Cyclic Voltammetry Experiments Research Articles

BiO 2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO 2 Reduction to Formate

BiO _2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO ₂ Reduction to Formate

Extraordinary electrochemical performance of lithium–sulfur battery with 2D ultrathin BiOBr/rGO sheet as an efficient sulfur host

There are many challenges such as the shuttling effect of soluble lithium polysulfides species (LiPSs) and the slow solid-state conversion between Li2S4 and Li2S in the development process of lithium-sulfur battery (LSB), so it is vital how to design and fabricate sulfur hosts with strong adsorption and good electrocatalysis. In this work, BiOBr in-situ forms onto both sides of reduced graphene oxide (rGO) to obtain a novel ultrathin BiOBr/rGO sheet, then self-constructing a hydrogel cylinder in shape, via a one-step hydrothermal process. The BiOBr/rGO composite with sandwich structure not only shows the outstanding adsorption effect on LiPSs, resulting from a strong bonding interaction between BiOBr/rGO and Li2S6 demonstrated by XPS technique, but also exhibits the extraordinary electrocatalytic performance on both the LiPSs conversion reaction in cyclic voltammetry experiment of symmetric cell and the Li2S nucleation process in potentiostatic deposited experiment, which will significantly improve the electrochemical performance of LSB. The S@BiOBr/rGO electrodes deliver the superior capacity and long cyclic stability with 882.2 mA h g−1 at 0.5 C after 1000 cycles, as well as displays the excellent rate performance with 823.9, 692.6 and 554.2 mA h g−1 at 1 C, 3 C and 5 C, respectively, after 400 cycles. Even though the sulfur loading reaches 4.9 mg cm−1, the reversible specific capacity of 424.6 mA h g-1can be maintained at 0.5 C after 400 cycles. Based on the in-situ X-ray diffraction and in-situ Raman spectroscopy, it could be revealed that the initial discharge process of active sulfur on the BiOBr/rGO cathode is α-S8 → Li2S8 → Li2S6 → Li2S3 → Li2S2 → Li2S, while the charging progress is the corresponding reverse reaction, but the final substance is β-S8. This research not only shows that the two-dimensional ultrathin BiOBr/rGO hybrid is successfully developed in LSB with excellent electrochemical performances, but also provides a strategy for exploring the construction of sulfur host materials.

Thermal imaging and deep optical and electrochemical study of C70 fullerene derivatives with thiophene, pyrrolidine or indene moieties along with electropolymerization with thiophene substituted imine: Blends with P3HT and PTB7

Three C70 fullerene derivatives, namely, C70-BTB and C70-MTB with thiophene or C70-MTP thiophene and pyrrolidyne moieties were synthesized and compared with synthesized C70-IPH containing indene moieties. Moreover, C70-BTB was compared with C60-BTB to analyse in deep the influence of fullerene football and rugby balls on the selected opto-electrical properties of new fullerene derivatives. All fullerene derivatives were characterized theoretically by using both time-dependent and independent density functional theory with the Perdew-Burke-Ernzerhof and Becke-Lee, W. Yang, R.G. Parr. The energy levels of the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) were calculated and compared with corresponding values determined experimentally by cyclic voltammetry (CV). It was found that the LUMOHOMO energy gaps determined by the DFT/B3LYP/6–31G(d) method agree very precisely with the corresponding values obtained in the CV experiments. For the first time a possibility of electropolymeryzation of C60-MTB C70-BTB, C70-MTB and C70-MTP with (E)-1-([2,2′:5′,2′'-terthiophen]-5-yl)-N-{4-[4-(4-fluorophenyl)-1,3-thiazol-2-yl]phenyl}methanimine (PV-BLJ-SC14) was shown. All fullerene derivatives and blends with poly(3-hexylthiophene-2,5-diyl) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophene-4,6-diyl) were investigated in deep by UV–Vis spectroscopy in the solution and as the solid layers together with photoluminescence spectra. Structural defects of created layers based on new fullerene derivatives were studied by atomic force microscopy and thermal imaging. To summarize, the investigated fullerene derivatives present much better electrical properties than widely used PC70BM. Moreover, the indene and pyrrolidine modifications demonstrated the best stability (thermally and at passing current) and electrical performance for all tested modifications. Additionally, a possible molecule rearrangement was observed resulting in improvement of electric conductivity through the layer. Finally, simple bulk-heterojunction polymer solar cells were constructed based on new fullerene derivatives as acceptors.

