Comment on Electrochemical Kinetics at Ordered Graphite Electrodes

Research progress on the surface modification of carbon fiber

Carbon fiber (CF) has high strength, high modulus, and excellent high-temperature resistance and chemical stability; therefore, it is used in diverse fields. However, due to the lack of active functional groups on the surface of CF and surface defects generated during the preparation of CF, the wettability of the fiber surface is poor, which seriously affects the interface performance between the fiber and a resin matrix. In recent years, extensive research has been conducted on the surface modification of CF. In this review, studies on the surface modification of CF are summarized, including the various methods utilized, such as dry modification, wet modification, and nanomodification, as well as their current application status. As interest in this material increases, high-performance CFs will likely play an important role in many fields in the future.

Surface Modification of Thermoplastic Electrodes for Biosensing Applications via Copper-Catalyzed Click Chemistry

Cu(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC), also known as click chemistry, has been demonstrated to be highly robust while providing versatile surface chemistry. One specific application is biosensor fabrication. Recently, we developed thermoplastic electrodes (TPEs) as an alternative to traditional carbon composite electrodes in terms of cost, performance, and robustness. However, their applications in biosensing are currently limited due to a lack of facile methods for electrode modification. Here, we demonstrate the feasibility of using CuAAC following the diazonium grafting of TPEs to take advantage of two powerful technologies for developing a customizable and versatile biosensing platform. After a stepwise characterization of the electrode modification procedures was performed, electrodes were modified with model affinity reagents. Streptavidin and streptavidin-conjugated IgG antibodies were successfully immobilized on the TPE surface, as confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.

SECM Investigation of Carbon Composite Thermoplastic Electrodes

Thermoplastic electrodes (TPEs) are carbon composite electrodes consisting of graphite and thermoplastic polymer binder. TPE production is a solvent-based method, which makes it easy to fabricate and pattern into complex geometries, contrary to classical carbon composite electrodes. Depending on the composition (carbon type, binder, and composition ratio), TPEs can give excellent electrochemical performance and high conductivity. However, these TPEs are relatively new electrode materials, and thorough electrochemical characterization is still missing to understand and predict why large differences between TPEs exist. We used scanning electrochemical microscopy (SECM) as a screening tool to characterize TPEs. SECM data treatment based on scanning probe microscopy imaging allows a fast and easy comparison of the numerous images, as well as the optimization of the preparation. Experiments suggest that TPEs behave as a network of interacting microelectrodes made by electrochemically active islands isolated between less active areas. Higher carbon content in TPEs is not always indicative of more uniform electrodes with better electrochemical performances. Using various SECM redox probes, it is possible to select a specific graphite or polymer type for the analyte of interest. For example, TPEs made with COC:3569 are the best compromise for general detection, whereas PMMA:11 μm is better suited for catechol-like polyphenol analysis.

Electrocatalytic Activity of Modified Graphite Felt in Five Anthraquinone Derivative Solutions for Redox Flow Batteries

Redox flow batteries have received wide attention because of their unique advantages such as high efficiency, long cycle life, low operating cost, and independent adjustment of energy power. In this study, five types of anthraquinone derivative organic redox couple were selected, and the surfaces of graphite felt were modified. When the number of functional groups is increased or the substitution position is closer to the carbonyl (C=O) groups, a more pronounced hindrance for the C=O reaction on the benzene ring is observed; thus, the electrochemical performance and reversibility decreases. Sodium 9,10-anthraquinone-2-sulfonate solution is the best organic redox couple in terms of both reversibility and electrochemical performance. It was also found that all the surface treatment methods of graphite felt are beneficial for improving their electrochemical performances. All these superior results demonstrate that the graphite felt treated under air exposure at 550 °C for 3 h exhibited the best electrochemical performance, which might be attributed to the increase in the content of C-OH functional groups.

pH sensitivity of interfacial electron transfer at a supported graphene monolayer

Electrochemical devices based on a single graphene monolayer are often realized on a solid support such as silicon oxide, glassy carbon or a metal film. Here, we show that, with graphene on insulating substrates, the kinetics of the electron transfer at graphene with various redox active molecules is dictated by solution pH for electrode reactions that are not proton dependent. We attribute the origin of this unusual phenomenon mainly to electrostatic effects between dissolved/dissociated redox species and the interfacial charge due to trace amounts of ionizable groups at the supported graphene-liquid interface. Cationic redox species show higher electron transfer rates at basic pH, while anionic species undergo faster electron transfer at acidic pH. Although this behavior is observed on graphene on three different insulating substrates, the strength of this effect appears to differ depending on the surface charge density of the underlying substrate. This finding has important implications for the design of electrochemical sensors and electrocatalysts based on graphene monolayers.

