| With the consumption of fossil fuels, depletion of fossil energy sources and environmental pollution are becoming severe problems for the Earth. We must look for clean, green, renewable energy to ensure the sustainable development of economy and society. In past years, varieties of energy conversion and storage materials have been applied to many environmentally friendly high-powered energy devices (e.g., lithium batteries, supercapacitors, and solar energy cells). Both Lithium-ion batteries and Supercapacitors are new energy-storage devices, and have been wildly investigated and used in portable electrical appliances such as the mobile phone and laptop, power station and electric vehicles. Electrode materials are usually considered to play the most important role. Among various electrode materials, carbonaceous materials are the most widely used ones because their abundant sources, large specific surface area, high conductivity, and stable physicochemical properties.Supercapacitors with carbonaceous electrode materials are called electrical double layer (EDL) capacitors. Nevertheless, the capacitance of EDL capacitors is still far from satisfactory, which is also the disadvantage of all commercially available supercapacitors. To date, lots of methods have been promoted to overcome this problem. Doping carbonaceous materials with heteroatoms can couple the pseudocapacitance to the EDLCs while maintain the excellent intrinsic characteristics of carbonaceous materials at the same time. Polyaniline (PANI) is considered as the most potentially precursor because of its facile synthesis, environmental stability and the high N/C atomic ratio (0.167). PANI is aslo usually used as pseudocapacitor active materials. However, severe volume swelling and shrinkage during charge/discharge processes lead to the mechanical degradation, which causes the obvious capacity fading. In addition, low electrical conductivity can aslo influence the pseudocapacitive performance of PANI when structured as electrode material of supercapacitors. The combination of PANI with carbon materials has been proved to be attractive to reinforce the stability and the electrical conductivity of PANI as well as maximize the capacitance value.In this paper, we focus on polyaniline as the research object. Several kinds of doped carbon materials were prepared by using PANI as precursor through polymerization, carbonization and activation. The composite was achieved during polymerization of aniline. The morphologies, porous structures and electrochemical performances were studied in detail by SEM, TEM, XRD, FT-IR, BET adsorption, and the electrochemical measurement tools.A kind of nitrogen- and oxygen- containing activated carbon nanotubes (ACNTs) has been prepared by carbonization and activation of PANI nanotubes obtained by rapidly mixed reaction. The ACNTs show oxygen content of 15.7% and nitrogen content of 2.97% (atomic ratio). The ACNTs perform high capacitance and good rate capability (468 F g-1 at the current density of 1 A g-1 and 327 F g-1 at the current density of 10 A g-1) when used as the electrode materials for supercapacitors. Hydrogen reduction has been further used to investigate the effects of surface functional groups on the electrochemical performance. The changes for both structural component and electrochemical performance reveal that the quinone oxygen, pyridinic nitrogen, and pyrrolic nitrogen of carbon have the most obvious influence on the capacitive property because of their pseudocapacitive contributions.A novel kind of heteroatom-doped hollow carbon spheres (HHCSs) was prepared via the carbonization of PANI hollow spheres, which were synthesized by one-pot polymerization. It was found that the carbonized PHSs at 700 ℃ show oxygen content of 9.3% and nitrogen content of 7.3% (atomic ratio). The obtained materials perform high capacitance and good rate capability (241 Fg-1 at the current density of 1 Ag-1 and 120F g-1 at the current density of 10 Ag-1) when used as the electrode materials for supercapacitors. The excellent electrochemical performance can be attributed to the heteroatom-doping and hollow carbon nanostructure of the HHCSs electrodes. Heteroatom groups in the HHCSs not only improve the wettability of the carbon surface, but also enhance the capacitance by the presence of a pseudocapacitive redox process. Their unique structure provides a large specific surface area along with reduced diffusion lengths.A kind of novel porous hollow carbon spheres (PHCSs) was prepared via the carbonization and activation of PANI hollow spheres synthesized by one-pot polymerization for supercapacitors and lithium ion batteries (LIBs) electrodes. The lithium ion storage capacity of PHCSs is evaluated by galvanostatic charge/discharge measurements. The initial reversible capacities of the materials are 1004 mA hg-1 at a current density of 0.05 Ag-1. A specific capacity of 325 mA hg-1 is still retained when charge/discharged at 3 Ag-1 for 50 cycles. The large reversible capacity, high rate performance and good cycleability are attributed to the unique structure of the hollow cores and the high porosity.A novel PANI/porous hollow carbon spheres (P-PHCSs) composite was achieved during polymerization of aniline, and was further employed as an electrode for supercapacitors. The kind of novel PHCSs were prepared via the carbonization and activation of PANI hollow spheres synthesized by one-pot polymerization. Compared with traditional activated carbon, PHCSs demonstrate unique nanostructures. The influences of the mass ratios of aniline and PHCSs on morphologies and electrochemical performance of P-PHCSs nanocomposites have been investigated. As the mass ratio of aniline and PHCSs is 2:1, the P-PHCSs composite demonstrates a large specific capacity of 559 F g-1 at a current density of 0.1 A g-1. Particularly, an outstanding rate capability of 386 F g-1 under 5 A g-1 after 1000 cycles was obtained. Scanning electron microscopy showed that polyaniline nanoparticles were uniformly deposited on PHCSs. Therefore, this unique nanostructure is promising for high-performance electrochemical applications.A novel tremella-like graphene/PANI (TGP) composite was achieved from self-assembly of graphene nanosheets during polymerization of aniline in H2O/N, N-Dimethylformamide solution, and was further employed as an electrode for supercapacitors. The influences of the mass ratios of aniline and graphene on the sizes and morphologies of polyaniline/grapheme nanocomposites have been investigated. As the mass ratio of aniline and graphene is 10:1, polymerization reaction of aniline occurs on the surfaces of graphene nanosheets by heterogeneous nucleation to form tremella-like graphene/PANI composite. This graphene/PANI composite demonstrates a spherical tremella-like structure and a large specific capacity of 497 F g-1 at a current density of 0.5 A g-1. Particularly, an outstanding rate capability of 426 F g-1 under 5 A g-1 after 1000 cycles was obtained. Scanning electron microscopy showed that polyaniline nanoparticles were uniformly deposited on free-standing graphene nanosheets, and self-assembled to a spherical tremella-like structure. Therefore, this unique nanostructure is promising for high-performance electrochemical applications. |
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