Active Knowledge Extraction from Cyclic Voltammetry

Cyclic Voltammetry (CV) is an electro-chemical characterization technique used in an initial material screening for desired properties and to extract information about electro-chemical reactions. In some applications, to extract kinetic information of the associated reactions (e.g., rate constants and turn over frequencies), CV curve should have a specific shape (for example an S-shape). However, often the characterization settings to obtain such curve are not known a priori. In this paper, an active search framework is defined to accelerate identification of characterization settings that enable knowledge extraction from CV experiments. Towards this goal, a representation of CV responses is used in combination with Bayesian Model Selection (BMS) method to efficiently label the response to be either S-shape or not S-shape. Using an active search with BMS oracle, we report a linear target identification in a six-dimensional search space (comprised of thermodynamic, mass transfer, and solution variables as dimensions). Our framework has the potential to be a powerful virtual screening technique for molecular catalysts, bi-functional fuel cell catalysts, and other energy conversion and storage systems.

Enlightening the Alkali Ion Role in the Photomagnetic Effect of FeCo Prussian Blue Analogues

FeCo Prussian blue analogues of general formula AxCoy[Fe(CN)6]z are responsive, non-stoichiometric materials whose magnetic and optical properties can be reversibly switched by light irradiation. However, elucidating the critical influence of the inserted alkali ion, A+, on the material's properties remains complicated due to their complex local structure. Here, by investigating soluble A ⊂ [Fe4-Co4] cyanido cubes (A = K, Rb, and Cs), both accurate structural and electronic information could be obtained. First, X-ray diffraction analyses reveal distinct interactions between the inserted A+ ions and the {Fe4-Co4} box, which impacts the structural distortion in the cubic framework. These distortions vanish, and a displacement of the small K+ ion from a corner toward the center is observed, as a cobalt corner CoIIHS is oxidized to CoIIILS. Second, cyclic voltammetry experiments performed at variable temperatures show distinct splitting of the CoIIHS ⇔ CoIIILS peak potentials for the different A+ cations, which can be qualitatively linked to different thermodynamic (standard potentials) and kinetic (energy barriers) parameters associated with the structural reorganization accompanying this redox-coupled spin state change. Moreover, for the first time, photomagnetism was investigated in frozen solution to avoid effects of intermolecular interactions. The results show that the metastable state is stabilized following the trend K > Rb > Cs. The outcome of these studies suggests that the interaction of the inserted alkali ions with the cyanide cage and the structural changes accompanying the electron transfer impact the stability of the photoinduced state and the relaxation temperature: the smaller the cation, the higher the structural reorganization and the associated energy barrier, and the more stable the metastable state.

Preparation of a supercapacitor electrode based on carbon nano-onions/manganese dioxide/iron oxide nanocomposite

A facile synthesis of a new supercapacitor electrode based on carbon nano-onions/manganese dioxide/iron oxide (CNO/MnO2/Fe3O4) nanocomposite is reported in this work. Prepared nanomaterials were characterized by FE-SEM (field emission scanning electron microscopy), HRTEM (high-resolution transmission electron microscopy), XRD (X-ray powder diffraction), EDX (energy-dispersive X-ray), and FTIR (Fourier transform infrared spectroscopy). Characterization results greatly showed the successful synthesis of nanomaterials. A three-electrode system in sodium sulfate (0.5 M) was used to evaluate supercapacitor characteristics. Cyclic voltammetry experiments showed CNO/MnO2/Fe3O4 nanocomposite had a suitable supercapacitors property with a rectangular shape. The specific capacitance of electrodes prepared by MnO2, CNO, MnO2/Fe3O4, and CNO/MnO2/Fe3O4 calculated based on chronopotentiometry results were 202. 59, 340, 400 and 730 F/g at a current density of 4 A/g. A two-electrode symmetric supercapacitor was evaluated in which nanocomposite of CNO/MnO2/Fe3O4 was used as positive and negative poles. The specific capacitance, power density, and energy density calculated at a currency density of 4 A/g were 456 F/g, 160 Wh/kg, and, 400 W/kg, respectively. The value of capacitance obtained for the CNO/MnO2/Fe3O4 was obtained by the cyclic voltammetry method equal to 441.18 A/g (scan rate: 10 mV·s). Also, after 5000 consecutive cycles, it has decreased by about 17.76 % of the initial capacitance, which indicates that the electrode has good stability. A very low charge transfer resistance was concluded by electrochemical impedance spectroscopy.

