Multi-electrode Devices Research Articles

Development and Field Testing of Multi-Electrode Mixed Potential Electrochemical Sensors for Natural Gas-Hydrogen Mixture Emissions Monitoring

Transportation of hydrogen is one of the greatest hurdles to overcome in the development of a clean hydrogen economy [1]. A cost-effective solution to transportation of hydrogen is to mix it with natural gas (NG) and utilize current pipeline infrastructure for transportation [2]. However, hydrogen embrittlement, the higher diffusivity of H2, and the uncertain state of much of existing infrastructure makes leaks of H2 an environmental and safety concern. Current NG leak detection technologies largely use optical sensors such as IR spectrometers that are incapable of detecting H2 gas [3]. Mixed potential electrochemical sensors (MPES) are low-cost, robust devices capable of detecting a wide variety of gases [4], with the sensitivity and selectivity necessary for point source monitoring of natural gas leaks [5].Multi-electrode MPES devices using Indium Tin Oxide, Au, and La0.87Sr0.13CrO3 and Pt electrodes have previously successfully quantified CH4 in natural gas at the 10-40 ppm level [5]. In this work, we demonstrated that the Au vs. Pt electrode has a low limit of detection of < 3 ppm for H2 in an air atmosphere. We also performed field testing of H2 emissions at CSU’s Methane Emissions Technology Evaluation Center (METEC) in both underground and above-ground emissions of H2 and H2 + natural gas mixes (Figure 1) with successful detection of H2 at the ppm level. Finally, we evaluate the stability of the selectivity and sensitivity during prolonged exposure to H2 and CH4.This work was supported by US Department of Energy Award DE-FE0031864.

Complex phase modulation of liquid crystal devices with deep learning.

A deep learning-based phase modulation method for liquid crystal (LC) devices was demonstrated. For LC devices with a single-electrode structure, achieving complex phase distributions is highly challenging. Meanwhile, multi-electrode LC devices, as pixel resolution increases and electrode size decreases, encounter issues of cumbersome modulation steps and reduced modulation accuracy during the phase modulation process. This method uses the concept of field to modulate the phase of the LC device, providing an effective phase modulation scheme. By establishing a deep learning model, it maps the phase retardation distribution of LC devices onto the electric field distribution. This method effectively mitigates the phase modulation issues arising from the fringe field effect, enabling an accurate and precise phase modulation distribution.

Composite carbon electrode with a coating of nanostructured, reduced graphene oxide for water electrodialysis

Abstract Electrodialysis (ED) and electrodeionization (EDI) are the new methods that are being used in water desalination processes. Reliable, electrochemically stable and efficient electrodes are the crucial components of the ED/EDI electrodialysers. The article proposes a new material for electrodes in electromembrane desalination systems. Graphene composite electrodes were created by bonding carbon fibres with epoxy resin and then coated with a layer of nanostructured, reduced graphene oxide. The graphene electrode material underwent electrochemical characterization by cyclic voltammetry, electrochemical impedance spectroscopy and potentiostatic polarization techniques. FTIR and Raman spectroscopy were used to determine the material’s chemical structure. The change in the surface morphology and elemental composition of the electrodes after fabrication and exploitation of the composite was studied by SEM and EDS. The electrodes were used successfully in multi-electrode electrodialysis devices, resulting in a desalination rate of over 90%. The electrodes were proven to be functional and durable. It was also confirmed that the oxidation/reduction phenomena on the electrode surfaces were fully reversible after changing their polarization, which was used cyclically to clean the electrodialyser. The parameters obtained indicate that this material can also be successfully used in other electrode processes. Graphical Abstract

A multi-electrode two-dimensional position sensitive diamond detector

In multi-electrode devices, charge pulses at all the electrodes are induced concurrently by the motion of the excess charge carriers generated by a single ion. This charge-sharing effect is such that the pulse amplitude at each sensitive electrode depends on the device geometry, its overall electrostatic configuration, and the charge transport properties of the detecting material. Therefore, the cross-analysis of the charge pulses induced at each electrode offers implicit information on the position of the ion impact. In this work, we investigate the two-dimensional position sensitivity of a diamond detector fabricated by deep ion beam lithography. By exploiting the ion beam induced charge technique, the device was exposed to a 2 MeV Li+ ion micro-beam to map the spatial dependence of the charge collection efficiency (CCE) on the nominal micro-beam scanning position. The combination of the CCE maps revealed a two-dimensional position sensitivity of the device with micrometric resolution at the center of the active region.

