Electrochemical Data Research Articles

Luminescent cyclometalated alkynylplatinum(II) complexes with 1,3-di(pyrimidin-2-yl)benzene ligands: synthesis, electrochemistry, photophysics and computational studies.

In this article, we report on a series of cyclometalated chloro- and alkynyl-platinum(II) complexes bearing various tridentate N^C^N-cyclometalated ligands derived from 1,3-bis(pyrimidin-2-yl)benzene. The X-ray crystal structures of two alkynyl-platinum(II) complexes were determined and other structures were DFT-calculated. Electrochemical and DFT-computational studies suggest a ligand-centred reduction on the R1-substituted N^C^N ligand, whereas oxidation likely occurs either on the Pt-phenylacetylide moiety and/or the cyclometalated ligand. In CH2Cl2 solution at room temperature, the complexes show phosphorescent emissions ranging from green to orange, depending on the R1 and R2 substituents on the ligands. In KBr solid state matrix, excluding complexes bearing a trifluoromethyl substituted ligand, all compounds exhibit red emission. The presence of an alkynyl ancillary ligand has limited influence on absorption and emission spectra except in the case of the complex with the strongly electron-donating diphenylamino R2 substituent on the alkynyl ligand, for which a significant red-shift was observed. The alkynyl Pt(II) complex with OMe groups as both R1 and R2 substituents shows the best emission quantum yield (0.81 in CH2Cl2 solution) in this series. The full series of DFT calculated band gaps correlated generally well with the electrochemical and absorption data and reasonably model the impact of the substituents on the electronics of these complexes.

Impedance-based Solid Oxide Fuel Cell testing as scalable and reliable Quality Control tool for cell and batch manufacturing: first findings

Testing is a necessary step in the manufacturing process of Solid Oxide Fuel Cells (SOFC) to assess the performance of the produced cells before on-field deployment. In this work, the implementation of Electrochemical Impedance Spectroscopy (EIS) and subsequent data elaboration via Equivalent Circuit Modelling (ECM) is evaluated as a viable experimental framework for characterization and Quality Control (QC) of cells or cell batches, complemented to standard polarization-based methods. By performing a statistical analysis of the ECM parameters (representative of each physico-chemical process) the cell and batch operational parameters can be determined and compared. The validity of the proposed methodology is assessed using a wide experimental dataset of a significant number of SOFC samples (20 cells from 3 batches – two of which identical and the third with an intentional modification in the manufacturing process in order to validate the proposed methodology) tested in identical conditions. Results show that the impedance-based method provide detailed information in terms of impedance breakdown (anode gas diffusion process resulting the main criticality), as well as confirming the preliminary results obtained from the polarization approach (Batch#2 showing the lowest total performance and highest uniformity). Highly reproducible intra-batch distributions of the ECM parameters encourage the applicability of such methodology for QC purposes, even with few data collected only in Open Circuit Voltage (OCV) conditions. A relevant deviation of charge transfer and diffusion resistances in Batch#3 respect to other batches is observed (not visible from the polarization curves), which is reconducted to the modified anode functional layer, opening potential applications of the proposed methodology to assess the impact of targeted modifications of manufacturing methods on specific cell electrochemical performances.

Achieving Reliable and Repeatable Electrochemical Impedance Spectroscopy of Rechargeable Batteries at Extra-Low Frequencies

There is a need for techniques for efficient and accurate measurement of the impedance of rechargeable batteries at extra-low frequencies (ELFs, of the order of microhertz), as these reflect real usage and cycling patterns, and their importance in fractional battery circuit modeling is becoming increasingly apparent. Major impediments include the time required to perform such measurements, and ’drift’ in impedance values when measurements are taken from the same battery at different times. Moreover, commercial impedance analyzers are generally unable to measure at these frequencies. We describe here our use of programmable two-quadrant power supplies to deliver multiple small signal measurement tones in the presence of large signal ’working’ currents, and our use of these data to generate impedance measurements with good precision and in reasonable time. The improvement in quality of electrochemical impedance spectroscopy data is verified through root mean square error when fitting equivalent-circuit models.

