Electrochemical Modulation Research Articles

Electrochemical Modulation of the Photophysics of Surface-Localized Trap States in Core/Shell/(Shell) Quantum Dot Films.

In this work, we systematically study the spectroelectrochemical response of CdSe quantum dots (QDs), CdSe/CdS core/shell QDs with varying CdS shell thicknesses, and CdSe/CdS/ZnS core/shell/shell QDs in order to elucidate the influence of localized surface trap states on the optoelectronic properties. By correlating the differential absorbance and the photoluminescence upon electrochemically raising the Fermi level, we reveal that trap states near the conduction band (CB) edge give rise to nonradiative recombination pathways regardless of the CdS shell thickness, evidenced by quenching of the photoluminescence before the CB edge is populated with electrons. This points in the direction of shallow trap states localized on the CdS shell surface that give rise to nonradiative recombination pathways. We suggest that these shallow trap states reduce the quantum yield because of enhanced hole trapping when the Fermi level is raised electrochemically. We show that these shallow trap states are removed when additional wide band gap ZnS shells are grown around the CdSe/CdS core/shell QDs.

Electrochromic Properties of NiO Thin Coatings

In this work, we report the role of structure on electrochromic behavior of nickel oxide thin coatings deposited via chemical vapor deposition on ITO-coated glass in (EtCp)2Ni–O2–Ar and (EtCp)2Ni–O3–O2–Ar reaction systems. The structure and chemical composition were analyzed and then correlated with electrochemical response and transmittance modulation when immersed in 1 M KOH electrolyte. The NiO exhibits an anodic coloration, reaching an optical density modulation of 0.66 between colored and bleached state at 550 nm, with a color efficiency of 30.7 cm2C-1. Very fast switching between states was obtained, the coloration and bleaching time did not exceed 0.05 sec.

(Invited) Performance Modeling of Hydrogen-Production Electrolysis Cells for Scaling up Electrochemical Materials

This presentation will introduce modeling methods of an electrochemical cell and correspondent computational tools that enable the implementation of materials into a component design for assessing their performance, lifetime and reliability through high-fidelity modeling methods. The component modeling tools use ANSYS software as a solution framework, by adding fundamental thermochemical, electrochemical, and thermomechanical models, for simulations from basic material properties to a full-product design. The thermochemical and electrochemical modeling tools are developed from the fundamental transport and chemical processes from basic material performance data and correlations to reduce prediction uncertainties. By incorporating the specific mathematical descriptions of hydrogen-production processes, the modeling methods can be adapted to various electrolysis cell types as a general tool for electrolyzer design or performance optimization, because a common solver platform was used and expands the functionalities of the computational fluid dynamics (CFD) software, ANSYS/Fluent with an add-on electrochemical module based on Fluent User Defined Function (UDF). In particularly, we have developed models for high-temperature electrolysis (HTE) using proton-conducting solid oxide electrolysis cell (H-SOEC), low-temperature electrolysis (LTE) of proton-exchange-membrane electrolysis cell (PEMEC), and carbon-dioxide reduction (CO2R) cells. The multi-scale electrochemical modeling tools have been used for component performance simulations and are for material scale-up and implementation in cell and stack level. Appropriate mathematical descriptions of the electrochemical and thermochemical processes need to be developed for a given system based on the underlying material performance from either experimental data or theoretical modeling results. The modeling practices were previously successfully applied for fuel cell design and transformed to electrolysis cells. The integral modeling tool provides insights for the new materials or components to be implemented into electrochemical cell and stacks. The computational tools can support the electrolyzer design, performance, degradation and life cycle predictions, and can accelerate the material implementation into a product with proper design and optimum performance. The presentation will show that the computational modeling links experimental materials research integrated into a component or product using high-fidelity thermochemical and electrochemical models. The focus of this presentation will be on modeling method and results for H-SOEC electrolysis cells. The approach will facilitate material R&D in general and improve the computational tools to support industry for predicting product and life cycle performance. Validation of component performance and system integration results against prototype designs can allow iterative model improvement and enhance for various types, processes, and scales of systems.

