Preparations Of SnO₂?MnOOH And Bi₂O₃/Carbon Cloth Composites And Their Applications In Supercapacitors

Supercapacitor is a new kind of energy storage device with the feature of high power density, excellent cycle stability, wide temperature range and fast charge-discharge rate. However, the relatively low energy density limits its practical application. To over the challenge, three dimensional?3D? electrode materials have being designed and synthesised. Compared to the low-dimensional materials, the 3D electrode materials can effectively enhance the electrochemical performances for supercapacitor by increasing the active sites and making more facets of active materials expose in electrolyte. Additionally, carbon cloth?CC? is widely used as conductive substrate to support active species as electrode because of its network structure, excellent conductivity and good flexibility. The as-prepared electrode can be directly acted as working electrode without the need of binder or/and other additives, which could decrease the internal resistance and total weight of electrode to enhance the performance. Given this, in present paper, we design and synthesis 3D metal oxide/ hydroxide growing on CC acted as current collector to prepare the integrated electrode. Then, the morphology, composition and electrochemical performance of the composite electrode are discussed in detailed. Meanwhile, to match capacitive behavior of different electrode materials, we successfully assemble asymmetric/symmetric supercapacitors to evaluate the practical application of electrode materials. The main contents of this paper are presented as follows:1. A three-dimensional?3D? lamellar SnO₂ is grown on CC substrate?donated as 3D lamellar SnO₂/CC? through hydrothermal reactions and subsequent thermal treatments. The resulting 3D lamellar SnO₂/CC can be directly used as electrode of supercapacitors with no need for addition of either binder or conductive species. Meanwhile, the electrode could achieve a specific capacitance as high as 247 F g-1 at a current density of 1 A g-1 within a potential window ranging from-0.6 to 0.3 V because of the unique porous structure accessible to electrolyte ions. In order to match the capacitive behaviors of 3D lamellar SnO₂/CC in the two-electrode system, reduced graphene oxide/carbon cloth?rGO/CC? is prepared by starting from GO. The rGO/CC and 3D lamellar SnO₂/CC are respectively used as positive and negative electrode to assemble asymmetric supercapacitor. The device exhibits not only an excellent cycle stability?76.9 % after 10000 cycles at 3 A g-1?, but also high energy density of 22.8 Wh kg-1 at the power density of 850 W kg-1 under a cell voltage of 1.7 V. Moreover, the as-fabricated supercapacitor has green and environmentally friendly features because aqueous neutral electrolyte is employed in it.2. We grew MnOOH on CC fibers by employing electrodeposition method, in which the mixed solution including 0.5 M MnCl2·H2O and 0.5 M NaNO3 as electrolyte and CC as working electrode. The morphology, microstructure and composition of the as-obtained samples were characterized by using FE-SEM, XRD, XPS, Raman and FT-IR. The MnOOH nanosheets are grown vertically on CC fibers to form a thin-wall cell structure with open pores?donated as thin-wall MnOOH/CC?, which can be directly acted as working electrode without other binders or conductive additions. The thin-wall MnOOH/CC electrode in the three-electrode configuration reveals a high specific capacitance of 330.2 F g-1 under a wide potential window of 1.7 V?ranging from-0.9 V to 0.8 V? as well as excellent cycle stability?6.3% decay after 5000 cycles?. Furthermore, the symmetric supercapacitor?SSC? assembled by using thin-wall MnOOH/CC as both negative and positive electrodes shows an energy density of 32.5 Wh kg-1 at power density of 850 W kg-1 with a remarkable cycle lifetime?84.6% of the initial value after 10000 cycles?. The unique thin-wall structure and binder-free electrode are responsible for the enhanced electrochemical performances.3. Hierarchical Bi₂O₃ nanosheets are vertically grown on etched CC by using a facile solvothermal route to form a porous structure?donated as Bi₂O₃/CC?. The special structure makes it a highway for electron transfer and easy access for electrolyte. Then the sample is directly used as electrode without any other binder or active additive, resulting excellent electrochemical performances, such as high specific capacitance of 315.2 F g-1 at 1 A g-1 and a small internal resistance. To accurately evaluate the feasibility of Bi₂O₃/CC electrode, an asymmetric supercapacitor is fabricated by using Bi₂O₃/CC and Co₃O₄/carbon cloth?Co₃O₄/CC? as negative and positive electrodes, respectively. The as-assembled ASC device also delivers a high specific capacitance of 73.8 F g-1 at 1 A g-1, a good rate capability as well as high energy density of 26.2 Wh kg-1 under a cell voltage of 1.6 V.