Fast-Rate Capable Electrode Material with Higher Energy Density than LiFePO4: 4.2V LiVPO4F Synthesized by Scalable Single-Step Solid-State Reaction

Use of compounds that contain fluorine (F) as electrode materials in lithium ion batteries has been considered, but synthesizing single-phase samples of these compounds is a difficult task. Here, it is demonstrated that a simple scalable single-step solid-state process with additional fluorine source can obtain highly pure LiVPO4F. The resulting material with submicron particles achieves very high rate capability approximate to 100 mAh g(-1) at 60 C-rate (1-min discharge) and even at 200 C-rate (18 s discharge). It retains superior capacity, approximate to 120 mAh g(-1) at 10 C charge/10 C discharge rate (6-min) for 500 cycles with >95% retention efficiency. Furthermore, LiVPO4F shows low polarization even at high rates leading to higher operating potential >3.45 V (approximate to 3.6 V at 60 C-rate), so it achieves high energy density. It is demonstrated for the first time that highly pure LiVPO4F can achieve high power capability comparable to LiFePO4 and much higher energy density (approximate to 521 Wh g(-1) at 20 C-rate) than LiFePO4 even without nanostructured particles. LiVPO4F can be a real substitute of LiFePO4.1114Ysciescopu

Time-resolved detection of surface oxide formation at individual gold nanoparticles : role in electrocatalysis and new approach for sizing by electrochemical impacts

Nanoparticle (NP) impacts on electrode surfaces has become an important method for analyzing the properties and activity of individual NPs, by either: (i) electrocatalytic reactions; or (ii) volumetric (dissolution) analyses. Using Au NPs as an exemplar system, this contribution shows that it is possible to detect surface oxide formation at individual NPs, which occurs on a rapid timescale (ca. 500 µs). The charge associated with this ‘surface oxidation method’ can be used for sizing (with results that are comparable to TEM) despite charges of only fC being measured. This platform further allows the role of surface oxides in electrocatalysis to be elucidated, with the timescale of oxide formation being controllable (i.e., ‘tunable’) through the applied potential, as illustrated through studies of borohydride and hydrazine electro-oxidation. Finally, all of these studies are carried out on an oxide-covered gold substrate, which can be prepared and regenerated straightforwardly on a gold electrode, through the applied potential

Scanning electrochemical cell microscopy : new perspectives on electrode processes in action

Scanning electrochemical probe microscopy (SEPM) methods allow interfacial fluxes to be visualized at high spatial resolution and are consequently invaluable for understanding physicochemical processes at electrode/solution interfaces. This article highlights recent progress in scanning electrochemical cell microscopy (SECCM), a scanning-droplet-based method that is able to visualize electrode activity free from topographical artefacts and, further, offers considerable versatility in terms of the range of interfaces and environments that can be studied. Advances in the speed and sensitivity of SECCM are highlighted, with applications as diverse as the creation of movies of electrochemical (electrocatalytic) processes in action to tracking the motion and activity of nanoparticles near electrode surfaces

Nanoscale surface structure–activity in electrochemistry and electrocatalysis

Nanostructured electrochemical interfaces (electrodes) are found in diverse applications ranging from electrocatalysis and energy storage to biomedical and environmental sensing. These functional materials, which possess compositional and structural heterogeneity over a wide range of length scales, are usually characterized by classical macroscopic or “bulk” electrochemical techniques that are not well-suited to analyzing the nonuniform fluxes that govern the electrochemical response at complex interfaces. In this Perspective, we highlight new directions to studying fundamental electrochemical and electrocatalytic phenomena, whereby nanoscale-resolved information on activity is related to electrode structure and properties colocated and at a commensurate scale by using complementary high-resolution microscopy techniques. This correlative electrochemical multimicroscopy strategy aims to unambiguously resolve structure and activity by identifying and characterizing the structural features that constitute an active surface, ultimately facilitating the rational design of functional electromaterials. The discussion encompasses high-resolution correlative structure–activity investigations at well-defined surfaces such as metal single crystals and layered materials, extended structurally/compositionally heterogeneous surfaces such as polycrystalline metals, and ensemble-type electrodes exemplified by nanoparticles on an electrode support surface. This Perspective provides a roadmap for next-generation studies in electrochemistry and electrocatalysis, advocating that complex electrode surfaces and interfaces be broken down and studied as a set of simpler “single entities” (e.g., steps, terraces, defects, crystal facets, grain boundaries, single particles), from which the resulting nanoscale understanding of reactivity can be used to create rational models, underpinned by theory and surface physics, that are self-consistent across broader length scales and time scales

The impact of RASopathy-associated mutations on CNS development in mice and humans

The RAS signaling pathway is involved in the regulation of developmental processes, including cell growth, proliferation, and differentiation, in the central nervous system (CNS). Germline mutations in the RAS signaling pathway genes are associated with a group of neurodevelopmental disorders, collectively called RASopathy, which includes neurofibromatosis type 1, Noonan syndrome, cardio-facio-cutaneous syndrome, and Costello syndrome. Most mutations associated with RASopathies increase the activity of the RAS-ERK signaling pathway, and therefore, most individuals with RASopathies share common phenotypes, such as a short stature, heart defects, facial abnormalities, and cognitive impairments, which are often accompanied by abnormal CNS development. Recent studies using mouse models of RASopathies demonstrated that particular mutations associated with each disorder disrupt CNS development in a mutation-specific manner. Here, we reviewed the recent literatures that investigated the developmental role of RASopathy-associated mutations using mutant mice, which provided insights into the specific contribution of RAS-ERK signaling molecules to CNS development and the subsequent impact on cognitive function in adult mice

