Anodic Pole Research Articles

Wireless electrochemical preparation of gradient nanoclusters consisting of copper(II), stearic acid and montmorillonite on a copper wire for headspace in-tube microextraction of chlorobenzenes.

This work introduces a new gradient fiber coating for microextraction of chlorobenzenes. Nanoclusters of organoclay-Cu(II) on a copper wire were fabricated by wireless electrofunctionalization. The resultant gradient coatings are more robust, and thermally and mechanically stable. Wireless electrofunctionalization was carried out in a bipolar cell under a constant deposition potential and using an ethanolic electrolyte solution containing stearic acid and montmorillonite. Stearic acid acts as an inexpensive and green coating while montmorillonite acts as a modifier to impart thermal stability. The gradient morphology of the nanoclusters was investigated by scanning electron microscopy, thermogravimetric analysis and energy dispersive X-ray spectroscopy. The coated wire was placed in a hollow needle and used for headspace in-tube microextraction (HS-ITME) of chlorobenzenes (CBs). Effects of various parameters affecting synthesis and extraction were optimized. Following extraction, the needles were directly inserted into the GC injector, and the CBs (chlorobenzene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene) were quantified by GC-MS. The limits of detection under optimized conditions range from 0.5 to 10ng.L-1. The intra- and inter-day relative standard deviations (RSDs) (for n = 10, 5 respectively) using a single fiber are 6-10 and 10-15%, respectively. The fiber-to-fiber RSDs (for n = 3) is between 17 and 24%. The method was successfully applied to the extraction of CBs from real water samples, and relative recoveries are between 91 and 110%. Graphical abstract A gradient coating of organoclay-Cu nanoclusters was fabricated on a copper wire by wireless electrofunctionalization. The oxidation of copper takes place at the anodic pole (red) while dissolved oxygen in ethanol solution is reduced at the cathodic pole (blue).

Visual electrochemiluminescence biosensing of aflatoxin M1 based on luminol-functionalized, silver nanoparticle-decorated graphene oxide

A sensitive electrochemiluminescence (ECL) aptasensor for aflatoxin M1 (AFM1) detection by a closed bipolar electrode (BPE) array has been introduced. The thiolated AFM1 aptamer was immobilized on gold nanoparticle-coated magnetic Fe3O4 nanoparticles (Apt-GMNPs). Luminol-functionalized silver nanoparticle-decorated graphene oxide (GO-L-AgNPs) participates in π-π interactions with the unpaired bases of the immobilized aptamer (Apt-GMNPs-GO-L-AgNPs). After the Apt-GMNPs-GO-L-AgNPs were introduced to a gold anodic BPE array, the individual electrodes were subjected to different concentrations of AFM1. Upon the interaction of AFM1 with the aptamers, the GO-L-AgNPs detach from the aptamer; the resulting ECL of luminol and H2O2 at the anodic poles is monitored using a photomultiplier tube (PMT) or smartphone, and the images are analyzed using ImageJ software. This process triggers thionine reduction at the cathodic poles. Under the optimal conditions obtained by a face-centered central composite design (FCCD), the PMT-based detection of the BPE-ECL aptasensor exhibit a linear response over a wide dynamic range from 5 to 150ngmL−1, with a detection limit of 0.01ngmL−1. Additionally, smartphone-based detection shows a linear relationship between the ECL image gray value and the logarithmic concentration of the AFM1 target over a range of 10–200ngmL−1, with a detection limit of 0.05ngmL−1. Furthermore, the BPE-ECL aptasensor was successfully used to detect AFM1 in milk complex media without any serious interferences with reliable reproducibility (average relative standard deviation (RSD = 2.3%)). This smartphone-based detection opens a new horizon for bioanalysis that does not require a trained technician to operate and is a promising technology for point-of-care testing.

