Surface modification via the attachment of organic molecules with specific end functionalities has attracted significant attention, driven by applications in chemical sensors and biosensors, electrocatalysis, and molecular electronics. Among the available approaches, electrochemical reduction of diazonium salts to form surface-bound organic thin films is one of the most widely used methods for chemically modifying metals, carbon materials, and semiconductors. Here, we report a nonelectrochemical approach to diazonium-derived thin-film formation, in which surfaces are immersed in a dilute diazonium solution (1 mM) containing traces of water and dimethyl sulfoxide and exposed to probe ultrasonication (400 W, 24 kHz). Ultrasonication induces cavitation, generating a transient reducing environment, primarily via hydrogen radicals formed upon bubble collapse, which enables diazonium reduction at the surface. Prior to reduction, interfacial electrostatics regulate the local concentration of the cationic diazonium precursor near the surface by promoting or hindering its pre-accumulation at the surface. For semiconducting Si-H, this electrostatic effect can be controlled by the doping type, with p-type and n-type Si producing opposite surface potentials and therefore different degrees of diazonium accumulation. Thus, sonication supplies the hydrogen radicals required for reduction, whereas substrate electrostatics determine precursor pre-concentration and thereby influence the extent of grafting. This method enables grafting of organic thin films across diverse substrates and establishes interfacial electrostatics as a promising control parameter for surface reactions involving charged species.

Our previous reports demonstrated augmented electrodeposition rates at the insulating oil droplet-electrolyte-electrode triple point. This enhancement was hypothesized to arise from convection that results from a localized increase in current density. Here, we use time-resolved microscopy to track gold microstructures migrating toward the triple point and to elucidate how electrolyte identity and concentration influence electrolysis-induced convection around a fluid insulating droplet fouling an electrode. By fitting a logistic model on the microscopy data, the maximum particle assembly rate (alpha) and saturation level (K) were estimated from aqueous samples that contained HAuCl4-Na2SO4, HAuCl4-K2SO4, and HAuCl4-CH3COONa. The alpha and K values were comparable in samples that were electrolyzed in 75-300 mM Na2SO4. However, the particle assembly parameters generally decreased in 600 mM Na2SO4 due to a less dispersed electric double layer and higher bulk solution viscosity. In terms of the effect of the electrolyte species, both alpha and K were remarkably lower in the acetate-containing samples than in the sulfate-containing samples. This phenomenon could be explained by pH effect, capping effect, and, more importantly, specific ion effects represented by the Hofmeister series. In the series, CH3COO- lies at the borderline of chaotropicity. For this reason, it tends to destabilize the growth or agglomeration of gold particles. The findings in this manuscript are useful for micropatterning in various devices and the emerging field of electrolyte engineering.

Electrochemical processes at gas-liquid interfaces remain largely unexplored, despite the ubiquity and functional importance of bubbles in both natural systems as well as in analytical, separation, and purification technologies. Impedance measurements of electrode-bubble junctions demonstrate that a stable nanoscale liquid film persists between a nitrogen bubble and a platinum ultramicroelectrode. This aqueous disjoining film has an unexpectedly high ionic conductivity, which further increases with increasing bubble deformation. The efficiency of ionic transport within this confined liquid pocket is ion-specific and linked to the ability of electrolyte ions, principally anions, to accumulate at the air-water interface. The presence of surface ions and mechanical stiffening of the bubble, as it deforms under the pressure of the electrode, modulate the junction's resistance, while its capacitance is influenced by the electrostatics of overlapping anionic clouds on the bubble with the positive charge of the electrode. Electrochemiluminescence imaging data confirm sustained charge transfer across the junction, which indicate effective solution bulk-to-confined film mass transport. Our findings establish gas bubble-metal junctions as a new electrochemical platform, and help advance the understanding of bubbles as chemically active entities rather than passive insulating voids.

Objects made from the same insulator can sometimes acquire different charges when rubbed together, owing to a thin layer of carbon-based material on the object’s surface. Objects made from the same insulator can sometimes acquire different charges when rubbed together, owing to a thin layer of carbon-based material on the object’s surface.

