Electrostatics and Electrochemistry: Mechanism and Scope of Charge-Transfer Reactions on the Surface of Tribocharged Insulators

Interfacial electrostatic charges promoted chemistry: Reactions and mechanisms

Interfacial electrostatic charges are a universal phenomenon in nature. In recent years, interest in the chemical reactivity of electrostatic charges has grown. Interfacial electrostatic charge-driven chemical synthesis reduces the reliance on redox reagents, catalysts, and hazardous solvents, which promotes environmental sustainability and cost-effectiveness in the chemical industry. Electrostatic charges can be generated at the interfaces between solids, liquids, and gases. The chemical properties of electrostatic charges have been observed at interfaces between solids and liquids, and between liquids and gases. This review summarized the chemical reactivity of interfacial electrostatic charges and its mechanisms. Electrostatic charges play a fundamental role in providing electrons and creating electric fields, which in turn induce charge transfer, radical formation, and molecular orientation. We classified the role of interfacial charges in chemical reactions and provided new perspectives. Interfacial electrostatic charges can be generated with mechanical energy input, a power supply and interface transition from solid-liquid to liquid-gas. Redox and catalytic reactions involving inorganic, organic compounds and biomolecules are driven by interfacial electrostatic charges. Electrostatic chemistry mechanisms are currently a subject of debate because there is insufficient experimental evidence. Challenges and opportunities associated with interfacial electrostatic chemistry are discussed. Knowledge of the reactivity of interfacial electrostatic charges could be used to understand electrostatic phenomena in nature, advance green chemistry, and even study the origins of life. We expect this emerging topic will appeal to scientists in disciplines including interfacial chemistry and electrostatics.

Cross-Electrophile Coupling of Aryl Chlorides with Alkyl Chlorides Using Rotating Magnetic Field and Metal Rods

The pursuit of sustainable and environmentally benign methods and techniques continues to challenge organic chemists. Herein, we report the development of a novel approach in which electromagnetic induction could participate in the coupling of organic chlorides using a rotating magnetic field and metal rods. In particular, we describe the application of this strategy to the nickel-catalyzed cross-electrophile coupling of aryl chlorides with alkyl chlorides. Using these abundant and commercially available organochlorides, such a system allows reactions to proceed with a broader scope than the current protocols under mild conditions.

Recent Progress of Chemical Reactions Induced by Contact Electrification

Contact electrification (CE) spans from atomic to macroscopic scales, facilitating charge transfer between materials upon contact. This interfacial charge exchange, occurring in solid-solid (S-S) or solid-liquid (S-L) systems, initiates radical generation and chemical reactions, collectively termed contact-electro-chemistry (CE-Chemistry). As an emerging platform for green chemistry, CE-Chemistry facilitates redox, luminescent, synthetic, and catalytic reactions without the need for external power sources as in traditional electrochemistry with noble metal catalysts, significantly reducing energy consumption and environmental impact. Despite its broad applicability, the mechanistic understanding of CE-Chemistry remains incomplete. In S-S systems, CE-Chemistry is primarily driven by surface charges, whether electrons, ions, or radicals, on charged solid interfaces. However, a comprehensive theoretical framework is yet to be established. While S-S CE offers a promising platform for exploring the interplay between chemical reactions and triboelectric charge via surface charge modulation, it faces significant challenges in achieving scalability and optimizing chemical efficiency. In contrast, S-L CE-Chemistry focuses on interfacial electron transfer as a critical step in radical generation and subsequent reactions. This approach is notably versatile, enabling bulk-phase reactions in solutions and offering the flexibility to choose various solvents and/or dielectrics to optimize reaction pathways, such as the degradation of organic pollutants and polymerization, etc. The formation of an interfacial electrical double layer (EDL), driven by surface ion adsorption following electron transfer, plays a pivotal role in CE-Chemical processes within aqueous S-L systems. However, the EDL can exert a screening effect on further electron transfer, thereby inhibiting reaction progress. A comprehensive understanding and optimization of charge transfer mechanisms are pivotal for elucidating reaction pathways and enabling precise control over CE-Chemical processes. As the foundation of CE-Chemistry, charge transfer underpins the development of energy-efficient and environmentally sustainable methodologies, holding transformative potential for advancing green innovation. This review consolidates recent advancements, systematically classifying progress based on interfacial configurations in S-S and S-L systems and the underlying charge transfer dynamics. To unlock the full potential of CE-Chemistry, future research should prioritize the strategic tuning of material electronegativity, the engineering of sophisticated surface architectures, and the enhancement of charge transport mechanisms, paving the way for sustainable chemical innovations.

