Ordered Mesoporous Carbon Composite Films Containing Cobalt Oxide and Vanadia for Electrochemical Applications

Abstract

Mesoporous carbon composite thin films (<500 nm) containing cobalt and vanadium oxide were synthesized by triconstituent self-assembly using Pluronic F127 as template, phenol-formaldehyde oligomer (resol) as carbonizable precursor, and cobalt (or vanadyl) acetylacetonate (acac) for the metal source. The ordered mesostructure of the composite films was confirmed by both X-ray diffraction (XRD) and transmission electron microscopy (TEM). During pyrolysis at 800 °C to carbonize the film, the d-spacing decreases significantly because of uniaxial contraction; however addition of Co/V content leads to a decrease in the contraction from approximately 68% to 50%, which indicates the Co/V mechanically strengthens the framework. The decrease in contraction also leads to an increase in the average pore size by as much as 60%. Nanoparticles are found to be dispersed within the continuous carbon framework from both high resolution (HR)-TEM and scanning transmission electron microscopy (STEM); small sub-2 nm particles are observed in all cases for V containing films, while particles greater than 10 nm are found at high Co contents. In addition to these structural changes, the electrical conductivity of the mesoporous carbon film can be increased from 22 S/cm to approximately 40 S/cm by adding 10 wt % of either Co(acac) 3 or VO(acac) 2 in the precursor solution. The conductivity decreases as the organometallic content is further increased, but still remains quite conductive (19.6 S/cm for 50% VO(acac) 2 ). The addition of the transition metals also greatly enhances the electrochemical performance because of their pseudocapacitance. Even after 500 cycles, the composite films maintain a specific capacitance as high as 113 F 3 g À1 (for Co) and 159 F 3 g À1 (for V) in comparison to the neat carbon, which is initially approximately 22 F 3 g À1 . These materials exhibit favorable electrochemical properties for potential energy storage applications such as insertion batteries and supercapacitors.

High capacity magnetic mesoporous carbon–cobalt composite adsorbents for removal of methylene green from aqueous solutions

“…In addition to the diffraction related to the carbon structure, two additional diffraction peaks are observed for the C-Co composite materials, which match the (1 1 1) and (2 0 0) planes of metallic cobalt. Thus, unlike thin films where CoO is formed [37], metallic cobalt nanocrystals are formed in the powders. To explain this apparent contradiction, the relative reducing atmosphere must be considered.…”

“…For this second criteria, it is known that some organometallic cobalt precursors yield a graphene shell around Co nanoparticles by simple heating in an inert atmosphere [36]. We have previously introduced Co into ordered carbon framework through tri-constituent self-assembly method by using Co(acac) 3 as precursor [37] where a graphitic shell is obtained around nanoparticles dispersed in a mesoporous carbon matrix. This precursor may also be more apt to segregate into the resol phase to minimize the loss of Co nanoparticles when etching silica to increase surface area.…”

Cobalt monoxide-doped porous graphitic carbon microspheres for supercapacitor application

“…3 (d)). At the hydrothermal temperature of 200°C, α-CD is converted to carbon while the dissolved Co salt is wrapped in the carbon matrix, which is assisted by the hydrogen bonding between Co-gluconate with α-CD and F12734. Upon pyrolysis, the soft template of F127 is decomposed to generate a porous structure inside the Co-GPCMs.…”

Synthesis of metal-incorporated graphitic microporous carbon terminated with highly-ordered graphene walls—Controlling the number of graphene layers by ambient-temperature metal sputtering

“…6(d). Previous reports on the HRTEM imaging of semi-graphitic porous carbon showed either the formation of short range partially graphitized domains or ordering in the pores [3,[13][14][15][58][59][60][61][62] (cf. Table 2).…”