Quantitative Principles for Precise Engineering of Sensitivity in Graphene Electrochemical Sensors

A major difficulty in implementing carbon-based electrode arrays with high device-packing density is to ensure homogeneous and high sensitivities across the array. Overcoming this obstacle requires quantitative microscopic models that can accurately predict electrode sensitivity from its material structure. Such models are currently lacking. Here, it is shown that the sensitivity of graphene electrodes to dopamine and serotonin neurochemicals in fast-scan cyclic voltammetry measurements is strongly linked to point defects, whereas it is unaffected by line defects. Using the physics of point defects in graphene, a microscopic model is introduced that explains how point defects determine sensitivity. The predictions of this model match the empirical observation that sensitivity linearly increases with the density of point defects. This model is used to guide the nanoengineering of graphene structures for optimum sensitivity. This approach achieves reproducible fabrication of miniaturized sensors with extraordinarily higher sensitivity than conventional materials. These results lay the foundation for new integrated electrochemical sensor arrays based on nanoengineered graphene.

Self-Inhibitory Electron Transfer of the Co(III)/Co(II)-Complex Redox Couple at Pristine Carbon Electrode

Applications of conducting carbon materials for highly efficient electrochemical energy devices require a greater fundamental understanding of heterogeneous electron-transfer (ET) mechanisms. This task, however, is highly challenging experimentally, because an adsorbing carbon surface may easily conceal its intrinsic reactivity through adventitious contamination. Herein, we employ nanoscale scanning electrochemical microscopy (SECM) and cyclic voltammetry to gain new insights into the interplay between heterogeneous ET and adsorption of a Co(III)/Co(II)-complex redox couple at the contamination-free surface of electron-beam-deposited carbon (eC). Specifically, we investigate the redox couple of tris(1,10-phenanthroline)cobalt(II), Co(phen)₃²⁺, as a promising mediator for dye-sensitized solar cells and redox flow batteries. A pristine eC surface overlaid with KCl is prepared in vacuum, protected from contamination in air, and exposed to an ultrapure aqueous solution of Co(phen)₃²⁺ by the dissolution of the protective KCl layer. We employ SECM-based nanogap voltammetry to quantitatively demonstrate that Co(phen)₃²⁺ is adsorbed on the pristine eC surface to electrostatically self-inhibit outer-sphere ET of nonadsorbed Co(phen)₃³⁺ and Co(phen)₃²⁺. Strong electrostatic repulsion among Co(phen)₃²⁺ adsorbates is also demonstrated by SECM-based nanogap voltammetry and cyclic voltammetry. Quantitatively, self-inhibitory ET is characterized by a linear decrease in the standard rate constant of Co(phen)₃²⁺ oxidation with a higher surface concentration of Co(phen)₃²⁺ at the formal potential. This unique relationship is consistent not with the Frumkin model of double layer effects, but with the Amatore model of partially blocked electrodes as extended for self-inhibitory ET. Significantly, the complicated coupling of electron transfer and surface adsorption is resolved by combining nanoscale and macroscale voltammetric methods.

Stabilization of electrogenerated copper species on electrodes modified with quantum dots

Quantum dots (QDs) have special optical, surface, and electronic properties that make them useful for electrochemical applications. In this work, the electrochemical behavior of copper in ammonia medium is described using bare screen-printed carbon electrodes and the same modified with CdSe/ZnS QDs. At the bare electrodes, the electrogenerated Cu(i) and Cu(0) species are oxidized by dissolved oxygen in a fast coupled chemical reaction, while at the QDs-modified electrode, the re-oxidation of Cu(i) and Cu(0) species can be observed, which indicates that they are stabilized by the nanocrystals present on the electrode surface. A weak adsorption is proposed as the main cause for this stabilization. The electrodeposition on electrodes modified with QDs allows the generation of random nanostructures with copper nanoparticles, avoiding the preferential nucleation onto the most active electrode areas.