Wireless Electrocoagulation in Water Treatment Based on Bipolar Electrochemistry

The present study reports the wireless electrocoagulation (WEC) based on bipolar electrochemistry where the iron sheets were used as sacrificial bipolar electrodes (BPEs) and two graphite plates served as driving electrodes. Driven by the interfacial potential difference induced by electric field in solution, the iron dissolution started at the anodic pole, achieving the generation of iron coagulant and thus turbidity removal. The total iron concentration produced was found to be more dependent on the geometrical configuration of BPE rather than electrochemical parameters. That is, placing the BPE with the length in parallel to electric field could generate iron concentration of 84.6% higher than that when placed vertically. Besides, increasing the number of BPE from one to three led to the increase in coagulant production by 2.1 times. Moreover, to maximize the voltage drop and minimize the material used, the BPE was designed into different geometrical shapes. The “H-shaped” BPE could achieve almost the same iron concentration as the unmodified BPE even the relative cathode/anode surface area was as low as 0.36. This accounted for efficient coagulant production by saving as great as 40% of the electrode material and cost. The wireless operation can not only solve the problems caused by electrode connection, but also allow arbitrary number of sacrificial BPEs working simultaneously in a very simple setup. In addition, the WEC performance can be easily controlled by the geometrical configuration of BPE. All these factors will be expected to make the electrocoagulation process much easier, more economical and more reliable in water treatment.

Closed Bipolar Electrochemistry for the Detection of Human Immunodeficiency Virus Short Oligonucleotide

Although a monumental progress has been made in case of Human Immunodeficiency Virus researches, there are still more than 34 million people living with this viral disease. Therefore, the development of a fast and cost-effective protocol that can sensitively and selectively detect HIV gene sequence is essential. In the present study, a protocol for the molecular detection of HIV genome taking advantage of closed bipolar electrochemistry integrated with electrogenerated chemiluminescence detection is described. In this case, a closed split bipolar electrochemical cell is applied to detect the short specific oligonucleotide target of HIV1. Anthraquinone disulfonic acid, as a negative electroactive reporter, intercalates with hybridized double-strand DNA on the sensing site. By reduction of redox reporter (AQDS) on the cathodic pole, luminol is oxidized on the anodic pole and subsequent oxidized diazo product generates light that is followed using a photomultiplier tube. The experimental condition is optimized to obtain the highest sensitivity. The results demonstrate the high sensitivity and selectivity of this fast and economical method toward Human Immunodeficiency Virus genome detection in the range of 0.1 to 300nM with the detection limit of 30pM (S/N=3).

Enhancing the Bipolar Redox Cycling Efficiency of Plane-Recessed Microelectrode Arrays by Adding a Chemically Irreversible Interferent.

The individual electrochemical anodic responses of dopamine (DA), epinephrine (EP), and pyrocatechol (CT) were investigated at arrays of recessed gold disk-microelectrodes arrays (MEAs) covered by a gold plane electrode and compared to those of their binary mixture (CT and EP) when the top-plane electrode was operated as a bipolar electrode or as a collector. The interferent species (EP) displays a chemically irreversible wave over the same potential range as the chemically reversible ones of DA or CT. As expected, in the generator-collector (GC) mode, EP did not contribute to the redox cycling amplification that occurred only for DA or CT. Conversely, in the bipolar mode, the presence of EP drastically increased the bipolar redox cycling efficiency of DA and CT. This evidenced that the chemically irreversible oxidation of EP at the anodic poles of the top plane floating electrode provided additional electron fluxes that were used to more efficiently reduce the oxidized DA or CT species at the cathodic poles. This suggests an easy experimental strategy for enhancing the bipolar efficiency of MEAs up to reach a performance identical to that achieved when the same MEAs are operated in a GC mode.

A Study for Balance and Gait Ability on Stroke Patients

This study was to identify correlations between balance and gait according to polarity when transcranial direct current stimulation (tDCS) with the cathodal and anodal poles was applied to the brain region corresponding to the lower extremity of stroke patients. Subjects of this study were 40 individuals consisting of 20 individuals in which tDCS were applied with the anodal pole and 20 individuals with the cathodal pole. This research was conducted from June 1 2015 to June 26 2015. Balance ability results, anodal and cathodal groups showed significant difference of left/right, anterior/posterior weight-bearing. group differentiation is appeared on left/right weight-bearing after tDCS. gait ability results, anodal and cathodal groups showed significant difference of affected side stance and swing phase. And anodal group showed significant difference of cadence. Anodal group statistically significant correlations were shown in the difference in left/right and anterior/posterior weight-bearing among the variables of balance ability, and the stance phase on the affected side, the swing phase on the affected side, and cadence among the variables of gait ability. Cathodal group statistically significant correlations were exhibited in differences in anterior/posterior weight-bearing and left/right weight-bearing among the variables of balance ability, and the stance phase on the affected side, and the swing phase on the affected side among the variables of gait ability. Study suggests that tDCS applied with the anodal pole is more important than tDCS applied with the cathodal pole to improve balance and gait abilities in stroke patients. Future application of a proper intervention combined with tDCS may result in more effective functional improvements.

