This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.
This protocol enables the deposition of a smooth single layer of silver chloride with designated coverage on thin film silver electrodes. This is the first time a technique that can precisely control the coverage of single layer silver chloride on thin films of electrode is introduced. To begin, flush the chip using isopropanol followed by DI water.
Pour 0.01 molar hydrochloric acid solution into the acrylic container. Using laboratory clean wipes, wipe dry the macro silver/silver chloride reference electrodes pipette exterior and electrode. Connect the chip and the macro electrodes to the analyzer such that a thin film silver electrode on the chip is defined as the working electrode, the macro silver/silver chloride reference electrode is defined as the reference electrode, and the bare macro silver/silver chloride electrode is defined as the counter-electrode.
Place the macro electrodes into the container. Use Blu-Tack as the lid of the container to anchor the macro electrodes. Place the setup into a Faraday cage.
In the CHI660D software, click on the setup tab in the top left corner of the window. Then click technique, amperometric IT curve and OK to perform cathodic cleaning of the electrodes. In the popup menu, modify the parameters for cathodic cleaning.
Set the initial voltage as minus 1.5, the sample interval as 0.1 seconds, the run time as 900 seconds, the quiet time as zero second, and the scales during run as one. For an 80 micrometers by 80 micrometers electrode, set the sensitivity as one e minus 006. Press OK.Start the process by pressing the start icon under the menu bar.
Let the experiment run and finish. Open the Faraday cage, remove the macro reference and counter-electrodes and wipe them dry. Pour the used electrolyte in a waste container and flush the acrylic container using DI water.
Pour 0.1 molar potassium chloride solution into the acrylic container. Connect the chip and the macro electrodes to the analyzer such that the cleaned thin film silver electrode on the chip is defined as the working electrode, the macro silver/silver chloride reference electrode is defined as the reference electrode, and the bare macro silver/silver chloride electrode is defined as the counter-electrode. Place the macro electrodes into the container.
Use Blu-Tack as the lid of the container to anchor the macro electrodes. Place the setup into a Faraday cage. In the CHI660D software, click on the setup tab at the top left corner of the window, click technique, chronopotentiometry, and OK to perform galvanostatic fabrication of single layer silver chloride on the silver electrodes.
In the popup menu, modify the parameters. Set the cathodic current as zero amps. Set the anodic current such that the current density applied to the thin film electrode is 0.5 milliamps per square centimeter.
Keep the high end low voltage limit and hold time as default. Set the cathodic time as 10 seconds. Set the anodic time correspondingly to achieve the degree of silver chloride coverage needed.
Set the initial polarity as anodic, the data storage interval as 0.1 seconds, the number of segments as one, and the current switching priority as time. Uncheck the auxiliary signal recording when sample interval is greater than or equal to 0.0005 seconds. Press OK.Start the process by pressing the start icon under the menu bar.
Let the experiment run and finish. Open the Faraday cage and remove the macro reference and counter-electrodes and wipe dry their surfaces. Submerge the macro electrodes in 3.5 molar potassium chloride solution for storage.
Then discard the used electrolyte in a waste container and flush the acrylic container using DI water. Cover the opening of the acrylic container using paraffin film until ready to use. This image shows an 80 micrometer by 80 micrometer silver/silver chloride electrode with a designed silver chloride coverage of 50%There was a clumping of adjacent silver chloride particles, but stacked silver chloride particles were not observed.
A distinctive silver/silver chloride intersection could be seen. More successful examples of thin film silver/silver chloride electrodes fabricated are shown here. 80 micrometer by 80 micrometer electrodes with a designated silver chloride coverage of 70%and 30%together with 160 micrometer by 160 micrometer electrodes with a designated silver chloride coverage of 75%and 90%Shown here is a polished electrode surface and an unpolished electrode surface.
For the unpolished electrode, finger-like structures were observed on the surface whereas the polished electrode surface is smooth with minor scratch marks caused by the polishing process. Here is an unpolished 80 micrometer by 80 micrometer silver/silver chloride electrode with a designed silver chloride coverage of 50%The silver chloride formed appeared to be recessed inwards instead of protruding outwards. When forming the silver chloride layer on electrodes of different surface areas, it's important to remember to retune the applied current to maintain the same current density.
This protocol enables researchers to the assigned thin film silver/silver chloride electrodes for impedance sensing as a previous research demonstrated that the silver/silver chloride electrodes impedance depend on silver chloride coverage.