Surface Depletion Layers in Plasmonic Metal Oxide Nanocrystals.

Strong infrared (IR) light-matter interaction and spectral tunability combine to make plasmonic metal oxide nanocrystals (NCs) a compelling choice for IR applications. In particular, visible transparency paired with strong, dynamically tunable IR absorption has motivated their implementation in electrochromic smart windows, but these NCs hold promise for a far broader range of plasmonically driven processes such as surface-enhanced infrared sensing, photothermal therapy, and enhanced photocatalysis. These unique properties result from localized surface plasmon resonance (LSPR) sustained by a relatively low free charge carrier concentration, which in turn requires consideration of distinct materials physics relative to traditional plasmonic materials (i.e., metals). Particularly important is the formation of insulating shells devoid of charge carriers (depletion layers) near the NC surface. Surface states as well as applied surface potentials can give rise to a potential difference between the NC surface and its core that depletes free charge carriers from the surface, forming an insulating shell that reduces the conductivity in NC films, lowers the dielectric sensitivity of the LSPR, and diminishes the incident electric field enhancement. In this Account, we report recent investigations of depletion layers in plasmonic metal oxide NCs that have advanced understanding of the semiconductor physics underlying the optoelectronic properties of these NCs and the electrochemical modulation of their LSPR, establishing a conceptual framework with which to broaden their applicability and optimize their performance. As a result of surface depletion, larger, highly doped NCs have improved dielectric sensitivity compared with their smaller, lightly doped counterparts. Concentrating dopants near the NC surface compresses the depletion layer, resulting in improved conductivity of NC films. Moreover, atomic layer deposition of alumina to infill NC films enhances the film conductivity by more than 2 orders of magnitude, ascribed to the elimination of depletion effects by reactive removal of surface water species. At the conclusion, we reflect on how our newfound understanding of surface depletion in plasmonic metal oxide NCs is quickly leading to rational material design. This insight is already resulting in significant performance improvements, and the same principles can be applied to new, exciting opportunities in hot carrier extraction and resonant IR energy transduction.

Application of electrochemistry to single-molecule junctions: from construction to modulation

State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level. Experimentally, molecular electronics face two primary challenges. One challenge is the reliable construction of single-molecule junctions, and the second challenge is the arbitrary modulation of electron transport through these junctions. Over the past decades, electrochemistry has been widely adopted to meet these challenges, leading to a wealth of novel findings. This review starts from the application of electrochemical methods to the fabrication of nanogaps, which is an essential platform for the construction of single-molecule junctions. The utilization of electrochemistry for the modification of molecular junctions, including terminal groups and structural backbones, is introduced, and finally, recent progress in the electrochemical modulation of single-molecule electron transport is reviewed.

Mechanisms of alamethicin ion channel inhibition by amiloride in zwitterionic tethered lipid bilayers

The effect of amiloride, an acid-sensing ion channel (ASIC) blocker, on the formation of alamethicin ion channels in tethered zwitterionic phospholipid bilayers was investigated using electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). EIS measurements show a decrease in conductivity indicating that ion transported across the alamethicin-rich phospholipid membrane is inhibited by the presence of amiloride. The PM-IRRAS spectra indicate that amiloride has no effect on the secondary structure of the alamethicin peptide. The IR data suggests that amiloride does not block ion translocation through the alamethicin ion pore but prevents the insertion of alamethicin peptides into the biomembrane suppressing the formation of ion channels. The mechanism responsible for amiloride inhibition is explained in terms of the electrostatic interactions between the molecule and membrane surface. Amiloride is positively charged at physiological pH levels invoking a repulsive force on the positive pole of the alamethicin molecular dipole. These repulsive interactions prevent the insertion of the alamethicin peptides into the hydrophobic core of the lipid bilayer. The present paper offers a molecular view of the interactions that occur between amiloride, an ion channel inhibitor, with the lipids and ion channel forming peptides in model tBLMs.

