Cyclic Voltammetry Traces Research Articles

Investigation of Redox Shuttle Generation in LiFePO4/Graphite and NMC811/Graphite Cells for Different Additives and Conducting Salts

LFP/Graphite cells are attractive because they are cheaper[1], safer[2,3] and can achieve acceptable energy density for most applications. A limitation of the LFP/Graphite cells is their inferior capacity retention at elevated temperature when compared to NMC/Graphite cells especially in the absence of electrolyte additives, e.g., VC (Vinylene carbonate), as observed by our group in a recent study[4].The time it takes for a LFP graphite cell to completely self-discharge at 60oC is around 500 hours with a base electrolyte of 1.5 M LiPF6 (Lithium hexafluorophosphate) dissolved in 7:3 DMC:EC (Dimethyl carbonate/ethylene carbonate)[4]. It also has been observed that during cycling some Fe will accumulate on the anode which can be explained by dissolution of Fe from the cathode and subsequent deposition on the anode. With the same electrolyte as mentioned before we can observe up to 0.2 μg/cm2 on the anode after 60 cycles at 40⁰C[4].The goal of this research is to understand what is happening inside the LFP/Graphite cells by analyzing the electrolyte from cells that only did a formation procedure. We were able to extract different electrolytes from LFP/Graphite and NMC811/Graphite pouch cells. We expected the electrolyte to stay clear as it was just after preparation, but we observed yellow and red colors depending on the temperature of formation. If the electrolyte contained 2%wt VC, no color change was observed. The different electrolytes used for the experiments were LiPF6, LiFSI (Lithium bis(fluorosulfonyl)imide) and LiPF6+2%wt VC all dissolved in 7:3 DMC:EC. The extracted electrolytes were put inside coin cells with an Al foil working-electrode (WE) and a Li foil counter-electrode (CE) and cyclic voltammetry (CV) was done on them from 2.6 V - 3.75 V vs. Li+/Li. The CV traces show the presence of current in the μA range for electrolyte without VC extracted from LFP cells, indicating the presence of a reversible shuttle species. The electrolyte with no VC expected from LFP cells showed more current than the corresponding electrolyte extracted from NMC811 cells. There was almost no current in the coin cells using electrolytes with 2% VC extracted from the LFP and NMC811 cells. We also made systematic experiments at different formation temperature and different wait times before extraction.Figure 1: Observation of the different electrolytes extracted from LFP/Graphite cells with a) 1.5 M LiPF6 EC:DMC 3:7 and b) 1.5 M LiPF6 +2%wt VC EC:DMC 3:7 that did formation at 25, 40 ,55 and 70⁰C (left to right). References W. Li, Y. Cho, W. Yao, Y. Li, A. Cronk, R. Shimizu, M. A. Schroeder, Y. Fu, F. Zou, V. Battaglia, A. Manthiram, M. Zhang, and Y. S. Meng. “Enabling high areal capacity for Co-free high voltage spinel materials in next-generation Li-ion batteries”, Journal of Power Sources, 473 (2020).D. Jian, T. Xuan, D. Haifeng, Y. Ying, W. Wangyan, W. Xuezhe, and H. Yunhui. “Building Safe Lithium-Ion Batteries for Electric Vehicles: A Review”, Electrochem. Energ. Rev. 3, 1–42 (2020).W. Li, H. Wang, Y. Zhang, and M. Ouyang. “Flammability characteristics of the battery vent gas: A case of NCA and LFP lithium-ion batteries during external heating abuse”, Journal of Energy Storage, 24 (2019)E. R. Logan, H. Hebecker, A. Eldesoky, A. Luscombe, M. B. Johnson, and J. R. Dahn. “Performance and Degradation of LiFePO4/Graphite Cells: The Impact of Water Contamination and an Evaluation of Common Electrolyte Additives”, Journal of The Electrochemical Society, 167, 13 (2020) Figure 1

Sulfite food additive electrochemical determination by nucleophilic addition on poly(4-aminodiphenylamine)-4-aminothiophenol-Au composite electrode