Reduced Graphene Oxide Thin Film on Conductive Substrates by Bipolar Electrochemistry.

Recent years have shown an increased interest in developing manufacturing processes for graphene and its derivatives that consider the environmental impact and large scale cost-effectiveness. However, today’s most commonly used synthesis routes still suffer from their excessive use of harsh chemicals and/or the complexity and financial cost of the process. Furthermore, the subsequent transfer of the material onto a substrate makes the overall process even more intricate and time-consuming. Here we describe a single-step, single-cell preparation procedure of metal-supported reduced graphene oxide (rGO) using the principle of bipolar electrochemistry of graphite in deionized water. Under the effect of an electric field between two stainless steel feeder electrodes, grapheme layers at the anodic pole of the wireless graphite were oxidized into colloidal dispersion of GO, which migrated electrophoretically towards the anodic side of the cell, and deposited in the form of rGO (d(002) = 0.395 nm) by van der Waals forces. For substrates chemically more susceptible to the high anodic voltage, we show that the electrochemical setup can be adapted by placing the latter between the wireless graphite and the stainless steel feeder anode. This method is straightforward, inexpensive, environmentally-friendly, and could be easily scaled up for high yield and large area production of rGO thin films.

Electrogenerated Chemiluminescence Reporting on Closed Bipolar Microelectrodes and the Influence of Electrode Size.

We report a fundamental study of the use of Ru(bpy)32+-based electrogenerated chemiluminescence (ECL) as an optical reporting system for the detection of redox-active analyte on closed bipolar microelectrodes, focused on gaining an in-depth understanding of the correlation between ECL emission intensity and electrochemical current. We demonstrate the significant effect that the size of the anodic and cathodic poles has on the resulting ECL signal and show how this influences the quantitative detection of analyte on a closed bipolar electrode. By carefully designing the geometry of the bipolar electrode, the detection performance of the system can be tuned to different analyte concentration ranges. We show that through a simple voltammetric study of the individual reactions, one can understand the coupled bipolar behavior and accurately predict the ECL signal response to a range of analyte concentrations, enabling the accurate prediction of calibration curves.

Digital versatile disc bipolar electrode: A fast and low-cost approach for visual sensing of analytes and electrocatalysts screening

This work represents a new, extremely low cost and easy method for fabrication of bipolar electrode (BPE) for rapid and simultaneous screening of potential candidates for electrocatalytic reactions and sensing applications. Our method takes advantage of the silver reflective layer deposited on already available recordable digital versatile disc (DVD-R) polycarbonate substrate which acts as BPE. Oxidation of the reflective layer of the DVD-R in anodic pole of the BPE results in a permanent and visually measurable dissolute length. Therefore, one could correlate the electrocatalytic activity of the catalyst at the cathodic pole of the BPE, as well as the concentration of analyte in the solution, to the dissolution length of the BPE. To illustrate the promising applications of this new substrate as BPE, p-benzoquinone (BQ) and hydrogen peroxide were tested as model targets for the sensing application. Moreover, in order to show the feasibility of using DVD BPEs for screening applications, the electrocatalytic activity of Pt, Pd, Au, and pristine DVD substrate toward hydrogen evolution reaction (HER) were compared using an array of BPEs prepared on DVD substrate.

Wireless electrochemiluminescence bipolar electrode array for visualized genotyping of single nucleotide polymorphism.

The development of simple, inexpensive, hand-held, user-friendly biosensor for high throughput and multiplexed genotyping of various single nucleotide polymorphisms (SNPs) in a single run experiment by a nonspecialist user is the main challenge in the analysis of DNA. Visualizing the signal and possibility to monitor SNPs by a digital camera opens a new horizon for the routine applications. In the present manuscript, a novel wireless electrochemiluminescence (ECL) DNA array is introduced for the visualized genotyping of different SNPs on the basis of ECL of luminol/hydrogen peroxide system on a bipolar electrode (BPE) array platform. After modification of anodic poles of the array with the DNA probe and its hybridization with the targets, genotyping of various SNPs is carried out by exposing the array to different monobase modified luminol-platinum nanoparticles (M-L-PtNPs). Upon the hybridization of M-L-PtNPs to mismatch sites, the ECL of luminol is followed using a photomultiplier tube (PMT) or digital camera and the images are analyzed by ImageJ software. This biosensor can detect even thermodynamically stable SNP (G-T mismatches) in the range of 2-600 pM. Also, by combining the advantages of BPE and the high visual sensitivity of ECL, it could be easily expected to achieve sensitive screening of different SNPs. The present biosensor demonstrates the capability for the discrimination between PCR products of normal, heterozygous, and homozygous beta thalassemia genetic disorders.

