•Al2O3-coated LiCoO2 was prepared via simple method.•The cyclic stability was investigated by CV method.•The cyclic stability was studied in different potential ranges.•The electrode is suitable for application in the potential range of 3.70–4.50 V.•It has still 113 mAh/g discharge capacity even after 500 cycles.In this article, Al2O3-coated LiCoO2 cathode is synthesized by high-temperature solid-state reaction method, i.e. sintering the mixture of Al2O3 and LiCoO2 powder. X-ray diffraction (XRD) analysis shows that there is no Al2O3 impurity being found in the final product. Scanning electron spectroscopy (SEM) and transmission electron spectroscopy (TEM) measurements show that the micro-morphology of pristine LiCoO2 grains is sustained after coating Al2O3. We analyze the surface chemistry of the pristine and Al2O3-coated LiCoO2 by X-ray photoelectron spectroscopy (XPS) technique. The electrochemical behavior is systematically investigated. The cathodes are cycled in different potential ranges (3.70 V–4.30, 4.35, 4.40, 4.45, 4.50, 4.55 and 4.60 V). The charge-discharge, cyclic voltammetry (CV) and Electrochemical impedance spectroscopy (EIS) measurements show that coating Al2O3 can obviously improve the cyclic stability and decrease the total interfacial resistance. We could conclude that Al2O3-coated LiCoO2 cathode is suitable for practical application in the potential range of 3.70–4.50 V vs. Li/Li+. The discharge capacity can reach 113 mAh/g after 500 cycles. It is very possible that the LiCo1 − xAlxO2-like surface phase, formed on the surface of LiCoO2, prevents Co-dissolution. As results, the operation potential range is extended and the cyclic stability is improved.

LiCoO2-based cathode does still have a powerful competition in high-end mobile electronics due to its relatively high true density (about 5.2 g/cm3). When the operation potential range is extended, the improvement in its cycle stability has attracted more attention. The extension of its operation potential can be realized by partial replacement of Co by Ni and Mn or by surface modification. However, Ni and Mn replacing partial Co results in decreased true density; for example, the true density of LiNi0.5Mn0.3Co0.2O2 is about 4.6 g/cm3. In this case, the increase in its practical energy density is impossible. As a result, the surface modification technology becomes very important to extend its operation potential range. In this article, an Al2O3-coated LiCoO2 cathode was synthesized. X-ray diffraction test did not show any impurity. Scanning electron spectroscopy measurements showed that the basic microstructure of pristine LiCoO2 grain is sustained after coating Al2O3. The surface characteristic of pure and Al2O3-coated LiCoO2 was also analyzed using an X-ray photoelectron spectroscopy (XPS) technique. Unusual XPS peaks of O 1s, Al 2p, and Co 2p binding energy were found and may be caused by the possible H existence in crystal structure. The electrochemical behavior was systematically investigated, and the cathode was cycled at different charge cutoff voltages (4.30∼4.60 V). The charge-discharge and cyclic voltammetry measurements showed an obviously improved cyclic performance after coating Al2O3. The electrocatalytic activity is not clearly changed before and after coating Al2O3. From our systematical investigation, it could be concluded that the Al2O3-coated LiCoO2 cathode is suitable for practical application in the potential range of 3.70∼4.50 V vs. Li/Li+.

•We investigate the electro-oxidation of glycol ethylene.•We study the dependence of the impedance spectroscopy on the applied potential.•We analyze the origin of all redox peaks in cyclic voltammetries.•We study the dependence of oscillation on the applied potential and concentration.In the present article, a full investigation of the electrochemical characteristics of the electro-oxidation reaction of ethylene glycol on platinum (Pt) electrode in sulfuric acid has been performed to comprehensively understand and explore the details of the reaction mechanism. The dependence of the basic characteristics of the potentiostatic-mode electrochemical impedance spectroscopy (EIS) on the externally applied potentials has been studied in detail. The influence of the externally applied potentials and the ethylene glycol concentration on the galvanostatic potential's oscillation has been investigated in-depth. Finally, the origin of all oxidation/reduction peaks in the cyclic voltammetries (CV) has been discussed based on the CV and linear sweeping measurements and the reports by other groups.

