Large Area Electrodes Research Articles

Instrumentation for multi-channel vertical electrical impedance scanning of concrete bridge decks

This paper documents a new design for a vertical electrical impedance (VEI) scanner that has increased VEI scanning speeds by an order of magnitude. Specifically, a new impedance analyzer was designed with improved circuitry and signal processing; this analyzer is accurate over a large range of impedance magnitudes, has a high sampling rate, is inexpensive, has low power consumption, and has a small form factor. Additionally, the physical moving platform, the localization equipment, and the large-area electrodes (LAEs) of the VEI scanner were all significantly improved. The improved VEI scanner was used to scan a concrete bridge deck in a field demonstration. The VEI scanner was able to collect data at sufficiently high speeds to scan the bridge deck without stationary traffic control, and the resulting data were highly self-consistent and correlated well with both delamination and surface cracking data that were measured separately.

Human Breast Cancer Cells Demonstrate Electrical Excitability.

Breast cancer is one of the most prevalent types of cancers worldwide and yet, its pathophysiology is poorly understood. Single-cell electrophysiological studies have provided evidence that membrane depolarization is implicated in the proliferation and metastasis of breast cancer. However, metastatic breast cancer cells are highly dynamic microscopic systems with complexities beyond a single-cell level. There is an urgent need for electrophysiological studies and technologies capable of decoding the intercellular signaling pathways and networks that control proliferation and metastasis, particularly at a population level. Hence, we present for the first time non-invasive in vitro electrical recordings of strongly metastatic MDA-MB-231 and weakly/non-metastatic MCF-7 breast cancer cell lines. To accomplish this, we fabricated an ultra-low noise sensor that exploits large-area electrodes, of 2 mm2, which maximizes the double-layer capacitance and concomitant detection sensitivity. We show that the current recorded after adherence of the cells is dominated by the opening of voltage-gated sodium channels (VGSCs), confirmed by application of the highly specific inhibitor, tetrodotoxin (TTX). The electrical activity of MDA-MB-231 cells surpasses that of the MCF-7 cells, suggesting a link between the cells’ bioelectricity and invasiveness. We also recorded an activity pattern with characteristics similar to that of Random Telegraph Signal (RTS) noise. RTS patterns were less frequent than the asynchronous VGSC signals. The RTS noise power spectral density showed a Lorentzian shape, which revealed the presence of a low-frequency signal across MDA-MB-231 cell populations with propagation speeds of the same order as those reported for intercellular Ca2+ waves. Our recording platform paves the way for real-time investigations of the bioelectricity of cancer cells, their ionic/pharmacological properties and relationship to metastatic potential.

Flexible self-supported bi-metal electrode as a highly stable carbon- and binder-free cathode for large-scale solid-state zinc-air batteries

Flexible (Ni, Co)3O4 nanosheets are grown on the surface of a Ni-foam by a facile electrodeposition coupled electrochemical oxidation process. The as-synthesized (Ni, Co)3O4 nanosheets are self-supported and can be directly used as the oxygen electrode without an addition of carbon or binder. As expect, the physical measurements and density functional theory (DFT) calculation reveal that Ni doping decreases Co3O4 surface activity towards the O, OH, OOH species, thus reducing the OER and ORR over-potentials. As a result, the (Ni, Co)3O4@Ni-foam electrode exhibits an unprecedented performance with a lower potential gap (⊗E: 0.57 V) than Pt/C+IrO2. This nanosheet can be readily applied as an electrode for Zn-air battery with a large area up to 24 cm2. The improved performance of this large-area electrode includes: a small charge-discharge voltage drop (0.56 V) and super stability with a high voltage efficiency of 69 % across all cycles.

Highly-robust, solution-processed flexible transparent electrodes with a junction-free electrospun nanofiber network.

