Metallocene/carbon hybrids prepared by a solution process for supercapacitor applications

Abstract

Efficient and scalable solution-based processes are not generally available to integrate wellstudied pseudocapacitive materials (i.e., metal oxides and conducting polymers) with other components such as porous carbon, mainly because these classes of pseudocapacitive systems have poor solubilities in solvents and exhibit no specific interactions with the other component.Here we report, for the first time, the integration of a metallocene polymer, polyvinylferrocene (PVF), with carbon nanotubes (CNTs) via a simple solution process for supercapacitor applications. The solution processability of the PVF/CNT hybrid is due to the high solubilities of PVF in organic solvents and the unique ability of the metallocene/carbon system to form stable heterogeneous inks through the π-π stacking interactions between the two components. The nanostructure and electrochemical properties of the hybrid can be manipulated systematically by adjusting the composition of the heterogeneous ink. The hybrid with the optimized composition exhibits unusually high capacitance (1452 F/g) and energy density (128.9 Wh/kg) obtained in a standard two-electrode configuration, outperforming previously reported pseudocapacitive materials. Broader ContextSupercapacitors with extremely high capacitance, enhanced energy and power densities, and excellent reliability offer great potential as complements to, and replacements for, batteries and conventional electrolytic capacitors for energy storage applications. Carbon nanomaterials, metal 2 oxides and conducting polymers have been investigated widely as supercapacitor electrode materials. Many emerging high-performance supercapacitor devices benefit from the integration of these different capacitive materials to exploit their synergies for enhanced capacitance and energy density. Meanwhile, solution processing is low-cost, high-throughput, and readily scalable.It is the preferred fabrication method for many devices such as solar cells, transistors, batteries and single-component supercapacitors, but is very difficult to use for the integration of either metal oxides or conducting polymers with other capacitive materials such as carbon nanotubes.Instead, the common integration methods rely for the most part on electrochemical deposition processes, which are time-consuming, low-throughput and difficult to scale up. In this study we have developed a metallocene/carbon hybrid system amenable to solution processing, with control of the nanostructure and electrocapacitive performance of the hybrid materials realized through manipulation of the ink composition. The optimized hybrid system, as determined by its composition, consists of a highly porous nanoscale architecture in which a three-dimensional conductive carbon nanotube network with interconnected nanopores is coated conformally by the redox-active metallocene polymer. This unique morphology simultaneously facilitates electron transport, reduces ion diffusion length, and increases metallocene utilization efficiency. Thus this hybrid exhibits si...

Microwave-Assisted Oxidation of Electrospun Turbostratic Carbon Nanofibers for Tailoring Energy Storage Capabilities

“…This performance is already comparable to that of batteries (SI Figure S10). [58,93] ECNF-M3 demonstrated an energy-power combination comparable to or even better than previously reported high performance carbon-based symmetrical supercapacitor cells (solid triangles in black or gray in Figure 3f); [40,[94][95][96][97][98] all values are shown on an active mass normalized basis.…”

“…All four systems possessed power densities ranging from 10 3 to 10 6 Wh/kg, which are similar to those of conventional electrolytic capacitors (SI Figure S10). [58,93] Compared to uECNF, ECNF-M2 showed higher energy densities at low power densities and lower energy densities at high power densities. ECNF-M5 showed the worst energy-power combination among the four samples.…”

“…Nonetheless, carbon electrodes are still the most popular choice to date for use in commercial supercapacitor devices due to their ease of synthesis, low cost, and exceptional chemical and electrochemical stability. [48][49][50] Metal oxides (e.g., RuO 2 , [51,52] MnO 2 [53,54] ) and electroactive polymers (e.g., polyaniline, [55,56] polyvinylferrocene) [57,58] exhibit pseudocapacitive characteristics, and have been shown to deliver remarkably higher capacitance values than those of carbon materials possessing only DL capacitances. However, several challenges still remain -the high cost of Ru-based oxides may prohibit them from use in practical applications, while the cycling instability and the poor rate performance of Mn-based oxides and electroactive polymers remain critical issues that require careful examination.…”

Nanocarbon-based electrochemical systems for sensing, electrocatalysis, and energy storage

“…[162] For example, Mao 7 et al [17] showed that a polyvinylferrocene (PVF)/CNT hybrid had a much higher specific capacitance and energy 8 density than did each of the individual components alone. The PVF/CNT hybrid can be prepared by an efficient, 9 low-cost, solution-based process, and the nanostructures and electrochemical performance of the hybrid can be 10 easily varied by adjusting the composition of the precursor solution before deposition.…”

“…One way to improve the energy density of CNT-based supercapacitors is through incorporation of pseudo-6 capacitive materials (e.g., redox polymers [17,157,158] and metal oxides [159][160][161] in most cases). [162] For example, Mao 7 et al [17] showed that a polyvinylferrocene (PVF)/CNT hybrid had a much higher specific capacitance and energy 8 density than did each of the individual components alone.…”