Ultraflat, Pristine, and Robust Carbon Electrode for Fast Electron-Transfer Kinetics

Electron-beam (e-beam) deposition of carbon on a gold substrate yields a very flat (0.43 nm of root-mean-square roughness), amorphous carbon film consisting of a mixture of sp²- and sp³-hybridized carbon with sufficient conductivity to avoid ohmic potential error. E-beam carbon (eC) has attractive properties for conventional electrochemistry, including low background current and sufficient transparency for optical spectroscopy. A layer of KCl deposited by e-beam to the eC surface without breaking vacuum protects the surface from the environment after fabrication until dissolved by an ultrapure electrolyte solution. Nanogap voltammetry using scanning electrochemical microscopy (SECM) permits measurement of heterogeneous standard electron-transfer rate constants (k°) in a clean environment without exposure of the electrode surface to ambient air. The ultraflat eC surface permitted nanogap voltammetry with very thin electrode-to-substrate gaps, thus increasing the diffusion limit for k° measurement to >14 cm/s for a gap of 44 nm. Ferrocene trimethylammonium as the redox mediator exhibited a diffusion-limited k° for the previously KCl-protected eC surface, while k° was 1.45 cm/s for unprotected eC. The k° for Ru(NH₃)₆^3+/2+ increased from 1.7 cm/s for unprotected eC to above the measurable limit of 6.9 cm/s for a KCl-protected eC electrode.

Laser-Scribed Graphene Electrodes for Aptamer-Based Biosensing

Graphene as a transducer material has produced some of the best-performing sensing approaches to date opening the door toward integrated miniaturized all-carbon point-of-care devices. Addressing this opportunity, laser-scribed graphene (LSG) electrodes are demonstrated here as highly sensitive and reliable biosensor transducers in blood serum analysis. These flexible electrodes with large electrochemical surface areas were fabricated using a direct-write laser process on polyimide foils. A universal immobilization approach is established by anchoring 1-pyrenebutyric acid to the graphene and subsequently covalently attaching an aptamer against the coagulation factor thrombin as an exemplary bioreceptor to the carboxyl groups. The resulting biosensor displays extremely low detection limits of 1 pM in buffer and 5 pM in the complex matrix of serum.

Interaction of the Helium, Hydrogen, Air, Argon, and Nitrogen Bubbles with Graphite Surface in Water

The interaction of the confined gas with solid surface immersed in water is a common theme of many important fields such as self-cleaning surface, gas storage, and sensing. For that reason, we investigated the gas-graphite interaction in the water medium. The graphite surface was prepared by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG). The surface chemistry and morphology were studied by X-ray photoelectron spectroscopy, profilometry, and atomic force microscopy. The surface energy of HOPG was estimated by contact angle measurements using the Owens-Wendt method. The interaction of gases (Ar, He, H₂, N₂, and air) with graphite was studied by a captive bubble method, in which the gas bubble was in contact with the exfoliated graphite surface in water media. The experimental data were corroborated by molecular dynamics simulations and density functional theory calculations. The surface energy of HOPG equaled to 52.8 mJ/m² and more of 95% of the surface energy was attributed to dispersion interactions. The results on gas-surface interaction indicated that HOPG surface had gasphilic behavior for helium and hydrogen, while gasphobic behavior for argon and nitrogen. The results showed that the variation of the gas contact angle was related to the balance between the gas-surface and gas-gas interaction potentials. For helium and hydrogen the gas-surface interaction was particularly high compared to gas-gas interaction and this promoted the favorable interaction with graphite surface.

