| All vanadium redox flow battery (VFB) is one of the most promising electrochemical energy storage systems, which can be applied in a wide range of renewable energy. Although VFB has been successfully implemented in various fields around the world, the low energy density imposes great limits on its large-scale production. Therefore, the composition material of VFB was studied to improve its performance and energy density.The electrode is one of the key components of a VFB, which serves as a conducting platform for electron transfer. Typically, graphite felt (GF) electrodes are used in practice. In this thesis, the graphite felts (GFs) were treated at 400℃,500℃ and 600℃ respectively, and evaluated by cyclic voltammetry (CV), AC impedance (EIS), polarization curves and Infrared spectroscopy (IR.) test. The results showed that -OH and -COOH bonds were formed on the surface of the GFs, which have a significant catalytic effect on VO2+/VO2+ and could improve the electrochemical performance of the surface of GFs. The optimum treated temperature was found to be 500℃After heat treatment, the GFs were coated by Ga2O3, SnO2 and Y-doped SnO2, and their electrochemical properties were evaluated by CV, EIS, polarization curves, and charge discharge test. The changes in their microscopic were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that these modification could improve the electrochemical performance and the of VFB, mainly due to the oxygen vacancy of Ga2O3 and SnO2 lattices, which can combine with VO2+/VO2+ to combine and promote the transformation of VO2+/VO2+; the poor conductivity of SnO2 led to the decrease in energy efficiency (EE) of VFB, while doping Y can improve the conductivity of SnO2 crystal as well as the surface area of VFB, which enhanced the EE and the capacity of VFB; The optimal concentration of the thermal decomposition of Ga and Sn was 0.1 M and the best percentage of Y was 2%. |
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