Fabrication of carbon-metal oxide nanocomposites as electrode materials for supercapacitors
Date of Issue2017-04-21
School of Materials Science and Engineering
Supercapacitors (SCs) are deemed as the promising energy storage devices because of their remarkable power density, long cycle life and their special status in terms of power and energy densities that bridges the gap between conventional capacitors and batteries/fuel cells. However, the current SC technique is still confronted with low energy density and high fabrication cost. These issues can be tackled by developing high-performance electrode materials, especially the composites that incorporate high electrically conductive carbon (C) materials with pseudocapacitance-abundant transition metal oxides (TMO). The wet-chemistry approach based solutions/suspensions is an efficient way to prepare TMO-C composites on a large. The performance of the composites made by this method is strongly affected by the starting carbon suspensions. However, the common strategies to prepare homogeneous and stable carbon suspensions suffer from one or more shortcoming, such as tedious processes, high cost, high risk and low efficiency. Thus, in this thesis, I utilized the commercial Chinese ink as a starting material, aiming to develop a cheap, simple and scalable method to fabricate high-performance carbon-based composites as electrode materials for SCs. To this end, firstly, Chinese ink was incorporated with multiwalled carbon nanotubes (MWCNTs) and vapor-grown carbon nanofibers (VGCNFs), and investigated its effect on the dispersion MWCNTs and VGCNFs under the wet mechanical grinding. I found that, the addition of Chinese ink is beneficial to the dispersion of MWCNTs and VGCNFs in aqueous suspensions, and their distribution in the poly(vinyl alcohol) and the filter paper. Therefore, the resulting conductive composites were ready to be the electrodes for electrical double-layer capacitors or applicable to be the substrate for the electrodeposition of TMOs. Secondly, Chinese ink was applied to synthesis of birnessite-type MnO2 through the redox reaction between KMnO4 and the carbon black from Chinese ink. The results showed that these carbon black particles served as the reducing agent for KMnO4, and provided anchoring sites for the resulting MnO2. The in-situ deposition of MnO2 on carbon black particles led to well-defined nanostructures, which could be adjusted by changing the addition amount of Chinese ink or the reaction temperture. Benefiting from the good dispersion of the carbon black, the obtained MnO2-ink composites showed high specific surface area and improved electrochemical performance. Thirdly, Chinese ink was employed as an inert additive during the synthesis of nickel cobaltite (NiCo2O4) via chemical co-precipitation and calcination. I found that during the chemical co-precipitation process, the carbon black particles from Chinese ink served as the nanoscale spacers to alleviate the agglomeration of the precipitated NiCo2O4 precursors. Thus, NiCo2O4 nanoflakes with a high specific surface area were obtained after calcination at a low temperature (less than 300 °C), which showed much better specific capacitance than pure NiCo2O4. Therefore, Chinese ink can be used as a building block to prepare high-performance electrode materials for SCs, due to its advantages of ready-made suspension system and the well-dispersed carbon black particles. It is believed that the preparation methods developed in this thesis can be also extended to other TMO-C composites. Furthermore, the methods hold promise for large-scale applications, due to their unique merits, such as low cost, low risk and easy processing.
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