Realizing reagentless selective sodium sulfite (SO32−) food-additive sensors for real-time applications is challenging. Regular SO32− additive monitoring is necessary for providing harmless food to consumers. In this study, Au nanoparticles were prepared by electrodepositing Au3+ (+0.75 V vs. saturated calomel electrode) on a glassy carbon (GC) surface. An Au/GC surface self-assembled 4-aminothiophenol (4-ATP) (denoted as 4-ATP-Au/GC). The 4-ATP head group (-SH) was chemisorbed on S-Au/GC, while tail –NH2 was functionalized using 4-aminodiphenylamine (ADPA) via a chemical/electrochemical approach. The as-prepared p-ADPA-4-ATP-Au/GC was thoroughly investigated stepwise by cyclic voltammetry traces and ex situ spectroscopy. We propose an E→CE→-mechanism-based SO32− determination: p-ADPA-4-ATP-Au/GC was electrochemically oxidized to a quinonimine unit and chemically sulfonated by the nucleophilic addition reaction by SO32−. This product was further electrochemically oxidized. The sulfonation of the polymer chains was confirmed using ex situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. The p-ADPA-4-ATP-Au/GC composite electrode exhibited a wide linear range of SO32− detection, from 5 to 160 μM. The sensitivity and detection limit were 0.0176 μA μM−1 and 1.5 μM, respectively. Finally, the p-ADPA-4-ATP-Au/GC was used in food samples containing SO32−, which yielded a recovery in the range of 101.3–102.6%.

(Invited) Activity and Stability of Atomically Dispersed (AD) Fe-C-N ORR Catalyst in Polymer Electrolyte Fuel Cell Environment

Activity and stability of (AD)Fe-N-C catalyst with low Fe content (1.5 at%) have been investigated in a polymer electrolyte fuel cell environment. Previous electron microscopy analyses (SEM, EDS and EELS) have revealed the presence of atomically dispersed Fe atoms coordinated with nitrogen (Fe-Nx) and a partially graphitized microporous carbon structure. In this study, 5-cm2 membrane electrode assemblies (MEAs) were prepared by hot pressing anode gas diffusion electrodes (GDEs, 0.2 mgPt/cm2) to N211 membrane, and brush painting the PGM-free cathode catalyst ink; Sigracet SG29BC GDL was used on cathode side without hot pressing. All performance tests were conducted under differential cell conditions with fixed H2, O2 and air flow rates. Polarization curves obtained in H2/O2 show double Tafel slopes which, in conjunction with the position of the redox potential observed in cyclic voltammetry traces, forms the basis for formulating a distributed ORR (oxygen reduction reaction) kinetic model with potential-dependent available sites and extracting reaction order for P(O2) and relative humidity (RH) dependence and activation energy for temperature dependence. Application of this model to polarization data collected in H2/air provides the basis for formulating the oxygen transport model and leads to 7.7±0.6 mA/cm2 modeled catalyst activity (defined as areal current density at 0.9 V IR-corrected cell voltage in H2/O2,1.5 atm, 80oC, and 100% RH), 31.5-34.3 mA/cm2 cell performance at 1.5 atm, 80oC, 100% RH, and 0.8-2 s/cm O2 transport resistance (Rcf) in the cathode catalyst layer (CCL). The derived value of Rcf for ~100-μm thick PGM-free electrode is 2-3 times higher than the measured Rcf for <10-μm thick low-Pt loaded (<0.1 mgPt/cm2) electrodes. As such, Rcf includes resistance to O2 transport in the CCL secondary pores, and the primary pores and ionomer film surrounding the Fe-Nx active sites within the microporous carbon support. Catalyst durability was characterized in accelerated stress tests (AST) with 0.6-0.95 V trapezoid potential cycles in H2/N2. Although the (AD)Fe-N-C catalyst has low initial activity, it exhibits excellent stability in ASTs considering that the measured polarization curves in H2/air show voltage losses of only 5, 15 and 30 mV after 10k, 20k and 30k cycles, respectively, for an average degradation rate of 3.5 mV/h. The voltage losses are nearly independent of the current density, suggesting that the observed performance degradation is mainly due to loss in catalyst activity and the transport resistance is nearly unaffected by AST. The kinetic model indicates a 50% loss in catalyst activity after 30k AST cycles. We observe similar degradation rate on a load cycle (LC) consisting of H2/air polarization curves under different operating pressures (1-2.5 atm), temperatures (60-95oC), O2 mole fraction (2-21%), and relative humidity (30-100%). The degradation rate is faster under a combined AST and LC, with majority of losses occurring in the load cycles. Figure 1 summarizes the modeled loss in active sites for load cycles in H2/O2 (cell 1), load cycles in H2/air (cell 2), AST cycles in H2/N2 (cell 3), and combined AST and load cycles (cell 4). The model indicates <20% increase in the O2 transport resistance in the (AD)Fe-N-C catalyst layer with >75% loss of inactive sites. We have used the coupled kinetic, O2 transport and stability model to project the improvements needed in catalyst activity and electrode structure to approach the automotive target of 1000 mW/cm2 stack power density while meeting the 1.45 kW/oC heat rejection (Q/ΔT) constraint at 2.5 atm inlet pressure, 95oC coolant exit temperature, and 1.5 cathode stoichiometry. The model indicates that we need twelve-fold higher mass activity for reducing the kinetic losses, doubling of active site density and an engineered electrode structure for 50% lower sheet resistance, as well as a 50% reduction in electrode thickness to limit the O2 transport losses. Such an automotive competitive PGM-free catalyst will exceed 22.6 mA/mg mass activity for >43.3 mA/cm2 specific activity at 1.9 mg/cm2 catalyst loading in an electrode structure that is <50-μm thick and engineered for <50 mΩ.cm2 sheet resistance. It will reach 1150 mA/cm2 current density at 656 mV for 750 mW/cm2 power density at Q/ΔT relevant operating conditions, after incurring voltage losses of 405 mV for ORR kinetics, 70 mV for combined proton transport in membrane and CCL, and 35 mV for O2 transport across the gas channel, GDL and CCL. Figure 1

