Bipolar Electrochemistry Research Articles

Resistance measurements for the wireless evaluation of electrocatalytic activity

Electrochemical water-splitting is one of the key reactions that lay the basis for the storage of energy produced by sustainable sources. The development of fast methods to evaluate the electrocatalytic activity of electrode materials with respect to the oxidation and reduction of water are therefore required to make further progress in this exciting field of research. Here, we present a novel method based on bipolar electrochemistry, which allows evaluating the electrocatalytic activity of a material towards hydrogen and oxygen evolution (HER and OER, respectively) with a single device. This method is based on the capability of a conducting polymer layer to behave as a variable-resistance switch as a function of its electrochemical doping. This approach was used to evaluate the electrocatalytic activity of Au, Pt and Ni surfaces towards HER and OER in terms of the half-wave electric field, ε1/2, obtained during the insulating/conducting transition of poly-3,4-ortho-xylen-dioxythiophene (PXDOT). The trends of ε1/2 variations are in agreement with data reported with classical electrochemical methods. In this work, we developed an easy and straightforward method to evaluate the electrocatalytic activity of electrode materials for water-splitting.

Controlled Patterning of Complex Resistance Gradients in Conducting Polymers with Bipolar Electrochemistry

AbstractConducting polymers have gained considerable attention for the possible design of localized electroactive patterns for microelectronics. In this work, the authors take advantage of the properties of polypyrrole, in synergy with a wireless polarization, triggered by bipolar electrochemistry, to produce localized resistance gradient patterns. The physicochemical modification is caused by the reduction and overoxidation of polypyrrole, which produces highly resistive regions at different positions along the conducting substrate at predefined locations. Due to the outstanding flexibility of polypyrrole, U‐, S‐, and E‐shaped bipolar electrodes can be formed for prove‐of‐concept experiments, and electrochemically modified in order to generate well‐defined resistance gradients. Energy‐dispersive X‐ray spectroscopy analysis of the samples confirms the localized physicochemical modifications. This approach presents as main advantages the wireless nature of bipolar electrochemistry and the possible fine‐tuning of the spatial distribution of the electrochemical modification, in comparison with more conventional patterning methods.

Electric Potential Distribution Inside the Electrolyte during High Voltage Electrolysis

Applying an external potential difference between two electrodes leads to a voltage drop in an ion conducting electrolyte. This drop is particularly large in poorly conducting electrolytes and for high currents. Measuring the electrolyte potential is relevant in electrochemistry, e.g., bipolar electrochemistry, ohmic microscopy, or contact glow discharge electrolysis. Here, we study the course of the electrolyte potential during high voltage electrolysis in an electrolysis cell using two reversible hydrogen electrodes as reference electrodes, placed at different positions in the electrolyte. The electrolysis is performed with a Pt working and stainless steel counter electrode in a KOH solution. A computational COMSOL model is devised which supports the experimentally obtained potential distribution. The influence of the cell geometry on the electrolyte potentials is evaluated. Applying the knowledge of the potential distribution to the formation of a Au oxide surface structure produced during high voltage electrolysis, we find that the amount of oxide formed is related to the current rather than the applied voltage.

Nanoparticle Printing for Microfluidic Applications: Bipolar Electrochemistry and Localized Raman Sensing Spots

The local integration of metal nanoparticle films on 3D-structured polydimethylsiloxane (PDMS)-based microfluidic devices is of high importance for applications including electronics, electrochemistry, electrocatalysis, and localized Raman sensing. Conventional processes to locally deposit and pattern metal nanoparticles require multiple steps and shadow masks, or access to cleanroom facilities, and therefore, are relatively imprecise, or time and cost-ineffective. As an alternative, we present an aerosol-based direct-write method, in which patterns of nanoparticles generated via spark ablation are locally printed with sub-mm size and precision inside of microfluidic structures without the use of lithography or other masking methods. As proof of principle, films of Pt or Ag nanoparticles were printed in the chambers of a multiplexed microfluidic device and successfully used for two different applications: Screening electrochemical activity in a high-throughput fashion, and localized sensing of chemicals via surface-enhanced Raman spectroscopy (SERS). The versatility of the approach will enable the generation of functional microfluidic devices for applications that include sensing, high-throughput screening platforms, and microreactors using catalytically driven chemical conversions.

