MnOx/carbon nanotube/reduced graphene oxide nanohybrids as high-performance supercapacitor electrodes

Abstract

Nanohybrids consisting of both carbon and pseudocapacitive metal oxides are promising as high-performance electrodes to meet the key energy and power requirements of supercapacitors. However, the development of high-performance nanohybrids with controllable size, density, composition and morphology remains a formidable challenge. Here, we present a simple and robust approach to integrating manganese oxide (MnO x ) nanoparticles onto flexible graphite paper using an ultrathin carbon nanotube/ reduced graphene oxide (CNT/RGO) supporting layer. Supercapacitor electrodes employing the MnO x /CNT/RGO nanohybrids without any conductive additives or binders yield a specific capacitance of 1070 F g − 1 at 10 mV s − 1 , which is among the highest values reported for a range of hybrid structures and is close to the theoretical capacity of MnO x . Moreover, atmosphericpressure plasmas are used to functionalize the CNT/RGO supporting layer to improve the adhesion of MnO x nanoparticles, which results in theimproved cycling stability of the nanohybrid electrodes. These results provide information for the utilization of nanohybrids and plasma-related effects to synergistically enhance the performance of supercapacitors and may create new opportunities in areas such as catalysts, photosynthesis and electrochemical sensors. NPG Asia Materials (2014) 6, e140; doi:10.1038/am.2014.100; published online 31 October 2014 INTRODUCTIONSupercapacitors are promising energy storage systems for diverse applications such as portable electronics, roll-up displays, hybrid electric vehicles, self-powered sensors, artificial muscles and biomedical implants. 1,2 The performance of supercapacitors fills the gap between batteries and conventional electrolytic capacitors, with such advantages as fast dynamic response, high power density, high rate capability, safe operation and long lifespan. The most common materials for current supercapacitor electrodes are high-surface-area carbon-based nanostructures, including activated carbons, porous/ templated graphite, carbon nanotubes (CNTs) and graphene. [3][4][5][6] However, the relatively low specific capacitance and energy density of these carbon-based electrodes have so far hampered their widespread applications in real devices.To address this challenge, hybrid materials that can synergistically combine the attributes of both carbon and pseudocapacitive materials such as metal oxides and conductive polymers have been actively pursued. [7][8][9] Pseudocapacitive materials store electrochemical energy in a similar manner as carbon-based materials but have a specific capacitance that is usually one order of magnitude larger. Among various pseudocapacitive materials, manganese oxides (MnO x ) have attracted the strongest interest because of their natural abundance, low cost and environmental friendliness. 10 Numerous studies have

MoS2-coated vertical graphene nanosheet for high-performance rechargeable lithium-ion batteries and hydrogen production

“…First, VGNS has outstanding electronic conductivity to improve the electron transfer rate. 19 Second, the vertically aligned VGNS can effectively inhibit the restacking of the MoS 2 layered structure and maintain its structure integrity. Third, given that lithium ions can effectively penetrate into the electrode and contact with active MoS 2 through submillimeter pores, lithiation and delithiation can be greatly facilitated in the nano-sized layered structure of MoS 2 , which can provide a mass of active sites to enhance ion accessibility and shorten the path of Li diffusion.…”

“…18,19 VGNS consists of few-layered graphene sheets self-organized in a vertical orientation with an inherently open and interconnected array structure. The structural rigidity of VGNS can prevent the restacking of graphene nanosheets, a commonly observed problem in horizontal graphene.…”

Carambola-shaped VO2 nanostructures: a binder-free air electrode for an aqueous Na–air battery

“…For the growth of carambola-shaped VO 2 nanostructures, a carbon paper has been used as a conductive air electrode, which is beneficial in the reduction of cost and weight of electrode compared to other air electrodes such as the Ni foam, Ti mesh and Cu mesh. In addition, rGO was coated on the carbon paper to improve the conductivity of the system 21,22 and wettability of electrode. 13 The fabricated Naair battery with VGC air electrode displays 0.64 V overpotential gap, 81% round trip efficiency, 2.81 V terminated discharge potential, 104 mW g -1 power density at 80 mA g -1 current density, and good cyclic stability up to 50 cycles.…”

Synthesis of Graphene on Conducting Substrate by Electrochemical Deposition Method

“…Four samples were done with different coated number of layers of graphene according to the numbers of cycles applied as shown in Figure 4. Less concentrated samples had a larger amount of inter-lamellar water that is present in stacked GO films and a Hydrogen bond network is formed between the water molecules and the oxygenated groups on GO (Han et al, 2014). Whereas sample 3 was coated with 1 layer and sample 4 with 2 cycles in a concentrated buffer solution with 1.5 mg mL −1 GO as shown in Figure 4 of thin film deposition.…”

“…The shape of curves is not affected much at a scan rate less than 20 mV s −1 , indicating the good stability rate of the electrode material. The results show linear response to current peaks rise that was due to redox confined reactions at the modified electrode's surface (Beitollahi et al, 2014;Han et al, 2014). Figure 6 makes a comparison of the resultant integrated surface area as more graphene layers are deposited that shows a clear increase in the surface area from ITO to RGO/ITO and RGO/RGO/ITO that also favors charge/discharge along with redox process of electron transfer of increased mobility and thus conductivity improvement on the modified electrode's surface at a fixed slow scan rate in order to eliminate most of the noise present in the background (Devadas et al, 2012).…”