Gas bubbles are ideal hydrophobic structures that underpin technologies ranging from mineral processing to chemical analysis. The technological value of bubbles lies in their ability to create hydrophobic-hydrophilic phase boundaries, simply and efficiently. However, bubbles remain largely incompatible with electrochemical processes: they block charge transfer reactions by interrupting solution-electrode contact. We demonstrate a path to integrate bubbles with electrode reactions. For micrometer-sized electrodes and surface-active reactants (<60 mN/m), a nanoscale disjoining liquid film forms under bubbles that visually appear as surface-adherent. Gas-solution-electrode junctions sustained by repulsive van der Waals (vdW) forces allow the oil-like properties of bubbles to be harnessed in aqueous electrolytes. Through vdW-stabilized junctions, bubbles are redefined from detrimental dielectric blocks to facilitators of electrode processes. This is demonstrated by 10-fold rate enhancements, improved reaction reversibility and ionic conductivity, and the redox cycling of enzymes stabilized by confinement between bubbles and electrodes.

Electrochemical systems are often limited by the mass transport of reactants to the electrode and products away from the electrode. Convective transport arising from gravity acting on reaction‐induced density gradients is frequently overlooked. Recent studies have shown that partial electrode fouling can enhance this form of convection, thereby increasing reaction rates. Using electrochemiluminescence (ECL) microscopy in both aqueous and organic electrolytes, we investigate how electrode fouling and orientation relative to gravity can serve as design parameters to couple electrochemical reactions with immobilized enzymatic processes. We first examine how fouling‐induced convection depends on electrolyte composition and cell orientation. We then demonstrate that electrodes partially fouled with non‐conductive agar domains containing immobilized enzymes enable controlled coupling between electrochemical reactions at clean electrode regions and subsequent chemical reactions occuring on insulating islands. Horseradish peroxidase (HRP) immobilized in agar on glassy carbon electrodes creates conductor–insulator–electrolyte boundaries that stabilize enzymatic activity. Applying density gradient‐driven convection enhances phenol degradation, yielding ~30% conversion after 30 min of electrolysis. These results establish electrode heterogeneity and cell orientation as powerful design parameters for enhancing electrochemically coupled chemical processes.

Organic electrosynthesis offers sustainable pathways for chemical manufacturing. Electrode surface properties strongly influence electrosynthetic efficiency; hence, electrode contamination by non-conductive materials generally suppresses reaction rates. However, recent studies indicate that lateral surface heterogeneity-conductive regions interspersed with insulating domains-induces density gradients that, under gravity, augment rates by promoting natural convection in otherwise quiescent systems. Here, we show that convection triggered by partial electrode fouling enhances the rate of model electrosynthetic processes. We have quantitatively assessed the extent to which fouling promotes mass transport and increases net electrolytic rates per unit area for the electro-reduction of levulinic acid (LA) to valeric acid (VA) and for the electro-oxidation of L-ascorbic acid (LAA) to dehydroascorbic acid (DHAA). Specific patterns of microscopic insulating features were deposited on glassy carbon, lead, and indium tin oxide electrodes through photolithography. Despite a reduction in electroactive area, fouled electrodes showed higher yields than pristine ones. Large-scale patterns of relatively hydrophilic novolak resin (nLOF 2035) enhanced LA-to-VA conversion by up to 1.8-fold, while the epoxy-based SU-8 2002 photoresist improved LAA oxidation by 1.22-fold. Moreover, when electrodes were aligned vertically relative to gravity, buoyancy-driven convection, hence electrolytic rates, are further amplified. This work establishes a new framework for reactor and electrode design in which controlled surface blocking is harnessed to augment, rather than hinder mass transport, opening new opportunities for organic electrosynthesis.

Electrode reactions are central to analytical chemistry and a green approach to chemical synthesis. Here, it is demonstrated that sacrificing electrode-electrolyte contact to microscale polymeric blocks creates fouled electrodes that outperform unobstructed ones. By tuning the dielectric's geometry, surface chemistry, and charge - and controlling electrode alignment relative to gravity - a paradigm shift in electrode design, from "clean" to "fouled," as a strategy to enhance reaction rates is proposed. Electrochemiluminescence (ECL) microscopy reveals that strategic electrode fouling enhances mass transport, primarily through electrochemically actuated lateral density gradients. Engineered fouling induces flow velocities up to 0.4 cm s-1 in otherwise quiescent systems. Sub-millimeter plastic features boost local rates by up to 290%, while micrometer-scale arrays yield a 30% net electrolysis gain. Through electrolyte engineering, it is shown that beyond expected hydrophobic reactant enrichment, the chemistry of the insulator influences reaction rates via electroosmotic flow and Marangoni-driven convection at the insulator-electrode-electrolyte boundary. This work establishes engineered fouling as a powerful strategy for enhancing electrochemical processes and provides a framework for designing advanced electrode architectures for ECL and electrosynthetic applications.

Bullvalene is the archetypical "shape shifting" molecule, undergoing continuous Cope rearrangements in solution at room temperature at a rate of about 3 kHz. In the confined spaces of an scanning tunneling microscopy break junction (STMBJ) setup, isolated bisarylbullvalene molecules have recently been shown to exhibit very restricted isomerization and slower interconversion rates. The restricted number of populated bullvalene isomers displayed large variances in conductivity with the confinement to manifest high piezoresistivity. Herein, the confinement is increased by forming self-assembled monolayers (SAMs), focusing on measuring the resulting electron-transfer rates, as well as identifying viable SAM structural possibilities. First, bis-4-phenyl acetylene bullvalene was synthesized and its SAMs were produced on Au(111). Redox active ferrocene tail groups were then attached via a copper catalyzed azide-alkyne cycloaddition (CuAAC) to enable electrochemical measurements of SAM coverages and electron-transfer rates. The results are consistent with only a single isomeric form being present on the surface at any one time, with its nature varying with monolayer coverage density. Density functional theory (DFT) simulations indicate that a combination of steric interactions induced by the bisarylbullvalene substitution, combined with head group and SAM packing effects, results in this coverage-dependent isomeric selectivity. A small number of very different types of SAM structural possibilities are identified. These findings provide a pathway forward for the exploitation of bullvalene's constitutional isomerism in facilitating nano-electromechanical systems (NEMS).

Hydrogen peroxide (H2O2) is an essential chemical for environmental remediation, chemical synthesis, and energy storage, yet conventional synthetic methods are energy-intensive and environmentally taxing. Herein, we report a catalyst-free strategy for H2O2 synthesis by exploiting the gas-liquid-solid triple phase boundary formed at bubble-pinned porous carbon electrodes. The process involves three key mechanisms: (i) hydroxide anions enrichment in the electric double layer reduces the energy barrier for their oxidation to hydroxyl radicals, (ii) the hydrophobic bubble interface suppresses overoxidation, favoring the two-electron water oxidation pathway, and (iii) oxygen molecules capture electrons from previous steps to form H2O2. Density functional theory calculations indicate a 30% reduction in work function at the bubble-pinned interface compared to bubble-free counterparts, which thermodynamically promotes the electrochemical oxidation of hydroxide anions. Experiments verify that both water and oxygen are involved in H2O2 generation, and mechanistic details are confirmed by trapping different radical intermediates. This study demonstrates an efficient and sustainable alternative for H2O2 production, advancing interface-driven and catalyst-free chemistry.

Functionalized glass plays a crucial role in various fields, including materials and biomedical sciences. Traditionally, it has been produced through silanization reactions or by coating the glass with polymers. But these approaches involve toxic chemicals and result in films that are prone to hydrolysis upon long-term exposure to water. In this report, a novel, simple method for functionalizing glass using ultrasonication of aryl diazonium salts is introduced. When these salts are exposed to ultrasound under mild conditions (24 kHz/400 W), aryl radicals are generated, which spontaneously react with the glass surface. This reaction forms a thin organic polymeric film whose surface properties, such as hydrophobicity or charge, can be tailored by the terminal group of the diazonium salt employed. The film is covalently bonded to the glass surface via Si-O-C bonds, which offer enhanced stability compared to the more hydrolysis-prone Si-O-Si bonds that govern traditional silanization techniques. This newly functionalized glass is shown to adhere microorganisms such as microalgae (Chlorella vulgaris C. vulgaris), bacteria (Escherichia coli, E. coli), and yeast (Saccharomyces cerevisiae, S. cerevisiae), suggesting potential applications in enzyme production, filtration, environmental remediation technologies, biofuels, and biofuel cells.

Fluorescence-based imaging and assays are essential in biomedical diagnostics, environmental monitoring, and materials science. The capabilities of these techniques are further expanded via metal-enhanced fluorescence (MEF), which exploits plasmonic interactions to amplify emission signals and reduce photobleaching. However, the broad implementation of MEF is hindered by the need of a fine-tuned spacer around the metal nanoparticles to ensure optimal metal-to-fluorophore separation. Here, we demonstrate spacer-free MEF through nanomaterials that are electro-generated in a reactor consisting of an aqueous tetrachloroauric acid-fluorescein solution in contact with an ITO-glass working electrode that is strategically fouled with insulating oil droplets. Spectroscopic data indicate that the 1:4 complexation of Au(III) with zwitterionic fluorescein is critical to achieve the nanoparticle morphology that leads to optimal MEF. Microscopy data reveal that the application of an appropriate reduction potential to the reactor results in current-heterogeneity-induced convection toward the insulator-electrode-electrolyte interface (triple-point), thereby generating arrays of suitably spaced nanoparticle-fluorophore complexes and, consequently, a characteristic MEF "ring". More importantly, we report a maximum bulk fluorescence enhancement of 115%, which we attribute to potential-dependent nanoparticle growth and hyperbranching. This study lays the groundwork for spacer-free MEF and it advances the understanding of hydrophobic effects.

Triboelectric nanogenerators (TENGs) are advanced devices designed to harness mechanical energy from various sources such as vibrations, friction, or shear and convert it into electrical energy. Schottky-based tribovoltaic nanogenerators TVNGs are a type of TENG that incorporates a semiconductor–metal barrier, known as a Schottky barrier, into their design. This barrier aids in rectifying the generated electrical output, eliminating the need for external current rectification circuits. Further, silicon-based Schottky TVNGs can leverage existing surface functionalization procedures to improve device output and durability. Almost without exception, these procedures commence with an oxide-free and hydrogen-terminated silicon surface (Si–H). Replacing hydrogen with its heavier isotope deuterium (Si–D) does not hinder access to established surface chemistry procedures, and based on previous reports the isotope exchange is likely to improve resistance of the non-oxide semiconductor against its anodic decomposition. In this report we have developed the optimal surface chemistry procedures for preparing Si–D surfaces and explored to what extent this isotope effect translates into improved performances and durability of Schottky TVNGs. Our findings reveal that the maximum current output of TVNGs constructed on Si–D Si(111) crystals is comparable to that of mainstream Si–H devices. Additionally, we highlight a generally higher density of surface electrical defects in Si–D compared to Si–H, and verify the contribution of a flexoelectric term to the mechanic-to-electrical energy conversion mechanism. Ultimately, our experiments demonstrate that the primary advantage of replacing hydrogen with deuterium lies in enhancing device longevity.

The catalysis of nonredox reactions by external electric fields is one of the most rapidly expanding areas of chemistry. The Menshutkin reaction, a classic example of bimolecular nucleophilic substitution (SN2), involves the conversion of a tertiary amine to a quaternary ammonium salt by coupling it with an alkyl halide. The reaction barrier of the Menshutkin reaction is theoretically predicted to be highly sensitive to the magnitude and direction of an external electric field experienced by the transition state. In this study, we investigate how near-surface electric fields can drive this prototypical nucleophilic substitution by examining the coupling of a diffusive redox-tagged tertiary amine with an electrode-tethered alkyl bromide under a variable external bias. Our findings reveal a competition between electrostatically assisted reactions, solvent effects, and electrochemically triggered side reactions involving radical intermediates. We estimate that only about 5% of the coupling events are attributable to the external field, while the majority of the reaction products originate from electrochemically generated radical intermediates.

Chemical analysis of ions and small organic molecules in liquid samples is crucial for applications in chemistry, biology, environmental sciences, and health monitoring. Mainstream electrochemical and chromatographic techniques often suffer from complex and lengthy sample preparation and testing procedures and require either bulky or expensive instrumentation. Here, we combine triboelectrification and charge transfer on the surface of electrical insulators to demonstrate the concept of triboelectric spectroscopy (TES) for chemical analysis. As a drop of the liquid sample slides along an insulating reclined plane, the local triboelectrification of the surface is recorded, and the charge pattern along the sample trajectory is used to build a fingerprinting of the charge transfer spectroscopy. Chemical information extracted from the charge transfer pattern enables a new nondestructive and ultrafast (<1 s) tool for chemical analysis. TES profiles are unique, and through an automated identification, it is possible to match against standard and hence detect over 30 types of common salts, acids, bases and organic molecules. The qualitative and quantitative accuracies of the TES methodology is close to 93%, and the detection limit is as low as ppb levels. Instruments for TES chemical analysis are portable and can be further miniaturized, opening a path to in situ and rapid chemical detection relying on inexpensive, portable low-tech instrumentation.

Nearly four decades have passed since IBM scientists pioneered atomic force microscopy (AFM) by merging the principles of a scanning tunneling microscope with the features of a stylus profilometer. Today, electrical AFM modes are an indispensable asset within the semiconductor and nanotechnology industries, enabling the characterization and manipulation of electrical properties at the nanoscale. However, electrical AFM measurements suffer from reproducibility issues caused, for example, by surface contaminations, Joule heating, and hard-to-minimize tip drift and tilt. Using as experimental system nanoscale Schottky diodes assembled on oxide-free silicon crystals of precisely defined surface chemistry, it is revealed that voltage-dependent adhesion forces lead to significant rotation of the AFM platinum tip. The electrostatics-driven tip rotation causes a strain gradient on the silicon surface, which induces a flexoelectric reverse bias term. This directional flexoelectric internal-bias term adds to the external (instrumental) bias, causing both an increased diode leakage as well as a shift of the diode knee voltage to larger forward biases. These findings will aid the design and characterization of silicon-based devices, especially those that are deliberately operated under large strain or shear, such as in emerging energy harvesting technologies including Schottky-based triboelectric nanogenerators (TENGs).

Adherent bubbles at electrodes are generally treated as reaction penalties. Herein, in situ hydroxylation of indium tin oxide surfaces can be easily achieved by applying a constant potential of +1.0 V in the presence of bubbles. Its successful hydroxylation is further demonstrated by preparing a ferrocene-terminated film, which is confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy.

The chemical industry is a major consumer of fossil fuels. Several chemical reactions of practical value proceed with the gain or loss of electrons, opening a path to integrate renewable electricity into chemical manufacturing. However, most organic molecules have low aqueous solubility, causing green and cheap electricity-driven reactions to suffer from intrinsically low reaction rates in industry's solvent of choice: water. Here, we show that a strategic, partial electrode fouling with hydrophobic insulators (oils and plastics) offsets kinetic limitations caused by poor reactant solubility, opening a new path for the direct integration of renewable electricity into the production of commodity chemicals. Through electrochemiluminescence microscopy, we reveal for the oxidation of organic reactants up to 6-fold reaction rate increase at the "fouled" oil-electrolyte-electrode interface relative to clean electrolyte-electrode areas. Analogously, electrodes partially masked (fouled) with plastic patterns, deposited either photolithographically (photoresists) or manually (inexpensive household glues and sealants), outperform clean electrodes. The effect is not limited to reactants of limited water solubility, and, for example, net gold electrodeposition rates are up to 22% larger at fouled than clean electrodes. In a system involving a surface-active reactant, rate augmentation is driven by the synergy between insulator-confined reactant enrichment and insulator-induced current crowding, whereas only the latter and possibly localized decrease in iR drop near the insulator are relevant in a system composed of non-surface-active species. Our counterintuitive electrode design enhances electrolysis rates despite the diminished area of intimate electrolyte-electrode contact and introduces a new path for upscaling aqueous electrochemical processes.

In recent years, the hybrid silicon-molecular electronics technology has been gaining significant attention for applications in sensors, photovoltaics, power generation, and molecular electronics devices. However, Si-H surfaces, which are the platforms on which these devices are formed, are prone to oxidation, compromising the mechanical and electronic stability of the devices. Here, we show that when hydrogen is replaced by deuterium, the Si-D surface becomes significantly more resistant to oxidation when either positive or negative voltages are applied to the Si surface. Si-D surfaces are more resistant to oxidation, and their current-voltage characteristics are more stable than those measured on Si-H surfaces. At positive voltages, the Si-D stability appears to be related to the flat band potential of Si-D being more positive compared to Si-H surfaces, making Si-D surfaces less attractive to oxidizing OH- ions. The limited oxidation of Si-D surfaces at negative potentials is interpreted by the frequencies of the Si-D bending modes being coupled to that of the bulk Si surface phonon modes, which would make the duration of the Si-D excited vibrational state significantly less than that of Si-H. The strong surface isotope effect has implications in the design of silicon-based sensing, molecular electronics, and power-generation devices and the interpretation of charge transfer across them.