Bipolar Electrochemical Analysis of Chirality in Complex Media through Miniaturized Stereoselective Light-Emitting Systems

Environmentally relevant contaminants endowed with chirality may include pharmaceutical compounds, flame retardants, perfluoroalkyl chemicals, pesticides, and polychlorinated biphenyls. Despite having similar physicochemical properties, enantiomers may differ in their biochemical interactions with enzymes, receptors, and other chiral molecules leading to different biological responses. In this work, we have designed a wireless miniaturized stereoselective light-emitting system able to qualitatively detect a chiral contaminant (3,4-dihydroxyphenylalanine, DOPA) dissolved in reduced volumes (in the microliters range), through bipolar electrochemistry. The diastereomeric environment was created by mixing the enantiomers of an inherently chiral inductor endowed with helical shape (7,8-dipropyltetrathia[7]helicene) and the chiral probe (DOPA) in micro-solutions of a commercial ionic liquid. The synergy between the inductor, the applied electric field, and the chiral pollutant was transduced by the light emission produced from a miniaturized light-emitting diode (LED) exploited in such an approach as a bipolar electrode.

Wireless Electronic Light Emission: An Introduction to Bipolar Electrochemistry

Electrochemistry is taught in most undergraduate chemistry programs. Although this topic is important for students due to its broad interest in industry (energy, diagnostics, car industry, etc.), they often find it difficult, because it is based on a combination of various physical concepts such as electric fields, interfacial processes or charge and mass transport. Among electrochemical concepts, bipolar electrochemistry is of special interest and might be easier to teach due to a very simple general setup. In this case, an oxidation reaction and a reduction reaction occur at the two ends of a single conductive object exposed to an electric field in solution. Such an object is therefore called a bipolar electrode. The nature of the electrochemical reactions and their amplitude can be tuned by playing with the electric field. The fundamental concepts of bipolar electrochemistry are introduced here with a series of basic experiments designed to be carried out in a standard teaching laboratory. These simple and affordable experiments illustrate the key-parameters driving electrochemical reactions at a bipolar electrode. Their influence can be readily visualized using a cheap, commercially available light emitting diode (LED) acting as the bipolar electrode, which illuminates when the current generated by the electrochemical reactions flows through it. The concept of bipolar electrochemistry with eye-catching experiments enables a good introduction to general electrochemistry. It points out the importance of fundamental aspects such as the electric field or the necessity of an electrolyte and a counter-reaction.

Selective corrosion of β-Sn and intermetallic compounds in an Ag–Sn alloy at different potentials in NaCl and Na2SO4 solutions

The corrosion behavior of β-Sn and intermetallic compounds in Ag–28Sn alloy was investigated by potentiodynamic polarization and bipolar electrochemistry tests. The potential distribution along the bipolar electrode was measured. The results show that the potential distribution is linear along the center of the bipolar electrode. In the Na2SO4 solution Ag4Sn intermetallic compounds preferentially corrode at high potential and β-Sn at low potential; in the NaCl solution, β-Sn preferentially corrodes at both high and low potential. Based on the potential–pH diagram, the selective corrosion mechanism of the Ag–Sn alloy is elucidated.

The Promises and Future Directions of Wireless Stimulation in Biomedical Applications

Wireless stimulation (WS) technologies have been developed as powerful strategies to modulate cellular behaviour and biological activity remotely and noninvasively through wireless manipulation of electrical signal. These WS systems are constructed from the electrically stimulus-responsive materials (magnetoelectric, piezoelectric, optoelectronic, and bipolar electroactive materials) that are triggered by the primary driving force, general like magnetic field, ultrasound, light, and electric field. With a deeper understanding of the integral role of electrical stimulation played in biological cells, tissues, and organs, WS has become the promising technique to work on neural cell stimulation, for either functional or repair effects, and other biological activities including drug release, electroporation and cancer treatment. This paper summarises existing WS systems in accordance with the utilised stimulus-responsive materials. Also, future directions of WS in potential biomedical applications are discussed. Along with the development of emerging techniques such as bipolar electrochemistry and 3D printing, more effective WS systems will be allowed to apply in biosystems with a change of paradigm.

Wireless electrochemical actuation of soft materials towards chiral stimuli.

