Biomorphic Synthesis Of Transition Metal Oxide-based Electrodes For High-performance Supercapacitor

Supercapacitors, also known as electrochemical capacitors, can store high energy and transport high power within a very short period and are therefore projected to be one of the best candidates for portable electronic devices and hybrid electric vehicles. Carbon materials, transition metal oxides and conducting polymers are conventional electrode materials for supercapacitors. Among then, transition metal oxides can provide higher energy density than conventional carbon materials and better electrochemical stability than polymer materials. However, their applications were restricted based on the rapid development of supercapacitor with higher performance. Thus, the development of newly advanced electrode materials with high performance for supercapacitors is essential. Porous electrode materials with tailored pore size and distribution can be synthesized by templating and template-free methods. Most biological materials have the fudamental feature of hierarchy,multifuctionality and self-organization, which have risen from hundreds of million years of evolution. Biomaterials, as a kind of relatively abundant and renewable materials, can be used as an alternative to synthetic templates to produce hierarchical porous structures by nanocasting or by chemical conversion, and assembly of biological building blocks.In the present work, biotemplates, such as wood, cotton and biomacromolecule (such as amino acid) have been introduced into the fabrication of biomorphic porous electrode materials for supercapacitors and the electrochemical performance of as-obtained materials has been investigated. The main contents and results are as follows:A novel process has been developed for the fabrication of biomorphic composite electrodes from pinewood template and nitrate precursor. The production of biomorphic electrodes was performed using the following process. Firstly, Pinewood pieces were vacuum infiltrated with precursor solution. Secondly, pyrolysis in inert atmosphere at 500℃ resulted in the formation of hierarchically porous composite electrodes. C/Co/CoO and C/Ni/NiO composite electrode materials were prepared by simple impregnation and calcination method. The microstructure and phase formation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), isothermal of N2 adsorption-desorption (BET). The results show that composite electrode materials retained well the microstructure of the original morphology of wood, Co (Ni) and CoO (NiO) nanoparticles were distributed mainly at the surface layer of the cellular wall, the specific area of C/Co/CoO and C/Ni/NiO were up to 369 m2/g and 376 m2/g respectively. C/Co/CoO and C/Ni/NiO composite electrode materials exhibited high specific capacitance of 711 F/g and 976 F/g at a scan rate of 10 mV/s respectively, and good cycling stability along with 73.7% and 73.9% specific capacitance were retained after 500 cycles tests at 5 A/g.Biomorphic Mn2O3/Mn3O4/C composite electrode materials were prepared with cotton as biological template and carbon precursor. Manganese source, concentration and calcination temperature played key roles in controlling the microstructure and composition of composite materials. The results showed that biomorphic Mn2O3/Mn3O4/C composites retained hollow tubular structure of cotton fiber when manganese sulphate as manganese source. N2 adsorption-desorption and electrochemical test demonstrated that the specific area of Mn2O3/Mn3O4/C was up to 76 m2/g, but control sample was prepared without template was only 3 m2/g; the specific capacitance of 438 F/g and 19 F/g at a scan rate of 10 mV/s respectively.Fe3O4 and Ni(OH)2 electrode material with micro/nano structure was prepared by hydrothermal in the present of basic amino acid (lysine). As obtained Fe3O4 has a greater surface area, which the specific area was up to 93 m2/g. Micro/nano structure Fe3O4 electrode exhibited excellent capacitance of 633 F/g at a scan rate of 10 mV/s. Micro/nano structure Ni(OH)2 electrode material with remarkable electrochemical performances was prepared by the same method. Micro/nano structure Ni(OH)2 electrode exhibited high specific capacitance of 710 F/g at a scan rate of 10 mV/s, and good cycling stability along with 78.9% specific capacitance were retained after 500 cycles tests at 5 A/g.