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[en] Highlights: • Sulfur particles supported on the surface of graphene (SPG) were prepared through electrochemical exfoliation. • The possible mechanism for the formation of SPG is explained. • Temperature of electrochemical exfoliation was reduced to investigate of regulation of radicals and thus to control exfoliation. • The SPG and EG-15 exhibit enhanced electrochemical properties. - Abstract: Manipulating conditions of electrochemical exfoliation of graphite for high-quality graphene has become a research hotspot in recent years. In this study, based on controlled electrochemical exfoliation of graphite in aqueous ammonium sulfate electrolyte to produce graphene, a green, economic, and facile one-step method was developed to synthesize sulfur particles supported on the surface of graphene (SPG). Thiourea (CH4N2S), acted as sulfur source, and regulated radicals (e.g., HO), thus controlling the exfoliation, and subsequently resulting in formation of sulfur particles supported on SPG. During electrochemical exfoliation at room temperature, electrochemical performance of the as-prepared SPG (1% CH4N2S) electrode exhibited a high specific capacitance of 186.3 F g−1 at a scan rate of 1 mV s−1 compared with that of the graphene (112.1 F g−1, 1 mV s−1) without added thiourea. Temperature of electrochemical exfoliation was reduced to investigate of regulation of radicals and thus to control exfoliation. Electrochemical performance of the graphene prepared by reducing electrode temperature exhibited a high specific capacitance of 174.2 F g−1 at a scan rate of 1 mV s−1, when temperature of electrochemical exfoliation was reduced to 15 °C.
[en] The efficiency of zinc electrodeposition is of fundamental importance for improving long-term performance of aqueous zinc-ion batteries. In order to improve the efficiency of electrodeposition, as well as morphology and reactivity of the zinc deposit, it is possible to use organic additives in the electrolyte. Here, the effect of branched polyethyleneimine (BPEI) as an electrolyte's additive on morphology and kinetics of zinc electrodeposition in 0.5 M of ZnSO4 solution is investigated. The presence of BPEI changes the morphology of the electrodeposited layer from laminated hexagonal large crystals to compact layer without preferential growth morphology. Moreover, we observe that BPEI adsorption on the surface of the substrate suppresses the kinetics of zinc electrodeposition and decreases the grain growth rate, thus favoring the nucleation over the growth. As a result, BPEI ensures a homogeneous distribution of the current densities and can guarantee uniformity of the deposited layer.
[en] A model relating potential and current in continuous parallel plate iron electrocoagulation (EC) was developed for application in drinking water treatment. The general model can be applied to any EC parallel plate system relying only on geometric and tabulated input variables without the need of system-specific experimentally derived constants. For the theoretical model, the anode and cathode were vertically divided into n equipotential segments in a single pass, upflow, and adiabatic EC reactor. Potential and energy balances were simultaneously solved at each vertical segment, which included the contribution of ionic concentrations, solution temperature and conductivity, cathodic hydrogen flux, and gas/liquid ratio. We experimentally validated the numerical model with a vertical upflow EC reactor using a 24 cm height 99.99% pure iron anode divided into twelve 2 cm segments. Individual experimental currents from each segment were summed to determine total current, and compared with the theoretically derived value. Several key variables were studied to determine their impact on model accuracy: solute type, solute concentration, current density, flow rate, inter-electrode gap, and electrode surface condition. Model results were in good agreement with experimental values at cell potentials of 2-20 V (corresponding to a current density range of approximately 50-800 A/m2), with mean relative deviation of 9% for low flow rate, narrow electrode gap, polished electrodes, and 150 mg/L NaCl. Highest deviation occurred with a large electrode gap, unpolished electrodes, and Na2SO4 electrolyte, due to parasitic H2O oxidation and less than unity current efficiency. This is the first general model which can be applied to any parallel plate EC system for accurate electrochemical voltage or current prediction
[en] Electrochemical material etching techniques have attracted a significant amount of attention in the 'wet' metal etching arena, as the process typically involves neutral salt electrolytes and is relatively safe to operate. There are also economical and environmental advantages associated with these techniques compared with competing etching methods. A new concept of electrochemical microfabrication on substrates has been developed. In the technique the workpiece, which is the anode in the electrochemical reactor, is placed closely to a tool, which is the cathode containing the micro-pattern. Selective pattern transfer results in a higher etching rate on the areas opposing 'exposed' regions of the cathode, and lower etching rates in the areas directly opposite to the areas, on the cathode, covered by an insulator. In this investigation the electrochemical micro-patterning process has been evaluated and characterised in a vertical flow system described previously in literature. The experiments were carried out using copper disk anodes and patterned cathodes in a 0.1 M copper sulphate electrolyte. A 24 factorial experimental design procedure was adopted to determine the influence of process parameters on the electrochemical microfabrication process in terms of variability in pattern transfer over the electrode's surface area
[en] A copper-copper sulfate electrode (CSE) was constructed and tested at elevated temperatures. Experimental cell potentials versus a silver-silver chloride electrode were compared against results from Gibbs energy minimization (GEM) calculations. After accounting for irreversible thermodynamic processes, experimental and calculated CSE potentials, were generally within 3% of the observed potential from 25 to 150 °C at 3 MPa. The CSE potentials changed by less than 20 mV with increasing temperature, compared to 120 mV for the silver-silver chloride electrode. With its repeatability and small temperature dependence, the CSE electrode appears to be a viable reference electrode for measuring in-situ real time cell potentials in aqueous phase-containing media at elevated temperature and pressure.