Comparison of Methodologies to Estimate State-of-Health of Commercial Li-Ion Cells from Electrochemical Frequency Response Data

Comparison of Methodologies to Estimate State-of-Health of Commercial Li-Ion Cells from Electrochemical Frequency Response Data

Modelling the Impedance Response of Graded LiFePO4 Cathodes for Li-Ion Batteries

Graded electrodes for Li-ion batteries aim to exploit controlled variations in local electrode microstructure to improve overall battery performance, including reduced degradation rates and increased capacity at high discharge rates. However, the mechanisms by which grading might deliver performance benefit, and under what conditions, are not yet fully understood. A Li-ion battery electrochemical model (a modified Doyle-Fuller-Newman type model capable of generating impedance functions) is developed in which local microstructural changes are captured in order to understand why and when graded electrodes can offer performance benefits. Model predictions are evaluated against experimental electrochemical impedance data obtained from electrodes with micro-scale, controlled variations in microstructure. A region locally enriched with carbon at the electrode/current collector interface is shown to significantly reduce the overpotential distribution across the thickness of a LiFePO4-based Li-ion battery cathode, resulting in a lower charge transfer resistance and impedance. The insights gained from the LiFePO4-based electrodes are generalised to wider design principles for both uniform and graded Li-ion battery electrodes.

Study of the electrochemical betanidin oxidation path using computational methods.

Betalains can be used in the food, drug, and cosmetic industries and have shown their bioactive potential. For these reasons, unraveling their oxidation mechanism is of high importance and demands a systematic and multidisciplinary study. Moreover, the properties mentioned above are drastically influenced by pH and other physicochemical conditions. Betanidin (1) is a relevant molecule of this family and is crucial to elucidating the oxidation mechanism in which its pigment is involved. In the present study, the pKas and oxidation potential values for all protic groups of 1 were analyzed using B3LYP/6-31+G(d,p)/SMD as the computational methodology. Moreover, six explicit water molecules were added to improve the solvation-free energy values. The oxidation mechanism at each pH was constructed and analyzed in depth. On the other hand, cyclic voltammetry simulations allowed obtaining electrochemical data from experiments and support the proposed mechanism. In the present work, the main oxidation path of 1 is described and consists of a concerted electron-proton transfer followed by a sequential electron and proton transfer to obtain the o-quinone product or a quinone methide molecule.

Кинетические параметры процесса получения молекулярного водорода в присутствии акридина и его производных

In order to study in more detail the mechanism of hydrogen evolution reaction, knowledge of which is ne- cessary for the practical implementation of existing ideas and developments in the field of modern electrocatalysis and hydrogen energy in general, the electrocatalytic properties of acridine and its derivatives in the presence of acids of var- ious natures were studied. The obtained electrochemical data made it possible to calculate the kinetic parameters of these systems, as well as to reveal the dependence of the rate constant of the limiting stage of the hydrogen generation process on the рКа of the acids used. The results of the work will make it possible to treat with greater understanding the creation of «molecular platforms» based on organic compounds, as well as improving the efficiency of the catalytic process and varying the available parameters.

Unsupervised classification of voltammetric data beyond principal component analysis.

In this study, we evaluate different apoproaches to unsupervised classification of cyclic voltammetric data, including Principal Component Analysis (PCA), t-distributed Stochastic Neighbour Embedding (t-SNE), Uniform Manifold Approximation and Projection (UMAP) as well as neural networks. To this end, we exploit a form of transfer learning, based on feature extraction in an image recognition network, VGG-16, in combination with PCA, t-SNE or UMAP. Overall, we find that t-SNE performs best when applied directly to numerical data (noise-free case) or to features (in the presence of noise), followed by UMAP and then PCA.

Electrochemical data mining: from information to knowledge: general discussion.

Electrochemical data mining: from information to knowledge: general discussion.

Data Mining and Application of Decision Tree Modelling on Electrochemical Data Used for Damaged Starch Detection

In this study, unsupervised and supervised machine learning techniques, principal component analysis and classification tree modelling which could be improved with additional input variables were applied on iodine oxidation voltammetric data in order to determine routes and extract information about the electrochemical conditions leading to different damaged starch ratios in flour. For this purpose a database of 3542 observations which was normalized and filtered from outliers was used. It was seen that although it was almost impossible to generalize information or determine correlations from voltammetric data at different conditions, principal component analysis indicate that on platinum electrode UCD values of 16.5 mostly seen at high potentials, optimized decision tree indicate that the impact of variables on UCD values can be ordered as current density > potential > electrode type > KI concentration and give routes to UCD values with high class membership leaf nodes. Therefore machine learning with decision tree modelling could open perspectives for practical and fast prediction of damaged starch ratio which would help food industry to speed up and economize costs for analysis in flour.

