In the present work, sixty-four sample electrodes were separately generated by electrodeposition in methanesulfonic acid (MSA) solutions. The concentrations of the lead (II) methanesulfonate and MSA were compared, as well as the effect of current density and temperature were investigated. The surface characterizations were analysed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). All conditions were researched to make sure the precise conditions of obtaining relative pure α/β-PbO2 phase compositions. Based on this, long-period galvanostatic electrolysis was performed by means of cyclic voltammograms (CV), Electrochemical Impedance Spectroscopy (EIS) and Tafel curves in order to evaluate the effect of different ratios of α/β-PbO2 phases on the corrosion resistance and electrocatalytic activity of the electrodes. The conclusion of this research can help confirm an ideal ratio of α/β-PbO2 phase compositions in Pb-0.6%Sb/α-PbO2/β-PbO2 composite anodes, thus show better prospective application in zinc electrowinning.
An electrical double layer typically behaves as a constant phase element (CPE) rather than a pure capacitor. To separate the non-faradaic current contributed by the electrical double layer from the total current, which is obtained from cyclic voltammetry using modeling, the CPE parameters—the CPE parameter (Y0) and the CPE exponent (γ)—need to be determined. In this work, a semi-theoretical equation for directly evaluating the CPE parameters from cyclic voltammetry experiments was developed by investigating cyclic voltammetry performed under a narrow potential window. The experiments were performed using a ferri/ferrocyanide solution with a cylindrical graphite electrode. The obtained parameters were quantitatively different from those obtained from electrochemical impedance spectroscopy analysis. However, the obtained parameters were in an excellent agreement with cyclic voltammograms. This suggested that to model a non-faradaic current using a CPE in cyclic voltammetry, it is important to evaluate the CPE parameters using cyclic voltammetry. An application of the CPE parameters for simulating cyclic voltammograms that contain both faradaic and non-faradaic currents is also presented. The results show that the model can satisfactorily simulate entire cyclic voltammograms.
Potassium ferricyanide (K3Fe(CN)6) as a stabilizer was used for electroless copper plating in EDTA/THPED dual-ligands system. The deposition behavior and surface structure of copper layer were studied systematically. The results indicated that the overall deposition process was divided into three regions designated as induction, transitional and stable regions. It was confirmed that K3Fe(CN)6 can delay the fall-off trend of electrode potential, which may be related to the competitive adsorption between Fe(CN)63− with large radius and OH− with small radius on the electrode surface. The addition of K3Fe(CN)6 led to a decrease of 70% in redox current density, which reduced obviously Cu deposition rate. Meanwhile, the decomposition time of electroless solution sharply increased and the reoxidation of Cu(I) ion was effectively inhibited in the presence of K3Fe(CN)6. Metallographic studies of copper layers with and without K3Fe(CN)6 stabilizer revealed that surface structures and fine particle distribution were uniform. The resultant product was high-purity without detectable iron impurities. Moreover, the addition of K3Fe(CN)6 was favorable to the formation of the preferred orientation on (220) crystal plane, and the grain size decreased from 61.5 nm to 40.4 nm with the addition of 50 mg L−1 K3Fe(CN)6.
MgCo2−xMnxO4 (x = 0.1, 0.2, 0.4) was prepared using an inverse co-precipitation method. The primary product was determined to have a spinel structure (space group Fd3m) based on powder X-ray diffraction data. A Rietveld analysis of synchrotron X-ray diffraction data showed that Mg, Co and Mn in this material were distributed in a disordered manner, meaning that cation mixing had occurred. Charge-discharge testing using MgCo2−xMnxO4/AZ31 cells with Ag reference electrodes demonstrated a discharge capacity of 80 mAhg−1 and a high coulombic efficiency below 60°C, with cut-off voltages in the range of 0.345 to −1.155 V vs. Ag/Ag+ (3.5 to 2.0 V vs. Mg/Mg2+). The improved cycling performance of this material is ascribed to the replacement of a portion of the Co atoms with Mn. The stability of the crystal structure was investigated based on first-principles calculations and the results showed that a model in which Mn occupied only the 16d sites was the most stable. The ordered Mg/Co/Mn structure of this material would be expected to facilitate the diffusion of Mg2+ ions throughout the cathode material in a magnesium secondary battery.
A Si-porous carbon composite, prepared by the carbonization of clathrate compounds including nano-Si particles, was proposed as a new anode for Li-ion batteries offering the advantages of low manufacturing cost and better electrochemical properties. The porous carbon obtained from the clathrate compounds of α-cyclodextrin and surfactant had a high specific surface area of 2000 m2 g−1, and its initial delithiation capacity was 363 mAh g−1 at a rate of 0.1 C. In addition, the initial delithiation capacity of the obtained Si-porous carbon composite was 556 mAh g−1 at a rate of 0.1 C. In addition, its capacity retention was 96% after 100 cycles, because the low electronic conductivity of Si was improved by preparing the composites of Si and porous carbon.
Different oxide-based surface coatings were applied to the LiCoO2 positive electrode material to improve its interfacial Li-ion transfer and current rate performance. Zr-oxide and Al-oxide were selected as coating materials, as the former hardly forms a solid-solution with LiCoO2 while the latter readily does so. Zr-oxide-coated LiCoO2 showed higher current rate performance and lower charge transfer resistance (Rct) compared to bare and Al-oxide-coated LiCoO2. The difference in current rate performance was quantitatively explained by the different Rct. The activation energy (Ea) for the charge transfer reaction was approximately 10 kJ mol−1 lower for Zr-oxide-coated LiCoO2 than the other two. The lower Ea of the former, which suggests lower activation barriers for the elementary processes of Li-ion transfer at the electrode/electrolyte interface, lowered the Rct and increased the current rate performance. The Rct of Zr-oxide-coated LiCoO2 decreased from the 2nd to 4th cycle, while for Al-oxide-coated LiCoO2 it remained almost constant during the early cycles. The formation of the new electrode/electrolyte interface during the early cycles that depends on the solubility of cations in the oxide coatings into LiCoO2 contributes to the different Rct change and Ea values.
Simultaneous electrochemical determination of isoquercitrin (ISQ) and epigallocatechingallate (EGCG) at a carbon nanotube electrode is presented. The carbon nanotube electrode for ISQ and EGCG sensing has attractive properties in terms of well-defined current peaks, high sensitivity, and high reproducibility. Two well-distinguished anodic peaks +0.23 V and +0.38 V due to EGCG and ISQ are observed by cyclic voltammetry and those peaks are independent from each other. The linear ranges of ISQ and EGCG are 0.76–94 µM and 4.0–94 µM, respectively. The ISO and EGCG values of real sample determined by this method show good agreement with the actual ones.