Measurements of Potential on and Current through Bipolar Electrode in U-Type Electrolytic Cell with a Shielding Wall

Abstract

The bipolar electrochemistry in a U-type cell equipped with a shielding wall was investigated in detail using a number of electrochemical measurements for the bipolar electrode (BPE). Measurement of the IR-drop in a U-type cell and the potential on the BPE afforded similar sigmoidal potential distribution profiles at around the shielding wall. The current through the BPE was also measured using a split BPE with and without a conducting polymer on its surface. The conducting polymer film lowered the potential threshold for electrochemical reaction at the anode, but prevented cathodic reactions such as the reduction of contaminant oxygen. These results strongly support our preliminary work on the electrochemical modification of conducting polymers using bipolar electrochemistry.Through their long-standing and important role in industry, bipolar electrodes (BPE), which can involve anodic and cathodic reactions on the same substrate, 1 have become applicable to sensor applications, 2-4 the formation of gradient surfaces 5,6 and the deposition of microstructures. 7-13 In a microfluidic space with a thin conducting substrate, an electric field from a pair of external driving electrodes can induce the BPE to realize anodic and cathodic reactions at both sides. The BPE is driven by IR-drop in the electrolyte, so that a low concentration of electrolyte is favorable to induce BPE under low current (moderate) conditions. Thus, there are thresholds of the electrolytic conditions, such as the concentration of electrolyte and the supply of current between the driving electrodes to induce the BPE. Electrochemical reactions on both poles of the BPE can then generate a current flow. Previous intensive research has investigated the BPE induced in the microfluidic space using both experimental and theoretical approaches. 14,15 The potential gradient distribution is applied on the BPE in a manner proportional to the direction of the electric field.We have previously fabricated a U-type electrolytic cell for a bipolar electrolytic system, in which a BPE is positioned to face to the driving anode and cathode. 16,17 The electric field in the cell is controlled by an insulator shielding wall. The BPE fixing conducting polymers was effectively induced by the supply of a constant current between the driving electrodes, which makes it possible to involve electrochemical reactions such as anodic doping and chlorination of the conducting polymers, depending on the supporting salt used. 16 We have also recently demonstrated gradient surface functionalization of a conducting polymer using an electrogenerated copper (I)-mediated azide-alkyne cycloaddition reaction on a BPE. 18 Interestingly, the behavior of the electrochemical reactions indicated that the potential distribution applied on the BPE in a U-type cell was not proportional, but rather sigmoidal, in contrast to that for the microfluidic cell. However, the actual potential distribution on the BPE has not been studied, and therefore warrants further investigation.The main purpose of thi...

Fabrication of gradient polymer surfaces using bipolar electrochemistry

“…The current that passed between the driving electrodes changed the steepness of the potential slope on the BPE, indicating the significant change in the doped area of the P3MT film. 11 Similarly, the poly(3,4-ethylenedioxythiophene) (PEDOT) film on the BPE exhibited a drastic change in color from deep blue to being rather transparent on its anodic side. For polyaniline (PANI) in 5 mM H 2 SO 4 , a multicolored gradient was observed on the film, depending on the applied potential on the BPE.…”

“…However, we have successfully controlled the potential slope on the BPE by designing a cell configuration that includes insulating walls ( Figure 1). 11,12 Herein, the use of this type of potential distribution is demonstrated for the fabrication of gradients on polymeric materials. Thus, a redox active, conducting polymer film was employed as a substrate on a BPE to directly or indirectly reflect the potential gradients.…”

Electrochemical Post‐Functionalization of Conducting Polymers

“…Many interesting approaches involving reactions of substrates being fixed or deposited on the BPE have been reported with the aim of exploiting this phenomenon for material applications. A typical potential distribution is linear and reflects the linearly applied electric field, although we have successfully controlled the potential slope on the BPE by designing a cell configuration which includes insulating walls (Figure ) . This design makes it possible to synthesize a wide variety of functional materials, as described below.…”

“…As already described, the site‐controlled application of potential to a BPE is possible by careful design of the electrolysis apparatus,[27b] such as in the case of the spot‐bipolar configuration shown in Figure . Using this apparatus, conducting polymer films were prepared on an ITO electrode by electropolymerization.…”

“…To explore more practical applications of bipolar patterning, we prepared an array‐type device in which feeder electrodes could be controlled independently and fabricated a 3 × 3 array device composed of nine independent cathodes and an anode split into four line segments (Figure ). [27b] Electricity was fed to all the anode lines while the electricity supply to the individual cathodes could be manipulated independently. Figure shows the results of chlorination patterning obtained with a P3MT film using the array of driving electrodes; when all of the feeder cathodes were active, nine corresponding yellow spots appeared, one under each cylinder.…”