Dendritic CuO structures synthesized by bipolar electrochemical process for electrochemical energy storage

Cupric oxide is an inexpensive material with electrochemical behavior that can be used for energy storage applications. Here, we prepare CuO materials by a simple bipolar electrochemical process in deionized water, where a high voltage is applied between two stainless steel feeding electrodes symmetrically surrounding an electrically floating copper plate. CuO is mainly formed in the locally alkaline region facing the anodic pole of the copper plate, where electro-dissolved Cu2+ undergo successive reactions of complexation–dehydration with OH− ions. The morphology, composition, and phase structure of as-prepared materials were characterized by scanning electron microscopy, powder X-ray diffraction, micro-Raman spectroscopy, and Vis-near-IR spectroscopy. We have found that CuO materials are self-assembled in three-dimensional dendritic structures that can grow up to millimeters in size. The electrochemical characterization in 1molL−1 KOH by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy shows a capacitive behavior of CuO structures, with an average capacitance value reaching 202Fg−1 at 10Ag−1, giving an energy density of 7.0Whkg−1 for a power density of 2.5kWkg−1. At 20Ag−1 current density, the materials exhibit 90% capacitance retention over 2000 charge/discharge cycles with a coulombic efficiency exceeding 95%.

Visual Electrochemiluminescence Detection of Cancer Biomarkers on a Closed Bipolar Electrode Array Chip

This paper describes a novel electrochemiluminescence (ECL) imaging platform for simultaneous detection of cancer biomarkers based on a closed bipolar electrode (BPE) array. It consists of two separated channel arrays: detection channel array and sensing channel array, which are connected by a group of parallel ITO BPEs on a glass substrate. Besides, two parallel ITO strips are fabricated at the two sides of BPE array and employed as driving electrodes. After Au films are electrochemically deposited on the cathodes of the BPE array, nanobioprobes including biorecognition elements (aptamer or antibody) and a novel electrochemical tag, which is synthesized by doping thionine in silica nanoparticles (Th@SiO2 NPs), are introduced into the cathodes by immunoreaction or DNA hybridization. The Th@SiO2 coupled nanobioprobes as both recognition probes and signal amplification indicators could mediate the ECL signals of Ru(bpy)3(2+)/tripropylamine (TPA) on the anodes of BPE array through faradaic reaction due to the charge neutrality of BPE. Thus, multiplex detection of cancer biomarkers (adenosine triphosphate (ATP), prostate-specific antigen (PSA), α-fetoprotein (AFP) and thrombin) is realized by forming specific sensing interfaces onto the cathodic poles of BPEs in different sensing channels and reported by the ECL images of the Ru(bpy)3(2+)/TPA system on the anodic poles of BPEs in detection channels. The results demonstrate that this visual ECL platform enables sensitive detection with excellent reproducibility, which may open a new door toward the development of simple, sensitive, cost-effective, and high throughput detection methods on biochips.

Linking glucose oxidation to luminol-based electrochemiluminescence using bipolar electrochemistry

The range of potential analytes for bipolar electrochemistry can be significantly extended by modification of bipolar electrodes with enzymatic biosensing layers. In this study, we employed a Prussian blue-based glucose detection system involving electrochemical reduction of enzymatically generated hydrogen peroxide at the cathodic pole. The concentration of glucose in solution can be correlated with oxidative luminol electrochemiluminescence at the opposite anodic pole, which was recorded with a photomultiplier tube. This opens a route for novel analytical systems using glucose oxidase as an amplification element for the reporter reaction.

Electrochemiluminescence Behavior of Luminol at Closed Bipolar Electrode and Its Analytical Application

Abstract A new closed bipolar electrode electrochemiluminescence (ECL)-based device was designed and used to investigate the ECL behaviors of luminol in this device. The results showed that while a suitable voltage was applied to the two poles of the closed bipolar electrode, both the positive charge ions and luminol-based anionic ions could be enriched on the two poles of the closed bipolar electrode, respectively. More importantly, the ECL signals, generated from the electro-oxidation of luminol on anodic pole, was found to be related to the total amount of positive charged ions on the cathodic pole of the closed bipolar electrode. Under the optimum conditions, the ECL response was linearly to the concentration of analyte in the range of 1.0 × 10−9−1.0 × 10−8 M with a detection limit of 1.1 × 10−10 M. Based on this finding, a new ECL method for sensing the solution conductance was firstly developed.

Detecting Subtle Plasma Membrane Perturbation in Living Cells Using Second Harmonic Generation Imaging

The requirement of center asymmetry for the creation of second harmonic generation (SHG) signals makes it an attractive technique for visualizing changes in interfacial layers such as the plasma membrane of biological cells. In this article, we explore the use of lipophilic SHG probes to detect minute perturbations in the plasma membrane. Three candidate probes, Di-4-ANEPPDHQ (Di-4), FM4-64, and all-trans-retinol, were evaluated for SHG effectiveness in Jurkat cells. Di-4 proved superior with both strong SHG signal and limited bleaching artifacts. To test whether rapid changes in membrane symmetry could be detected using SHG, we exposed cells to nanosecond-pulsed electric fields, which are believed to cause formation of nanopores in the plasma membrane. Upon nanosecond-pulsed electric fields exposure, we observed an instantaneous drop of ∼50% in SHG signal from the anodic pole of the cell. When compared to the simultaneously acquired fluorescence signals, it appears that the signal change was not due to the probe diffusing out of the membrane or changes in membrane potential or fluidity. We hypothesize that this loss in SHG signal is due to disruption in the interfacial nature of the membrane. The results show that SHG imaging has great potential as a tool for measuring rapid and subtle plasma membrane disturbance in living cells.

Paired Electrochemical Reactions of a Fluorene-Based Conjugated Polymer

Bipolar electrochemistry using a wireless electrode driven by an external electric field from feeder electrodes is attractive because electrochemical oxidation and reduction takes place simultaneously on the same surface of the bipolar electrode with a potential slope between both poles. The redox ability of parent polymer P1 containing fluorenol moiety to form P2 (fluorenone) and P3 (fluorene), which is accompanied by a drastic color change, is expected to exhibit a multi-colored gradient film by the application of a potential slope on the bipolar electrode according to the bipolar polymer reaction. A BDD plate (3 × 3 cm2) covered with P1 was placed between driving stainless electrodes (1 × 4 cm2) in a bipolar cell and a constant current (0.1 mA/cm2) was passed between them in 5 mM Et4NOTs/i-PrOH. After the electrolysis, the emission color of the polymer film under UV-irradiation was a gradation with yellow-blue-dark orange from the cathodic pole to the anodic pole. The gradient polymer film was peeled off from the BDD plate with scotch tape, and divided into three pieces for PL measurements. The PL spectra corresponded well to those of P1-P3. Previous reports on the bipolar electrolysis for producing gradient materials focused only on anodic reaction with sacrificial cathodic reaction or vice versa. This paired bipolar electrolysis successfully provided a new class of composition-gradient polymer film.

Computational modelling of multi-cell migration in a multi-signalling substrate

Cell migration is a vital process in many biological phenomena ranging from wound healing to tissue regeneration. Over the past few years, it has been proven that in addition to cell–cell and cell-substrate mechanical interactions (mechanotaxis), cells can be driven by thermal, chemical and/or electrical stimuli. A numerical model was recently presented by the authors to analyse single cell migration in a multi-signalling substrate. That work is here extended to include multi-cell migration due to cell–cell interaction in a multi-signalling substrate under different conditions. This model is based on balancing the forces that act on the cell population in the presence of different guiding cues. Several numerical experiments are presented to illustrate the effect of different stimuli on the trajectory and final location of the cell population within a 3D heterogeneous multi-signalling substrate. Our findings indicate that although multi-cell migration is relatively similar to single cell migration in some aspects, the associated behaviour is very different. For instance, cell–cell interaction may delay single cell migration towards effective cues while increasing the magnitude of the average net cell traction force as well as the local velocity. Besides, the random movement of a cell within a cell population is slightly greater than that of single cell migration. Moreover, higher electrical field strength causes the cell slug to flatten near the cathode. On the other hand, as with single cell migration, the existence of electrotaxis dominates mechanotaxis, moving the cells to the cathode or anode pole located at the free surface. The numerical results here obtained are qualitatively consistent with related experimental works.