Characterization of the Intrinsic Water Wettability of Graphite Using Contact Angle Measurements: Effect of Defects on Static and Dynamic Contact Angles

Elucidating the intrinsic water wettability of the graphitic surface has increasingly attracted research interests, triggered by the recent finding that the well-established hydrophobicity of graphitic surfaces actually results from airborne hydrocarbon contamination. Currently, static water contact angle (WCA) is often used to characterize the intrinsic water wettability of graphitic surfaces. In the current paper, we show that because of the existence of defects, static WCA does not necessarily characterize the intrinsic water wettability. Freshly exfoliated graphite of varying qualities, characterized using atomic force microscopy and Raman spectroscopy, was studied using static, advancing, and receding WCA measurements. The results showed that graphite of different qualities (i.e., defect density) always has a similar advancing WCA, but it could have very different static and receding WCAs. This finding indicates that defects play an important role in contact angle measurements, and the static contact angle does not always represent the intrinsic water wettability of pristine graphite. On the basis of the experimental results, a qualitative model is proposed to explain the effect of defects on static, advancing, and receding contact angles. The model suggests that the advancing WCA reflects the intrinsic water wettability of pristine (defect-free) graphite. Our results showed that the advancing WCA for pristine graphite is 68.6°, which indicates that graphitic carbon is intrinsically mildly hydrophilic.

Are Graphitic Surfaces Hydrophobic?

Graphitic carbons are important solid materials with myriad applications including electrodes, adsorbents, catalyst support, and solid lubricants. Understanding the interaction between water and graphitic carbons is critically important for both fundamental material characterization and practical device fabrication because the water-graphitic interface is essential to many applications. Research interests in graphene and carbon nanotubes over the past decades have brought renewed interest to elucidate wettability of graphitic carbons and understand their interaction with the surrounding environment. Research on this topic can be traced back to the 1940s, and the prevailing notion has been that graphitic carbons are hydrophobic. Though there have been different voices, this conclusion is supported by many previous water contact angle tests and well accepted by the community since sp² carbon is nonpolar in nature. However, recent results from our groups showed that graphitic surfaces are intrinsically mildly hydrophilic and adsorbed hydrocarbon contaminants from the ambient air render the surface hydrophobic. This unexpected finding challenges the long-lasting conception and could completely change the way graphitic materials are made, modeled, and modified. With several other research groups reporting similar findings, it is important for the community to realize the importance of airborne contamination on the surface-related properties of graphitic materials and revisit the intrinsic water-graphite interaction. This Account aims to summarize our recent work on water wettability of graphitic surfaces and discuss future research directions toward understanding the intrinsic water-graphite interaction. Historical perspective will first be provided highlighting the long accepted notion that graphite is hydrophobic along with a few reports suggesting otherwise. Next, our recent experimental data will be presented showing that pristine graphene and graphite are mildly hydrophilic; chemical analysis showed that hydrocarbons adsorb onto the clean surfaces thus rendering them hydrophobic. These results are further rationalized by analyzing the change in surface energy of the graphitic surfaces before and after hydrocarbon contamination. Facile methods to remove hydrocarbons from a contaminated surface will be discussed along with a convenient water treatment method that we developed to inhibit hydrocarbon adsorption onto a pristine graphitic surface. Implications of contamination will be illustrated through comparing the electrochemical activity of pristine and contaminated graphite. Lastly, consequences of these findings and future research directions to address a few important unanswered questions will be discussed.

Heterogeneous Electron-Transfer Rates for the Reduction of Viologen Derivatives at Platinum and Bismuth Electrodes in Acetonitrile

The standard heterogeneous rate constants for the reduction of a series of viologen derivatives with a range of inter‐ring torsion angles were measured at Bi and Pt electrodes. The electrode potentials for the first one‐electron reduction of the viologens vary from −684 mV to −1070 mV vs. Ag/0.01 m Ag⁺; this enabled a comparison of the behaviour of metallic (Pt) and semi‐metallic (Bi) electrodes over a wide range of applied potentials. The differential capacitance (6.5 μF cm⁻²) of Bi/MeCN,TBAPF₆ interfaces at the potential of zero charge (pzc=−0.60 V) is at least an order of magnitude greater than that calculated on the basis of the bulk Bi carrier density (3×10¹⁷ cm⁻³) and the differential capacitance (9.5 μF cm⁻²) of Pt/MeCN interfaces at their pzc (−0.43 V) is of the same order. The series of viologen derivatives exhibited simple one‐electron redox behaviour and showed similar rate constants at Pt (1.8×10⁻⁴–1.6×10⁻³ cm s⁻¹) and Bi electrodes (1.1×10⁻⁴–1.9×10⁻³ cm s⁻¹) after application of the Frumkin correction. These results demonstrate that the density of states at the Bi surface is much higher than in bulk. Finally, the Frumkin‐corrected standard rate constants were observed to be inversely correlated with the inter‐ring torsion angle of the viologens.

