochem. Soc., 160, D501-516 (2013). 7. Ö. Ö. Çapraz et al., Electrochim. Acta, 238, 368-374 (2017). 8. S. Ide, P. Mishra and K. R. Hebert, Electrochim. Acta, 221, 1-7 (2016). Figure 1

Potential‐Driven On/Off Switch Strategy for the Electrosynthesis of [7]Helicene‐Derived Polymers

AbstractNew materials bearing thiophene and helicene moieties were prepared by using a potential‐driven on/off switch strategy on the surface of glassy carbon and indium tin oxide substrates. Specifically, a 3‐([7]helicen‐9‐yl)‐thiophene hybrid monomer was electrooxidized in acetonitrile by using cyclic voltammetry with anodic potential limits of +1.5 or +2.5 V, resulting in a conductive and non‐conductive polymer, respectively. The electrochemical findings were supplemented by microscopy investigations, UV/Vis, fluorescence and vibrational spectroscopies, and 1H NMR spectroscopy as well as ellipsometry measurements and computational chemistry. The electrodeposited polymers could be used for the further development of materials applicable in organic electronics, optoelectronics, and sensing technologies.

Influence of boron content on the morphological, spectral, and electroanalytical characteristics of anodically oxidized boron-doped diamond electrodes

The effect of boron content in nanocrystalline anodically polarized boron doped diamond (BDD) thin films deposited at B/C ratio 500ppm – 8000ppm on their morphology, quality, and electrochemical and spectral properties was investigated using scanning electron and atomic force microscopies and Raman spectroscopy, where the shift of maximum Lorentzian component of diamond phonon at ∼1332cm−1 was used as the function of boron concentration. Cyclic voltammetry with the outer- and inner sphere redox markers ([Ru(NH3)6]3+/2+ and [Fe(CN)6]3−/4−) enables to differentiate among the semiconductive films (500ppm and 1000ppm) and films with metallic conductivity (2000ppm – 8000ppm). Nevertheless, only the inner sphere character of [Fe(CN)6]3−/4− redox marker enables to visualize the differences between individual boron content for metallic films. Further, reversible behavior with ΔEp of 59.8±0.9mV (n=5) and Ipa/Ipc ratio 1.00 at the scan rate of 100mVs−1 was achieved for this redox marker at 2000ppm film; this film just above the semiconductive/metallic threshold exhibited also favorable spectral (e.g., roughness surface factor) and electrochemical characteristics. The width of the potential window in aqueous media of different pH values and in wide variety of supporting electrolytes decreases with increasing boron content, with independence of anodic potential limit for 2000ppm – 8000ppm electrodes and more pronounced dependence of cathodic potential limit on boron content for all tested BDD films. Further, well-defined and highly reproducible anodic DP voltammetric peak of 2-aminobiphenyl with peak current increasing with boron content were obtained at ca +0.7V (vs. Ag/AgCl/3molL−1 KCl) at all BDD films tested.

Pitting Corrosion of Zn Peculiarly Caused by Acetate Anions

Abstract The corrosion behaviour of zinc metal was studied in acetate solutions. The potentiodynamic polarization curve in 0.1 M acetate solution displays an anodic peak (A1) owing to the anodic dissolution of zinc followed by a passive layer formation region. Breakdown of the passive film and the initiation of pitting corrosion were observed beyond the pitting potential (E pit) and confirmed by SEM images. The reverse scan of the cyclic voltammogram shows three cathodic peaks; CI, CII and CIII. CI was attributed to the reduction of the pitting corrosion product formed at potentials more anodic than E pit, while the overlapped CII and CIII peaks were attributed to the reduction of the exterior and the interior passive layers, respectively. The potentiostatic current time transients at different applied potentials (around the pitting potential) for different electrolyte concentrations involved three stages. The first stage exhibited rapid current decrease with time till a minimum value (i m) at the incubation time (t i). The second and the third stages, where the current increases again linearly with time through two different slopes, are correlated to the pit nucleation and growth, respectively. An increase of the pit nucleation rate and a decrease in its growth were observed with increasing the anodic potential limit (E a). Electrochemical impedance spectroscopy (EIS) measurements, at different potentials before and after E pit were performed. The effect of the acetate concentration was studied as well. A suggested equivalent circuit was used to fit the EIS data. The impedance results confirmed that the thickness of the formed passive layer increases with proceeding of the anodic potential reaching a maximum value at E pit. The passive film thickness decreased again at more anodic potentials.

Investigation of the Oxidative Stability of Li-Ion Battery Electrolytes Using Cathode Materials

In this study, anodic oxidation limits of Li-ion cell electrolytes are investigated against cathode materials containing various metal ions. These results are compared with inactive cell materials (PVDF/carbon black) and Pt working electrodes. The oxidative stability limits are extracted from galvanostatic cycling tests at low C-rates of (~C/100) which can be used as a measure for electrolyte decomposition limits. It is found that inactive cathode materials affect significantly the anodic decomposition limit of the electrolyte. Therefore such electrode materials can be used instead of inactive electrodes (Pt, stainless steel or glassy carbon) to investigate anodic electrolyte potential limits more reliable.

A Study of the Electrochemical Properties of a New Graphitic Material: GUITAR

AbstractPrevious studies of graphite from the University of Idaho thermolyzed asphalt reaction (GUITAR) indicated two unique properties that distinguish this material from other sp2 hybridized carbon electrodes. In property i, the standard heterogeneous rate constant across the basal plane (BP) of GUITAR with Fe(CN)63−/4− of 0.01 cm s−1 was 2–7 orders of magnitude greater than for BP‐graphite and graphene. With property ii, the anodic potential limit exceeds other graphite forms by 500 mV. Two new properties are now described. In iii, the hydrogen overpotential in 1 M H2SO4 exceeds other graphitic materials by 500 mV. The combination of ii and iii gives a 3 V window in 1 M H2SO4, which is the largest reported for a graphitic material and competitive with diamond electrodes. In iv, effects of air oxidation on the edge planes (EPs) is reversed by mild cathodic reduction and does not allow for electrolyte intercalation. Based on these characteristics and on atomic force micrographs, we hypothesize that GUITAR may be a new allotrope of carbon. Coupled with expected low costs, GUITAR will find a myriad of applications in electrochemical sensors, water purification, as well as energy storage and conversion.