π-Self-Assembly of a Coronene on Carbon Nanomaterial-Modified Electrode and Its Symmetrical Redox and H₂O₂ Electrocatalytic Reduction Functionalities

Abstract

The structure–electroactivity relationship of graphene has been studied using coronene (Cor), polyaromatic hydrocarbon (PAH), and a subunit of graphene as a model system by chemically modified electrode approach. In general, graphene and PAH do not show any redox activity in their native form. Herein, we report a simple electrochemical approach for the conversion of electro-inactive coronene to a highly redox-active molecule (Cor-Redox; E°′ = 0.235 ± 0.005 V vs Ag/AgCl) after being adsorbed on graphitic carbon nanomaterial and preconditioned at an applied potential, 1.2 V vs Ag/AgCl, wherein, the water molecule oxidizes to dioxygen via hydroxyl radical (•OH) intermediate, in acidic solution (pH 2 KCl–HCl). When the same coronene electrochemical experiment was carried out on an unmodified glassy carbon electrode, there was no sign of faradic signal, revealing the unique electrochemical behavior of the coronene molecule on graphitic nanomaterial. The Cor-Redox peak is found to be highly symmetrical (peak-to-peak potential separation of ∼0 V tested by cyclic voltammetry (CV)) and surface-confined (ΓCor‑Redox = 10.1 × 10–9 mol cm–2) and has proton-coupled electron-transfer (∂E°′/∂pH = −56 mV pH–1) character. Initially, it was speculated that Cor is converted to a hydroxy group-functionalized Cor molecule (dihydroxy benzene derivative) on the graphitic surface and showed the electrochemical redox activity. However, physicochemical characterization studies including Raman, IR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), redox-site selective oxidation probe, cysteine (for dihydroxy benzene), radical scavenger ((2,2,6,6-tetramethylpiperidin-1-yl)­oxyl, TEMPO), and scanning electrochemical microscopy (SECM) using ferricyanide redox couple have revealed that coronene cationic radical species like electroactive molecule is formed on graphitic material upon the electrochemical oxidation reaction at a high anodic potential. It has been proposed that •OH generated as an intermediate species from the water oxidation reaction is involved in the coronene cationic radical species. Studies on coronene electrochemical reaction at various carbon nanomaterials like multiwalled carbon, single-walled carbon, graphite, graphene oxide, and carbon nanofiber revealed that graphitic structure (without any oxygen functional groups) and its π–π bonding are key factors for the success of the electrochemical reaction. The coronene molecular redox peak showed an unusual electrocatalytic reduction of hydrogen peroxide similar to the peroxidase enzyme-biocatalyzed reduction reaction in physiological solution.

High-Performance Electrocatalytic Reduction and Sensing of Hazardous Hexavalent Chromium Using a Redox-Active Binol Species-Impregnated Carbon Nanofiber-Modified Electrode

“…The peak-to-peak potential difference, Δ E p ( E pa – E pc ) was found to be 10 ± 2 mV, which is close to 0 mV, ascribing that the redox-peak is facile electron-transfer in nature. Such a surface-confined organic redox feature with Δ E p ∼ 0 V was rarely reported in the literature. − The calculated relative standard deviation between the 1st and 10th CV-cycles of the redox peak was 2.5%, highlighting the excellent stability of the modified electrode.…”

Surface Functionalization of a γ‐Graphyne‐like Carbon Material via Click Chemistry

“…Prevalently, most decorated molecules stabilized on the substrate surface undergo weak interactions like electrostatic adsorption or van der Waals attraction. For example, on the typical carbonaceous material of graphite, graphene, and carbon nanotubes, the immobilization of molecular modifiers is primarily achieved by π‐π interaction or hydrophobic forces, which can dramatically change the physicochemical characteristics of the host materials, making them promising candidates in various fields [15–17] . In comparison, the covalent bond can certainly provide a stronger interlinkage between modifiers and host materials, reinforcing the stability of the bounded molecules and further broadening their applications, particularly under harsh operating conditions [18] .…”

“…For example, on the typical carbonaceous material of graphite, graphene, and carbon nanotubes, the immobilization of molecular modifiers is primarily achieved by π-π interaction or hydrophobic forces, which can dramatically change the physicochemical characteristics of the host materials, making them promising candidates in various fields. [15][16][17] In comparison, the covalent bond can certainly provide a stronger interlinkage between modifiers and host materials, reinforcing the stability of the bounded molecules and further broadening their applications, particularly under harsh operating conditions. [18] Nevertheless, surface functionalization of the aforementioned carbonaceous materials via the covalent interaction is synthetically challenging due to the inert nature of benzene rings and lack of reactive ligands on the surface; introducing additional specific functional groups, such as À NH 2 , À CN and À COOH, is then required, as shown in Scheme 1a and 1b.…”

Multi‐Redox Active Carbons and Hydrocarbons: Control of their Redox Properties and Potential Applications

“…The electrochemical functionalization of C x H y molecules adsorbed on graphitic surfaces including multi‐walled carbon nanotube (MWCNT), single‐walled carbon nanotube (SWCNT), graphitized mesoporous carbon (GMC), carbon nanofiber (CNF), graphite nanopowder (GNP), graphene oxide (GO), and activated charcoal (AC) was reported by Kumar's group [85–91] . They succeeded in functionalizing C x H y molecules ranging from benzene (C 6 H 6 ) to higher aromatic rings like pyrene (C 16 H 10 ) and coronene (C 24 H 12 ) (the details including the experimental condition and proposed products are summarized in Section II‐1 in the Supporting Information).…”

“…Interestingly, the reaction amounts of obtained C x H y molecules evaluated by CV, i. e., the conversion efficiencies depend on the type of the graphitic surface. This implies that a strong π–π interaction between C x H y molecules and graphitic structures is essential for the successful conversion of C x H y molecules to redox‐active species [86] . Furthermore, the redox activity of the radical cation occurs in the presence of water, which suggests that the generation and cleavage of the single bond between the H atom and the radical cation results in a highly‐symmetric bell‐shaped redox couple [85,86,88] …”