Performance of Polymer Electrolyte Fuel Cell Electrodes with Atomically Dispersed (AD) Fe-C-N ORR Catalyst

Activity of (AD)Fe-N-C catalyst with low Fe content is investigated in differential cells prepared by hot pressing anode gas diffusion electrodes (0.2 mgPt/cm2) to N211 membrane and brush painting the cathode catalyst ink. Polarization curves obtained in H2/O2 show double Tafel slopes which, in conjunction with the redox potential observed in cyclic voltammetry traces, forms the basis for a distributed ORR (oxygen reduction reaction) kinetic model with potential-dependent available sites. Application of this model to polarization data in H2/air provides the basis for formulating an oxygen transport model and leads to 7.7 ± 0.6 mA/cm2 catalyst activity at 0.9 V, 31.5–34.3 mA/cm2 cell performance at 0.8 V, and 0.8-2 s/cm O2 transport resistance. A coupled kinetic, O2 transport and proton transport illustrates the projected improvements needed in catalyst activity and electrode structure to approach the automotive target of 1000 mW/cm2 stack power density while meeting the 1.45 kW/°C heat rejection constraint at 1.5 cathode stoichiometry. The model indicates that we need twelve-fold higher mass activity for reducing the kinetic losses, doubling of active site density and an engineered electrode structure for 50% lower proton transport resistance, as well as a 50% reduction in electrode thickness to limit the O2 transport losses.

Carbazolyl-substituted quinazolinones as high-triplet-energy materials for phosphorescent organic light emitting diodes

A series of carbazolyl-substituted quinazolinones were designed and synthesized by the Pd-catalyzed Buchwald-Hartwig, Suzuki and Heck cross-coupling reactions. Their optical, photophysical, thermal, electrochemical, and electroluminescent properties were investigated. The characterization of the synthesized compounds was carried out using experimental and theoretical methods. The determined geometries of the compounds lead to the HOMO distribution on the quinazolinone moiety and the different donor substituents. The synthesized compounds form glasses with the glass transition temperatures ranging from 97 to 159 °C. Their solutions in tetrahydrofuran absorb electromagnetic radiation in the range of 210–420 nm and emit in the range of 350–600 nm. The Stokes shifts recorded for the dilute solutions of compounds ranged from 48 to 134 nm, while those observed for the solid films were similarly in the range of 46–113 nm. The highest fluorescence quantum yield of 44.3% was recorded for the solution of 3-(9-ethyl-9H-carbazol-3-yl)-5-((E)-2-(9-ethyl-9H-carbazol-3-yl)ethenyl)-2-methylquinazolin-4(3H)-one. The triplet energy levels established for the dilute solutions of the compounds from their phosphorescence spectra at 77 K were found to be in the range of 2.55–2.99 eV. The ionization potentials of the synthesized compounds established by photoelectron emission technique in air ranged from 5.35 to 5.66 eV. The electrochemical properties of the derivatives were studied by cyclic voltammetry. All the studied compounds showed irreversible oxidation and no reduction waves. Their repeated cyclic voltammetry scans displayed increasing changes in the cyclic voltammetry traces, proving that a series of electro-polymerization reactions of the radical cations occurred. Time-of-flight hole drift mobility of the solid layer of 5-(bis(4-tert-butyldiphenyl)amino)-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one reached 1.1 × 10−3 cm2/Vs at an electric field of 8.1 × 105 V/cm. This compound was tested as a host in the green and blue phosphorescent organic light emitting diodes achieving maximum external quantum efficiencies of ca. 7.1 and 6.9%, respectively.

Nanocomposite Thin Film of Poly(3-aminobenzoic acid) and Multiwalled Carbon Nanotubes Fabricated through an Electrochemical Method

The composite thin films of poly(3-aminobenzoic acid) (PABA) and multiwalled carbon nanotubes (MWNTs) are successfully fabricated through an electrochemical method. The composite mixtures containing 50 mM of 3-aminobenzoic acid with various concentrations of MWNTs (1.0, 2.5, 5.0, 7.5, and 10 mg/mL) in 0.5 M H2SO4were prepared and used in this study. Cyclic voltammetry (CV) was used for fabrication and monitoring the electropolymerization of the composite thin films with potential range of 0 to 1100 mV for 5 cycles at scan rate of 20 mV/s on indium tin oxide- (ITO)-coated glass substrate. UV-vis absorption spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques were employed to characterize the obtained composite thin films. It was found that MWNTs can enhance the peak current of CV traces of the PABA/MWNTs composite thin films without affecting the UV-vis absorption spectra. The surface morphology of the thin films can be studied using AFM and SEM techniques.

Antioxidant activity of flavone C-glucosides determined by updated analytical strategies

The antioxidant activity of flavone C-glucosides, namely orientin (OR), homoorientin (hOR), vitexin (VT) and isovitexin (iVT) in comparison to quercetin (Q) was measured against 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation (ABTS +), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH ), superoxide anion radical O 2 - whilst the reducing activity was determined by cyclic voltammetry (CV) method. The order of the antioxidant activity determined against ABTS + and DPPH radicals was as follows: Q ≥ hOR > OR ⋙ iVT > VT . Orientin (OR) and homoorientin (hOR) showed the highest ability to scavenge superoxide anion radicals whilst about threefold lower was found for VT and iVT. The order of the antioxidant activity determined against superoxide anion radicals was hOR > OR > Q > iVT = VT. The reducing activity of hOR and OR derived from CV experiments performed within the range from −100 to +1300 mV showed twofold higher values than those determined for VT and iVT. In contrast, when CV tracing was carried out from −100 to +800 mV, the order of the antioxidant activity was as follows: Q > hOR = OR, and no antioxidant activity of VT and iVT was noted.

Room-Temperature Mechanosynthesis of Ni3S2 as Cathode Material for Rechargeable Lithium Polymer Batteries

The formation of was realized by mechanical alloying with metallic nickel and sulfur powder as precursors. The products were characterized by X-ray diffraction, thermoanalysis, and scanning electron microscopy. Electrochemical properties of cells were also presented. The initial discharge capacity of was , with a platform at about vs . A capacity fading rate of 0.5% per cycle was achieved within . The charge–discharge mechanism of was implied by the analysis of the charge–discharge potential profiles, the cyclic voltammetry traces, and the ex situ XRD patterns of the cathode.

The antioxidant activity of Californian red wines does not correlate with wine age

AbstractA range of physico‐chemical properties of 21 Californian red wines from 1 to 28 years old were correlated with wine age. The level of monomeric phenolics and low molecular‐weight phenolic oligomers decreased with age, while the level of high molecular‐weight phenolics increased. On the other hand, total phenols given by the Folin–Ciocalteau method, antioxidant capacity determined using a controlled chain reaction of methyl linoleate and the intensity of the anodic peak determined by cyclic voltammetry (CV) did not show any significant correlation with wine age. Total phenols and the shapes of CV traces were more dependent on the grape variety and the particular viticultural and wine‐making practices rather than on wine age. At the same time, young and aged wines showed a pronounced difference in the shape of [O2] traces recorded during the oxidation of methyl linoleate in a micellar solution inhibited by wine addition. Possible reasons why the antioxidant activity of red wines does not correlate with wine age are discussed. Copyright © 2006 Society of Chemical Industry

Antioxidant status and human health. Use of cyclic voltammetry for the evaluation of the antioxidant capacity of plasma and of edible plants.

The low molecular weight antioxidants (LMWA) play a major role in protecting biological systems against reactive oxygen-derived species (ROS), and reflect the antioxidant capacity of the system. The cyclic voltammetry (CV) has been conveniently used and validated for the quantitation of the antioxidant capacity of the LMWA of blood plasma, tissue homogenates, and plant extracts. The CV tracing provides the biological oxidation potential (E and E1/2 which relate to the nature of the molecule(s)), the intensity of the anodic current wave (Ia), and its area S (both relate to the concentration of the molecule(s)). The components of the first anodic wave of plasma were identified by comparison with HPLC-electrochemical detection. CV together with another plasma parameter R, which reflects the level of oxidized ascorbate, were used for the evaluation of the antioxidant status and the oxidative stress in healthy subjects and in chronic (diabetes mellitus) and acute patients (subjected to total body irradiation prior to bone marrow transplantation). These methodologies could be widely employed for rapid evaluation of subjects, in health and disease, for monitoring of their response to treatment and nutritional supplementation, and for screening of specific populations.

Oxidatively Induced Isomerization of Square-Planar [Ni(1,4,8,11-tetraazacyclotetradecane)](ClO(4))(2).

Previous proton NMR and electronic spectroscopy studies have demonstrated that the square-planar complex of Ni(II) and 1,4,8,11-tetraazacyclotetradecane (cyclam) exists in two stable isomeric conformations, namely the R,S,R,S form or trans-I isomer and the R,R,S,S form or trans-III isomer. Electrochemical analysis of the trans-I isomer of Ni(II)-cyclam has demonstrated rapid conversion to the trans-III cyclam conformation following oxidation to Ni(III). The mechanism and kinetics for this oxidatively-induced isomerization were studied by the technique of cyclic voltammetry (CV) with simulation of CV traces by finite-difference computations. The most crucial mechanistic indicator was found to be the transient trans-I-Ni(III) species. This intermediate was detected by CV over a pH range 2-4 and was found to have an apparent half-life of ca. 400 ms at room temperature. Remarkably, this life-time was approximately a billionfold shorter than the corresponding trans-I-Ni(II) species. Measurements made at varied solution temperature and pH demonstrated that the oxidatively induced isomerization followed an apparent square-scheme, where the trans-I/III isomerization process of Ni(III) was independent of pH. This finding precluded a base-catalyzed isomerization process that has been previously identified for the Ni(II) system. Arrhenius plots of the forward isomerization rate constant allowed the extraction of activation parameters for the Ni(III) process. These parameters are discussed with respect to possible rate-determining steps.

The antioxidant properties of thioctic acid: characterization by cyclic voltammetry.

Thioctic acid (TA) level and its antioxidant capacity were monitored by cyclic voltammetry (CV), in solution and in human plasma. A linear correlation between the anodic wave current Ia at 900 mV and [TA] was obtained. This indicates that TA, commonly found in human plasma, is an antioxidant component characterized by a potential E1/2 = 900 mV and constitute, at least in part, the second anodic wave of the CV tracing. When plasma from diabetic patients was analyzed by CV, those patients under treatment with TA showed higher Ia than others not taking the drug. When the patients under treatment with TA were divided into groups according to the severity of their nephropathy, or according to the severity of their total complication count, Ia levels representing TA were significantly higher in those patients with more severe complications.

Evaluation of Plasma Low Molecular Weight Antioxidant Capacity by Cyclic Voltammetry

The low molecular weight antioxidants (LMWA) of biological samples include many compounds and contribute to the total antioxidant capacity of the system. They act as direct chemical scavengers neutralizing, reactive oxygen-derived species (ROS), and contribute to the ability of the sample to cope with oxidative stress. We propose cyclic voltammetry (CV) as a new method for evaluating the antioxidant capacity of plasma-LMWA and the severity of oxidative stress exerted on the plasma. It is based on the reducing properties of these molecules. CV has been proven to be a simple, sensitive and reliable method. Its tracing does not change during storage of frozen plasma for up to six months. We analyzed the CV tracings by the oxidation potential E 1 2 , and the current heights Ia of its anodic wave(s). E 1 2 indicates the specific component of the LMWA and its ability to donate electron(s); Ia indicates the concentration of this component. Two anodic waves have been identified in human plasma, at E 1 2 = 420 ± 25 and 920 ± 25 mV. Ascorbate (AA) and urate (UA) were identified as major LMWA components of the first anodic wave, and were confirmed by HPLC-electrochemical detection. Ia was shown to depend linearly on the concentration of either of these LMWA, both in buffer and in plasma. Oxidative stress exerted by exposure to peroxyl radicals, copper ions and ionizing irradiation caused marked changes in the CV tracing. These changes represent corresponding alterations particularly in Ia, rather than in E 1 2 . The Ia and E 1 2 values reflect the antioxidant capacity of the plasma, while the change of Ia value represents the severity of the oxidative stress induced. Copyright © 1996 Elsevier Science Inc.