Preparation, Characterization And Electrochemical Performance Of Electrode Materials For Aqueous Supercapacitors

A significant worldwide increase in the consumotion of fossil fuels, resulting from the ripid growth of the global economy, produces two major associated issues. The first is the accelerating exhaustion of existing fossil fuel reserves and the second is the affiliated environmental problem. Such as increasing greenhouse gas emissions and the general air and water pollution. Taken together these items constitute the basis of an urgent, worldwide concern about the futher, sustainable development and health of our society's ecosystem. The need ro develop and scale up sustainable, clean energy sources and their associated technologies is recognized worldwide as an urgent priority. Most renewable clean energy sources are highlu dependent on the time of day and regional weather conditions. Development of realated energy conversion and energy storage devices is therefore required in order to effectively harvest these intermittent energy sources. In this regard, batteries, electrochemical supercapacitors(ESs) and fuel cells are all recognized as three kinds if the most important electrochemical energy storage/conversion devices.Electrochemical capacitor is also known as supercapacitor. The device is able to fully charge and discharge in seconds, excellent cycle performance, and high power density, but its energy density is low. In terms of energy storage, supercapacitor is between conventional capacitors and batteries. According to charge storage mechanisms, supercapacitors can be divided into:1) Electrochemical double layer capacitors(EDLCs), store energy through the charge separation at the electrode/electrolyte interface, this kind of capacitor has the very high power density and excellent circulation performance;2) Hybrid supercapacitors, Its two electrodes have different energy storage mechanism, one of the electrodes chooses electric double layer capacitor electrode materials such as activated carbon, the other electrode is opposite.3) Faradic pseudo-capacitors, store energy by using the fast chemical absorption/desorption or redox reactions on the electrode surface.Compared with organic electrolyte, water electrolyte has higher ionic conductivity, so it has much higher power density. Supercapacitors used aqueous solution as the electrolyte was paly an important role in the energy storage system. Aqueous electrolyte has higher ionic conductivity, so its power density is much higher than the organic electrolyte. Moreover, the aqueous solution as electrolyte compartion organic electrolyte lot of advantage, such as it is low cost, better security, environment friendly and the assembling easy. Therefore, aqueous electrolyte is more suitable as the electrolyte for supercapacitor. The main factors affecting electrochemical performance of green energy storage device is electrode materials and electrolyte, and the matching relationship between them.This work main discusses the electrode materials for the aequous supercapacitor, and research their characterization and electrochemical performance, the mainly work as follows.This research work is focused on the synthesis of nanomaterials with high specific surface area and upgrading the capacity to improve the energy density.The results of this paper include the following several parts:(1) With the typical solution reaction methods to preparation of MOF-5, and make it carbonization at high temperature to obtained the high specific surface area of porous carbon materials(PC).BET test show that the porous carbon have high specific surface area of 2618.7 m2 g-1 and porous.To the PC as the electrode material for supercapacitor, the single electrode capacitance can reach 148.8 g F-1 at current density of 5 A g-1, and even the current density at 50 A g-1, the specific capacitance is still up to 136.6 F g-1.When we use gel of PVA/Na2SO4 as the electrolyte to assembly PC/Na2SO4 /PVA/C for supercapacitor, it show that the supercapacitor at voltage window 0~1.8 V has a good charging and discharging cycle performance, at current density of 10 A g-1 10 000 times than capacitance loss only 5.2%.Based on PC/Na2SO4/ PVA/PC for forming supercapacitor under power density 449.9 W kg-1 with energy density 17.37 Wh kg-1, respectively, when the power density increased to 13516.4 W/kg, the energy density still is 8.26 Wh kg-1.(2) Synthesized Ni O@CNT nanocomposite by hydrothermal method, based on the Ni O@CNT positive material, activated carbon as negative material, used 6 mol L-1 KOH aqueous solution as the electrolyte to assemble a kind of high energy density and power density of the hybrid supercapacitors.Charging and discharging window of the hybrid supercapacitor is 0-1.4 V, the energy density can be reached 52.6 Wh kg-1.The hybrid supercapacitor reversible recharge cycles at current density of 10 A g-1 with 1000 times the capacitance loss less than 12%.This is mainly because the CNT provides a good base to support the Ni O in the process of cycle test.(3) By the hydrothermal method to preparation MoO3 nanorod, using PPy by in situ oxidation polymerization at low temperature to coating Mo O3 nanorod and composite with graphene.The electrode material using 2 mol L-1 KOH aqueou solutions as the electrolyte was showed excellent electrochemical performance. electrochemical tested shown that PPy@Mo O3/r GO nano composites than with virginal PPy@Mo O3 has higher capacity performance and smaller equivalent series resistance.PPy@Mo O3/r GO nanocomposite materials in the current density is 500 m A g-1, the specific capacitance of 124 F g-1;Compartion with PPy@Mo O3 electrode material under the same current density than the capacitance of 96 Fg-1, the specific capacitance increased by 29.2%.Charge and discharge cycle after 600 times, PPy@Mo O3/r GO nancomposite capacitance attenuation rate is only 12%.