Recent advances in nanocollision electrochemistry

Recent Trends and Perspectives in Single-Entity Electrochemistry: A Review with Focus on a Water Splitting Reaction

Electrochemical measurements involving single nanoparticles have attracted considerable research attention. In recent years, various studies have been conducted on single-entity electrochemistry (SEE) for the in-depth analyses of catalytic reactions. Although, several electrocatalysts have been developed for H2 energy production, designing innovative electrocatalysts for this purpose remains a challenging task. Stochastic collision electrochemistry is gaining increased attention because it has led to new findings in the SEE field. Importantly, it facilitates establishing structure activity relationships for electrocatalysts by monitoring transient signals. This article reviews the recent achievements related to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) using different electrocatalysts at the nanoscale level. In particular, it discusses the electrocatalytic activities of noble metal nanoparticles, including Ag, Au, Pt, and Pd nanoparticles, at the single-particle level. Because heterogeneity is a key factor affecting the catalytic activity of nanostructures, our work focuses on the influence of heterogeneities in catalytic materials on the OER and HER activities. These results may help to achieve a better understanding of the fundamental processes involved in the water splitting reaction.

Artificial Intelligence-Assisted Multiparameter Size Discrimination of Silver Nanoparticles through Electrochemical Collision

Single particle collision is an important tool for size analysis at the individual particle level; however, due to complex dynamic behaviors of nanoparticles on the surface of an electrode, the accuracy of size discrimination is limited. A silver (Ag) nanoparticle (NP) was chosen as the research target, and the dynamic behavior of Ag NPs was simplified by enhancing adsorption between Ag NP and Au ultramicroelectrode (UME) in alkaline media. Immediately after, accurate dynamic and thermodynamic information on single Ag NP was accurately extracted from collision events, including current intensity, transferred charge, and duration time. On the basis that there were differences between parameters of different-sized Ag NPs, multiparameter size discrimination was proposed, which improved the accuracy compared to single-parameter discrimination. More intriguingly, multiparameter analysis was combined with artificial intelligence, a tool adept at processing multidimensional data, for the first time. Finally, artificial intelligence-assisted multiparameter size discrimination was successfully used to intelligently distinguish mixed Ag NPs, with an optimal accuracy of more than 95%. To sum up, the artificial intelligence-assisted multiparameter method showed an excellent ability to quickly achieve the most accurate size discrimination of nanoparticles at the level of individual particle and provide an effective guidance for the application of nanoparticles.

Confined Electrochemical Behaviors of Single Platinum Nanoparticles Revealing Ultrahigh Density of Gas Molecules inside a Nanobubble

Understanding the basic physicochemical properties of gas molecules confined within nanobubbles is of fundamental importance for chemical and biological processes. Here, we successfully monitored the nanobubble-confined electrochemical behaviors of single platinum nanoparticles (PtNPs) at a carbon fiber ultramicroelectrode in HClO₄ and H₂O₂ solution. Due to the catalytic decomposition of H₂O₂, a single oxygen nanobubble was formed on individual PtNPs to block the active surface of particles for proton reduction and to suppress their stochastic motion, resulting in significantly distinguished current traces. Furthermore, the combination of theoretical calculations and high-resolution electrochemical measurements allowed the nanobubble size and the oxygen gas density inside a single nanobubble to be quantified. Moreover, the ultrahigh oxygen density inside (1046 kg/m³) was revealed, indicating that gas molecules in a nanosized space existed with a high state of aggregation. Our approach sheds light on the gas aggregation behaviors of nanoscale bubbles using single-entity electrochemical measurements.