Electrochemical modulation of plasmon-induced charge separation behaviour at Au-TiO2 photocathodes.

Plasmon-induced charge separation (PICS) at the interface between a plasmonic nanoparticle and a semiconductor becomes less efficient as the plasmon resonance wavelength increases, because the energy of a photon may not be sufficiently higher than the interfacial Schottky barrier height. In this study, we developed PICS photocathodes by coating Au nanoparticles of different sizes on an ITO electrode with a thin TiO2 layer, and applied negative potentials to those photocathodes so as to suppress back electron transfer and improve the PICS photocurrent responses. The photocurrent enhancement factor was increased as the particle size was decreased, and enhancement of about two orders of magnitude was observed for small Au nanoparticles when bias voltage of 0.5 V was applied. In some cases the photocurrent enhancement was accompanied by a slight redshift of the photocurrent peak, which was caused by a lowered barrier. This technique would be useful for tuning the photocurrents when it is applied to devices such as electrochemical LSPR sensors and photodetectors.

Influence of environment on response characteristics of a high-strength aluminum alloy

This paper presents the results of a study aimed at understanding the stress corrosion cracking behavior of aluminum (Al) alloy 2219 with specific reference to understanding the mechanisms governing initiation of cracks and their progressive growth through the alloy microstructure. The influence of stress level on the initiation of stress corrosion cracks was determined. Results of this study revealed pitting to be the main type of corrosion that occurred during the early stages of exposure of the chosen aluminum alloy to an acidic environment. After the formation and presence of a pit, the applied stress was found to induce local stress concentration, promoting the early initiation of one or more microscopic cracks, while concurrently enabling fine microscopic cracks to expand and grow through the alloy microstructure. The cracks were observed to propagate along the grain boundaries, with few of the cracks growing through the crystals. With appropriate selection of electrochemical parameters, the influence of applied stress, coupled with the use of a solid mechanics module in synergism with an electrochemical corrosion module, on the stress corrosion behavior of the chosen aluminum alloy 2219 was studied using an iterative approach, and numerical prediction of corrosion was made possible.

A Protonic Biotransducer for Controlling ATP Synthesis in Mitochondria

Controlling the flow of ions and electrons at the device/biological interface has become an important challenge in broad fields such as bioelectronics and medical biology. These devices provide a new way to translate bidirectionally between the ionic language of biology and the electronic language of circuitry. The current strategy to develop such ion and electron controlling devices is to use new functional materials at the device/biological interface. For example, silicon nanowire and carbon nanotube based transistors use ions to read out biological functions. Aluminum nanostraws and carbon nanotube porins can selectively deliver molecules such as cations, DNA, and nicotine into biological materials. Since conductive polymers allow the transport of both ions and electrons, there are many conductive polymer based examples including organic field effect transistors for biosensing and organic ion pumps for locally delivering ions and neurotransmitters into cells and the brain. Along with ions and small molecules, protons (H+) play an important role in biology. Examples include the homeostatic pH regulation in body and bacteria, acid sensing ion channels activating in neuron cells, proton activated bioluminescence in dinoflagellates, and pH responsive flagella in bacteria. Mitochondria in particular are a noteworthy organelle that utilize the transport of protons and electrons across a membrane to synthesize adenosine triphosphate (ATP) molecules. To translate H+ signals from biological environments into measureable electronic signals, Rolandi and co-workers developed a prototype bioprotonic device using a Pd/PdHx protode. In his group, the metallic protode was used to measure the protonic conductivity in biological materials such as chitosan and jelly from in the ampullae of Lorenzini of sharks, and to integrate electronic signals with an enzymatic flip flop circuit, ion channels, and light-sensitive bacteriorhodopsin. Gorodestky and co-workers have separately demonstrated high proton conductivity in reflectin squid proteins and Pd/PdHx based transistors. All attempts however focused on the interfacing between Pd-based metal and biological materials, even though the Pd protode may occur side reactions such as oxygen conversion (PdO, PdO2 and Pd(OH)x) at the potentials beginning at 0.9 V vs. NHE and toxic hydrogen peroxide production. Here, we develop an organic biotransducer using a high H+-coupling conductive polymer of sulfonated polyaniline (SPA) that monitors and modulates the pH in the vicinity of the SPA electrode, even in solutions with the high buffering capacity typical of mitochondrial environments (Fig.1). We integrate this biotransducer with mitochondria isolated from pig hearts to translate the H+ signal from the activated mitochondria into a measureable protonic current, and also to control the activity of ATP synthase through electrochemical pH modulation at the SPA surface. Figure 1