Flexible transparent electrodes (FTEs) are widely used in a variety of applications, including flexible displays and wearable devices. Important factors in FTE design include active control of electrical sheet resistance, optical transparency and mechanical flexibility. Because these factors are inversely proportional to one another, it is essential to develop a technique that maintains flexibility while actively controlling the sheet resistance and transparency for a variety of applications. This research presents a new method for fabricating transparent electrodes on flexible polyimide films using electrospinning and copper electroless deposition methods. A flat metal network-based electrode without contact resistance was fabricated by heat treatment and electroless deposition onto the electrospun seed layer. The fabricated FTEs exhibited a transparency exceeding 80% over the entire visible light range and a sheet resistance of less than 10.0 Ω sq−1. Due to the heat treatment process, the adhesion between the metal network and the substrate was superior to other electrospinning-based transparent electrodes. Applicable to the large-area manufacturing process, the standard deviation of the network density of the fabricated large-area FTE was about 1%. This study does not require the polymer casting technique and has further advantages for mass production of electrodes and application to various fields.

A scalable Al–Ni alloy powder catalyst prepared by metallurgical microstructure control

Metallurgical microstructure control of Al–Ni alloys enabled scalable and facile synthesis of large-area electrodes for alkaline hydrogen evolution catalysts comparable to conventional Pt catalysts.

A Heterogeneous Integrated MEMS Inertial Switch With Compliant Cantilevers Fixed Electrode and Electrostatic Locking to Realize Stable On-State

A novel heterogeneous integrated inertial micro-switch has been designed with adjustable acceleration threshold and a stable ‘on’-state due to a predefined bias voltage. The bias voltage is applied onto the large-area parallel-plate electrodes, which endows the movable proof-mass with electrostatic forces. With an external excitation acceleration, the movable electrode moves to the fixed electrode and it can be locked by the electrostatic force onto the compliant electrical contacts, which are composed of micro-cantilever array to eliminate the contact rebound during electrostatic pull-in process. Both the dynamic response of the proof-mass and the relationship between the bias voltage and the inertial excitation acceleration were analyzed using theoretical model and finite element simulation. A unique heterogeneous integration process including both the silicon-based and non-silicon surface micromachining processes was adopted to fabricate the switch. The tests using a standard dropping hammer system demonstrated that the switch could keep a stable switch-on at the 57 g excitation acceleration and 38 V bias voltage. As wide as 52% adjustment range of the acceleration threshold was obtained when the applied bias voltage was from 38 V to 44 V. The tested relationship between the bias voltage and the external acceleration was very consistent with the simulated relationship. [2019-0038]

Upscaling high activity oxygen evolution catalysts based on CoFe2O4 nanoparticles supported on nickel foam for power-to-gas electrochemical conversion with energy efficiencies above 80%

We investigate cobalt ferrite nanoparticles (NPs) supported on large-scale electrodes as oxygen evolution reaction (OER) catalysts. Colloidal CoFe2O4 NPs were loaded on low-cost and high surface area nickel foam (NF) scaffolds. The coating process was optimized for large electrode areas, ensuring a proper distribution of the NPs on the NF that allowed overcoming the electrical conductivity limitations of oxide NPs. We were able to produce CoFe2O4-coated NFs having 10 cm2 geometric surface areas with overpotentials below 300 mV for the OER at a current density of 50 mA/cm2. Such impressively low overpotentials suggested using CoFe2O4 NP-based electrodes within a water electrolysis device. In this prototype device, stable operating currents up to 500 mA at remarkably low cell-voltages of 1.62 and 1.53 V, at ambient and 50 °C electrolyte temperatures, respectively, were reached during operation periods of up to 50 h. The high electrochemical energy efficiencies reached at 50 mA/cm2, 75% and 81% respectively, rendered these devices particularly appealing to be combined with low-cost photovoltaic systems for bias-free hydrogen production. Therefore, CoFe2O4 NP-based electrolysers were coupled to low-cost thin-film silicon solar cells with 13% efficiency to complete a system that afforded solar-to-fuel efficiencies above 10%.

A hematite photoelectrode grown on porous and conductive SnO2 ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.

