Achieving electrochemical capacitor functionality from nanoscale LiMn2O4 coatings on 3-D carbon nanoarchitectures

Abstract

Conformal nanoscale coatings of Na + -birnessite manganese oxide (MnOx) produced via redox reaction between aqueous permanganate (NaMnO 4 $H 2 O) and the carbon surfaces of fiber-paper-supported carbon nanofoams are converted to LiMn 2 O 4 spinel through topotactic exchange of Na + for Li + in the as-deposited lamellar birnessite, followed by mild thermal treatments to complete the transformation to LiMn 2 O 4 . The evolution of the birnessite-to-spinel conversion is verified with X-ray diffraction, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy, electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The mild conditions used to convert birnessite to spinel ensure that the conformal nanoscale nature of the oxide coating is retained throughout the macroscopically thick (170 mm) carbon nanofoam substrate during the conversion process. The architecture of the LiMn 2 O 4 -carbon nanofoam facilitates rapid ion/electron transport, enabling the LiMn 2 O 4 to insert and extract Li + from aqueous electrolytes at scan rates as high as 25 mV s À1 , and with a relaxation time of 37 s as derived from electrochemical impedance. This architectural expression of nanoscale LiMn 2 O 4 delivers full theoretical capacity (148 mA h g À1 ) at 2 mV s À1 .

Preparation and characterization of partially reduced graphene oxide aerogels doped with transition metal ions

“…No correlation between obtained volumes and C/O ratios could be estimated. The less dense aerogel was obtained for Cr-doped prGO aerogel (2.5 mg/cm 3 ), and still it is around 16 9 denser than the lightest reported aerogel and simultaneously, lightest solid-state material known to the mankind [41].…”

“…electrodes [3,[31][32][33][34][35][36] or filters [37], demands from them to be stable under mechanical stress. Large effort has been made to improve their mechanical properties and stability.…”

“…However, for some specific applications like electrocatalysis [12,13] or electrode fabrication [14,15], there is a need of modifying the structure with transition metal ions (TMi) in order to grant electro-catalytic properties or improve the conductivity and capacity of electrodes. From the state of the art, it is known that the GO reduction and hydrogel formation can be also achieved via application of reducing agents such as NaHSO 3 , Na 2 S, ascorbic acid or HI [16] and also transition metal chlorides [17]. Therefore, in this work we performed simultaneous reduction and modification of GO by TMi and investigated the influence of different type of transition metal ions onto prGO hydrogel formation process as well as structure and properties of TMi-doped prGO aerogels.…”

“…Depending on building material, strength of the bonds between forming particles/rods/sheets and presence of the dopants in the porous matrix, aerogels can be applied as adsorbents [2], filters [3], catalysts [4,5] or sensors [5,6]. Among the others, graphene oxide (GO) is one of the most interesting building materials for aerogel structures [7], which thanks to the high specific surface area and threedimensional structure can be applied as electrodes in supercapacitors [8,9].…”

The Effect of Calcination Temperature on the Electrochemical Performance of ZnO Coated LiMn2O4/MWCNT Nanocomposite Cathodes

“…2c). Theoretically, LiMn 2 O 4 has 148 mAh g −1 discharge capacity [13]. However, it is believed that increasing the calcination temperature resulted in increase of amount of layered LiMn 2 O 3 structure.…”