Non-Conjugated Poly(Diphenylene Phthalide)-New Electroactive Material.

In organic electronics, conjugated conductive polymers are most widely used. The scope of their application is currently very wide. Non-conjugated polymers are used much less in electronics and are usually used as insulation materials or materials for capacitors. However, the potential of non-conjugated polymers is much wider, due to the fact that new electronic materials with unique electronic properties can be created on the basis of non-conjugated polymers, as well as other inorganic dielectrics. This article demonstrates the possibilities of creating electrically conductive materials with unique electronic parameters based on non-conjugated polymers. The results of the study of the sensory properties of humidity are given as examples of the practical application of the structure. The abnormal electronic properties are realized along the interface of two polymer dielectrics with functional polar groups. The submicron films of polydiphenylenephthalide were used as a dielectric. It is shown that a quasi-two-dimensional electronic structure with abnormally large values of conductivity and mobility of charge carriers occurs along the interface. These structures are often called quasi-two-dimensional electron gas (Q2DEG). This article describes the manufacturing processes of multielectrode devices. Polymer films are deposited via the spin-coating method with polymer solutions in cyclohexanone. The metal electrodes were manufactured through thermal deposition in a vacuum. Three types of metal electrodes made of aluminum, copper and chromium were used. The influence of the electron work function of contacting metals on the electronic parameters of the structure was studied. It was established that the work function decrease leads to an increase in the conductivity and mobility of charge carriers. The charge carrier parameters were estimated based on the analysis of the current-voltage characteristics within the space-charge-limited current technique. The Richardson-Schottky thermionic emission model was used to evaluate values a potential barrier at metal/organic interfaces. It was established that the change in ambient humidity strongly affects the electronic transport properties along the polymer/polymer interface. It is demonstrated that the increase in conductivity with an increase in humidity occurs due to an increase in the mobility of charge carriers and a decrease in the height of the potential barrier at the three-dimensional metal contact with two-dimensional polymer interface. The potential barrier between the electrode and the bulk of the polymer film is significantly higher than between the electrode and the quasi-two-dimensional polymer structure.

CMU Array: A 3D nanoprinted, fully customizable high-density microelectrode array platform.

Microelectrode arrays provide the means to record electrophysiological activity critical to brain research. Despite its fundamental role, there are no means to customize electrode layouts to address specific experimental or clinical needs. Moreover, current electrodes demonstrate substantial limitations in coverage, fragility, and expense. Using a 3D nanoparticle printing approach that overcomes these limitations, we demonstrate the first in vivo recordings from electrodes that make use of the flexibility of the 3D printing process. The customizable and physically robust 3D multi-electrode devices feature high electrode densities (2600 channels/cm2 of footprint) with minimal gross tissue damage and excellent signal-to-noise ratio. This fabrication methodology also allows flexible reconfiguration consisting of different individual shank lengths and layouts, with low overall channel impedances. This is achieved, in part, via custom 3D printed multilayer circuit boards, a fabrication advancement itself that can support several biomedical device possibilities. This effective device design enables both targeted and large-scale recording of electrical signals throughout the brain.

Genetic algorithm parallel optimization of a new high mass resolution planar electrostatic ion trap mass analyzer.