From Perception Threshold to Ion Channels—A Computational Study

Small-surface-area electrodes have successfully been used to preferentially activate cutaneous nociceptors, unlike conventional large area-electrodes, which preferentially activate large non-nociceptor fibers. Assessments of the strength-duration relationship, threshold electrotonus, and slowly increasing pulse forms have displayed different perception thresholds between large and small surface electrodes, which may indicate different excitability properties of the activated cutaneous nerves. In this study, the origin of the differences in perception thresholds between the two electrodes was investigated. It was hypothesized that different perception thresholds could be explained by the varying distributions of voltage-gated ion channels and by morphological differences between peripheral nerve endings of small and large fibers. A two-part computational model was developed to study activation of peripheral nerve fibers by different cutaneous electrodes. The first part of the model was a finite-element model, which calculated the extracellular field delivered by the cutaneous electrodes. The second part of the model was a detailed multicompartment model of an Aδ-axon as well as an Aβ-axon. The axon models included a wide range of voltage-gated ion channels: NaTTXs, NaTTXr, Nap, Kdr, KM, KA, and HCN channel. The computational model reproduced the experimentally assessed perception thresholds for the three protocols, the strength-duration relationship, the threshold electrotonus, and the slowly increasing pulse forms. The results support the hypothesis that voltage-gated ion channel distributions and morphology differences between small and large fibers were sufficient to explain the difference in perception thresholds between the two electrodes. In conclusion, assessments of perception thresholds using the three protocols may be an indirect measurement of the membrane excitability, and computational models may have the possibility to link voltage-gated ion channel activation to perception threshold measurements.

Carbon-free Mn-doped LiFePO4 cathode for highly transparent thin-film batteries

The search for transparent battery cathodes primarily focuses on patterned electrodes with feature sizes below the optical absorption limit. This significantly limits the electrode capacity, as a large electrode area remains unused to maintain transparency. Herein, we report transparent olivine LiFe0.77Mn0.23PO4 thin-film electrodes discovered through high-throughput continuous-composition-spread sputtering. After investigating six different Mn doping ratios, we found the optimal Mn-doped olivine composition with an enhanced discharge capacity of 45.7 μA h/cm2∙μm without using excessive nanosized features or carbon coating. The thin-film electrode exhibits a clear redox activity for both Fe3+/2+ and Mn3+/2+, resulting in an enhanced average voltage over LiFePO4 composition. A 250-nm-thick film exhibits an optical transmittance of over 80% in the visible region. The results in this study demonstrates that transparent cathode thin films can be developed based on phospho-olivines via doping strategies with high-throughput continuous-composition-spread sputtering methods.

Flexible, stable and indium-free perovskite solar cells using solution-processed transparent graphene electrodes

With the dramatic advances in performance of perovskite solar cells (PSCs) in the recent years, the flexible PSCs have triggered huge attention to distributed generation. Due to the fragility of traditional indium-based transparent electrodes, the alternatives such as graphene have been widely investigated and used in the flexible devices. However, the lack of a solution-processed method to prepare large-area and low-cost graphene electrode limits the future production via the roll-to-roll process. Here, with the assistance of ethyl cellulose, we demonstrate a highly dispersed graphene composite transparent electrode which satisfies the demand of conductivity and transmittance for flexible PSCs. Moreover, the excellent mechanical flexibility and diffusive transmittance of the graphene electrode show a great improvement in flexible PSCs, resulting in a best efficiency of 15.71%. With this strategy, the solution-processed G:EC could greatly reduce the cost of electrode in wearable and foldable electronics. The G:EC shows promising possibility to replace the indium-based transparent electrodes in the future.

Buckypaper-Bilirubin Oxidase Biointerface for Electrocatalytic Applications: Buckypaper Thickness.

Electrode materials play an important role on the electrocatalytic properties of immobilized biocatalysts. In this regard, achieving direct electronic communication between the electrode and redox sites of biocatalysts eliminates the need for additional electron transfer mediators for biocatalytic applications in fuel cells and other electrochemical energy devices. In order to increase electrocatalytic currents and power in fuel cells and metal-air batteries, conductive carbon-nanostructure-modified large surface area electrodes are quite useful. Among various electrode materials, freestanding buckypapers made from carbon nanotubes have gained significance as they do not require a solid support material and thus facilitate miniaturization. In this article, we present the effect of buckypaper (BP) thickness on the electrocatalytic properties of a bilirubin oxidase (BOD) enzyme. In this study, we prepared BPs of varying thicknesses ranging from 87 μm, the minimum thickness for suitable handling with a good stability in aqueous experiments, to 380 μm. BOD was adsorbed overnight onto the BPs, mostly via hydrophobic and π-π interactions since the nanotubes used were not chemically functionalized. Furthermore, intercalation of the BOD molecules onto the nanotubes' multicylindrical network is feasible. We determined that the lower range BP thickness (<220 μm) exhibited better sigmoidal shaped electrocatalytic currents than the higher BP-thickness-based BOD biofilms with larger capacitive currents. An oxygen reduction current density of up to 3 mA cm-2 is achieved without the use of any redox mediators or tedious electrode modifications. Using the 87 μm thick BP as the representative case, we were able to obtain distinguishable peaks for all Cu sites of BOD and assign their types, T1, T2, and T3, based on the peak-width at half-maximum in anaerobic cyclic voltammograms. Our peak assignment is further supported by the appearance of dual electrocatalytic oxygen reduction waves at a higher scan rate region (>10 mV s-1) in oxygen-saturated buffer, which is identified to be driven by an ∼3.5 times faster electron transfer rate from the buckypaper to the T2/T3 center than the T1 Cu site. Findings from this study are significant for designing enzyme electrocatalytic systems and biosensors in general and fuel cells and aerobic energy storage devices in particular, where the cathodic oxygen reduction current is often inadequate.