Different areas of modern chemistry, require wireless systems able to transfer chirality from the molecular to the macroscopic event. The ability to recognize the enantiomers of a chiral analyte is highly desired, since in the majority of cases such molecules present different physico-chemical properties that could lead, eventually, to dangerous or harmful interactions with the environment or the human body. From an electrochemical point of view, enantiomers have the same electrochemical behavior except when they interact in a chiral environment. In this Feature Article, different approaches for the electrochemical recognition of chiral information based on the actuation of conducting polymers are described. Such a dynamic behavior of π-conjugated materials is based on an electrochemically induced shrinking/swelling transition of the polymeric matrix. Since all the systems, described so far in the literature, are achiral and require a direct connection to a power supply, new strategies will be presented in the manuscript, concerning the implementation of chirality in electrochemical actuators and their use in a wireless manner through bipolar electrochemistry. Herein, the synergy between the wireless unconventional actuation and the outstanding enantiorecognition of inherent chiral oligomers is presented as an easy and straightforward read out of chiral information in solution. This approach presents different advantages in comparison to classic electrochemical systems such as its wireless nature and the possible real-time data acquisition.

Current oscillations from bipolar nanopores for statistical monitoring of hydrogen evolution on a confined electrochemical catalyst.

Taking advantage of bipolar electrochemistry and a glass nanopipette, continuous single bubbles can be controlled which are generated and detached from a nanometer-sized area of confined electrochemical catalysts. The observed current oscillations offer opportunities to rapidly collect data for the statistical analysis of single-bubble generation on and departure from the catalysts.

Endogenous and exogenous wireless multimodal light-emitting chemical devices.

Multimodal imaging is a powerful and versatile approach that integrates and correlates multiple optical modalities within a single device. This concept has gained considerable attention due to its potential applications ranging from sensing to medicine. Herein, we develop several wireless multimodal light-emitting chemical systems by coupling two light sources based on different physical principles: electrochemiluminescence (ECL) occurring at the electrode interface and a light-emitting diode (LED) switched on by an electrochemically triggered electron flow. Endogenous (thermodynamically spontaneous redox process) and exogenous (requiring an external power source) bipolar electrochemistry acts as a driving force to trigger both light emissions at different wavelengths. The results presented here interconnect optical imaging and electrochemical reactions, providing a novel and so far unexplored alternative to design autonomous hybrid systems with multimodal and multicolor optical readouts for complex bio-chemical systems.

Bipolar electrochemistry for high throughput screening of localised corrosion in stainless steel rebars

The corrosion performance of stainless steel rebars is assessed by using bipolar electrochemistry. This method produces a quasi-linear potential gradient across the sample, with the technique providing rapid access to test for the nucleation and growth of pits across a wide range of applied potentials. The localised corrosion behaviour and resulting growth kinetics of Types 304L and 316L austenitic stainless steels (ASSs) are compared to Type 2101 and 2205 duplex stainless steels (DSSs). The difference in selective phase dissolution between pitting and trans-passive corrosion in DSSs is compared, with critical pitting potential, pit nucleation numbers, growth kinetics, volume loss, and aspect ratio of these four stainless steels discussed.

Co3O4/carbon felt three‐dimensional electrode promoted electrocatalytic oxidation – peroxymonosulfate system for p‐nitrophenol degradation: effect of radical and non‐radical mechanisms

AbstractBACKGROUNDConventional electrochemical oxidation (EO) processes do not easily activate peroxymonosulfate (PMS) and are susceptible to the effects of electrode size, material and large‐distance two‐dimensional (2D) electrode structures, resulting in low mass transfer efficiency and low electrolytic productivity, limiting their ability to degrade pollutants. It is still a challenge to design and prepare a system and materials to enhance the activation of PMS and the EO process.RESULTSCo3O4‐loaded carbon felt three‐dimensional (3D) electrode material (Co/CF) was prepared and used to construct a 3D electrocatalytic synergistic system (EO‐Co/CF‐PMS). The system combined the advantages of bipolar electrochemistry, three‐dimensional electrochemistry and advanced oxidation processes based on sulfate radical (SR‐AOPs) to facilitate the activation of PMS for degradation of p‐nitrophenol (PNP) in water. In addition, the synergistic system showed excellent pollutant degradation performance, achieving 89.51% PNP degradation in 10 min with an energy consumption of 0.4255 kWh m−3. After being used for four consecutive cycle experiments, the synergistic system still achieved 83% PNP removal. Besides, the EO process also facilitated the Co cycle, resulting in a continuous and efficient degradation of the pollutants. The effects of experimental parameters (initial pH, PMS dose, and applied voltage) on PNP elimination were determined. The results of a reactive oxygen species scavenging experiment and electron spin resonance analysis showed that ·OH, SO4·−, and 1O2 all played a major role in the PNP elimination process.CONCLUSIONSThe research demonstrated that the composite catalyst Co/CF improved the property of the EO process for catalyzing PMS and thus enlarged the practical application of AOPs in pollutant degradation in aqueous solution. © 2022 Society of Chemical Industry (SCI).

High-Throughput Electrosynthesis of Gradient Polypyrrole Film Using a Single-Electrode Electrochemical System

As an effective approach for materials synthesis, bipolar electrochemistry has been earning a renewed interest nowadays thanks to its unique features compared to conventional electrochemistry. Indeed, the wireless mode of electrode reactions and the generation of a gradient potential distribution above the bipolar electrode are among the most appealing qualities of bipolar electrochemistry. In particular, the gradient potential distribution is a highly attractive characteristic for the fabrication of surfaces with gradients in their chemical properties or molecular functionalities. Herein, we report the high-throughput electrosynthesis of gradient polypyrrole films by means of a new electrochemical cell design named the single-electrode electrochemical system (SEES). SEESs are made by attaching an inert plastic board with holes onto an indium tin oxide electrode, constructing multiple microelectrochemical cells on the same electrode. This type of arrangement enables parallel electrochemical reactions to be carried out simultaneously and controlled in a contactless manner by a single electrode. Several experimental conditions for polypyrrole film growth were extensively investigated. Furthermore, the gradient property of the polymer films was evaluated by thickness determination, surface morphology analysis, and contact angle measurements. The use of SEES has been demonstrated as a convenient and cost-effective strategy for high-throughput electrosynthesis and electroanalytical applications and has opened up a new door for gradient film preparation via a rapid condition screening process.

Wireless electromechanical enantio-responsive valves.

Microfluidic valves based on chemically responsive materials have gained considerable attention in recent years. Herein, a wireless enantio-responsive valve triggered by bipolar electrochemistry combined with chiral recognition is reported. A conducting polymer actuator functionalized with the enantiomers of an inherently chiral oligomer was used as bipolar valve to cover a tube loaded with a dye and immersed in a solution containing chiral analytes. When an electric field is applied, the designed actuator shows a reversible cantilever-type deflection, allowing the release of the dye from the reservoir. The tube can be opened and closed by simply switching the polarity of the system. Qualitative results show the successful release of the colorant, driven by chirality and redox reactions occurring at the bipolar valve. The device works well even in the presence of chemically different chiral analytes in the same solution. These systems open up new possibilities in the field of microfluidics, including also controlled drug delivery applications.

Efficient Removal of Mercury from Polluted Aqueous Solutions Using the Wireless Bipolar Electrochemistry Technique.

Mercury represents one of the major toxic pollutants in water that affect human and ecosystem. Extensive efforts have been globally invested to remove mercury using various chemical and electrochemical approaches. In this study, I propose the use of bipolar electrochemistry for the first time for mercury depollution process. Mercury(II) is removed from aqueous solutions by direct electrodeposition on millimeter scale graphite rods held in a bipolar setup. By adjusting the strength of the applied electric field and the number of the graphite rods the efficiency of the system can be controlled. This wireless technique allows the use of multiple graphite rod arrays within the bulk cell which resulted in high removal efficiency (98 %) of Hg2+ ions from the polluted solution. The method is straightforward, green, and efficient. The concept can be adapted to remove other heavy metal ions or electrochemically active contaminants from polluted water as long as their reduction potentials are within the water stability window.

Alternating-current nonlinear electrokinetics in microfluidic insulator-decorated bipolar electrochemistry