Utilization of Electric Fields to Modulate Molecular Activities on the Nanoscale: From Physical Properties to Chemical Reactions

As a primary energy source, electricity drives broad fields from everyday electronic circuits to industrial chemical catalysis. From a chemistry viewpoint, studying electric field effects on chemical reactivity is highly important for revealing the intrinsic mechanisms of molecular behaviors and mastering chemical reactions. Recently, manipulating the molecular activity using electric fields has emerged as a new research field. In addition, because integration of molecules into electronic devices has the natural complementary metal-oxide-semiconductor compatibility, electric field-driven molecular devices meet the requirements for both electronic device miniaturization and precise regulation of chemical reactions. This Review provides a timely and comprehensive overview of recent state-of-the-art advances, including theoretical models and prototype devices for electric field-based manipulation of molecular activities. First, we summarize the main approaches to providing electric fields for molecules. Then, we introduce several methods to measure their strengths in different systems quantitatively. Subsequently, we provide detailed discussions of electric field-regulated photophysics, electron transport, molecular movements, and chemical reactions. This review intends to provide a technical manual for precise molecular control in devices via electric fields. This could lead to development of new optoelectronic functions, more efficient logic processing units, more precise bond-selective control, new catalytic paradigms, and new chemical reactions.

Quantitative Insight into the Electric Field Effect on CO2 Electrocatalysis via Machine Learning Spectroscopy

During chemical reactions, especially for electrocatalysis and electrosynthesis, the electric field is the most central driving force to regulate the reaction process. However, due to the difficulty of quantitatively measuring the electric field effects caused at the microscopic level, the regulation of electrocatalytic reactions by electric fields has not been well digitally understood yet. Herein, we took the infrared/Raman spectral signals of CO2 molecules as descriptors to quantitatively predict the effects of different electric fields on the catalytic properties. Taking the metal-doped graphitic C3N4 (g-C3N4) catalyst as an example, we theoretically investigated the adsorption mode and energy of CO2 molecules adsorbed on 27 distinct metal single-atom catalysts under different directions and intensities of electric field. Through a machine learning approach, a spectroscopy-property model between infrared/Raman spectral descriptors and adsorption energy/charge transfer was established, which quantified the facilitation of electric field effects on the CO2 catalytic conversion. Meanwhile, based on the attention mechanism, the catalytic insight of the relationship between spectra and adsorption modes was mined, and the inverse prediction of electric field strength from spectra was realized. This work opens a new quantitative pathway for monitoring and regulating electrocatalytic reactions using machine learning spectroscopy.

Redox Reactions of Organic Molecules Using Rotating Magnetic Field and Metal Rods

In recent years, redox reactions have harnessed light or mechanical energy to enable the formation of chemical bonds. We postulated a complementary approach that electromagnetic induction could promote the redox reaction of organic molecules using a rotating magnetic field and metal rods. Here, we report that electromotive force activates the redox-active trifluoromethylating reagents. This magnetoredox system can be applied to the trifluoromethylation of heteroarenes with high regioselectivity and hydrotrifluoromethylation of alkenes without the need for catalysts and organic additives.

Melt electrowritten poly-lactic acid /nanodiamond scaffolds towards wound-healing patches

Multifunctional wound dressings, enriched with biologically active agents for preventing or treating infections and promoting wound healing, along with cell delivery capability, are highly needed. To address this issue, composite scaffolds with potential in wound dressing applications were fabricated in this study. The poly-lactic acid/nanodiamonds (PLA/ND) scaffolds were first printed using melt electrowriting (MEW) and then coated with quaternized β-chitin (QβC). The NDs were well-dispersed in the printed filaments and worked as fillers and bioactive additions to PLA material. Additionally, they improved coating effectiveness due to the interaction between their negative charges (from NDs) and positive charges (from QβC). NDs not only increased the thermal stability of PLA but also benefitted cellular behavior and inhibited the growth of bacteria. Scaffolds coated with QβC increased the effect of bacteria growth inhibition and facilitated the proliferation of human dermal fibroblasts. Additionally, we have observed rapid extracellular matrix (ECM) remodeling on QβC-coated PLA/NDs scaffolds. The scaffolds provided support for cell adhesion and could serve as a valuable tool for delivering cells to chronic wound sites. The proposed PLA/ND scaffold coated with QβC holds great potential for achieving fast healing in various types of wounds.

Triboelectric Spectroscopy for In Situ Chemical Analysis of Liquids

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.

Enhanced Triboelectric Charge Stability by Air-Stable Radicals

This paper demonstrates that air-stable radicals enhance the stability of triboelectric charge on surfaces. While charge on surfaces is often undesirable (e.g., static discharge), improved charge retention can benefit specific applications such as air filtration. Here, it is shown that self-assembled monolayers (SAMs) containing air-stable radicals, 2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO), hold the charge longer than those without TEMPO. Charging and retention are monitored by Kelvin Probe Force Microscopy (KPFM) as a function of time. Without the radicals on the surface, charge retention increases with the water contact angle (hydrophobicity), consistent with the understanding that surface water molecules can accelerate charge dissipation. Yet, the most prolonged charge retention is observed in surfaces treated with TEMPO, which are more hydrophilic than untreated control surfaces. The charge retention decreases with reducing radical density by etching the TEMPO-silane with tetrabutylammonium fluoride (TBAF) or scavenging the radicals with ascorbic acid. These results suggest a pathway toward increasing the lifetime of triboelectric charges, which may enhance air filtration, improve tribocharging for patterning charges on surfaces, or boost triboelectric energy harvesting.

High Electric Fields on Water Microdroplets Catalyze Spontaneous and Fast Reactions in Halogen-Bond Complexes

The use of external electric fields as green and efficient catalysts in synthetic chemistry has recently received significant attention for their ability to deliver remarkable control of reaction selectivity and acceleration of reaction rates. Technically, methods of generating high electric fields in the range of 1-10 V/nm are limited, as in-vacuo techniques have obvious scalability issues. The spontaneous high fields at various interfaces promise to solve this problem. In this study, we take advantage of the spontaneous high electric field at the air-water interface of sprayed water microdroplets in the reactions of several halogen bond systems: Nu:--X-X, where Nu: is pyridine or quinuclidine and X is bromine or iodine. The field facilitates ultrafast electron transfer from Nu:, yielding a Nu-X covalent bond and causing the X-X bond to cleave. This reaction occurs in microseconds in microdroplets but takes days to weeks in bulk solution. Density functional theory calculations predict that the reaction becomes barrier-free in the presence of oriented external electric fields, supporting the notion that the electric fields in the water droplets are responsible for the catalysis. We anticipate that microdroplet chemistry will be an avenue rich in opportunities in the reactions facilitated by high electric fields and provides an alternative way to tackle the scalability problem.

Spontaneous Reduction of Transition Metal Ions by One Electron in Water Microdroplets and the Atmospheric Implications

Freshman chemistry teaches that Fe³⁺ and Cu²⁺ ions are stable in water solutions, but their reduced forms, Fe²⁺ and Cu⁺, cannot exist in water as the major oxidation state due to the fast oxidation by O₂ and/or disproportionation. Contrary to these well-known facts, significant fractions of dissolved Fe and Cu species exist in their reduced oxidation states in atmospheric water such as deliquesced aerosols, clouds, and fog droplets. Current knowledge attributes these phenomena to the stabilization of the lower oxidation states by the complexation of ligands and the various photochemical or thermal pathways that can reduce the higher oxidation states. In this study, by spraying the water solutions of transition metal ions into microdroplets, we show the results of the spontaneous reduction of ligated Fe(III) and Cu(II) species into Fe(II) and Cu(I) species, presenting a previously unknown source of reduced transition metal ions in atmospheric water. It is the spontaneously generated electrons in water microdroplets that are responsible for the reduction. Control experiments in the atmosphere and in a glove box filled with precisely controlled gaseous contents reveal that O₂, CO₂, and NO₂ are the major competitors for the electrons, forming O₂^-, HCO₂^-, and NO₂^-, respectively. Taking these findings together, we opine that microdroplet chemistry might play significant but previously underestimated roles in atmospheric redox chemistry.

Triboelectric Nanogenerator Array as a Probe for In Situ Dynamic Mapping of Interface Charge Transfer at a Liquid-Solid Contacting

Contact between water droplets with hydrophobic surfaces is a common phenomenon at functional interfaces, and it has been extensively studied. However, quantifying the charge transfer between the liquid-solid interfacial contacting, especially for the charge density distribution throughout the movement of liquid droplet on a dielectric surface, remains to be investigated. Here, we developed a pixeled droplet triboelectric nanogenerator (pixeled droplet-TENG) array with high-density electrode array as a probe for measuring the charge transfer at a liquid-solid interface when a water drop moves on the hydrophobic surface. To intuitively observe the charge transfer between the liquid-solid interface, we "imaged" the transferred charges along movement trajectory of a water droplet as it slides along a tilted solid surface at a spatial resolution of 0.4 mm and time sensitivity of 0.02 s. Our study shows that the transferred charges are not uniformly distributed along the path, which is possibly due to the two-step model of electron transfer and ion adsorbed on the solid surface, and thus the formation of an electric double layer will inevitably shield the net surface on the solid surface. Our study presents a probe technology with potential applications in surface chemistry, physics, material science, and cell biology.