Quantitative visualization of molecular delivery and uptake at living cells with self-referencing scanning ion conductance microscopy (SICM) – scanning electrochemical microscopy (SECM)

A multifunctional dual-channel scanning probe nanopipette that enables simultaneous scanning ion conductance microscopy (SICM) and scanning electrochemical microscopy (SECM) measurements is demonstrated to have powerful new capabilities for spatially mapping the uptake of molecules of interest at living cells. One barrel of the probe is filled with electrolyte and the molecules of interest and is open to the bulk solution for both topographical feedback and local delivery to a target interface, while a solid carbon electrode in the other barrel measures the local concentration and flux of the delivered molecules. This setup allows differentiation in molecular uptake rate across several regions of single cells with individual measurements at nanoscale resolution. Further, operating in a ‘hopping mode’, where the probe is translated towards the interface (cell) at each point allows self-referencing to be employed, in which the carbon electrode response is calibrated at each and every pixel for comparison to the bulk measurement. This is particularly important for measurements in living systems where an electrode response may change over time. Finite element method (FEM) modeling places the technique on a quantitative footing to allow the response of the carbon electrode and local delivery rates to be quantified. The technique is extremely versatile, with the local delivery of molecules highly tuneable via control of the SICM bias to promote or restrict migration from the pipette orifice. It is expected to have myriad applications from drug delivery to screening catalysts

Frontiers in nanoscale electrochemical imaging : faster, multifunctional and ultrasensitive

A wide range of interfacial physicochemical processes, from electrochemistry to the functioning of living cells involve spatially localized chemical fluxes that are associated with specific features of the interface. Scanning electrochemical probe microscopes (SEPMs) represent a powerful means of visualizing interfacial fluxes, and this Feature Article highlights recent developments that have radically advanced the speed, spatial resolution, functionality and sensitivity of SEPMs. A major trend has been a coming together of SEPMs that developed independently, and the use of established SEPMs in completely new ways, greatly expanding their scope and impact. The focus is on nanopipette-based SEPMs, including scanning ion conductance microscopy (SICM), scanning electrochemical cell microscopy (SECCM), and hybrid techniques thereof, particularly with scanning electrochemical microscopy (SECM). Nanopipette-based probes are made easily, quickly and cheaply with tunable characteristics. They are reproducible and can be fully characterized, and their reponse can be modeled in considerable detail, so that quantitative maps of chemical fluxes and other properties (e.g. local charge) can be obtained and analyzed. This article provides an overview on the use of these probes for high speed imaging, to create movies of electrochemical processes in action, to carry out multifunctional mapping, such as simultaneous topography-charge and topography-activity, and to create nanoscale electrochemical cells for the detection, trapping and analysis of single entities, particularly individual molecules and nanoparticles (NPs). These studies provide a platform for the further application and diversification of SEPMs across a wide range of interfacial science

Characterization of nanopipettes

Nanopipettes are widely used in electrochemical and analytical techniques as tools for sizing, sequencing, sensing, delivery and imaging. For all of these applications, the response of a nanopipette is strongly affected by its geometry and surface chemistry. As the size of nanopipettes becomes smaller, precise geometric characterization is increasingly important, especially if nanopipette probes are to be used for quantitative studies and analysis. This contribution highlights the combination of data from voltage-scanning ion conductivity experiments, transmission electron microscopy (TEM) and finite element method (FEM) simulations to fully characterize nanopipette geometry and surface charge characteristics, with an accuracy not achievable using existing approaches. Indeed, it is shown that presently used methods for nanopipette characterization can lead to highly erroneous information on nanopipettes. The new approach to characterization further facilitates high-level quantification of the behavior of nanopipettes in electrochemical systems, as demonstrated herein for a scanning ion conductance microscope (SICM) setup

High-speed electrochemical imaging

The design, development, and application of high-speed scanning electrochemical probe microscopy is reported. The approach allows the acquisition of a series of high-resolution images (typically 1000 pixels μm–2) at rates approaching 4 seconds per frame, while collecting up to 8000 image pixels per second, about 1000 times faster than typical imaging speeds used up to now. The focus is on scanning electrochemical cell microscopy (SECCM), but the principles and practicalities are applicable to many electrochemical imaging methods. The versatility of the high-speed scan concept is demonstrated at a variety of substrates, including imaging the electroactivity of a patterned self-assembled monolayer on gold, visualization of chemical reactions occurring at single wall carbon nanotubes, and probing nanoscale electrocatalysts for water splitting. These studies provide movies of spatial variations of electrochemical fluxes as a function of potential and a platform for the further development of high speed scanning with other electrochemical imaging techniques

Scanning electrochemical cell microscopy : a natural technique for single entity electrochemistry

Scanning electrochemical cell microscopy (SECCM) is a robust and versatile scanning electrochemical probe microscopy technique that allows direct correlation of structure–activity at the nanoscale. SECCM uses a mobile droplet cell to investigate and visualize electrochemical activity at interfaces with high spatiotemporal resolution, while also providing topographical information. This article highlights diverse contemporary challenges in the field of single entity electrochemistry tackled by the increasing uptake of SECCM globally. Various applications of SECCM in single entity electrochemistry are featured herein, including electrocatalysis, electrodeposition, corrosion science and materials science, with electrode materials spanning particles, polymers, two-dimensional materials and complex polycrystalline substrates. The use of SECCM for patterning structures is also highlighted