Influence of Charged Self-Assembled Monolayers on Single Nanoparticle Collision

Studying nanoparticle (NP)-electrode interactions in single nanoparticle collision events is critical to understanding dynamic processes such as nanoparticle motion, adsorption, oxidation, and catalytic activity, which are abundant on electrode surfaces. Herein, NP-electrode electrostatic interactions are studied by tracking the oxidation of AgNPs at Au microelectrodes functionalized with charged self-assembled monolayers (SAMs). Tuning the charge of short alkanethiol-based monolayers and selecting AgNPs that can be partially or fully oxidized upon impact enabled probing the influence of attractive and repulsive NP-electrode electrostatic interactions on collision frequency, electron transfer, and nanoparticle sizing. We find that repulsive electrostatic interactions lead to a significant decrease in collision frequency and erroneous nanoparticle sizing. In stark difference, attractive electrostatic interactions dramatically increase the collision frequency and extend the sizing capability to larger nanoparticle sizes. Thus, these findings demonstrate how NP-monolayer interactions can be studied and manipulated by combining nanoimpact electrochemistry and functionalized SAMs.

J, Yao Y, Wang J, Shen Y, Gooding JJ, Liang K. Self-Propelled Initiative Collision at Microelectrodes with Vertically Mobile Micromotors

Impact experiments enable single particle analysis for many applications. However, the effect of the trajectory of a particle to an electrode on impact signals still requires further exploration. Here, we investigate the particle impact measurements versus motion using micromotors with controllable vertical motion. With biocatalytic cascade reactions, the micromotor system utilizes buoyancy as the driving force, thus enabling more regulated interactions with the electrode. With the aid of numerical simulations, the dynamic interactions between the electrode and micromotors are categorized into four representative patterns: approaching, departing, approaching-and-departing, and departing-and-reapproaching, which correspond well with the experimentally observed impact signals. This study offers a possibility of exploring the dynamic interactions between the electrode and particles, shedding light on the design of new electrochemical sensors.

Nanocollision mediated electrochemical sensing of host-guest chemistry at a nanoelectrode surface

Electrochemical (EC) measurements of dynamic nanoparticle collisions on a support electrode provide a powerful approach to study the electrical properties of interfacial molecules self-assembled on the electrode surface. By introducing a special cage-shaped macrocyclic molecule, cucurbit[7]uril (CB7), onto a gold nanoelectrode surface, we show that the dynamic interactions between CB7 and the colliding nanoparticles can be real-time monitored via the appearance of distinct EC current switching signals. When a guest molecule is included in the CB7 cavity, the changed host-guest chemistry can be probed via the amplitude change of the EC current signals. In addition, different guest molecules can be recognized by CB7 on the nanoelectrode surface, giving rise to distinguishable current jump signals for different host-guest systems. Remarkably, two well-defined current states are observed in the EC measurements of the CB7-ferrocene complex, indicating two orientation geometries of ferrocene inside the CB7 cavity can be resolved in this EC sensing platform. This work demonstrates an effective approach for studying the dynamics of host-guest chemistry at the liquid-solid interface and sheds light on a convenient EC sensor for the recognition of target molecules with the aid of CB7.

Single-nanoparticle spectroelectrochemistry studies enabled by localized surface plasmon resonance

This review describes recent progress of spectroelectrochemistry (SEC) analysis of single metallic nanoparticles (NPs) which have strong surface plasmon resonance properties. Dark-field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are three commonly used optical methods to detect individual NPs and investigate their local redox activities in an electrochemical cell. These SEC methods are highly dependent on a strong light-scattering cross-section of plasmonic metals and their electrocatalytic characteristics. The surface chemistry and the catalyzed reaction mechanism of single NPs and their chemical transformations can be studied using these SEC methods. Recent progress in the experimental design and fundamental understanding of single-NP electrochemistry and catalyzed reactions using DFS, PL, and ECL is described along with selected examples from recent publications in this field. Perspectives on the challenges and possible solutions for these SEC methods and potential new directions are discussed.

