Liu Suqin

Modification of Carbon Paper Electrode via Hydrothermal Oxidation Applied in the Vanadium Redox Battery

To improve the electrochemical activity of electrodes in the vanadium redox battery,carbon paper electrode was treated with a hydrogen peroxide and sulfuric acid solution,according to the hydrothermal acid oxidation method,in a Teflon-lined stainless steel autoclave over different time periods at 180 ℃.The water contact angle test showed that the contact angle of treated carbon paper samples changed from 120.0° to 100.8° by adjusting the treatment time from 6 to 18 h.Furthermore,a treatment time of 12 h resulted in the lowest contact angle observed,indicating that the wetting property of the carbon paper had been enhanced under these treatment conditions.Fourier transformation infrared spectroscopy results showed that oxygen-containing groups,such as the carbonyl and carboxyl groups,had been successfully introduced to the carbon papers.Scanning electron microscopy,cyclic voltammetry,electrochemical impedance spectroscopy,and charge-discharge tests were carried to characterize the surface topography and electrochemical properties of the carbon papers.The treated samples showed high activity in the redox reactions of V(IV)/V(V).A single-cell employing carbon paper was treated for 12 h as an electrode and exhibited an excellent performance.The energy efficiency reached 80% at a current density of 30 mA · cm-2.The corresponding coulombic and voltage efficiencies were 96% and 84%,respectively.

First-principle investigation on stability of Co-doped spinel λ-Mn4−x CoxO8

The mechanism of stability of Co-doped spinel λ-MnO2 that is referred to as spinel LixMn2O4 (x=0) was studied by using the first-principle calculation method. The total energy and formation enthalpy can be decreased remarkably due to the Co substation, resulting in a more stable structure of λ-MnxCr2−xO4. The bond order and DOS analysis were given in detail to explain the nature of stability improvement. The calculated results show that as the content of Co dopant increases, the bond order of Mn—O becomes larger and the peak of density of states around Fermi level shifts toward lower energy. The charge density distribution illustrates that the Mn—O bonding is ionic and partially covalent, and the covalent Mn—O bonding becomes stronger with the increase of Co dopant content. The results confirm that the Co-doping will enhance the stability of λ-MnO2 and hence improve the electrochemistry performance of LixMn2O4.

Effects of Oxalic Acid Addition on the Hydrothermal Synthesis of Kaolinite

Kaolinite was hydrothermally synthesized from alumina gel and silicate by dissolving alumina gel in oxalic acid before it was mixed with silicate, effects of the amount of addition on the species of synthetic products were discussed. The reaction product was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that analcite is the only phase of the reaction solution without oxalic acid, the proportion of kaolinite in product increases with the amount of addition, and kaolinite is the main species when the molar ratio of oxalic acid to alumina reaches 0.6:1.0. This is because oxalic acid addition is beneficial to the formation of kaolinite through changing the coordination number of aluminium from four to six, while the mixture of alumina gel, before it was dissolved in oxalic acid with silicate interfered with the crystallization of kaolinite.