Predicting Diagnostic Potential of Cathepsin in Epithelial Ovarian Cancer: A Design Validated by Computational, Biophysical and Electrochemical Data.

Background: Epithelial ovarian cancer remains one of the leading variants of gynecological cancer with a high mortality rate. Feasibility and technical competence for screening and detection of epithelial ovarian cancer remain a major obstacle and the development of point of care diagnostics (POCD) may offer a simple solution for monitoring its progression. Cathepsins have been implicated as biomarkers for cancer progression and metastasis; being a protease, it has an inherent tendency to interact with Cystatin C, a cysteine protease inhibitor. This interaction was assessed for designing a POCD module. Methods: A combinatorial approach encompassing computational, biophysical and electron-transfer kinetics has been used to assess this protease-inhibitor interaction. Results: Calculations predicted two cathepsin candidates, Cathepsin K and Cathepsin L based on their binding energies and structural alignment and both predictions were confirmed experimentally. Differential pulse voltammetry was used to verify the potency of Cathepsin K and Cathepsin L interaction with Cystatin C and assess the selectivity and sensitivity of their electrochemical interactions. Electrochemical measurements indicated selectivity for both the ligands, but with increasing concentrations, there was a marked difference in the sensitivity of the detection. Conclusions: This work validated the utility of dry-lab integration in the wet-lab technique to generate leads for the design of electrochemical diagnostics for epithelial ovarian cancer.

Surface Roughening Strategy for Highly Efficient Bifunctional Electrocatalyst: Combination of Atomic Layer Deposition and Anion Exchange Reaction.

Electrocatalytic water splitting, which is an interface-dominated process, can be significantly accelerated by increasing the number of front-line surface active sites (NA ) of the electrocatalyst. In this study, a unique method is used for increasing the NA by converting the smooth ultrathin atomic-layer-deposited nanoshells of the electrocatalysts into nano-roughened active shell layers using a controlled anion-exchange reaction (AER). The coarse thin nanoshells present abundant surface active sites, which are generated owing to the inherent unit-cell volume mismatch induced during the AER. Consequently, the nano-roughened electrodes accelerate the sluggish water reaction kinetics and lower the overpotentials required for the hydrogen and oxygen evolution reactions. In addition, the electronic modulation induced by the nanoshell layer at the core-nanoshell interface amplifies the local electron density, as confirmed using electrochemical analysis data and density functional theory calculations. Because of the integrity of the composite electrodes during water-splitting half-cell reactions, their durability for industrial seawater electrolysis is evaluated. The results indicate that their electrochemical activity does not change significantly after 10 days of continuous overall water splitting.

Nanocrystalline Sb-doped-BaSnO3 perovskite electron transport layer for dye-sensitized solar cells

Undoped and Sb-doped BaSn(1-x)SbxO3 (x = 0, 0.01 and 0.03) perovskite nanoparticles are synthesized using a facile peroxide-precipitate method and annealed at 900 °C for 2 h in air. Rietveld refinement of X-ray diffraction data indicates single-phase cubic structure which also corroborates with transmission electron microscopy data. Reduction in reflectance intensity and optical bandgap is observed with Sb-doping. Dye-sensitized solar cell fabricated using nanocrystalline BaSn(1-x)SbxO3 at x = 0.01 as electron transport layer shows maximum power conversion efficiency of 4.06% and short-circuit current density of 9.97 mAcm−2, substantiating the electrochemical impedance data.

Multiple established forms of palladium acetate binding to the four N-atom donor 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp

The reaction of the ligand 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp], with Pd(OAc)2, in CH3CN leads to the formation of three novel complexes which were characterized by thermogravimetric analysis, single crystal and powder X-ray measurements, MALDI-TOF mass spectra, IR and UV–visible spectroscopy as well as electrochemistry. As established by crystallographic work, the complex of formula [(CN)2dppPd(OAc)2]⋅H2O (molar ratio ligand/Pd(II) 1:1; species 3) shows a single Pd(OAc)2 unit coordinated to each nitrogen of the two pyridyl (py) groups of [(CN)2dpp]. i.e. the “py-py” mode of coordination previously established for the analogs [(CN)2dppMCl2] (M = Pd(II), Pt(II)). The second isolated species is a highly insoluble dinuclear Pd(II) complex of formula [(CN)2dpp{Pd(OAc)2}2]⋅5H2O (molar ratio ligand/Pd(II) 1:2; species 1), where the two Pd(OAc)2 units are each coordinated to one pyrazine nitrogen and one N atom of a pyridyl group on [(CN)2dpp] (“py-pyz” binding). Based on crystallographic work, the third isolated species is assigned the formula [(CN)(CONH)dppPd(OAc)] (molar ratio ligand/Pd(II) 1:1; species 2), which is formed by hydrolysis of a CN substituent on [(CN)2dpp] giving a –CONH- group and characterized by a “py-pyz” type of coordination. Electrochemical and spectroelectrochemical data of complexes 1, 2, and 3 in DMF and DMSO were used to assign the sites of electron transfer.

Localization and Absolute Quantification of Dopamine in Discrete Intravesicular Compartments Using NanoSIMS Imaging.

The absolute concentration and the compartmentalization of analytes in cells and organelles are crucial parameters in the development of drugs and drug delivery systems, as well as in the fundamental understanding of many cellular processes. Nanoscale secondary ion mass spectrometry (NanoSIMS) imaging is a powerful technique which allows subcellular localization of chemical species with high spatial and mass resolution, and high sensitivity. In this study, we combined NanoSIMS imaging with spatial oversampling with transmission electron microscopy (TEM) imaging to discern the compartments (dense core and halo) of large dense core vesicles in a model cell line used to study exocytosis, and to localize 13C dopamine enrichment following 4–6 h of 150 μM 13C L-3,4-dihydroxyphenylalanine (L-DOPA) incubation. In addition, the absolute concentrations of 13C dopamine in distinct vesicle domains as well as in entire single vesicles were quantified and validated by comparison to electrochemical data. We found concentrations of 87.5 mM, 16.0 mM and 39.5 mM for the dense core, halo and the whole vesicle, respectively. This approach adds to the potential of using combined TEM and NanoSIMS imaging to perform absolute quantification and directly measure the individual contents of nanometer-scale organelles.

Non‐traditional encryption methods: Moving toward electrochemical cryptography

AbstractCybersecurity and encryption are critical in diverse applications from simple emails to high‐priority government secrets. It is best accomplished by an “unbreakable” cipher or one which is only decrypted by those with a matching cipher key to the initial encryption. Recent advances have incorporated quantitative data as an asymmetric encryption key. With this method, the sender and receiver each run the same experiment to encode and decode the message of interest. Experimental asymmetric keys can come from DNA, enzymatic assays, and most recently, electrochemical data. This manuscript summarizes recent advances in cryptography and outlines new electrochemical techniques.

Electrochemical performance of Pleurotus ostreatus-derived carbon prepared by different methods as electrode in supercapacitor

In this research, the impact of precursor preparation methods of biomass-derived carbon materials were investigated. Hydrothermal treatment with phosphoric acid solution, hydrothermal treatment with water, and direct pyrolysis were applied to prepare the carbon precursors from Pleurotus ostreatus stipe. Potassium hydroxide was applied for further precursor activation. The physicochemical characteristics of carbons were tested by X-ray diffraction, elemental analysis, nitrogen sorption, scanning electron microscopy, X-ray photoelectron spectroscopy and so on. Moreover, the electrochemical data of these carbon material based supercapacitors were collected by using an electrochemical workstation with Na2SO4 solution as electrolyte. Certain differences, such as surface morphology, specific surface area and elemental composition, were observed for carbon from different precursor preparation methods. The contents of C= O/carboxylic C (32.83%) and C–N/C–O–C (27.38%) of carbon obtained by directly pyrolysis and further potassium hydroxide activation (PCK) were higher than other carbon. PCK as electrode in supercapacitor had higher specific capacitance than Pleurotus ostreatus-derived carbon materials. Much vertical Nyquist plot and small diameters of the semicycle for PCK were observed. After the continuous charge/discharge test for 10000 cycles, the supercapacitor using PCK as electrode still keeps about 98% of its initial value.

Vanadomanganate as a synergistic component in high-performance symmetric supercapacitor

Supercapacitor devices fabricated from capacitive and battery-type hybrid electrodes have been projected as a promising energy storage system because of their ability to produce high specific power and energy simultaneously. In this work, we have demonstrated a facile method of impregnation of faradaic type manganese (III) polyoxovanadate, [MnV14O40]−6 on the high surface area substrate of activated carbon (AC) as well as graphene oxide (GO). Materials and electrochemical characterizations data confirm the successful incorporation of capacitive and faradaic type manganese (III) polyoxovanadate into the nanohybrid electrode material. Furthermore, the synergic effect between the carbonaceous nanostructures (AC/GO) and redox-active oxometalate (MnV14) provides a better pathway for ion transport to the interface resulting in enhancement of the conductivity, diffusion ability of the nanohybrid. Moreover, the battery-type MnV14 clusters disperse in the micro/mesopores of AC, whereas the oxygen-containing functional groups in GO act as active sites for anchoring of MnV14 clusters. Thus, the surface modification with MnV14 clusters enhances the specific capacitance of nanohybrid with remarkable electrical and mechanical stability. The AC/MnV14 nanohybrid exhibits an enhanced specific capacitance of 547 F g−1 with specific energy and power of 76 Wh kg−1 and 1600 W kg−1, respectively, at 0.8 A g−1 current density. Additionally, GO/MnV14 shows a specific capacitance of 330 F g−1 with improved specific energy and power of 30 Wh kg−1 and 1276 W kg−1, respectively, at the same current density. Moreover, both the nanohybrids possess excellent cycle stability by retaining 92% (AC/MnV14) and 90.6% (GO/MnV14) of initial capacitance even after 5000 sweeping cycles.

Being Positive is Not Everything - Experimental and Computational Studies on the Selectivity of a Self-Assembled, Multiple Redox-State Receptor that Binds Anions with up to Picomolar Affinities.

The interaction of the self-assembled trinuclear ruthenium bowl 13+ , that displays three other accessible oxidation states, with oxo-anions is investigated. Using a combination of NMR and electrochemical experimental data, estimates of the binding affinities of 14+ , 15+ , and 16+ for both halide and oxo-anions were derived. This analysis revealed that, across the range of oxidation states of the host, both high anion binding affinities (>109 M-1 for specific guests bound to 16+ ) and high selectivities (a range of >107 M-1 ) were observed. As the crystal structure of binding of the hexafluorophosphate anion revealed that the host has two potential binding sites (named the α and β pockets), the host-guest properties of both putative binding sites of the bowl, in all of its four oxidation states, were investigated through detailed quantum-based computational studies. These studies revealed that, due to the interplay of ion-ion interactions, charge-assisted hydrogen-bonding and anion-π interactions, binding to the α pocket is generally preferred, except for the case of the relatively large and lipophilic hexafluorophosphate anionic guest and the host in the highest oxidation states, where the β pocket becomes relatively favourable. This analysis confirms that host-guest interactions involving structurally complex supramolecular architectures are driven by a combination of non-covalent interactions and, even in the case of charged binding pairs, simple ion-ion interactions alone cannot accurately define these recognition processes.

Role of acid‐base and hydration‐dehydration equilibria on reductions of chloral and chloral hydrate

AbstractThe electrochemical behavior of chloral hydrate in aqueous solutions at various pH values was investigated by using polarography. Reduction of chloral hydrate takes place in two steps: one appears as a small limiting current value that corresponds to the reduction of the unhydrated form, present in solutions in less than 3%, and another larger limiting current value at more negative potentials corresponding to a reduction of C‐Cl bonds in the hydrated form. Reduction schemes for both the hydrated and unhydrated forms and of an oxidation process for chloral hydrate are proposed. The reduction scheme supports the stepwise removal of chloride ions from the hydrated form of chloral that is electroactive in its protonated form, yielding ethanol as the final product. A rate constant for the protonation of chloral hydrate is calculated from its measured pKa value and electrochemical data. The role of hydration‐dehydration equilibria involving the reduction intermediates, which are reduced at more negative potentials than that of chloral, was concluded based on a comparison of limiting currents of chloral hydrate with those of 2,2,2‐trichloroethanol. The alcohol yields, in medium pH range a diffusion‐limited current, corresponding to cleavage of three C‐Cl bonds. This allowed the calculation of the equilibrium constant of the hydration‐dehydration equilibria.