Abstract
The capacitance of MnO2 supercapacitors (SCs) is not high as expected due to its low conductivity of MnO2. The synergistic effects of MnO2 with high theoretical specific capacitance and TiN with high theoretical conductivity can extremely enhance the electrochemical performance of the MnO2-TiN electrode material. In this work, we synthesized different nanostructured and crystalline-structured MnO2 modified TiN nanotube arrays electrode materials by hydrothermal method and explained the formation mechanism of different nanostructured and crystalline-structured MnO2. The influences of MnO2 nanostructures and crystalline-structures on the electrochemical performance has been contrasted and discussed. The specific capacitance of δ-MnO2 nanosheets-TiN nanotube arrays can reach 689.88 F g−1, the highest value among these samples TN-MO-SS, TN-MO-S, TN-MO-SR, TN-MO-RS, and TN-MO-R. The reason is explained based on MnO2 nanostructure and crystalline-structure and electron/ion transport properties. The specific capacitance retention rates are 97.2% and 82.4% of initial capacitance after 100 and 500 cycles, respectively, indicating an excellent charging-discharging cycle stability.
Highlights
The capacitance of MnO2 supercapacitors (SCs) is not high as expected due to its low conductivity of MnO2
SCs can be divided into electrical double-layer capacitors (EDLCs) and pseudocapacitors (PCs) depending on their energy storage mechanism[4], EDLCs mainly based on high surface area materials, such as carbon, graphene[5], graphite oxide[6] so on, which are all kinds of nanostructures, PCs mainly based on metal oxides and graphene-like layered metal compounds[7], using transition metal oxide (Co3O4, NiO, RuO2 and MnO2, etc.) nanomaterials with good electrochemical properties is a practical way to optimize the electrochemical performance of the electrode materials for the development of high-performance SCs8
MnO2 needs to be compounded with other materials with good electrical conductivity to improve the overall electrochemical performance including specific capacitance, charge/discharge performance, and cycle characteristics, researchers have made many attempts to prepare supercapacitor electrodes by mixing M nO2 with highly conductive m aterials[17,18,19,20,21,22,23,24], Since transition metal nitrides have great electrical conductivity, electrochemical characteristics, chemical stability and long service life, TiN, VN, WN, CrN and TiVN are widely used as electrode materials of S Cs25–27
Summary
The capacitance of MnO2 supercapacitors (SCs) is not high as expected due to its low conductivity of MnO2. SCs can be divided into electrical double-layer capacitors (EDLCs) and pseudocapacitors (PCs) depending on their energy storage mechanism[4], EDLCs mainly based on high surface area materials, such as carbon, graphene[5], graphite oxide[6] so on, which are all kinds of nanostructures, PCs mainly based on metal oxides and graphene-like layered metal compounds[7], using transition metal oxide (Co3O4, NiO, RuO2 and MnO2, etc.) nanomaterials with good electrochemical properties is a practical way to optimize the electrochemical performance of the electrode materials for the development of high-performance SCs8. Tang et al used urea and T iCl4 to prepare TiN as a SCs electrode material with a specific capacitance of 407 F g−131
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