Electrochemistry of Praseodymium in Aqueous Solution Using a Liquid Gallium Cathode

The electrochemistry of liquid Ga electrodes in aqueous media was examined in the presence of praseodymium acetate (PrOAc) as an alternate path for low temperature reduction of rare earth elements (REE). This study investigated the aqueous electrochemistry of Ga with and without REEs (Pr). Cyclic voltammetry experiments showed that in the presence of PrOAc, an order of magnitude increase in cathodic current was observed for the Ga electrode, compared to that in the absence of Pr. Decrease in the reduction current with the increase of scan rate, with and without Pr, suggests catalytic reactions following electron transfer, which was attributed to the Ga2O disproportionation reaction. Chronoamperometric experiments performed in Pr containing solutions formed a precipitate. Over 50% of the Pr ions from the aqueous electrolyte were immobilized in the precipitate; a solid Ga-rich phase. Formation of this precipitate was only possible when Ga oxidation was induced. This condition was achieved by circulation of liquid Ga from the pool via external pump and returned dropwise to the liquid Ga pool. When the collected precipitate was leached in dilute HCl, Pr was released with H2 evolved as a byproduct, and Ga returned to its initial liquid metallic state. These preliminary results show encouraging new routes that could be applied for the recovery of diluted REE leachates, such as those obtained from magnets, coal fly ash, and ores.

Effect of the presence of various natural organic matters on anodic oxidation of electrified carbon nanotube membrane.

The widespread adoption of electrified carbon nanotube membranes (ECM) requires to better understand process effectiveness according to limiting phenomena of natural organic matters (NOMs). In this study, the influences of various NOM fractions were investigated on the oxidative degradation of Rhodamine B (RhB) in ECM. The results showed the decolorizing efficiencies of RhB in the presence of humic acid (HA) were still above 96%, while bovine serum albumin (BSA) reduced firstly and then increased the decolorizing efficiencies of RhB. The decolorizing efficiencies of RhB with alginate (AA) were over 98% at the first 15 min but decreased gradually to 76% after 150 min. These different performances of HA, BSA and AA were mainly due to their influences on the electrochemical reactivity characterization of ECM. ECM with the BSA depositing layer showed the highest exchange current density (j0), while the AA depositing layer restrained electron-transfer activity of ECM. Cyclic voltammetry (CV) experiments showed that the partial electrooxidation of BSA would occur in ECM with its degradation product observed in the effluent. The variation of electrochemical reactivity characterization of ECM resulted into its electri-oxidation and electri-adsorption rates to be the largest with BSA, followed by AA and HA.

Access to Nitrones from Amines via Electrocatalysis at Room Temperature

AbstractA self‐enabled electrooxidative protocol for the synthesis of nitrones from bench stable amines has been developed under constant current electrolysis at room temperature, rendering metal and external oxidant‐free protocol in an alkaline medium. The electrocatalysis steps of reported strategy involve anodic oxidation of benzyl amines followed by cathodic reduction of nitro‐functional group in an undivided cell affording functional nitrones. The robustness of the electrocatalysis was reflected by tolerant substrate scope, oxidant‐free conditions, and an operationally friendly procedure. Moreover, the cyclic voltammetry and control experiment studies also support the electrochemical process in alkaline medium.magnified image

Insight on a Competitive Nucleophilic Addition Reaction of Nε-(Carboxymethyl) Lysine or Different Amino Acids with 4-Methylbenzoquinone.