A Multifunction Freestanding Liquid-Solid Triboelectric Nanogenerator Based on Low-Frequency Mechanical Sloshing

A simple rectangular-structured freestanding liquid-solid triboelectric nanogenerator (LS-TENG) was fabricated, which used fluorinated ethylene propylene (FEP) films and deionized water (DI) as friction materials. The LS-TENG can effectively convert mechanical energy into electrical energy under the extremely low-frequency shaking of 2 Hz and shows greatly reliable stability. The influence of liquid volume and units on the output performance of the LS-TENG was studied, and the mechanism of the triboelectric electrification process of the LS-TENG was analyzed by COMSOL Multiphysics software. The results show that friction materials, liquid types, and number of units have a great effect on the output performance of the LS-TENG. Under the optimized conditions, the designed array LS-TENG shows high output performance with the open-circuit voltage, short-circuit current, and transferred charge of 120 V, 3.9 μA, and 133 nC, respectively. The LS-TENG can be applied in capacitive storage, AC power, signal acquisition, and self-powered sensor. The multifunctional LS-TENG provides a potentially practical route for harvesting low-frequency mechanical energy in natural environments and enabling multifunctional applications.

Swamp Wetlands in Degraded Permafrost Areas Release Large Amounts of Methane and May Promote Wildfires through Friction Electrification

Affected by global warming, permafrost degradation releases a large amount of methane gas, and this part of flammable methane may increase the frequency of wildfires. To study the influence mechanism of methane emission on wildfires in degraded permafrost regions, we selected the northwest section of Xiaoxing’an Mountains in China as the study area, and combined with remote sensing data, we conducted long-term monitoring of atmospheric electric field, temperature, methane concentration, and other observation parameters, and further carried out indoor gas–solid friction tests. The study shows that methane gas (the concentration of methane at the centralized leakage point is higher than 10,000 ppm) in the permafrost degradation area will release rapidly in spring, and friction with soil, surface plant residues, and water vapor will accelerate atmospheric convection and generate electrostatic and atmospheric electrodischarge phenomena on the surface. The electrostatic and atmospheric electrodischarge accumulated on the surface will further ignite the combustibles near the surface, such as methane gas and plant residues. Therefore, the gradual release of methane gas into the air promotes the feedback mechanism of lightning–wildfire–vegetation, and increases the risk of wildfire in degraded permafrost areas through frictional electrification (i.e., electrostatic and atmospheric electrodischarge).

Electrostatic Charges Regulate Chemiluminescence by Electron Transfer at the Liquid-Solid Interface

The role of the electrostatic environment in chemical reactions has long been an important research field, but most studies have focused on the influence of external electric fields on chemical processes, while the effect from the intrinsic electrostatic charges on the solution itself has been ignored. How an electrostatic field generated by contact electrification affects the solvent environment in a chemical reaction and then the chemical reactivity is still ambiguous. Here, based on the inspiration of the droplet triboelectric nanogenerator, electrostatic interactions between a statically charged luminol droplet and the surrounding directional electrostatic field were analyzed, and we demonstrate a relationship between the sign of the luminol sample (negatively or positively charged) and its effect on the reaction reactivity. Our results show that the increased reaction activity and the enhanced chemiluminescence (CL) only occurred when the luminol droplet yields positive charges, while a negatively charged luminol, on the contrary, tends to inhibit the CL, which brings direct evidence of the charge carriers of triboelectricity being electrons at the liquid-solid interface. This work provides a strategy for electrostatically regulating CL by simply statically charging a reaction solution with a dielectric solid and also carries a cautionary message on what to consider when preparing a sample for a chemical reaction.

All-Weather Droplet-Based Triboelectric Nanogenerator for Wave Energy Harvesting

The liquid-solid triboelectric nanogenerator (LS-TENG) has been demonstrated to harvest energy efficiently through the contact electrification effect between liquid and solid triboelectric materials, which can avoid the wear issue in solid-solid TENG. However, the droplet-based LS-TENG reveals the problems that it generally works with the continuous falling droplets or needs to be fully packaged, which greatly limit its practical application. Here, a droplet-based triboelectric nanogenerator (DB-TENG) with a simple open structure is designed to effectively solve these problems. The nonpackaged DB-TENG can work stably under extreme conditions with high humidity or high concentrations of salt, acid, or alkali solutions, showing the DB-TENGs can be flexibly utilized in all types of working environments with better reliability and lower maintenance costs. It is of great significance that the integrated DB-TENG network array can realize the all-weather ocean energy harvesting. Furthermore, under the simulated ocean wave, a scaled-up DB-TENG with considerable output performance can charge capacitors and drive electrical devices. Overall, the DB-TENG shows many advantages: simple open structure, all-weather working ability, timely supplement of water loss, no tight packaging, wear resistance, suitable for extreme working environments. This work provides a convenient and feasible way toward all-weather wave energy harvesting in real marine environments.