Electron Transfer Kinetics at Graphene Quantum Dot Assembly Electrodes

Abstract

Electrochemical performance of nanostructured carbon electrodes was evaluated using cyclic voltammetry and a simple simulation model. The electrodes were prepared from soluble precursors by anodic electrodeposition of two sizes of graphene quantum dot assemblies (hexabenzocoronene (HBC) and carbon quantum dot (CQD)) onto a conductive support. Experimental and simulated voltammograms enabled the extraction of the following electrode parameters: conductivity of the electrodes (a combination of ionic and electronic contributions), density of available electrode states at different potentials, and tunneling rate constant (Marcus−Gerischer model) for interfacial charge transfer to ferrocene/ferrocenium (Fc/Fc + ) couple. The parameters indicate that HBC and CQD have significant density of electronic states at potentials more positive than −0.5 V versus Ag/Ag + . Enabled by these large densities, the electron transfer rates at the Fc/Fc + thermodynamic potential are several orders of magnitude slower than those commonly observed on other carbon electrodes. This study is expected to accelerate the discovery of improved synthetic carbon electrodes by providing fast screening methodology of their electrochemical behavior.

Electrochemical Syntheses of Polycyclic Aromatic Hydrocarbons (PAHs)

“…An alternative “bottom‐up” anodic electrodeposition was reported by the Glusac group using two kinds of graphene flake building blocks, HBC and carbon quantum dot (CQD), to assemble onto the electrode surface and generate carbon‐based semiconductor electrode materials ( Figure a). [ 52 ] Transmission electron microscopy (TEM) images revealed that both films featured molecular distances of ≈4−5 Å in good agreement with π − π stacking interactions (Figure 4b,c). In SEM images, HBC deposited as molecular fibrous structures with ≈100 nm diameter (as previously reported above, Figure 4d), while CQD assembled as a sponge‐like morphology (Figure 4e).…”

“…[73] Li and co-workers reported on an The pre-CQD 7 was synthesized through Suzuki coupling reactions. [52] b) TEM image of HBC deposited on a Pt electrode. The inset shows that the distance between molecules is ≈4−5 Å in good agreement with 𝜋−𝜋 stacking.…”

“…Figure 4. a) Electrochemical cyclodehydrogenation of HPB and pre-CQD to form HBC and CQD.The pre-CQD 7 was synthesized through Suzuki coupling reactions [52]. b) TEM image of HBC deposited on a Pt electrode.…”

“…e) SEM image of CQD on a carbon electrode. Reproduced with permission [52]. Copyright 2019, American Chemical Society.…”

Faradaic Quantized Capacitance as an Ideal Pseudocapacitive Mechanism

“…The electrochemical potential of the electrode is shifted from its equilibrium location (μ eq ) by an applied bias V such that μ = μ eq + V . Hence, the rate of forward electron transfer to a nanoparticle in the N th charge configuration at a bias of V is and the corresponding rate for backward electron transfer is where M el is the electronic coupling between the reactant and electrode arising due to tunneling and D s is the density of states of the electrode substrate. ,− ,− The expressions can be worked out through Fermi’s golden rule or quantum transport methodssee refs ,,, and citations therein. Note that a positive applied bias ( V > 0) is considered to have lifted the electrode electrochemical potential relative to that of the solvent (see Figure c).…”