The electrochemical performance of high-voltage LiCoPO4 electrode synthesized by high-temperature solid-state reaction was investigated. It is found that the existence of the carbon and Co2P decreases the discharge capacity; the LiCoPO4 with pure olivine phase has a maximum discharge capacity and it can reach 135 mAh/g. The cyclic voltammetric measurements have shown that the impurity of carbon and Co2P can change the Li-deintercalation reaction mechanism. There are two oxidation peaks when the impurity content is relatively low; however, there is only on oxidation peak with the larger amount of impurities in the cyclic voltammetry. The interface capacitance between the LiCoPO4 electrode and the electrolyte is about 16.9 μF/cm2 and the apparent diffusion coefficient of the lithium ion in the solid phase is (2.0∼3.4)×10−9 m2/s, based on the impedance measurements.

In the present work, ethanol electro-oxidation reaction on Pt electrode has been studied in details by measuring and analyzing the cyclic voltammetries (CV), the dependence of the electrochemical impedance spectroscopies (EIS) on the applied potentials and the galvanostatic potential oscillation. The CV measurement has exhibited a bistable characteristic. The origin of all the oxidation and reduction peaks has been analyzed. The origin of the bistable characteristic has also been studied by measuring the EIS at different potentials. In addition, the dependence of the galvanostatic oscillation on the applied potential and the ethanol concentration has been reported.Highlights► The origin of the peaks in CV was analyzed during ethanol electro-oxidation. ► Impedance spectrum is sensitive to the ethanol concentration and the potentials. ► The galvanostatic oscillation appears only in higher ethanol concentration.

The derivation and proposal of major electrochemical techniques used to determine and calculate the electrochemical kinetic parameters is basically based on the electrochemical reaction taking place at liquid/solid or liquid/liquid interface in which all the reactants and products are soluble in liquid aqueous solution or liquid mercury electrode, or are volatile gas. Such electrochemical reaction system is classical and traditional (ERS1). Recently, the electrochemical behavior of some materials used as the active electrode materials in chemical power sources has attracted much attention. In chemical power source systems, either reactant or product, or both are insoluble. This kind of electrochemical reaction system (ERS2) is slightly different from ERS1. The application of these electrochemical techniques/equations to chemical power sources’ system requires carefulness. The misuse of these electrochemical techniques can be easily found in the literatures and some of them even lead to a wrong conclusion.In this review, almost all the electrochemical techniques to measure the exchange current and diffusion coefficient were compiled for reference to the readers, including pulse step, electrochemical impedance, alternating cyclic voltammetry, etc. The necessary requirements/conditions to apply these techniques have been briefly discussed and some simple examples were also discussed for a better understanding.

It is just the best time to compile and compare the experimental data and to explore the possible laws and to discover the relation between the crystallographic parameters, thermodynamic and electrochemical properties, based on lot of the published experimental data about the hydrogen-storage alloys. An empirical correlation between the unit cell volume and the enthalpy change, equilibrium pressure, discharge capacity has been constructed. The violent change of the equilibrium pressure with the unit cell volume might indicate the change in the interaction nature between the host alloy atoms and the intercalated hydrogen atoms. The dependence of unit cell volume vs. average numbers of total electrons for AB5-type alloys exhibits same change tendency as that of the Vanderwaals radius vs. atomic numbers from Fe to Se in the elements' periodic table. It is possible that the total numbers of the electrons decides the unit cell volume.

As one of the important candidate of power sources for the future, the research and production of hydrogen gas has a significant importance. In this article, the emphasis is on the influence of impurities on hydrogen evolution reaction, i.e., the influence of an addition of decacyclene, C12H35C6H4SO4Na, CH3CH2OH, chromanone, H2SO4, HNO3, 4,4′-biphenediol and 1,2,3,4-tetraphenyl-1,3-cyclopentadiene was studied by electrochemical impedance technique. The adsorption structure for some organics was measured by scanning tunneling spectroscopy techniques. Superstructure of adsorbed decacyclene on Au(111) surface was captured. The ordered adsorption structure of 4,4′-biphenyldiol on Au(111) and (100) was also observed. The addition of decacyclene has shown an opposite effects on hydrogen evolution for Au(111) and (100) surface, i.e., it inhibits the reaction at Au(100) but enhances the one at Au(111). The results show that the addition of C12H35C6H4SO4Na and HNO3, especially the latter, can improve the hydrogen evolution. In the article the adsorption structure and hydrogen evolution reaction have been studied in order to give some useful information about the relation between the adsorption structure and the properties. The purpose of this article is to attempt to find the relation between electrochemical performance and the adsorption structure, and to explore the effect of some additives.