Detection of influenza virus by electrochemical surface plasmon resonance under potential modulation.

In this study we report the development of a novel viral pathogen immunosensor technology based on the electrochemical modulation of the optical signal from a surface plasmon wave interacting with a redox dye reporter. The device is formed by incorporating a sandwich immunoassay onto the surface of a plasmonic device mounted in a micro-electrochemical flow cell, where it is functionalized with a monoclonal antibody aimed to a specific target pathogen antigen. Once the target antigen is bound to the surface, it promotes the capturing of a secondary polyclonal antibody that has been conjugated with a redox-active methylene blue dye. The methylene blue displays a reversible change in the complex refractive index throughout a reduction-oxidation transition, which generates an optical signal that can be electrochemically modulated and detected at high sensitivity. For proof-of-principle measurements, we have targeted the hemagglutinin protein from the H5N1 avian influenza A virus to demonstrate the capabilities of our device for detection and quantification of a critical influenza antigen. Our experimental results of the EC-SPR-based immunosensor under potential modulation showed a 300pM limit of detection for the H5N1 antigen.

Family-Based Big Medical-Level Data Acquisition System

At present, the market of network-based family health management is undergoing a fast growth and predicted to be extremely huge in the near future. Integration between traditional digital device in a family and common healthcare products can lead to a new strategy for family health management. Hereby, we imbed blood glucose monitoring function into a normal TV remote controller, which serves as a glucometer. In addition to normal function of TV remote controller, the proposed device can also serve as a medical device glucometer. The buried electrochemical module in TV remote controller is capable of resolving the current generated by a disposable glucose test strip. The retrieved blood glucose information is transmitted and displayed on TV, which can be further transferred to online personal health management center via network. Comparative study on reliability and accuracy between the integrated device and clinical biochemical analyzer shows good agreement. Taking account of rising concerns on daily healthcare, the proposed device holds great potentials in medical data acquisition for family-based health management.

THE ELECTROCHEMICAL FACING OF POWDER IRON FOR THERMOGALVANIC ELEMENTS

Background. The oxygen impact for electrochemical formation of surface structures on iron particles is not sufficiently taken into account in the production technology of composite electrodes for thermogalvanic energy sources; the main conditions of the performance improvement are considered.Objective. The aim of the paper is to define the electrochemical conditions of oxide layers formation on the surface of the iron powder composite electrode with the presence of oxygen in neutral and basic media.Methods. For better performance of the oxygen impact the study of composite electrodes was conducted in open air and inert atmosphere, the assembly of cells with composite electrodes was carried out on air in two versions: herme­tic and perforated. Electrochemical studies were carried out on the electrochemical module Autolab 30 PGSTAT301N Metrohm Autolab using 3-electrode cells. The microtexture of the iron powder during redox reactions was examined using a high resolution scanning electron microscope Mira 3 FESEM Tescan USA Inc. on a cathode with field emission at SEM HV-10 KeV and automatic measurement on the image. The analytical regime of the scanning microscope was used to determine the surface components distribution and their degrees of oxidation.Results. It was determined that with a low oxygen partial pressure in potential range from - 0.23 to - 0.88 V surface iron structure has two stages of organization: 1 – mosaic stage with partial covering of iron surface FeO and Fe2O3 ; 2 – transformation of mosaic structure into core–shell structure. Under a high oxygen partial pressure and cathodic potential > - 0.88 V thick iron oxide layers have been formed on the surface structure of iron particles. Thus, the oxygen partial pressure has a key role in electrochemical formation of nanolayers on the surface of iron particles and realizes the thermoelectrochemical activity of composite electrodes.Conclusions. The study found that thermoelectric parameters of an electrode based on iron powder are determined as a function of the pH of the medium and the oxygen content. In the neutral medium electrodes lose ability to rever­sible processes needed for the formation of the thermogalvanic properties. The ability of a powdered iron-composite electrode to a thermo-galvanic element is formed in an alkaline medium.

