Synthesis Of A Nickel Based Compound And The Study Of Its Application In Single Flow Zinc-nickel Batteries And Pseudo-capacitors

Nickel hydroxides and its derive have been widely used in nickel metal hydride ?NiMH? batteries, redox flow batteries and supercapacitors for energy storage due to the advantages of abundance, low cost,preferential potential and high specific capacities. Because the compositions and structure of the two compounds have a significant effect on the electrochemical performances of redox flow batteries and supercapacitors, this thesis is mainly focused on the following four aspects:?1? improvement of the morphology of the deposited zinc on the negative electrode by the adding of additives; ?2? preparation of a-Ni?OH?₂ with high specific capacity; ?3? synthesis of Al-doped NiO nanosheets and ?4?design of a novel single flow zinc nickel oxygen battery.Lead ion and tetrabutylammonium bromide ?TBAB? have been employed as inhibitors to prevent spongy zinc from electro-growth in flowing alkaline zincate solutions. To assess the efficacy of the two additives, current-time technique, electro-deposition, scanning electron microscopy ?SEM? and cycling test were undertaken. Results show that the growth of spongy zinc in flowing alkaline zincate solutions can be effectively inhibited by separate addition of 10^-4 M Pb??? or 10^-4 M TBAB at -100 mV of cathodic potential. However, the simultaneous addition of both 10^-4 M Pb??? and 5 × 10^-5 M TBAB shows more effective inhibition from spongy zinc growth due to the synergistic effect of Pb??? and TBAB on the morphology improvement of the deposited spongy zinc. From the charge/discharge cycling tests of the single flow Zn-Ni test cells, it is shown that the rechargeability of Zn anode is considerably improved by introduction of both 10^-4 M Pb??? and 5 × 10^-5 M TBAB, further showing the synergistic effect.According to the Bode cycle, there are two polymorphic forms of nickel hydroxide, namely, ? and ? phases. The theoretical capacity of a-Ni?OH?₂ is much higher than that of ?-Ni?OH?₂. In the present study, Al-doped a-Ni?OH?₂ microspheres comprising densely packed irregular nano sheets have been synthesized via a dual complexation precipitation ?DCP?method. The resulting electrode offers a large specific capacity of 457.9 mAh g^-1 at remarkably high rate of 500 mA g^-1, which is 47.0% larger than that of ?-Ni?OH?₂ under the same condition. In addition, the electrode still keeps 95.3% of the initial capacity after 330 cycles. Moreover, the electrochemical performance of Al-doped ?-Ni?OH?₂ is further enhanced by co-precipitation of Co2+, and the resulting product exhibits a specific capacity of 470.3 mAh g^-1 at 500 mA g^-1 and a 95.2% retention after 500 cycles. The outstanding electrochemical performance benefits from the synergistic contribution of the doped metal ions and the unique hierarchical structure.In this thesis, Al-doped NiO nanosheet arrays were synthesized using a facile hydrothermal route followed by a calcination process. The synthesized product exhibits a superior pseudocapacitive performance with a high specific capacitance of 1653 F g^-1 at a current density of 1 A g^-1,while the pure NiO electrode only delivers 1138 F g^-1. In addition, the displayed excellent cycling performance, 99% of initial capacity was remained during the first 5000 cycles. The excellent electrochemical performance of Al-doped NiO is contributed to its large specific surface area and enhanced conductivity. Our proposed doping method will be beneficial to construct a high-performance supercapacitor system.To eliminate the zinc accumulation on the negative electrode in the charge/discharge process, a novel single flow zinc-nickel hybrid battery with a Ni?OH?₂-O₂ composite cathode was designed. The electrolyte in this battery is a high-concentration KOH-K₂[Zn?OH?₄] solution. The anode is copper foil electrodeposited with metallic zinc, and the cathode is a nickel hydroxide and oxygen composite electrode. The result shows a high efficiency with an average coulombic efficiency of 99.2% and an energy efficiency of 84.2% during the first 500 cycles. The battery has two discharge voltage platforms at 1.63 V and 1.31 V in the discharge process.At the same time, no zinc dendrites accumulate on the negative electrode at the end of the discharge process. The high performance indicates that the single flow zinc-nickel battery with the new designed nickel hydroxide and oxygen composite electrode is expected to become a promising energy storage system.