Clear-to-Black Dynamic Windows with Minute-Long Switching Using Reversible Metal Electrodeposition

Dynamic windows possess electronically tunable transparency, which allows them to transition from clear to dark on demand. By controlling the flow of light and heat into buildings, dynamic windows can substantially increase the energy efficiency of homes and offices. Installing these "smart" windows in automobiles could also extend the battery range of electric vehicles by attenuating energy-intensive air conditioning use. Smaller versions of these windows have applications in actively switchable sunglasses as opposed to current passive photochromic transition lenses. We are developing next-generation dynamic windows based on the reversible electrodeposition of metals. In this approach, window tinting is controlled via the electrochemical movement of metal between a transparent conducting working electrode and a counter electrode metal frame. This strategy offers several advantages over current windows based on electrochromic materials including minute-long switching times, neutral color, and the potential to be manufactured at low cost. To enable uniform electrodeposition over a large working electrode area, transparent conducting oxides are modified with a self-assembled monolayer of Pt nanoparticles, which serves as an inert metal seed layer for metal nucleation and enhances electrodeposit morphology. An aqueous electrolyte separates the two electrodes and consists of Ag+, Cu2+, and/or Bi3+ ions. We interrogated several electrodeposition chemistries and derived relationships between electrolyte composition and device performance. The 25 cm2 or 100 cm2 device prototypes we developed display clear-to-black transitions with ~80% optical contrast in 1 minute and cycle thousands of times without significant deterioration. Future improvements in electrode and electrolyte design will increase the scalability and functionality of these devices.

Epidermal electrophysiology at scale

Large-area electrode arrays for epidermal electrophysiology offer new possibilities for the control of prosthetic devices and the monitoring of brain function.

Confining vertical conducting filament for reliable resistive switching by using a Au-probe tip as the top electrode for epitaxial brownmillerite oxide memristive device

We had discovered novel resistance switching phenomena in SrCoOx epitaxial thin films. We have interpreted the results in terms of the topotactic phase transformation between their insulating brownmillerite phase and the conducting perovskite phase and the existence of a rather vertical conducting filament due to its inherent layered structure. However, the rough interface observed between the SrCoOx and the Au top electrode (area ~10000 μm2) was assumed to result in the observed fluctuation in key switching parameters. In order to verify the effect of rough interface on the switching performance in the SrCoOx device, in this work, we studied the resistive switching properties of a SrCoOx device by placing a Au-coated tip (end area ~0.5 μm2) directly on the film surface as the top electrode. The resulting device displayed much improved endurance and showed high uniformity in key switching parameters as compared to the device having a large top electrode area. A simulation result confirmed that the Au-coated tip provides a local confinement of the electrical field, resulting in confinement of oxygen ion distribution and therefore localization of the conducting filament. By minimizing other free and uncontrollable parameters, the designed experiment here provides the most direct and isolated evidence that the rough interface between electrode and ReRAM matrix is detrimental for the reproducibility of resistivity switching phenomena.

Large-area electrode design for vertical electrical impedance scanning of concrete bridge decks.

Vertical electrical impedance (VEI) testing is a method that was developed specifically for quantifying the level of protection against chloride ingress in concrete bridge decks. A significant operational difficulty associated with VEI testing has been establishing the required rebar tap as a ground reference. As described in this work, the use of a large-area electrode (LAE) can potentially remove the need for a rebar tap and therefore significantly simplify and accelerate the VEI testing process. The specific objective of the research was to develop both theoretical and practical guidance for the design of an LAE for VEI testing. To investigate several variables that can affect the accuracy of VEI measurements obtained using an LAE connection, including various combinations of deck cover and water resistivity values, electrode separation distance, counter electrode (CE) effective area, and area ratio between the LAE and the CE, an analytical model (AM) and a finite-element model (FEM) were developed and validated with laboratory and field experiments. From the results of the AM and FEM simulations and the results of the laboratory and field experiments, LAE design considerations were developed for each of these variables that should allow proper implementation of a VEI measurement system using an LAE connection.

Chronic intracochlear electrical stimulation at high charge densities results in platinum dissolution but not neural loss or functional changes in vivo

Objective. Although there are useful guidelines defining the boundary between damaging and non-damaging electrical stimulation they were derived from acute studies using large surface area electrodes in direct contact with cortical neurons. These parameters are a small subset of the parameters used by neural stimulators. More recently, histological examination of cochleae from patients that were long-term cochlear implant users have shown evidence of particulate platinum (Pt). The pathophysiological effect of Pt within the cochlea is unknown. We examined the response of the cochlea to stimulus levels beyond those regarded as safe, and to evaluate the pathophysiological response of the cochlea following chronic stimulation at charge densities designed to induce Pt corrosion in vivo. Approach. 19 guinea pigs were systemically deafened and implanted with a cochlear electrode array containing eight Pt electrodes of 0.05, 0.075 or 0.2 mm2 area. Animals were electrically stimulated continuously for 28 d using charge balanced current pulses at charge densities of 400, 267 or 100 µC/cm2/phase. Electrically-evoked auditory brainstem responses (EABRs) were recorded to monitor neural function. On completion of stimulation electrodes were examined using scanning electron microscopy (SEM) and cochleae examined histology. Finally, analysis of Pt was measured using energy dispersive x-ray spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS). Main results. Compared with unstimulated control electrodes and electrodes stimulated at 100 µC/cm2/phase, stimulation at 267 or 400 µC/cm2/phase resulted in significant Pt corrosion. Cochleae stimulated at these high charge densities contained particulate Pt. The extent of the foreign body response depended on the level of stimulation; cochleae stimulated at 267 or 400 µC/cm2/phase exhibited an extensive tissue response that included a focal region of necrosis close to the electrode. Despite chronic stimulation at high charge densities there was no loss of auditory neurons (ANs) in stimulated cochleae compared with their contralateral controls. Indeed, we report a statistically significant increase in AN density proximal to electrodes stimulated at 267 or 400 µC/cm2/phase. Finally, there was no evidence of a reduction in AN function associated with chronic stimulation at 100, 267 or 400 µC/cm2/phase as evidenced by stable EABR thresholds over the stimulation program. Significance. Chronic electrical stimulation of Pt electrodes at 267 or 400 µC/cm2/phase evoked a vigorous tissue response and produced Pt corrosion products that were located close to the electrode. Despite these changes at the electrode/tissue interface there was no evidence of neural loss or a reduction in neural function.

Junction-free copper wires with submicron linewidth for large-area high-performance transparent electrodes

Electrospinning and wet etching facilitate large-area fabrication of junction-free copper wires with the smallest linewidth of 550 nm.

Graphene electrode diagnostic with IR imaging of Joule heat emission

Conductive graphene electrode of large area is required for some applications like for example photovoltaics or touch screens. Such large area graphene membrane needs specific test methods to assess defects which may obstacle its performance. In this work the infrared imaging of Joule heated graphene was proposed to estimate its uniformity and mechanical continuity. Thermal signatures of the typical mechanical defects like scratches and local resistivity inhomogeneity were identified. Distribution of the heat emission around such defects were simulated using finite elements method and then experimentally verified by recording of thermal landscape around the corresponding real graphene defects. Proposed method gives micrometric resolution and ability to inspection of large area electrodes depending on applied optics. Presented results give suggestions how graphene imperfections generate observed hot points related to graphene layer defects.

Bulk electronic transport impacts on electron transfer at conducting polymer electrode–electrolyte interfaces

Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio-)electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4-ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation-based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors.