Communication pubs.acs.org/cm
Electrochemical Polymerization of Functionalized Graphene Quantum Dots Mark B. Miltenburg, Tyler B. Schon, Emily L. Kynaston, Joseph G. Manion, and Dwight S. Seferos* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada S Supporting Information *
substrates. The GQD/PEDOT films consist of short polymers, due to the limited mobility of covalently bonded monomers during polymerization. The polymerized composite demonstrates a capacitance of 152.8 F/cm3 at 1.84 A/cm3, which is an increase of ∼30% over poly(hydroxymethyl EDOT) films. This methodology can be extended to easily synthesize materials for applications such as catalyst hosts28 and electrode materials in energy storage devices.29−32 The GQD/PEDOT films showed a very different morphology to GQD/polyaniline (PANI) nanocomposite films.27 The previously demonstrated GQD/ PANI nanocomposites also showed larger voltage drops during charge−discharge processes, and smaller voltage windows due to the use of aqueous electrolyte. The only other use of GQDs in supercapacitor devices we are aware of shows their potential for microsupercapacitors.33 Our GQD/PEDOT films showed higher energy densities due to the pseudocapacitance contribution of the conjugated polymer compared to the double-layer capacitance of GQDs. GQDs were synthesized per the procedure developed by Sekiya et al.7 Analysis of as-synthesized GQDs by atomic force microscopy (AFM) found they were primarily 12−16 nm in diameter, with heights of approximately 1 nm, consistent with a single-layer sheet of graphene (Figure S1). The successful synthesis of the GQDs was further confirmed by X-ray photoelectron spectroscopy (XPS), as well as optical absorption and photoluminescence spectroscopy. The deconvoluted C 1s region of the XPS spectrum of the GQDs shows four different carbon environments at binding energies of 284.56, 286.11, 287.66, and 288.50 eV, corresponding to sp2 CC, COH, CO, and COOH functionalities, respectively (Figure S2). A high-energy tail is attributed to shakeup features arising from the conjugated graphene core.34 Optical absorption spectroscopy of the GQDs shows strong absorbance in the UV below 400 nm, with a tail extending across the visible region to 600 nm (Figure S3). Photoluminescene spectroscopy of the GQDs demonstrates excitation-dependent emission, with peak emission wavelengths shifting from 450 to 550 nm (Figure S4). These are consistent with previous reports of GQDs.35 Functionalization of GQDs with EDOT was achieved through condensation of acid chlorides on the outer edges of the GQDs and hydroxyl functionalized EDOT monomers (Scheme 1). Briefly, as-synthesized GQDs were treated with oxalyl chloride in a microwave reactor to convert carboxylic acid groups to acyl chlorides.36 After removal of excess oxalyl
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raphene is a two-dimensional sheet of sp2 hybridized carbon atoms. It has been extensively studied due to its intriguing optoelectronic properties.1,2 However, its application in commercialized products has been limited by difficulties associated with processing pristine graphene.3 Graphene quantum dots (GQDs) are small graphene sheets, constrained in their lateral dimensions to
