Fabrication Of Porous Electrode Materials And Their Application In Supercapacitors

With the rapid development of economy and population growth,energy crisis is a huge obstacle to sustainable our society development.As a new energy storage device,supercapacitor has the advantage of both high power density as conventional capacitors and large energy density as secondary batteries,therefore plays an important role in the field of energy storage and conversion.The high charge/discharge rate and large storage capacitance of it fill the gap between the two traditional technologies.The electrochemical performance of a supercapacitor depends on solid-liquid interface between the electrode material and electrolyte largely.Either an electric double layer capacitor or a pseudo-capacitor,porous electrode material presents a significant advantage compared to others.In this work,porous electrode materials were designed and fabricated via different methods to improve the electrochemical performance.The influence between micropores and alkaline ions in aqueous cells was investigated as well.The main contents and results are as follows:The VO₂/TiO₂ composite films with porous sponge structure were synthesized through electrostatic spray deposition?ESD?combined with a post heat treatment.The influence of experiment parameter changes on the film morphologies and the influence of precursor contents on the final products composition were studied.The composite film has large amounts of interconnected three-dimensional channels,which facilitate the wetting and transport process of electrolyte ions.This leads to a substantial increase in electrochemical capacitance,namely 86.2 mF cm-2??548 F g-1?at a scan rate of 10 mV s-1.VO₂ has a high theoretical capacitance,but it also has a shortcoming of large volume change during the electrochemical reaction.To solve it,a zero-strain material TiO₂ was introduced and designed as a structural stabilizer to further improve the stability of composite.The VO₂/TiO₂ composite films perform a capacitance retention rate of 84.3%after 1,000 cycles at a current density of 10 A g-1.This work presents a facile and effective synthetic strategy,which in potentially applied for fabrication of other thin film composites.The activated carbon/phosphomolybdic acid?denoted as AC/PMo 12?composites were prepared by introducing high pseudo-capacitive polyoxometalates?POMs?into commercial activated carbon.Activated carbon not only provides a conductive channel for phosphomolybdic acid,but also solve the dissolution of PMo12 by micropores adsorption.The addition of the pseudocapacitance from highly reversible redox reaction of POMs to the electric double-layer capacitance?EDLC?of carbon leads to an increase in the specific capacitance of?90%.Meanwhile,the application of aqueous solutions of protic ionic liquids?P-IL?as electrolyte instead of aqueous sulfuric acid solutions offers an opportunity to improve POM cycling stability significantly.Virtually no degradation in capacitance was observed in POM-based positive electrode after 10,000 cycles in an asymmetric capacitor with P-IL aqueous electrolyte.This work offers a facile strategy to increase capacitance of commercial EDLCs without any changes in the electrode or cell assembling,presentting a viable solution for enhancing energy density of EDLC on pure carbon electrodes.The complicated relationship between the capacitance and pore properties in the aqueous supercapacitors remains unclear.To expolre it,microporous carbon was prepared by using zeolite as a template through the route of low pressure chemical vapor deposition?LPCVD?.The morphology and pore distribution of zeolite templated carbon?denoted ZTC?with changing of deposition time was carefully studied.ZTC was assembled into symmetric cells and test in alkaline electrolytes to investigate the ions behavior in micropores.Generally,the capacitance sequence is as follow:C?Cs⁺?>C?K⁺?>C?Na⁺?>C?Li⁺?,in acoordance with increased ion hydrated radius.While the rate performance is highly dependent on pore size as well as functional groups.Therefore considering the factors both of electrochemical capacitance,rate performance,and economic reasons,etc.,KOH is an ideal electrolyte for testing microporous carbon materials in aqueous cells.