The study and design of high-resolution mass analyzers is a very important task in mass spectrometry. A planar electrostatic ion trap (PEIT) mass analyzer with image charge detection and FT-based data processing has been developed, theoretically simulated, and experimentally validated. However, the 10 ring electrode configuration (PEIT-10) is difficult for mechanical construction and voltage tuning; moreover, few methods have been reported for optimizing the performance of multi-electrode mass analyzers. In this article, a simplified PEIT-7 mass analyzer was designed, and a genetic algorithm parallel optimization (GAPO) method was developed for optimizing multiple voltage settings of the new PEIT-7 mass analyzer to achieve spatial and energy isochronicity as well as iso-coordinate property. The automatic voltage optimization processes for the reduction of time aberration and spatial aberration showed that the developed GAPO method can significantly improve the optimization efficiency (the optimal voltage set being found within 5 hours with a maximum time aberration of 15 ps and a maximum z aberration of 0.10 μm). Based on the results obtained from the GAPO method, the resolving power of the PEIT-7 mass analyzer for six groups of ions with closely packed masses (m/z = 117.000 Th to 117.010 Th) was demonstrated, and a mass resolution of 171k was achieved at an acquisition time of 200 ms. The established GAPO method facilitates the design and optimization of high-resolution mass analyzers and may be useful for the design of other multi-electrode ion optical devices.

The influence of the emitting bodies surface boundary conditions on particle streams in their vicinity

The problem of the influence of boundary conditions on the surface of emitting bodies on particle flows in their vicinity is studied in this paper. The solution to this problem is actual and relevant both for studying the behavior of electron plasma in a closed space (diodes and multi-electrode devices) and in open space (studying electron flows in the vicinity of natural and artificial celestial bodies). This research is theoretical. The emitting particles are electrons. Moreover, it is assumed that the emission of electrons occurs in vacuum. The electric field potential on the surface of the emitting bodies is considered constant (the first boundary condition). The second condition is determined by setting the field strength on the body surface. Four types of boundary conditions are considered: 1) fully screened electric field; 2) mono-speed flow from the surface; 3) monoenergetic isotropic flow; 4) the starting particles are distributed according to the Maxwell’s law. In the second of the above cases, the desired dependence is found analytically. In the third and fourth cases, the dependences of the electric potential strength are found numerically using the kinetic approach. The calculation results are presented in the graphs.

Highly efficient and stable Li extraction device by coupling Li4Ti5O12 electrode and matching perfluoro electrolyte

Abstract Based on the large extraction efficiency of 10–200 μg cm−2 h−1, the electrolysis-based technology is one of the most promising methods for large-scale extraction of lithium resources from natural seawater. The high potential safety hazard is the inherent defect of the conventional two-electrode electrolytic cell because of the threshold voltage of 3.9 V, which is very close to the decomposition voltage of carbonate electrolytes (4.5–5.0 V). Herein, we designed a novel triple-electrode device, using spinel Li4Ti5O12 and 1 M LiPF6/FEC + FEMC + HFE respectively as a temporary carrier for storing Li-ions and perfluorinated electrolyte. The threshold voltage of the multi-electrode device is lowered to 2.3 V, which expands the electrochemical window for lithium resource extraction from 1.1 V to 2.7 V. LTO electrode carrier is impossible to electrocatalyze the as-prepared fluoride electrolyte; the compound electrolyte is chemically stable to Li metal as well, avoiding the formation of lithium dendrites. Therefore, the Li4Ti5O12/Li battery exhibits outstanding cycle performances of 99.3% Coulombic efficiency and 95% capacity retention during 250 cycles. Multi-electrode electrochemical devices have shown high safety, stability and extraction efficiency in the practice of extracting Li metal from natural seawater, which is very beneficial to the development of marine mineral resources.

Comparison of radiofrequency ablation processes for monopolar and bipolar systems

