Three-dimensional α-Fe₂O₃/carbon nanotube sponges as flexible supercapacitor electrodes

Abstract

Flexible supercapacitors, which can sustain large deformations while maintaining normal functions and reliability, are playing an increasingly important role in portable electronics. Here we report the preparation of a three-dimensional α-Fe 2 O 3 /carbon nanotube (CNT@Fe 2 O 3 ) sponge electrode with a porous hierarchical structure, consisting of a compressible, conductive CNT network, coated with a layer of Fe 2 O 3 nanohorns. The specific capacitance of these hybrid sponges has been significantly improved to above 300 F/g, while the equivalent series resistance remains at about 1.5 Ω. The highly deformed CNT@Fe 2 O 3 sponge retains more than 90 % of the original specific capacitance under a compressive strain of 70% (corresponding to a volume reduction of 70%). The hybrid sponge still works stably and sustains similar specific capacitance as initial value even after 1000 compression cycles at a strain of 50%. The outstanding properties of this hybrid sponge make it a highly promising candidate for flexible energy devices.

Recent advances in flexible supercapacitors based on carbon nanotubes and graphene

“…In addition to CNT film and arrays, other CNT nanostructures have also been developed for use in flexible supercapacitors, such as CNT networks [72], CNT sponges [73][74][75], and CNT yarn [76][77][78]. These CNT structures are often used as conductive skeletons/substrates, and provide a large surface area for the deposition of secondary active materials by following the so-called core-sheath/shell model.…”

“…To achieve maximum electroactive surface area, the structure of the sheath layer must be carefully regulated rather than just simply coated onto the CNT core. Accordingly, Chen and co-workers prepared a 3D α-Fe 2 O 3 /carbon nanotube (CNT@Fe 2 O 3 ) sponge electrode with a hierarchical structure, consisting of a compressible and conductive CNT network coated with a layer of Fe 2 O 3 nanohorns [74]. First, FeOOH was uniformly deposited onto a CNT sponge by a hydrothermal method and then transformed into spindle-like Fe 2 O 3 crystals in the subsequent annealing process.…”

Carbon Nanotube Sponges, Aerogels, and Hierarchical Composites: Synthesis, Properties, and Energy Applications

“…The empty space between stacked CNTs create macropores with sizes of tens to hundreds of nm (an average of about 80 nm), with an estimated porosity of more than 99%. The skeletons are MWNTs with diameters of 20-40 nm and open ends as seen from transmission electron microscope (TEM) images, and residual Fe catalyst particles encapsulated in the tube cavities bring CNT sponges many exciting properties (Figure 2 d,e), such as ferromagnetism, [68][69][70] microwave absorption, [ 71,72 ] electrochemistry, [ 46,[73][74][75][76] and thermoelectric application. [ 31,[33][34][35]46,[65][66][67] The interconnected CNT network also renders the macroscopic sponge a good electrical conductivity (1.6 S cm −1 ).…”

“…In 2013, Zhong et al presented a Adv. [ 73 ] Copyright 2015, The Royal Society of Chemistry. 2016, 6, 1600554 www.MaterialsViews.com www.advenergymat.de Figure 10.…”

Atmospheric-pressure plasma jet processed SnO2/CNT nanocomposite for supercapacitor application

“…The general charge/energy storage mechanisms for a supercapacitor are pseudocapacitance and electrical double layer capacitance [25].…”