Study on the synthesis and properties of Zn/PANI two cell system
|Course||Physical and chemical|
|Keywords||Polyaniline wastewater Fenton reagent Seconary batteries Ionic liquid Zndendrites|
In the face of the deepening of energy crisis as well as the increasingly serious environmental pollution, energy use and management has been gradually taken seriously. Compared with lithium ion batteries and traditional lead-acid batteries, Zn/PANI secondary batteres with the advantages of low cost, non-pollution, safety and high capacity have more development potential. Zn/PANI secondary battery itself has some problems need to be solved. First of all, during charging, Zn dendrites are formed, easily puncture the battery separator and then cause the bateery short circuit. On the other hand, the overoxidation of PANI in the process of battery charging brings about the low capacity and the short cyclelife. For solving these problems, the following work has done in this thesis.Chemical oxidation was used to synthesize polyaniline in the presence of different volume fraction ethanol which were doped with different concentration zinc chloride and have different morphology. The obtained12polyaniline samples (PANI/Zn2+) were carried on the characterization of the scanning electron microscope (SEM), UV-vis spectroscopy, FT-IR spectroscopy, x-ray diffraction (XRD), four-point probe method and thermostability analysis (TGA). The experimental results show that both zinc ion and ethanol can affect the morphology of polyaniline. Ethanol and zinc ion can respectively prompt the formation of clubbed morphology and nanoparticles.12polyaniline samples were partially crystalline. The decomposition of polyaniline backbone happened at550℃which demonstrated that polyaniline samples have higher thermostability than pure polyaniline. When the molar ratio of zinc ions to anline monomer equeals to1:3in the reaction solution, the conductivity of the synthetized polyaniline (PANI-3) can highly reaches to5.18S·cm-1.The wastewater from preparing PANI-1was treated by the combination of Fenton reagent and active carbon. The wastewater was firstly treated by Fenton reagent, adjusted pH to near neutral, then remove the color by active carbon. The285nm absorption peak in UV-Vis spectroscopy was as a quantitative indicator of the byproducts. COD in water samples were measured by potassium dichromate method and the double-distilled water was used as the blank sample. The study shows that the optimum conditions for treating the wastewater were the1:1concentration ratio of FeSO4·7H2O to H2O2, reaction time50min, temperature19℃, pH1.1. The chemical oxygen demand (COD) value of water sample is1512mg·L-1and56mg·L-1for pre-and post-treatment, respectively. The removal efficiency of the COD is more than96%.According to the relevant reference, the ionic liquid1-ethyl-3-methylimidazolium ethyl sulfate (EMIES) was synthesized.8%volume fraction EMIES was added into the double-distilled water and formed the solvent of the electrolytes. The solvent was used to prepare the electrolytes:(a)1mol·L-1ZnCl2/2mol·L-1NH4C1;(b)1mol·L-1ZnCl2/2mol·L-1NH4Cl;(c)0.5mol·L-1ZnCl2/1mol·L-1NH4Cl;(d)0.5mol·L-1ZnCl2/1mol·L-1NH4Cl. The pH of both electrolyte (a) and (c) was adjusted with ammonia water and that of the electrolyte (b) and (d) was done with10mol·L-1KOH. The cyclic voltammograms of the polyaniline (PANI-4.PANI-8、PANI-9、PANI-11) were employed to study the the effect of zinc ion and ethanol on the electrochemical property of polyaniline. In four electrolytes, Zn electrodeposits were respectively deposited from the electrolytes at their reductive potential. However, only the SEM image indicated that Zn electrodeposit deposited from electrolyte (a) was tight and has non acute angles. It is demonstrated that the addition of ionic liquid is favor to inhibit the formation of Zn dendrites during the charging of batteries. Besides, elecchemical impedance spectroscopy (EIS) manifested that the impedance of the electrolyte adjudted pH by NH4OH was lower than that of the electrolyte adjudted pH by10M KOH. Especially, the impedance of the electrolyte (a) was only2.56Ω in which the oxidation of polyaniline samples occurs at0.0～0.2V (vs.SCE).Zinc-polyaniline secondary battery containing zinc electrode, polyaniline electrode and the electrolyte (1.0mol·L-1ZnCl2/2.0mol·L-1NH4Cl in8%v/v EMIES aqueous solution) was assembled into cylindrical shape. According to investigating the effect of time at constant voltage, the range of charge-siacharge voltage, current density, the pH of the electrolyte on the properties of battery, the finally results show that the specific capacity of the battery decreased least under the condition of1.3～0.7V, pH4.0～4.5,50mA·g-1,5min at constant voltage. The charge/discharge efficiency maintains about100%. At the optimum condition, several samples were cycled to investigate the effect of zinc ion and ethanol on the cycle performances. The results reveal that in the presence of volum fraction10%in the reaction solution, when the molar ratio of zinc ions to anline monomer equeals to1:3, the specific capacity of polyamine (PANI-11) was highly reached to around80mAh·g-1.