Electrochemically Active Thin Carbon Films with Enhanced Adhesion to Silicon Substrates

Thin carbon films deposited on technologically relevant substrates, such as silicon wafers, can be easily implemented in miniaturized electrochemical devices and used for sensing applications. However, a major issue in most carbon films is the weak film/substrate adhesion that shortens the working device lifetime. This paper describes the facile preparation of robust thin carbon films on silicon substrates by one-pot sol-gel synthesis. The improved adherence of these carbon films is based on the incorporation of silica through the controlled synthesis of a resorcinol/formaldehyde gel modified with aminopropyltriethoxysilane. The films demonstrate excellent adhesion to the silicon substrate, good homogeneity, excellent electrical conductivity and superior electrochemical performance. Moreover, this approach opens the door to the fabrication of carbon thin-film electrodes by photolithographic techniques.

Scanning Electrochemical Microscopy of Carbon Nanomaterials and Graphite

Carbon materials are tremendously important as electrode materials in both fundamental and applied electrochemistry. Recently, significant attention has been given not only to traditional carbon materials, but also to carbon nanomaterials for various electrochemical applications in energy conversion and storage as well as sensing. Importantly, many of these applications require fast electron-transfer (ET) reactions between a carbon surface and a redox-active molecule in solution. It, however, has not been well understood how heterogeneous ET kinetics at a carbon/solution interface is affected by the electronic structure, defect, and contamination of the carbon surface. Problematically, it is highly challenging to measure the intrinsic electrochemical reactivity of a carbon surface, which is readily passivated by adventitious organic contaminants. This Account summarizes our recent studies of carbon nanomaterials and graphite by scanning electrochemical microscopy (SECM) not only to reveal the fast ET kinetics of simple ferrocene derivatives at their graphitic surfaces, but also to obtain mechanistic insights into their extraordinary electrochemical reactivity. Specifically, we implemented new principles and technologies to reliably and reproducibly enable nanoscale SECM measurements. We took advantage of a new SECM imaging principle to resolve the high reactivity of the sidewall of individual single walled carbon nanotubes. In addition, we developed SECM-based nanogap voltammetry to find that monolayer graphene grown by chemical vapor deposition yields an unprecedentedly high standard ET rate constant, k(0), of ≥25 cm/s, which was >1000 times higher than that reported in the literature. Remarkably, the nonideal asymmetry of paired nanogap voltammograms revealed that the high reactivity of graphitic surfaces is compromised by their contamination with airborne hydrocarbons. Most recently, we protected the clean surface of highly oriented pyrolytic graphite from the airborne contaminants during its exfoliation and handling by forming a water adlayer to obtain a reliable k(0) value of ≥12 cm/s from symmetric pairs of nanogap voltammograms. We envision that SECM of clean graphitic surfaces will enable us to reliably address not only effects of their electronic structures on their electrochemical reactivity, but also the activity of carbon-based or carbon-supported electrocatalysts for fuel cells and batteries.

Nanoscale Electrochemistry of sp(2) Carbon Materials: From Graphite and Graphene to Carbon Nanotubes