We proposed herein a unique method of insulator-decorated bipolar electrochemistry (IDBE), for realizing large-scale separation of bioparticles in microchannels driven by AC dielectrophoresis (DEP). In IDBE, a pair of planar driving electrodes is placed at the bottom of channel sidewalls, between which an array of the rectangular floating electrode (FE) strips without external Ohmic contact are evenly spaced along transversal direction, and a series of insulating dielectric blocks are periodically deposited above all the inter-electrode gaps and in full contact with the channel bottom surface. By creating local field maximum and minimum at multiple sites, IDBE extends well the actuating range of DEP force field from the immediate vicinity of electrode tips in traditional bipolar electrochemistry to current fluid bulk. Considering DEP force plays the dominant role around 1 MHz, we utilize Lagrange particle tracing algorithm to calculate motion trajectories of incoming samples for testing the feasibility of microchip in continuous separation of live and dead yeast cells. By applying suitable voltage parameters, highly efficient DEP sorting is theoretically achievable under a moderate inlet flow rate, where most of the viable yeasts are trapped by positive-DEP to sharp dielectric edges, while all the incoming nonviable yeasts are repelled by negative-DEP to the top surface of both FE and insulating block to form multiple thin beams co-flowing into the channel outlet. The microfluidic device exploiting insulators on bipolar FE effectively expands the actuating range of nonlinear electrodynamics and provides invaluable guidelines for developing flexible electrokinetic frameworks in modern microfluidic systems.

Design of Multiphase Metal Balls via Maskless Localized Anodization Based on Bipolar Electrochemistry

AbstractNanoporous metal‐oxide films formed on some metals and their alloys during anodization are crucial for both basic research and commercial applications. They are used as important materials for various types of device fabrication due to their distinctive solid‐state shapes, such as nanopores and nanotubes. However, preparing nanoporous films using anodization, which is a surface treatment for plate‐like specimens, requires a direct electrical connection to the workpiece. Developing new materials independent of the specimen's shape and size will vary if the need for direct energization is eliminated. Here, bipolar electrochemistry is employed to fabricate two‐phase (insulator–conductor) and three‐phase (insulator–conductor–insulator) aluminum balls by controlling the redox reaction region in an electric field. The aluminum balls are site‐selectively anodized employing a wireless and maskless operation. The multiphase aluminum balls’ versatility is demonstrated in the site‐selective electroless deposition of copper on their exposed regions. Additionally, it is demonstrated that various types of materials, including aluminum and titanium, can be oxidized simultaneously in the same cell.

Bipolar Electrochemical Stimulation Using Conducting Polymers for Wireless Electroceuticals and Future Directions.

Electrochemistry has become a powerful strategy to modulate cellular behavior and biological activity by manipulating electrical signals. Subsequent electrical stimulus-responsive conducting polymers (CPs) have advanced traditional wired electrochemical stimulation (ES) systems and developed wireless cell stimulation systems due to their electroconductivity, biocompatibility, stability, and flexibility. Bipolar electrochemistry (BPE), i.e., wireless electrochemistry, offers an effective pathway to modify wired ES systems into a desirable contactless mode, turning out a potential technique to offer fundamental insights into neural cell stimulation and neural network formation. This review commences with a brief discussion of the BPE technique and also the advantages of a bipolar electrochemical stimulation (BPES) system compared to traditional wired ES systems and other wireless ES systems. Then, the BPES system is elucidated through four aspects: the benefits of BPES, the key factors to establish BPES platforms for cell stimulation, the limits/barriers to overcome for current rigid materials in particular metals-based systems, and a brief overview of the concept proved by CPs-based systems. Furthermore, how to refine the existing BPES system from materials/devices modification that combine CP compositions with 3D fabrication/bioprinting technologies is elaborately discussed as well. Finally, the review ends together with future research directions, picturing the potential of BPES system in biomedical applications.

Bipolar Electrochemistry - A Powerful Tool for Micro/Nano-Electrochemistry.

The understanding of areas for "classical" electrochemistry (including catalysis, electrolysis and sensing) and bio-electrochemistry at the micro/nanoscale are focus on the continued performance facilitations or the exploration of new features. In the recent 20 years, a different mode for driving electrochemistry has been proposed, which is called as bipolar electrochemistry (BPE). BPE has garnered attention owing to the interesting properties: (i) its wireless nature facilitates electrochemical sensing and high throughput analysis; (ii) the gradient potential distribution on the electrodes surface is a useful tool for preparing gradient surfaces and materials. These permit BPE to be used for modification and analytical applications on a micro/nanoscale surface. This review aims to introduce the principle and classification of BPE and BPE at micro/nanoscale; sort out its applications in electrocatalysis, electrosynthesis, electrophoresis, power supply and so on; explain the confined BPE and summarize its analytical application for single entities (single cells, single particles and single molecules), and discuss finally the important direction of micro/nanoscale BPE.