Abstract
The preparation, electrochemical behaviors and applications of some Zn-based materials (Zn, Zn-Al alloy, Zn-Fe alloy and ZnO) are elucidated in this dissertation. In the first part, two novel alkaline baths for electrodeposition of Zn-Fe anti-corrosion coatings were disclosed, namely ZnO-FeSO4-triethanolamine-KOH and ZnO-(ferrous gluconate)-KOH systems. The proposed formulae exhibit higher ionic conductivity (about 510-560 mS cm-1 vs. 200 mS cm-1), higher cathodic efficiency (about 16-31% vs. 10-17%) and simpler constituents than conventional alkaline baths. Besides the Fe content in the deposits can be adjusted by tuning the deposition conditions thus Zn-Fe coatings with varied properties can be obtained. In the second part, undoped and Bi-doped ZnO layers were prepared by galvanic deposition and/or electrodeposition on ITO substrates. Amorphous-like Zn-deficient ZnO layers were successfully galvanic-deposited at 65 0C. The surface morphology, Bi content and electrical property of the Bi-doped ZnO deposits were strongly dependent on the deposition conditions. The electrodeposited Bi-doped ZnO layer showed XRD-pure ZnO wurtzite structure and demonstrated p-type carrier property (carrier concentration and mobility equaled to 1.18*1017 cm3 and 32.7 cm2 V-1s-1, respectively) with much lower resistance (about 4-order of magnitude) compare to undoped ZnO layer which was n-type in nature. In the last part, some Zn-based testing cells (in the forms of Zn-air or Ni-Zn batteries) were assembled and testified. Zn-Al alloy sheet anodes were demonstrated to be better anode metals than pure Zn. They showed not only higher anode capacity (800 mAh g-1 vs. 520 mAh g-1, the highest tested values), higher OCP value (1480-1560 mV vs. 1460 mV) but also less passivation in the metal-air battery configuration. In order to make cycling tests, two kinds of rechargeable Ni(OH)2/NiOOH electrodes (homemade and commercial ones) were prepared. The use of Zn-Fe baths as the electrolytes in secondary Ni-Zn batteries exhibited significant inhibition of dendrite (no dendrite appeared at 800 mA cm-2 compared with 50 mA cm-2 as the bath without Fe) in the first charge (deposition). However, the ratio of discharge/charge capacity was too low (less than 25%) to render true application, further studies will be required. On the other hand, tetra-alkyl ammonium hydroxides (TAAH) have been proposed and proved feasible as the alternatives for conventional inhibitors of Zn dendrite (tetra-alkyl ammonium bromides). The inhibition effect of TAAH was found to strongly depend on the size of alkyl groups and/or added concentration. These additives are not detrimental to ionic conductivity of zincate solutions (0.45 M ZnO + 6.6 M KOH) and are non-toxic. Highly improved rechargeability was achieved during cycling tests of a Ni-Zn cell by the addition of 0.1 M TEAH or 0.005 M TPAH into the zincate solutions.