Carbon materials have a long history of use as electrodes in electrochemistry, from (bio)electroanalysis to applications in energy technologies, such as batteries and fuel cells. With the advent of new forms of nanocarbon, particularly, carbon nanotubes and graphene, carbon electrode materials have taken on even greater significance for electrochemical studies, both in their own right and as components and supports in an array of functional composites. With the increasing prominence of carbon nanomaterials in electrochemistry comes a need to critically evaluate the experimental framework from which a microscopic understanding of electrochemical processes is best developed. This Account advocates the use of emerging electrochemical imaging techniques and confined electrochemical cell formats that have considerable potential to reveal major new perspectives on the intrinsic electrochemical activity of carbon materials, with unprecedented detail and spatial resolution. These techniques allow particular features on a surface to be targeted and models of structure-activity to be developed and tested on a wide range of length scales and time scales. When high resolution electrochemical imaging data are combined with information from other microscopy and spectroscopy techniques applied to the same area of an electrode surface, in a correlative-electrochemical microscopy approach, highly resolved and unambiguous pictures of electrode activity are revealed that provide new views of the electrochemical properties of carbon materials. With a focus on major sp(2) carbon materials, graphite, graphene, and single walled carbon nanotubes (SWNTs), this Account summarizes recent advances that have changed understanding of interfacial electrochemistry at carbon electrodes including: (i) Unequivocal evidence for the high activity of the basal surface of highly oriented pyrolytic graphite (HOPG), which is at least as active as noble metal electrodes (e.g., platinum) for outer-sphere redox processes. (ii) Demonstration of the high activity of basal plane HOPG toward other reactions, with no requirement for catalysis by step edges or defects, as exemplified by studies of proton-coupled electron transfer, redox transformations of adsorbed molecules, surface functionalization via diazonium electrochemistry, and metal electrodeposition. (iii) Rationalization of the complex interplay of different factors that determine electrochemistry at graphene, including the source (mechanical exfoliation from graphite vs chemical vapor deposition), number of graphene layers, edges, electronic structure, redox couple, and electrode history effects. (iv) New methodologies that allow nanoscale electrochemistry of 1D materials (SWNTs) to be related to their electronic characteristics (metallic vs semiconductor SWNTs), size, and quality, with high resolution imaging revealing the high activity of SWNT sidewalls and the importance of defects for some electrocatalytic reactions (e.g., the oxygen reduction reaction). The experimental approaches highlighted for carbon electrodes are generally applicable to other electrode materials and set a new framework and course for the study of electrochemical and interfacial processes.

An Easily Fabricated Electrochemical Sensor Based on a Graphene-Modified Glassy Carbon Electrode for Determination of Octopamine and Tyramine

A simple electrochemical sensor has been developed for highly sensitive detection of octopamine and tyramine by electrodepositing reduced graphene oxide (ERGO) nanosheets onto the surface of a glassy carbon electrode (GCE). The electrocatalytic oxidation of octopamine and tyramine is individually investigated at the surface of the ERGO modified glassy carbon electrode (ERGO/GCE) by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Several essential factors including the deposition cycle of reduced graphene oxide nanosheets and the pH of the running buffer were investigated in order to determine the optimum conditions. Furthermore, the sensor was applied to the quantification of octopamine and tyramine by DPV in the concentration ranges from 0.5 to 40 μM and 0.1 to 25 μM, respectively. In addition, the limits of detection of octopamine and tyramine were calculated to be 0.1 μM and 0.03 μM (S/N = 3), respectively. The sensor showed good reproducibility, selectivity and stability. Finally, the sensor successfully detected octopamine and tyramine in commercially available beer with satisfactory recovery ranges which were 98.5%–104.7% and 102.2%–103.1%, respectively. These results indicate the ERGO/GCE based sensor is suitable for the detection of octopamine and tyramine.

Recent development of carbon electrode materials and their bioanalytical and environmental applications

New synthetic approaches, materials, properties, electroanalytical applications and perspectives of carbon materials are presented.

Electrochemistry of Fe3+/2+ at highly oriented pyrolytic graphite (HOPG) electrodes: kinetics, identification of major electroactive sites and time effects on the response

Electron transfer kinetics of Fe^3+/2+ on HOPG is as fast as on metals, with the electroactivity dominated by basal plane.

A review on amperometric-type immunosensors based on screen-printed electrodes

In this brief review, we summarize the recent research activities involved in the development of amperometric-type immunosensors based on screen-printed electrodes (SPEs). We focus on the underlying principle involved in these types of sensors, their fabrication and electrode surface modification. We also discuss the various factors involved in the designing of such immunosensors and how they affect their performances. Finally we provide an insight into the drawbacks associated with these SPEs.

Electron transfer kinetics on natural crystals of MoS2 and graphite

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.