Competition between Depletion Effects and Coupling in the Plasmon Modulation of Doped Metal Oxide Nanocrystals.

Degenerately doped semiconductor nanocrystals (NCs) exhibit strong light-matter interactions due to localized surface plasmon resonance (LSPR) in the near- to mid-infrared region. Besides being readily tuned through dopant concentration introduced during synthesis, this LSPR can also be dynamically modulated by applying an external electrochemical potential. This characteristic makes these materials candidates for electrochromic window applications. Here, using prototypical doped indium oxide NCs as a model system, we find that the extent of electrochemical modulation of LSPR frequency is governed by the depletion width and the extent of inter-NC LSPR coupling, which are indirectly controlled by the dopant density, size, and packing density of the NCs. The depletion layer is a near-surface region with a sharply reduced free carrier population that occurs whenever the surface potential lies below the Fermi level. Changes in the depletion width under applied bias substantially control the spectral modulation of the LSPR of individual NCs and also modify the inter-NC LSPR coupling, which additionally modulates the LSPR absorption on the NC film scale. Here, we show that both of these effects must be considered primary factors in determining the extent of LSPR frequency modulation and that the dominant factor depends on NC size. For a constant doping concentration, depletion effects govern LSPR modulation for smaller NCs, while LSPR coupling is prevalent in larger NCs. Consequently, as the size of the NCs is increased while keeping the doping concentration constant, we observe a reversal in the sign of the LSPR frequency modulation from positive to negative.

Nylon 6,6 modified screen printed carbon electrodes as electrochemical sensors for rapid chlorothalonil determination in water samples using differential pulse cathodic stripping voltammetry

A newly developed electrochemical sensor for chlorothalonil based on nylon 6,6 film deposited onto screen printed electrode (SPE) with electrochemical modulation of pH at the electrode/solution interface was studied for the first time. Differential pulse cathodic stripping voltammetry (DPCSV) was used to carry out the electrochemical and analytical studies. Experimental parameters such as accumulation potential, initial potential, accumulation time and pH of Britton-Robinson buffer have been optimized. Chlorothalonil gave optimum analytical signal in a medium of 0.04 M Britton-Robinson buffer at pH 6.0. A well-defined reduction peak was observed, at Ep= −0.851 and −0.938 V vs. Ag/AgCl (3.0 M KCl) for both bare SPE and modified SPE, respectively. The peak currents of modified SPE were significantly increased as compared to bare SPE. At the modified SPE, a linear relationship between the peak current and chlorothalonil concentration was obtained in the range from 0.1 to 2.8 × 10−6 M with a detection limit of 1.53 × 10−8 M (S/N= 3). The practical applicability of the newly developed method has been demonstrated on analyses of real water samples. The newly developed sensor shows good reproducibility with RSD of 3.92%. The nylon 6,6 modified SPE showed itself as promising sensor with good selectivity for chlorothalonil determination.

Structure and electrochemical performance modulation of a LiNi0.8Co0.1Mn0.1O2 cathode material by anion and cation co-doping for lithium ion batteries.