[en] Mn3O4 is an electrochemically inactive in alkaline Zn–MnO2 battery. Here, we show that Mn3O4 shows superior electrochemical performance in mild aqueous zinc sulfate electrolytes. Mn3O4 can be a new cathode material for neutral aqueous rechargeable zinc battery. Results reveal that spinel Mn3O4 transforms to intermediate Mn5O8 and finally to Zn-birnessite. The initial charge cycle proceeds without participation of zinc ions, while zinc ions participate in the subsequent reaction. The intercalation of zinc ions into the interlamination of birnessite leads to the generation of Zn-birnessite in discharge process, accompanied by the reduction of Mn4+ to Mn3+. Our results demonstrate a new manganese oxide cathode with average Mn valence state lower than four for rechargeable zinc batteries.
[en] Graphical abstract: An asymmetric supercapacitor (ASC) has been fabricated using α-Bi2O3 and bio-waste derived activated carbon (AC) as negative and positive electrodes respectively with Li2SO4 as electrolyte. Interestingly, the addition of KI into the Li2SO4 electrolyte can significantly enhances the ASC performance through the redox reaction between iodine/iodide ions. -- Highlights: •Flower like α-Bi2O3 is prepared. •An asymmetric supercapacitor is fabricated using α-Bi2O3 as negative electrode and bio-waste derived activated carbon as positive electrode. •Energy density is enhanced from 10.2 Wh kg−1 to 35.4 Wh kg−1 by using KI as redox additive in Li2SO4 electrolyte. -- Abstract: A new asymmetric supercapacitor (ASC) was fabricated using flower like α-Bi2O3as negative and bio-waste derived activated carbon (AC) as positive electrodes with Li2SO4as electrolyte. Here, the fabricated ASC was operated over the potential range of 0-1.6 V and evaluated by cyclic voltammetry (CV), galvano static charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle life. Further to improve the performance of ASC, KI was used as electrolyte redox additive with pristine (Li2SO4) electrolyte due to their possible redox reactions of iodine ions. Remarkably, a nearly threefold improved specific capacitance and energy density of 99.5 F g−1and 35.4 Wh kg−1respectively was achieved by adding of KI into Li2SO4 electrolyte, while it was only 29 F g−1and 10.2 Wh kg−1for pristine (Li2SO4) electrolyte used ASC at 1.5 mA cm−2
[en] The electrochemical corrosion behavior of high purity iron, nickel, and chromium is evaluated in sodium sulfate solutions at temperatures up to 473 K. The thermodynamic stability regions of the species involved in the X-H2O system (X = Fe, Ni, Cr) were evaluated. The stability regions were presented in a new form of potential vs. temperature diagrams in specific solutions rather than conventional E–pH diagrams. The open circuit potential and polarization resistance experiment data were used to demonstrate the viability and usefulness of the newly developed diagrams
[en] The objective of this work was to study the effect of the temperature and the lengthening of the linear alkyl chain of the anion in the transport physical properties of the pure ionic liquids 1-ethyl-3-methyl imidazolium n-alkyl sulphate (being n = 0, 1, 2, 4, 6 and 8). Density, viscosity and electrical conductivities were measured at atmospheric pressure in a wide temperature range. In the bibliography, data existed for these magnitudes for all ionic liquids studied but none of these had information about the electrical conductivity of 1-ethyl-3-methyl imidazolium n-alkyl sulfate whith n = 0, 4, 6 and 8. The experimental results show clearly 1-ethyl-3-methyl imidazolium hydrogen sulphate cannot be considered part of the 1-ethyl-3-methyl imidazolium n-alkyl sulphate family because of its hydrogen bonding ability. Results of density and viscosity behave as expected. However, in the case of the electrical conductivity due to the lack of alkyl chain in the hydrogen sulfate we expected to get extreme values but in practise, we obtained intermediate values between 1-ethyl-3-methyl imidazolium butyl sulphate and 1-ethyl-3-methyl imidazolium hexyl sulphate. This suggests that a Grotthus mechanism exists as result of a protonic current in addition to ionic conductivity, being Waldeńs plot consistent with this idea.
[en] The self-discharge (SD) of electrochemical capacitors based on activated carbon electrodes (AC/AC capacitors) in aqueous lithium sulfate was examined after applying a three-hour cell potential hold at U_i values from 1.0 to 1.6 V. The leakage current measured during the potentiostatic period as well as the amplitude of self-discharge increased with U_i; the cell potential drop was approximately doubled by 10 °C increase of temperature. The potential decay of both negative and positive electrodes was explored separately, by introducing a reference electrode and it was found that the negative electrode contributes essentially to the capacitor self-discharge. A diffusion-controlled mechanism was found at U_i ≤ 1.4 V and U_i ≤ 1.2 V for the positive and negative electrodes, respectively. At higher U_i of 1.6 V, both electrodes display an activation-controlled mechanism due to water oxidation and subsequent carbon oxidation at the positive electrode and water or oxygen reduction at the negative electrode.