Intrinsic electrocatalytic activity of a single IrOx nanoparticle towards oxygen evolution reaction

Identifying the intrinsic electrocatalytic activity of an individual nanoparticle is challenging as traditional ensemble measurements only provide average activity over a large number of nanoparticles and may be greatly affected by the ensemble properties, irrelevant to the nanoparticle itself. Here, single-particle collision electrochemistry is used to investigate the electrocatalytic activity of a single IrOx nanoparticle towards the oxygen evolution reaction (OER). The collision frequency is linearly proportional to the nanoparticle concentration. The mean peak current and transferred charge, extracted from current spikes of the collision, present a similar potential dependence relevant to IrOx intrinsic activity. The turnover frequency (TOF) is determined as 1.55 × 102 O2 s-1, which is orders of magnitude larger than TOFs of the reported ensemble systems. In addition, the deactivation of a single IrOx nanoparticle is also explored based on a half-width analysis of current spikes. This versatilely applicable method provides new insights into the intrinsic performance of a single nanoparticle, which is essential to reveal the structure-activity relations of nanoscale materials for the rational design of advanced catalysts.

Modified Co4N by B-doping for high-performance hybrid supercapacitors

High-performance energy storage systems are becoming essential to cope with the possible energy crisis in the future. Herein, unique hierarchical B-Co₄N have been reasonably designed and synthesized on Ni foam (NF) via a typical chemical reduction strategy. The successful realization of B-doping engineering effectively facilitates ion and electron transport, adding the electrochemically reactive sites, which endow the B-Co₄N-20/NF electrode with high specific capacity (817.9 C g^-1 at 1 A g^-1), excellent rate capability (maintained about 90.9% at 10 A g^-1) and cycling stability (about 93.06% retention of the initial capacity after 5000 cycles). The corresponding hybrid supercapacitor assembled with B-Co₄N-20/NF electrodes has an energy density of 25.85 W h kg^-1 at the power density of 800.2 W kg^-1 and a long cycle life (98.59% retention ratio after 5000 cycles). These remarkable properties indicate that the doping of heteroatom and the construction of hierarchical structure will provide a favorable reference for the performance promotion of next-generation energy storage devices.

Revealing the sub-50 ms electrochemical conversion of silver halide nanocolloids by stochastic electrochemistry and optical microscopy

Silver based ionic crystal nanoparticles (NPs) are interesting nanomaterials for energy storage and conversion, e.g. their colloidal solutions could be used as a reversible redox nanofluid in semi-solid redox flow cells. In this context, the reductive transformation of Brownian silver halide, AgX, NPs into silver NPs is probed by single NP electrochemistry, complemented by operando high resolution monitoring. However, their light sensitivity and poor conductivity make the operando monitoring of their chemical activity challenging. The electrochemical collisions of single AgX NPs onto a negatively biased electrode evidence a full conversion through multiple reduction steps within 3-10 ms. This is further corroborated by simulation of the conversion process and operando through a high resolution optical microscopy technique (Backside Absorbing Layer Microscopy, BALM). Both techniques are interesting strategies to infer at the single NP level the intrinsic charge capacity and charging rate of redox active Brownian nanomaterials, demonstrating the interest of the fast and reversible AgX/Ag system as a redox nanofluid.

Exploring dynamic interactions of single nanoparticles at interfaces for surface-confined electrochemical behavior and size measurement

With the development of new instruments and methodologies, the highly dynamic behaviors of nanoparticle at the liquid-solid interface have been studied. However, the dynamic nature of the electrochemical behavior of individual nanoparticles on the electrode interface is still poorly understood. Here, we generalize scaling relations to predict nanoparticle-electrode interactions by examining the adsorption energy of nanoparticles at an ultramicroelectrode interface. Based on the theoretical predictions, we investigate the interaction-modulated dynamic electrochemical behaviors for the oxidation of individual Ag nanoparticles. Typically, significantly distinct current traces are observed owing to the adsorption-mediated motion of Ag nanoparticles. Inspired by restraining the stochastic paths of particles in the vicinity of the electrode interface to produce surface-confined current traces, we successfully realize high-resolution size measurements of Ag nanoparticles in mixed-sample systems. This work offers a better understanding of dynamic interactions of nanoparticles at the electrochemical interface and displays highly valuable applications of single-entity electrochemistry.

Single-entity electrochemistry has been proposed for studying properties of single nanoparticles (NPs). Here, the authors make use of adsorption-mediated motion of Ag NPs to take individual NP size measurements using electrochemical impacts with excellent agreement to standard imaging techniques.