Most of the manufactured radiofrequency ablation devices use single electrodes inserted into the tumor for heating. In order to increase the volume of heating, they are cooled from the inside, and some have a system for wetting the outer surface of the electrode with saline. The need for necrosis of tumors with a diameter of more than 3 cm made us look for other design solutions that would significantly increase the volume of heated tissue. At the beginning, these were attempts to increase the number of heat sources inside the tumor by opening additional wires in the tumor, then the transition began to increase the number of electrodes to three and increase the number of working zones on each electrode. As a result, heating volumes of 90 cm3 were achieved with a heating time of 45 min. A study of the scientific and technical literature on RFA showed that foreign firms producing ablation devices already understand the need to replace monopolar electrodes with bipolar multi-electrode devices. The reason for this is not only the better postoperative characteristics of the use of bipolar electrodes, but also the emergence, in addition to oncology, of new areas of ablation application, where more complex forms of thermal fields are used during therapy, for example, tubular zones of necrosis. A radical solution to the problem of increasing the volume of coagulation is the transition from monopolar single electrodes to bipolar multielectrode designs. In this case, the electric field is concentrated in the areas between the electrodes and the heating efficiency increases significantly throughout the tumor volume, including the peripheral part. The most effective way is to incorporate bipolar electrodes into a circular cluster, allowing all electrodes to work simultaneously. Under the control of an ultrasound scanner, 4 to 12 electrodes are inserted, operating in bipolar mode. A model has been developed and the design of a four-electrode cluster has been developed, which allows for distributed heating of the tumor in a bipolar mode. As a result of the studies carried out, it was found that the use of bipolar systems allows: to significantly increase the volume of the area of necrosis due to the possibility of increasing the power supplied to the tumor; to reduce the unevenness of heating over the volume of the tumor by obtaining temperature fields, the shape of which is closest to the required one; improve patient survival rates by placing electrodes outside the tumor (“NO TOUCH” mode). The work performed indicates the technical possibility of a significant increase in the volume of destroyed tissue by increasing the number of electrodes and placing electrodes along the tumor volume closer to the periphery, including the ablastic zone. As a result, it became possible to heat tumors from their periphery without contacting the electrodes with the tumor. The increase in the number of heat sources made it possible not only to reduce the load on the electrodes, but also to shorten the procedure time. Ablation of large volumes entailed an inevitable increase in the number of electrodes in a multi-electrode system, which led to the complication of their connection to the generator. So far, an unresolved problem remains to reduce the total impedance of the generator load.

Differential electron yield imaging with STXM

Total electron yield (TEY) imaging is an established scanning transmission X-ray microscopy (STXM) technique that gives varying contrast based on a sample’s geometry, elemental composition, and electrical conductivity. However, the TEY-STXM signal is determined solely by the electrons that the beam ejects from the sample. A related technique, X-ray beam-induced current (XBIC) imaging, is sensitive to electrons and holes independently, but requires electric fields in the sample. Here we report that multi-electrode devices can be wired to produce differential electron yield (DEY) contrast, which is also independently sensitive to electrons and holes, but does not require an electric field. Depending on whether the region illuminated by the focused STXM beam is better connected to one electrode or another, the DEY-STXM contrast changes sign. DEY-STXM images thus provide a vivid map of a device’s connectivity landscape, which can be key to understanding device function and failure. To demonstrate an application in the area of failure analysis, we image a 100 nm, lithographically-defined aluminum nanowire that has failed after being stressed with a large current density.

Renal arteries denervation with second generation systems: a remedy for resistant hypertension?

Initial studies on renal denervation (RDN) for the treatment of non-controlled arterial hypertension (HTN) through radiofrequency ablation of renal arteries demonstrated that RDN is an effective therapeutic strategy to reduce arterial blood pressure (BP). Nonetheless, the first randomized study, SYMPLICITY-HTN-3, failed to demonstrate a clear benefit for RND over the control group. Technologic evolution, with the introduction of new second generation multi-electrode devices, allowed deep energy delivery along the full circumference of the vessel. Two recent randomized studies involving patients assuming (SPYRAL HTN-ON MED) or not (SPYRAL HTN-OFF MED) antihypertensive pharmacologic treatment, demonstrated the efficacy and safety of RDN using second generation systems for radiofrequency ablation. Another recent randomized study demonstrated that RDN with ultrasounds (RADIANCE-HTN SOLO) of the main renal arteries led to a significant BP reduction compared to the control group. These studies have once again raised the interest of the scientific community towards attempting to define the appropriate role of RDN in the treatment of hypertension. Nonetheless, larger and longer clinical trials will be necessary to draw further conclusions.