Electrochemiluminescence aptasensor based on bipolar electrode for detection of adenosine in cancer cells

Here we report a novel approach for the detection of adenosine in cancer cells by electrochemiluminescence (ECL) on a wireless indium tin oxide bipolar electrode (BPE). In this approach, ferrocene (Fc) which is labeled on adenosine aptamer is enriched on one pole of the BPE by hybridization with its complementary DNA (ssDNA) and oxidized to Fc+ under an external voltage of 5.0V at the two ends of BPE. Then, a reversed external voltage was added on the BPE, making Fc+ enriched pole as cathode. The presence of Fc+ promotes the oxidation reaction on the anodic pole of the BPE, resulting in a significant increase of ECL intensity using Ru(bpy)32+/tripropylamine (TPA) system as test solution. The presence of target adenosine was reflected by the ECL signal decrease on the anodic pole caused by the target-induced removal of ferrocene-aptamer on the cathodic pole. The decrease of ECL signal was logarithmically linear with the concentration of ATP in a wide range from 1.0fM to 0.10μM. This ECL biosensing system could accurately detect the level of adenosine released from cancer cells.

Integrating bipolar electrochemistry and electrochemiluminescence imaging with microdroplets for chemical analysis

Here we develop a microdroplet sensor based on bipolar electrochemistry and electrochemiluminescence (ECL) imaging. The sensor was constructed with a closed bipolar cell on a hybrid poly(dimethylsioxane) (PDMS)-indium tin oxide (ITO) glass microchip. The ITO microband functions as the bipolar electrode and its two poles are placed in two spatially separate micro-reservoirs predrilled on the PDMS cover. After loading microliter-sized liquid droplets of tris(2,2′-bipyridyl) ruthenium (II)/2-(dibutylamino) ethanol (Ru(bpy)32+/DBAE) and the analyte to the micro-reservoirs, an appropriate external voltage imposed on the driving electrodes could induce the oxidation of Ru(bpy)32+/DBAE and simultaneous reduction of the analyte at the anodic and cathodic poles, respectively. ECL images generated by Ru(bpy)32+/DBAE oxidation at the anodic pole and the electrical current flowing through the bipolar electrode can be recorded for quantitative analyte detection. Several types of quinones were selected as model analytes to demonstrate the sensor performance. Furthermore, the cathodic pole of bipolar electrode can be modified with (3-aminopropyl)triethoxysilane–gold nanoparticles–horseradish peroxidase composites for hydrogen peroxide detection. This microdroplet sensor with a closed bipolar cell can avoid the interference and cross-contamination between analyte solutions and ECL reporting reagents. It is also well adapted for chemical analysis in the incompatible system, e.g., detection of organic compounds insoluble in water by aqueous ECL generation. Moreover, this microdroplet sensor has advantages of simple structure, high sensitivity, fast response and wide dynamic response, providing great promise for chemical and biological analysis.

Parallel Screening of Electrocatalyst Candidates Using Bipolar Electrochemistry

Here we report simultaneous screening of bimetallic electrocatalyst candidates for the oxygen reduction reaction (ORR) using bipolar electrochemistry. The analysis is carried out by dispensing different bimetallic precursor compositions onto the cathodic poles of an array of bipolar electrodes (BPEs) and then heating them in a reducing atmosphere to yield the catalyst candidates. Because BPEs do not require a direct electrical connection for activation, up to 33 electrocatalysts can be screened simultaneously by applying a voltage to the electrolyte solution in which the BPE array is immersed. The screening of the electrocatalyst candidates can be achieved in about 10 min. The current required to drive the ORR arises from oxidation of Cr microbands present at the anodic poles of the BPEs. Therefore, the most effective electrocatalysts result in oxidation (dissolution) of the most microbands, and simply counting the microbands remaining at the end of the screen provides information about the onset potential required to reduce oxygen. Here, we evaluated three Pd-M (M = Au, Co, W) bimetallic electrocatalysts. In principle, arbitrarily large libraries of electrocatalysts can be screened using this approach.