Ni-rich layered transition metal oxides show great energy density but suffer poor thermal stability and inferior cycling performance, which limit their practical application. In this work, a minor content of Co and B were co-doped into the crystal of a Ni-rich cathode (LiNi0.8Co0.1Mn0.1O2) using cobalt acetate and boric acid as dopants. The results analyzed by XRD, TEM, XPS and SEM reveal that the modified sample shows a reduced energy barrier for Li+ insertion/extraction and alleviated Li+/Ni2+ cation mixing. With the doping of B and Co, corresponding enhanced cycle stability was achieved with a high capacity retention of 86.1% at 1.0C after 300 cycles in the range of 2.7 and 4.3 V at 25 °C, which obviously outperformed the pristine cathode (52.9%). When cycled after 300 cycles at 5C, the material exhibits significantly enhanced cycle stability with a capacity retention of 81.9%. This strategy for the enhancement of the electrochemical performance may provide some guiding significance for the practical application of high nickel content cathodes.

Locally pH controlled and directed growth of supramolecular gel microshapes using electrocatalytic nanoparticles

Controlled localization of platinum nanoparticles (Pt NPs) at a solid support assisted by a polarized liquid-liquid interface is reported. Electrocatalytic water oxidation resulted in local pH modulation followed by the directed self-assembly of a dibenzoyl-l-cystine hydrogelator forming a structured hydrogel retaining the shape of the Pt NP deposit.

Recovery of cadmium from stripping solutions based on ammonium nitrate. Industrial experience of the operation of the immersed electrochemical module

Recovery of cadmium from stripping solutions based on ammonium nitrate. Industrial experience of the operation of the immersed electrochemical module

Electrochemically-mediated selective capture of heavy metal chromium and arsenic oxyanions from water

The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies. Chromium and arsenic are among the most prevalent heavy metal pollutants in urban and agricultural waters, with current separation processes having severe limitations due to lack of molecular selectivity. Here, we report redox-active metallopolymer electrodes for the selective electrochemical removal of chromium and arsenic. An uptake greater than 100 mg Cr/g adsorbent can be achieved electrochemically, with a 99% reversible working capacity, with the bound chromium ions released in the less harmful trivalent form. Furthermore, we study the metallopolymer response during electrochemical modulation by in situ transmission electron microscopy. The underlying mechanisms for molecular selectivity are investigated through electronic structure calculations, indicating a strong charge transfer to the heavy metal oxyanions. Finally, chromium and arsenic are remediated efficiently at concentrations as low as 100 ppb, in the presence of over 200-fold excess competing salts.

Regeneration of Chromium Electroplating Electrolytes by the Application of Electromembrane Processes

The use of the electromembrane method for the purification of chromium plating electrolytes from cationic impurities (iron, copper, etc.) by three approaches are described. The first variant is based on the removal of these ions during their migration from the solution to be purified into a catholyte through a cationexchange membrane. The second variant is a transfer of chromate anions from a contaminated solution into the anolyte through an anion-exchange membrane. In the third method for the recuperation of chromic acid, accumulated in a recovery bath, it is proposed to use the immersed electrochemical module, combining the processes of concentration and purification from impurities, instead of evaporation.

Physical and Electrochemical Modulation of Polyoxometalate Ionic Liquids via Organic Functionalization

The synthesis and characterization of two new organic/inorganic hybrid polyoxometalate ionic liquids (POM‐ILs) is described. The POM‐ILs were formed by pairing bulky trihexyl(tetradecyl)phosphonium cations [THTP]+ with organosiloxane and organophosphonate‐functionalized Keggin‐type POMs [PW11O39(SiPh)2O]3– and [PW11O39{P(O)Ph}2]3–. The functionalized POM‐ILs were found to be more thermally stable than their molecular precursors and comparison of their electrochemical properties showed that the tunable electronic structures of the POM anions determined the redox chemistry of the hybrid materials.