Quantification of the Surface Diffusion of Tripodal Binding Motifs on Graphene Using Scanning Electrochemical Microscopy

Abstract

The surface diffusion of a cobalt bis-terpyridine, Co(tpy)(2)-containing tripodal compound (1·2PF(6)), designed to noncovalently adsorb to graphene through three pyrene moieties, has been studied by scanning electrochemical microscopy (SECM) on single-layer graphene (SLG). An initial boundary approach was designed in which picoliter droplets (radii ~15-50 μm) of the tripodal compound were deposited on an SLG electrode, yielding microspots in which a monolayer of the tripodal molecules is initially confined. The time evolution of the electrochemical activity of these spots was detected at the aqueous phosphate buffer/SLG interface by SECM, in both generation/collection (G/C) and feedback modes. The tripodal compound microspots exhibit differential reactivity with respect to the underlying graphene substrate in two different electrochemical processes. For example, during the oxygen reduction reaction, adsorbed 1·2PF(6) tripodal molecules generate more H(2)O(2) than the bare graphene surface. This product was detected with spatial and temporal resolution using the SECM tip. The tripodal compound also mediates the oxidation of a Fe(II) species, generated at the SECM tip, under conditions in which SLG shows slow interfacial charge transfer. In each case, SECM images, obtained at increasing times, show a gradual decrease in the electrochemical response due to radial diffusion of the adsorbed molecules outward from the microspots onto the unfunctionalized areas of the SLG surface. This response was fit to a simple surface diffusion model, which yielded excellent agreement between the two experiments for the effective diffusion coefficients: D(eff) = 1.6 (±0.9) × 10(-9) cm(2)/s and D(eff) = 1.5 (±0.6) × 10(-9) cm(2)/s for G/C and feedback modes, respectively. Control experiments ruled out alternative explanations for the observed behavior, such as deactivation of the Co(II/III) species or of the SLG, and verified that the molecules do not diffuse when confined to obstructed areas. The noncovalent nature of the surface functionalization, together with the surface reactivity and mobility of these molecules, provides a means to couple the superior electronic properties of graphene to compounds with enhanced electrochemical performance, a key step toward developing dynamic electrode surfaces for sensing, electrocatalysis, and electronic applications.

Noncovalent Chiral Functionalization of Graphene with Optically Active Helical Polymers

“…This is quite different from the present study of us. In addition, studies in literature demonstrated that pyrene‐derivatives could be efficiently attached on graphene via π – π interactions . These studies also provide additional evidence for our success in chiral functionalization of graphene, as reported above.…”

Redox Titrations via Surface Interrogation Scanning Electrochemical Microscopy at an Extended Semiconducting Surface for the Quantification of Photogenerated Adsorbed Intermediates

“…On substrate electrodes even a few radii larger than the SECM tip, open-circuit SECM positive feedback makes it technically challenging to discern between the SI-SECM signal and the background. However, a large subset of surface explorations can proceed on active semiconducting or kineticallylimited substrates that do not display open-circuit feedback [26,[47][48][49]. Here, we show this concept for a lightly n-doped sample of strontium titanate which generates adsorbed oxygenated O(H)Á ads intermediates during the photoassisted oxidation of water.…”

“…Often, kinetic theory can help to elucidate reaction mechanisms [10,16,17], but direct chemical information improves these models [18], especially when diverse chemical intermediates are possible [19]. In particular, SECM offers a unique opportunity to correlate the spatially-resolved information about reactivity at specific photo catalytic sites [20][21][22][23][24] to the surface coverage of reacting species [25,26] with potential applications at the nano-scale [27,28]. This work introduces the basic considerations towards applying redox micro-and nano-titrations via transient SECM [29,30] for the local quantification of reactive intermediates at a substrate of unconstrained dimensions.…”

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

“…[1][2][3][4] Glassy carbon (GC), boron doped diamond and graphite have long received attention for electroanalytical and electrocatalytic measurements, [5][6][7][8][9][10][11] and, more recently, carbon nanotubes and graphene have generated considerable interest. [12][13][14][15][16][17] However, despite well-defined bulk properties and structure, carbon materials can possess rather complex surface chemistry that may substantially impact the resulting electrochemistry. 6 Indeed, the range of functional groups present at different carbon electrode/electrolyte interfaces is yet to be fully understood 9 and is significantly impacted by electrode preparation.…”