preparation,Electrochemical Behavior, and Textural Characteristics of Zn-Based electrodes

• Main Authors: Chia-Yuan Chang, 張嘉元
• Other Authors: Chi-Chang Hu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/67735351792324145091

碩士 === 國立中正大學 === 化學工程研究所 === 92 === Abstract Zinc and Zn-Ni deposits were electroplated by means of cyclic voltammetric (CV), pulse-current (PC), and direct current (DC) models. The formation of dendrites and the plating efficiency were respectively depressed and promoted by the introduction of additives (including tetra-ethylene-pentamine (TEPA), potassium diphosphate (PDP), and potassium sodium tartrate-tetrahydrate (PSTT)) in the plating solutions. The effects of electroplating modes and additives on the electrochemical and textural properties of all deposits were systematically investigated. In addition, hydrogen evolution during the charge process was inhibited by the addition of aluminum oxide into the ZnO-coated electrodes. The influences of annealing temperatures and time on the discharge capacity of ZnO-coated electrodes were also studied. The onset potential of Zn oxidation/dissolution was determined by linear sweep voltammetry (LSV). The discharge efficiency of Zn-based electrodes was determined by chronopotentiometry (CP) at 1C. The crystalline information of all electrodes were obtained from X-ray diffraction (XRD) patterns. The morphologies and roughness factors of all deposits were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The morphologies and crystallinity of deposits were significantly affected by the plating modes and the introduction of additives into the plating solutions. The anodic dissolution behavior of Zn deposits was influenced by the anions of Zn precursors, additives, current density, and plating modes. The discharge efficiency and potentials reached the highest values, and hydrogen evolution and the dendrite formation during the charge process were also inhibited when PSTT was employed. The discharge efficiencies of Zn and Zn-based electrodes prepared by both CV and PC modes were higher than that prepared by a DC mode. In addition, the discharge efficiency and potential of Zn-Ni deposits reached higher values when the PC mode and the plating baths without any additives were used. The discharge efficiency and cycle life were significantly improved by the addition of 5 wt% Al2O3 as well as the annealing treatment. When TEPA was employed as the additives, rougher surfaces with many dendrites were observed clearly from SEM photographs. Surface morphologies became compact when PDP was used. When PSTT was used, the grain size is large while it decreased with the plating current density, resulting in a smoother surface. Deposits plated by the CV mode showed a compact morphology with finer grains, resulting in a high discharge efficiency. In addition, the growth of dendrites was inhibited by the employment of CV deposition mode. The morphologies of Zn-Ni deposits were changed by varying the plating variables. Better crystallinity of deposits and higher discharge efficiency were obtained when the PC mode was used. In addition, the grain size was larger in comparison with that prepared by a DC mode. The dendrite formation during the charge/discharge process was found to inhibited by annealing.