ο-benzoquinone is a common intermediate which is mostly formed by the oxidation of phenolics or polyphenols containing catechol structure. ο-benzoquinone has an outstanding nucleophilic ability, while advanced glycation end products (AGEs) are nucleophilic and can undergo a nucleophilic addition reaction with ο-benzoquinone to mitigate the harmful effects of AGEs on the body. As common nucleophilic substances, amino acids existing in large quantities in food processing and in vivo may bind competitively with ο-benzoquinone, thus influencing the trapping of ο-benzoquinone with AGEs. In this study, cyclic voltammetry and coexistence experiments were used to compare the reactivities of Nε-(carboxymethyl) lysine (CML) and amino acids with 4-methylbenzoquinone (4-MBQ). The results showed that CML is more reactive with ο-benzoquinone than most amino acids, and even in complex systems, ο-benzoquinone still captured CML. Moreover, almost all adducts were identified by UPLC-QTOF-MS/MS, and their chemical formulas were deduced. Quantum chemistry accurately predicts the efficiency and site of reactions of ο-benzoquinone and nucleophiles to a certain extent, and found that a secondary amine has a greater reactivity with 4-MBQ than a primary amine in a similar molecular structure. In general, ο-benzoquinone could capture AGEs, thereby showing potential to reduce the harmfulness of AGEs.

Giant Carbon Nano-Test Tubes as Versatile Imaging Vessels for High-Resolution and In Situ Observation of Proteins.

Cryogenic electron microscopy is one of the fastest and most robust methods for capturing high-resolution images of proteins, but stringent sample preparation, imaging conditions, and in situ radiation damage inflicted during data acquisition directly affect the resolution and ability to capture dynamic details, thereby limiting its broader utilization and adoption for protein studies. We addressed these drawbacks by introducing synthesized giant carbon nano-test tubes (GCNTTs) as radiation-insulating materials that lessen the irradiation impact on the protein during data acquisition, physical molecular concentrators that localize the proteins within a nanoscale field of view, and vessels that create a microenvironment for solution-phase imaging. High-resolution electron microscopy images of single and aggregated hemoglobin molecules within GCNTTs in both solid and solution states were acquired. Subsequent scanning transmission electron microscopy, small-angle neutron scattering, and fluorescence studies demonstrated that the GCNTT vessel protected the hemoglobin molecules from electron irradiation-, light-, or heat-induced denaturation. To demonstrate the robustness of GCNTT as an imaging platform that could potentially augment the study of proteins, we demonstrated the robustness of the GCNTT technique to image an alternative protein, d-fructose dehydrogenase, after cyclic voltammetry experiments to review encapsulation and binding insights. Given the simplicity of the material synthesis, sample preparation, and imaging technique, GCNTT is a promising imaging companion for high-resolution, single, and dynamic protein studies under electron microscopy.

Statistical Analysis of the Measurement Noise in Dynamic Impedance Spectra.

Different strategies can be used to acquire dynamic impedance spectra during a cyclic voltammetry experiment. The spectra are then analyzed by fitting them with a model using a weighted non‐linear least‐squares minimization algorithm. The choice of the weighting factors is not trivial and influences the value of the extracted parameters. At variance with the classic electrochemical impedance spectroscopy, dynamic impedance measurements are performed under non‐stationary conditions, making them typically more prone to errors arising from the voltage and current analog‐to‐digital conversion. Under the assumption that the noise in the voltage and current signals have a constant variance along the measurement and that it is uncorrelated between distinct samples, we calculate an expression for the expected variance of the error of the resulting immittances, which considers the specific procedure used to extract the spectra under the time‐varying nature of the measurements. The calculated variance of the error is then used as a rigorous way to evaluate the weighting factors of the least‐squares minimization, assuming that the fitted model is ideally exact and that there are no systematic errors. By exploring two classical electrochemical systems and fitting the measured spectra with a transfer function measurement model, namely with the Padé approximants, we show that the variance evaluated with our method captures the frequency dependence of the resulting residuals and can be used for reliably performing the complex non‐linear least‐squares fitting procedure.

Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids.

Direct electrocarboxylation of various N-acylimines with atmospheric CO2 is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62-95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support N-radical carbanion as the key intermediate.

Investigation of the Electrochemical Reduction of Porous CaTiO3 Pellets in CaCl2%–0.5%CaO Molten Salt

The formation of CaTiO3 during the electro-reduction of TiO2 pellets in CaCl2-based molten salts is unavoidable. So in present paper, the electro-deoxidation of porous CaTiO3 pellets was investigated. Cyclic voltammetry and constant potential electrolysis experiments were conducted to gain insight into the electro-deoxidation mechanism. From the results, two new reduction pathways of the porous CaTiO3 pellets were determined. The main factor influencing the reduction pathways is the porosity. When the porosity is low, CaTiO3 is directly reduced into TiO. With the porosity increases, some CaTiO3 will firstly be reduced into CaTi2O4 and then the CaTi2O4 is further reduced into TiO. The effect of the potential applied on the cathode on the possible reduction limit of the sample was discussed. The results indicated that the more negative the potential is, the faster the deoxidation rate is and the lower the deoxidation limit is. Only when the applied potential is more negative than −1.6 V vs Ag+/Ag, low-oxygen titanium (the oxygen content is lower than 1%) can be obtained in our experimental conditions. In addition, the microstructural kinetics of phase transformations during reduction of the CaTiO3 pellets were also discussed.

Preparation and Properties of Indium Ion Modified Graphite Felt Composite Electrode

Iron-chromium redox flow batteries (ICRFBs) have the advantages of high safety, long cycle life, flexible design, and low maintenance costs. Polyacrylonitrile-based graphite felt composite material has good temperature resistance, corrosion resistance, large surface area and excellent electrical conductivity, and is often used as the electrode material of ICRFB, but its chemical activity is poor. In order to improve the activity of the graphite felt electrode, In3+ was used for modification in this paper, and the modified graphite felt was used as the electrode material for iron-chromium batteries. The structure and surface morphology of the modified graphite felt were analyzed by the specific surface area analyzer and scanning electron microscope; the electrochemical impedance spectroscopy and cyclic voltammetry experiments were carried out on the electrochemical workstation to study the electro catalytic activity of In3+ modified graphite felt and its performance in ICRFBS. The results show that the graphite felt electrode modified with a concentration of 0.2 M In3+ was activated at 400°C for 2 h, and its surface showed a lot of grooves, and the specific surface area reached 3.889 m2/g, while the specific surface area of the untreated graphite felt was only 0.995 m2/g significantly improved. Electrochemical tests show that the electrochemical properties of graphite felt electrodes are improved after In3+ modification. Therefore, the In3+ modified graphite felt electrode can improve the performance of ICRFB battery, and also make it possible to realize the engineering application of ICRFB battery.

Chemical engineering around the 5,12-dihydroindolo[3,2-a]carbazole scaffold: Fine tuning of the optical properties of visible light photoinitiators of polymerization

5,12-Dihydroindolo[3,2-a]carbazole is a promising scaffold for the design of visible light photoinitiators of polymerization due to the simultaneous presence of two carbazole moieties that can be differently functionalized. Notably, redshift of the absorption spectra can be facilely obtained by nitration of one of the two carbazoles, the second carbazole group being functionalized with various groups. Dinitration of 5,12-dihydroindolo[3,2-a]carbazole is another efficient approach for designing dyes with strong absorptions extending over the visible range. In this work, a series of 36 compounds never reported in the literature and differing by the substitution pattern have been designed and synthesized. Notably, the possibility to design push–pull dyes by Knoevenagel and Claisen Schmidt reactions, to introduce electroactive groups such as thiophene by Suzuki cross-coupling reactions or to design water soluble chromophore has been explored. To evidence the interest of these structures, photopolymerization experiments have been carried out at 405 nm and the polymerization of acrylates has been examined in thick and thin films. To support the polymerization efficiency, mechanisms involved in the free radical polymerization of acrylates have been established by the combination of various techniques including UV–visible absorption and fluorescence spectroscopy, cyclic voltammetry and photolysis experiments.