Radiofrequency renal denervation with mono-electrode and multi-electrode device for treatment in patient with uncontrolled hypertension: results of a 6-month follow-up

Aim. To study the efficacy and safety of radiofrequency renal denervation with mono-electrode and multi-electrode devices in patients with uncontrolled arterial hypertension during а 6-month follow-up period.&#x0D; Materials and methods. The study included 52 patients with uncontrolled arterial hypertension, while receiving multicomponent antihypertensive therapy, including diuretic. Patients underwent radiofrequency renal denervation with a mono-electrode (group A; n=27) and multi-electrode devices (group B; n=25). The effectiveness of the procedure was study according to office blood pressure (BP) and ambulatory blood pressure monitoring (ABPM).&#x0D; Results. In group A and B, according to office BP after 6 months, there decreased in SBP/DBP by 32/14 and 30/10 mmHg (р=0.00001/р=0.00001 and p=0.00001/0.0004) respectively. According to ABPM, in group A there was a decrease in the average daily SBP and DBP by 7 and 4 mmHg (р=0.01 and р=0.03) respectively. According to ABPM, after 6 months in group B, there was a decrease in the average daily SBP and DBP by 12 and 6 mmHg (р=0.0003 and р=0.0007) respectively.&#x0D; Conclusions. The results confirm the safety and effectiveness of radiofrequency renal denervation. RDN of the distal branches of the renal arteries leads to a greater hypotensive effect.

Radiofrequency renal denervation with different device for treatment in patient with uncontrolled hypertension

Objective. To study the efficacy and safety of radiofrequency renal denervation with mono-electrode and multi-electrode devices in patients with uncontrolled arterial hypertension during follow-up period. Materials and methods. The study included 42 patients with uncontrolled arterial hypertension (mean age 51±12 years), while receiving multicomponent antihypertensive therapy, including diuretic. All patients underwent radiofrequency denervation of the renal arteries with a mono-electrode (n=27; group A) and multi-electrode devices (n=15; group B). The safety of the procedure was assessed using creatinine and glomerular filtration rate (MDRD equation), as well as according to ultrasound of the kidneys and renal arteries. The effectiveness of the procedure was study according to office blood pressure (BP) and ambulatory BP monitoring (ABPM). Results. In the general group, according to office BP after 6 months, there decreased in systolic (SBP)/diastolic BP (DBP) by 28/13 mm Hg (p=0.000001). According to ABPM, there was a decrease in the average daily SBP by 9 mm Hg (p=0.007) and DBP by 6 mm Hg (p=0.03). No significant changes in creatinine and glomerular filtration rate were detected in the general group. According to ABPM, after 6 months in group B, there was a decrease in the average daily SBP/DBP by 13 and 6 mm Hg (p=0.1). In group A, according to the ABPM, after 6 months, there was a decrease in the average daily SBP and DBP by 7 mm Hg (p=0.001) and 4 mm Hg (p=0.03). After 1 year, according to the office BP, there was a decrease in SBP/DBP by 14/11 mm Hg (p=0.002), and after 3 years at 15/17 mm Hg (p=0.3). Conclusion. The results confirm the safety and efficacy of radiofrequency renal denervation. Renal denervation in combination with drug therapy leads to decreasing of BP after 6 months and in the long-term

Fabrication and testing of multielectrode matrix of disordered Si nanowires for brain tissue sensing.

In the field of neuroscience there is interest on manufacturing new recording devices. The relationship between individual action potentials of neurons and field potentials in multicellular records is complex. For this reason, there is a big interest in multielectrode arrays. This work describes the unconventional fabrication process of an alternative multielectrode and its use for sensing neuronal activity. It consists of a matrix of Si nanowires randomly distributed, coated with Ag nanoparticles, and with macrometric Ag back contacts. The Si nanowires are prepared by metal-assisted chemical etching of a Si wafer, which is an economical and highly reproducible technique. Recordings using the multielectrode array of randomly distributed Si nanowires look promising and comparable with recordings obtained with other multielectrode devices.

Rapid Prototyping of Microfluidic Conductivity Detectors via Extrusion‐Based 3D Printing

ObjectiveTo develop a cost‐effective, single‐step method of rapidly prototyping microfluidic conductivity detectors via extrusion‐based 3D printing for the purpose of biomolecule characterization.BackgroundLab‐on‐a‐chip (LOC) devices are commonly viewed as an ideal rapid diagnostic modality in clinical biotechnology due to various design characteristics, including: portability, robustness, independence from external power sources, cost‐effectiveness, and ability to be used in remote locations. However, such devices have not been brought into realization in quantities nearly great enough to meet the demands of global healthcare. A significant reason is due to the use of labor‐intensive, complex, multi‐step microfabrication techniques, including: photolithography, soft lithography, metal evaporation &amp; sputtering, etching, and plasma bonding (many of which also require the use of a clean room). These time‐consuming fabrication methods lead to slow production of research prototypes, and subsequent testing. The newest generation of LOC devices integrate electronic components for the purposes of manipulation and detection, including multi‐electrode conductivity detectors, which have historically been utilized as an electrochemical detection method in chip and capillary electrophoresis. In this scenario, a pair of electrodes are used to apply an electromagnetic signal to the solution of interest and subsequently receive an attenuated signal based upon solution composition (i.e., analyte concentration). Here we propose utilizing dual‐extrusion 3D printing (widely used in engineering fields as a method of expediting design, development, and testing) as a method of rapid prototyping of microfluidic conductivity detectors. This could potentially convert a complex multi‐step process into a simple single‐step process.MethodsMicrofluidics devices were designed in SolidWorks 3D modeling software, and fabricated from polylactic acid (PLA) with inlaid conductive PLA electrodes. An Ultimaker 3 dual‐extrusion 3D printer was used for fabrication. Protein suspensions were added to device wells and a digital multimeter was used to confirm solution conductivity.ResultsMulti‐well, multi‐electrode devices were produced (Figure 1). Resolution was highly dependent upon print paths, temperature, and well geometries. A positive relationship was observed between protein concentration and solution conductivity, thus confirming detector functionality.DiscussionWhile rapid prototyping via 3D printing may not be suitable for all applications, it might be far more appropriate to test novel microfluidics prototypes via this method prior to pursuing higher‐order manufacturing techniques. Additionally, while alternative 3D printing technologies (i.e., stereolithography printers) can produce higher resolution devices, extrusion‐based 3D printing is the most economical, and also allows for the single‐step fabrication of devices with integrated electronic components. Here we have developed microfluidic conductivity detector prototypes, which can be used for the purposes of biomolecule detection, quantitation, and characterization (i.e., determination of DNA fragment length). We are also currently exploring printing more complex chip‐based microfluidic designs with integrated electronic components, including contactless conductivity detectors and multi‐layer PCB devices.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Impact of Advances in Atrial Fibrillation Ablation Devices on the Incidence and Prevention of Complications.

The number of patients with atrial fibrillation currently referred for catheter ablation is increasing. However, the number of trained operators and the capacity of many electrophysiology labs are limited. Accordingly, a steeper learning curve and technical advances for efficient and safe ablation are desirable. During the last decades several catheter-based ablation devices have been developed and adapted to improve not only lesion durability, but also safety profiles, to shorten procedure time and to reduce radiation exposure. The goal of this review is to summarise the reported incidence of complications, considering device-related specific aspects for point-by-point, multi-electrode and balloon-based devices for pulmonary vein isolation. Recent technical and procedural developments aimed at reducing procedural risks and complications rates will be reviewed. In addition, the impact of technical advances on procedural outcome, procedural length and radiation exposure will be discussed.

Numerical analysis of wavefront aberration correction using multielectrode electrowetting-based devices.

We present numerical simulations of multielectrode electrowetting devices used in a novel optical design to correct wavefront aberration. Our optical system consists of two multielectrode devices, preceded by a single fixed lens. The multielectrode elements function as adaptive optical devices that can be used to correct aberrations inherent in many imaging setups, biological samples, and the atmosphere. We are able to accurately simulate the liquid-liquid interface shape using computational fluid dynamics. Ray tracing analysis of these surfaces shows clear evidence of aberration correction. To demonstrate the strength of our design, we studied three different input aberrations mixtures that include astigmatism, coma, trefoil, and additional higher order aberration terms, with amplitudes as large as one wave at 633 nm.

Supercapacitors have an asymmetric electrode potential and charge due to nonelectrostatic electrolyte interactions

In recent years we have built up a theoretical framework which aims to explain ion specific effects observed in colloids at high salt concentrations. Our approach adds nonelectrostatic ion interactions (ion dispersion energies) alongside the usual electrostatic interactions of the ions.Using these techniques we have explored the impact that ion specificity may have on supercapacitors. Our model uses graphite electrodes at constant potential difference in 1.2M Li salt dissolved in propylene carbonate. For the counterion we used the common battery anions, PF6−, BF4− and ClO4− along with BrO4−, IO4− and Cl−.When nonelectrostatic ionic interactions are included, a potential difference V will not be split symmetrically between the two electrodes. We address two alternative mechanisms for partitioning the potential difference. If the circuit is isolated, then the charge at each electrode must be equal. This defines a potential ψeq≠V/2 at the positive electrode and therefore ψeq−V at the negative. Alternatively, if the circuit is connected to an external environment (ground, defining zero potential), then the state of the system is determined by minimisation of the total free energy, resulting in asymmetric electrode charges as well as potentials. The potentials determined by the two mechanisms are different, ψmin≠ψeq, with both the difference (averaging about 10%) and the direction of the difference between them depending on the ions. The free energy of the system with equalised charge exceeds the minimised free energy by less than 10%. Total free energies follow the Hofmeister series Cl−>PF6−>BF4−>ClO4−>BrO4−>IO4−.Despite the differences in electrode potential and charge under the two potential partitioning mechanisms, the capacitances under both mechanisms are similar. Local electrode capacitances C1=dσ/dψ relative to the positive electrode potential follow the same Hofmeister series as the energy. The energy–capacitance slope is nonlinear, becoming smaller as C1 increases. The Hofmeister series in the differential capacitance C2=dσ/dV relative to the potential difference V swaps BF4−>PF6−.The asymmetry in capacitance between positive and negative electrodes indicates that the capacitance of a two-electrode supercapacitor or battery ought be treated as a two-value quantity rather than as a single value, similar to the matrix of mutual capacitances used in multielectrode devices.

Predicting ion specific capacitances of supercapacitors due to quantum ionic interactions

A new theoretical framework is now available to help explain ion specific (Hofmeister) effects. All measurements in physical chemistry show ion specificity, inexplicable by classical electrostatic theories. These ignore ionic dispersion forces that change ionic adsorption.We explored ion specificity in supercapacitors using a modified Poisson–Boltzmann approach that includes ionic dispersion energies. We have applied ab initio quantum chemical methods to determine required ion sizes and ion polarisabilities. Our model represents graphite electrodes through their optical dielectric spectra. The electrolyte was 1.2M Li salt in propylene carbonate, using the common battery anions, PF6-,BF4- and ClO4- . We also investigated the perhalate series with BrO4- and IO4-.The capacitance C=dσ/dψ was calculated from the predicted electrode surface charge σ of each electrode with potential ψ between electrodes. Compared to the purely electrostatic calculation, the capacitance of a positively charged graphite electrode was enhanced by more than 15%, with PF6- showing >50% increase in capacitance. IO4- provided minimal enhancement. The enhancement is due to adsorption of both anions and cations, driven by ionic dispersion forces. The Hofmeister series in the single-electrode capacitance was PF6->BF4->ClO4->BrO4->IO4- . When the graphite electrode was negatively charged, the perhalates provided almost no enhancement of capacitance, while PF6- and BF4- decreased capacitance by about 15%.Due to the asymmetric impact of nonelectrostatic ion interactions, the capacitances of positive and negative electrodes are not equal. The capacitance of a supercapacitor should therefore be reported as two values rather than one, similar to the matrix of mutual capacitances used in multielectrode devices.