Investigation of the AgCl Formation Mechanism on the Ag Wire Surface for the Fabrication of a Marine Low-Frequency-Electric-Field-Detection Ag/AgCl Sensor Electrode

Abstract

One of the most widely used electric field sensors for low-frequency electric field detection (LFEFD) in seawater uses the Ag/AgCl electrode. The surface structure of the electrode including AgCl layers plays a critical role in the electrode’s electrochemical performance required for the sensor. In this study, the sequential AgCl formation process under the constant current was examined on the Ag wire in an electrode size for actual applications, and an optimal electrode surface structure was suggested for the LFEFD Ag/AgCl sensor. Upon mild anodization (0.2 mA/cm 2 ) in 3.3 M KCl solution that permits us to follow the AgCl formation process manageably, Ag dissolution from the wire surface begins leaving cavities on the surface, with the accompanied growth of initial Ag grains. During this period, AgCl deposits in sizes of about several micrometers to 10 μm with crystal planes also form primarily along scratch lines on the wire surface, but in a partial scale. Then, with further anodization, the assumed thin AgCl deposits start to form, covering a large portion of the wire surface. They grow to become deposits in sizes of about several micrometers to 10 μm with no clear facet planes next to one another and are connected to form the network structure, representing the main developing mode of the AgCl deposits. While they cover all the surface, AgCl deposits also form on the surface of the already formed ones, making multiple AgCl layers. All these deposits develop through the nucleation process with a relatively high surface energy barrier, and their formation rate is solely controlled by the release rate of Ag + from the wire, thus by the applied current magnitude. The Ag/AgCl electrode with a thick AgCl layer and many holes in the AgCl surface structure like microchannels is considered to work effectively for the LFEFD sensor in terms of both detection sensitivity and service lifetime.

Roll-to-roll fabrication of silver/silver chloride coated yarns for dry electrodes and applications in biosignal monitoring

“…The formation of AgCl begins with initial AgCl nuclei formation on preferential sites of the Ag surface, or adsorption of chloride ions through a partial charge transfer with the substrate. This is then followed by the nucleation and growth of the three-dimensional AgCl film in patches across the substrate, until a continuous film is formed 13 , 14 , 17 . This part of the process is thought to be controlled by either interfacial, or diffusion-controlled growth kinetics 14 .…”

Novel Flexible Ag/AgCl Quasi-Reference Electrode with Fishbone Nanowire Structure for Remarkable Potential Stability, Long-Term Reliability, and Noninvasive Electrocardiography

“…To compare the effects of electrochemical chlorination (EC) and chemical chlorination (CC) on the performance of the prepared qREs, a Ag/AgCl qRE was also prepared by CC according to our previous work. , To assure that all qREs were operating at optimal performance, all preparation conditions had been optimized (Figure S2 for EC and Figure S3 for CC). Figure a shows the SEM image of the NP-Ag/AgCl qRE prepared by CC.…”

Modeling the Transient Behavior of Ionic Diodes with the Nernst–Planck–Poisson Equations

“…A typical electrode preparation procedure [ 46 ] of 10 A m −2 for a few minutes forms an AgCl layer with a thickness of ≈1 µm, which stores ≈3.7× 10 3 C m −2 of charge. [ 47 ] Running at this same current density in a diode results in the same lifetime of a few minutes. Like with the capacitive electrodes, this run time can be improved by either increasing the electrode area compared to the junction area or decreasing the current that flows through the diode.…”