PH-Induced Changes in the SERS Spectrum of Thiophenol at Gold Electrodes during Cyclic Voltammetry.

Thiophenol is a model compound used in the study of self-assembly of arylthiols on gold surfaces. In particular, changes in the surface-enhanced Raman scattering (SERS) spectra of these self-assembled monolayers (SAMs) with a change of conditions have been ascribed to, for example, differences in orientation with respect to the surface, protonation state, and electrode potential. Here, we show that potential-induced changes in the SERS spectra of SAMs of thiophenol on electrochemically roughened gold surfaces can be due to local pH changes at the electrode. The changes observed during the potential step and cyclic voltammetry experiments are identical to those induced by acid–base switching experiments in a protic solvent. The data indicate that the potential-dependent spectral changes, assigned earlier to changes in molecular orientation with respect to the surface, can be ascribed to changes in the pH locally at the electrode. The pH at the electrode can change as much as several pH units during electrochemical measurements that reach positive potentials where oxidation of adventitious water can occur. Furthermore, once perturbed by applying positive potentials, the pH at the electrode takes considerable time to recover to that of the bulk solution. It is noted that the changes in pH even during cyclic voltammetry in organic solvents can be equivalent to the addition of strong acids, such as CF3SO3H, and such effects should be considered in the study of the redox chemistry of pH-sensitive redox systems and potential-dependent SERS in particular.

Influence of conductive porous electrodes on the apparent electrode kinetics of fenitrothion

• FT’s cyclic voltammetry response at planar and porous modified electrode is simulated. • Simulations reveal the occurrence of thin-layer effects at porous modified electrode. • Cyclic voltammetry experiment validates the simulation results. Planar bare electrodes fabricated with surface-modified multiwalled carbon nanotubes (MWCNT) are used to detect organophosphate (OP) compounds, which are used as herbicides and fungicides but are harmful to human health. Deposition of carbon nanotubes on the surfaces of bare electrodes enhances electrocatalysis, increasing the electrode to analyte current response and narrowing peak-to-peak potential separation during cyclic voltammetry (CV). We hypothesize that, as the thickness of the deposited MWCNT layer decreases, Fenitrothion (FT, an OP) mass transport between the layers of porous multiwalled carbon nanotubes changes from semi-infinite to thin-layer diffusion. This influences the electrode electrochemical response to the analyte. Using simulations and experiments, we show that when porous MWCNT are deposited on a conductive glassy carbon electrode the mass transport of FT changes from semi-infinite to thin-layer diffusion during CV. This alters the electrochemical response of the electrode and reduces peak-to-peak potential separation. To simulate CV response to multi-step and multi-electron electrochemical reactions of FT, both the semi-infinite and thin-layer diffusion models are employed for the planar bare and modified porous surface electrodes. The transition from thin layer to semi-infinite diffusion is clear when the nanotube layer thickness on the bare electrode increases. The model is applicable to other toxic chemicals, such as 4-nitrophenol, parathion, or methyl parathion that have similar electrode kinetics.

Double benzylidene ketones as photoinitiators for visible light photopolymerization

In this work, four novel double benzylidene ketone dyes (TPA-H, CZ-H, TPA-C, and CZ-C) with D–A structure were synthesized and showed good charge transfer characteristics and high absorption capability in the visible light range. The double benzylidene ketone dyes can be used as type II photoinitiators to initiate free radical photopolymerization (FRP) or as charge transfer sensitizers to sensitize diaryliodonium salt (ONI) synergistically for the initiation of FRP and cationic photopolymerization (CP) together with aromatic amine groups under 460 and 532 nm LED light sources. FRP and CP experiments revealed that TPA-C and CZ-C with polyarylamine groups had high sensitization and initiation activities under 460 and 532 nm LED light sources. The photochemical properties of the initiator system were investigated by means of steady-state photolysis, fluorescence quenching, cyclic voltammetry, and electron spin resonance spin trapping experiments.

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation