Design And Preparation Of Cobalt-Based Carbon Electrode Materials And Its Performance In Hydrogen Ion Capacitor Battery

The development and utilization of new energy has been considered as an effective way to solve the problems of environmental pollution and energy crisis.The synthesis of new energy storage materials and the construction of high-performance energy storage devices are considered as the key to the practical application of new energy sources.In recent years,hydrogen ion batteries have attracted widespread attention due to their environment-friendly,low cost,and high security advantages.To provide effective methods to solve shortcomings of hydrogen-based electrochemical energy storage materials,such as high cost,complicated synthetic process,and poor cycle performance,several new electrode materials had been synthesized in this work.Moreover,different kinds of hydrogen ion capacitor batteries were further investigated.A series of cobalt-based cathode materials and nickel hydroxide cathode material were fabricated.Synthesis methods such as nitrogen doping,carbon coating,and nano-sized were adopted to improve the electrochemical performance of electrode materials.Moreover,the energy storage mechanism of as-prepared hybrid devices was elucidated.The main research results of this dissertation were as follows:（1）A nitrogen-doped carbon material with uniformed micro-porosity structure was prepared by carbonizing an octa（aminophenyl）silsesquioxane copolymer（OAPS）and phenolic resin,among which OAPS acts as a microporous self-template.In the calcination process,OAPS could be pyrolyzed into monodisperse silica and nitrogen-containing carbon skeleton.Subsequently,uniformed micropores could be obtained after removing silicon dioxide by HF acid etching.The electrochemical hydrogen storage properties of as-synthesized materials were investigated in a three-electrode system.These results showed that the uniformly distributed micropores and nitrogen doping were beneficial to improving the electrochemical hydrogen storage performance of carbon materials.In addition,a series of cobalt nanoparticles/nitrogen-doped porous carbon composites were prepared by the impregnation method.Compared with OAPS derived nitrogen-doped porous carbon,the electrochemical hydrogen storage performance of cobalt nanoparticles/nitrogen-doped porous carbon composites has been significantly improved.Moreover,a new hydrogen ion capacitor battery was assembled by using cobalt nanoparticles/nitrogen-doped porous carbon hydrogen storage material（negative electrode）and commercial activated carbon（positive electrode）.In addition,the assembly process and energy storage mechanism of the device were preliminarily explored.（2）A Co@Meso-NC nanoparticle composite was successfully synthesized via a facile molecular self-assembling route,using hexamethylenetetramine（HMT）as carbon sources and cobalt nitrate as cobalt sources.In the synthesis process,HMT can assemble with cobalt ions through hydrogen bonding to form a stable supramolecular framework.After pyrolysis,cubic phase cobalt metal nanoparticles were obtained,which were coated with amorphous carbon.The results of the electrochemical hydrogen storage test revealed that as-synthesized Co@Meso-NC nanocomposites exhibit high electrochemical hydrogen storage capacity(300 m Ah g^-1 at 100 m A g^-1 current density),excellent hydrogen storage stability(the residual discharge specific capacity of the electrode is 261 m Ah g^-1 after 48 h resting in open circuit condition),and good rate performance(the discharge capacity is 190 m Ah g^-1 at 1000 m A g^-1 current density).The above results demonstrated that the construction of composites with carbon-coated cobalt structure is an effective method to improve the electrochemical hydrogen storage performance of the material.Furthermore,a new type of hydrogen ion supercapacitor-battery was assembled,by using Co@Meso-NC nanocomposites as a negative electrode and commercial activated carbon as a positive electrode（Co@Meso-NC//Commercial AC-K）.The electrochemical performances of both electrodes and the energy storage mechanism of the hybrid device were investigated by varying the mass ratio of the positive and the negative electrode.It was found to be that the capacity of this hybrid supercapacitor was highly correlated with the negative to the positive electrode mass ratio.The highest capacity(36.7 m Ah g^-1)was achieved at a ratio of 1:7.The optimized hybrid device demonstrated excellent rate performance.（3）To optimize the structure of hydrogen ion capacitor-battery,match the specific capacity of anode materials and cathode materials,and improve their electrochemical performance,nickel hydroxide/carbon nanotube（Ni（OH）₂/CNT）cathode material with a three-dimensional conductive network structure was prepared by chemical water bath deposition in this study.The as-fabricated composite was used as a positive electrode in a new Co@Meso-NC//Ni（OH）₂/CNT capacitor-battery hybrid device,which exhibited better electrochemical performance than the Co@Meso-NC//Commercial AC-K hydrogen ion capacitor-battery.The electrochemical test results of the Co@Meso-NC//Ni（OH）₂/CNT hybrid device showed that the optimal mass ratio of positive and negative active materials was 1:1.Meanwhile,the discharge specific capacity of the Co@Meso-NC//Ni（OH）₂/CNT hybrid device was 153 m Ah g^-1（based on the total mass of active material in both positive and negative electrodes）,close to the theoretical value.In addition,the hybrid device can provide a specific energy density of 78.6 Wh kg^-1 at a high power density of 1.6 k W kg^-1.（4）To obtain smaller cobalt nanoparticles,the porous spongy-like Co@NC and Co₃O₄@NC nanocomposites were prepared through the self-assembly of polyethyleneimine/acetic acid/cobalt nitrate.Co@NC composite can be obtained in a nitrogen atmosphere,which was composed of poly crystallized cobalt phase coated by spongy-like amorphous nitrogen-doped porous carbon.The cobalt nanoparticle size was ranged from 20 to 50 nm which was coated by a graphitized carbon layer,monodispersed on the carbon skeleton.Moreover,the Co₃O₄@NC nanoparticles were prepared in an air atmosphere,formed by the accumulation of cubic Co₃O₄nanoparticles coated by amorphous carbon.The average Co₃O₄ nanoparticle size was estimated to be 100 nm.The electrochemical hydrogen storage performance of Co@NC material was tested in a three-electrode system.The results showed that the discharge specific capacity of the Co@NC electrode in the alkaline electrolyte is 344 m Ah g^-1.Subsequently,a new type of cobalt-hydrogen capacitor battery Co@NC//Co₃O₄@NC was assembled by using porous sponge-like Co@NC material as a negative electrode and Co₃O₄@NC material as a positive electrode.The electrochemical test results of the Co@NC//Co₃O₄@NC hybrid device showed that the optimal mass ratio of the negative to the positive active materials is 1:7,and the discharge specific capacity reached 48.7m Ah g^-1.Furthermore,Co@NC//Ni（OH）₂/CNT ion capacitor battery had been fabricated.The optimal ratio of the negative electrode to positive electrode was 1:1.2,and the discharge specific capacity was 154.9 m Ah g^-1.Above all,this work provides a promising synthetic method and research idea for the large-scale preparation of cobalt-based nanocomposites and the construction of cobalt-hydrogen capacitor batteries.