Silver chloride electrode

In electrochemical cell notation, the silver chloride electrode is written as, e.g., for an electrolyte solution of KCl 3 M: The corresponding half-reaction can be presented as follows: Which is a summary of these two reactions: AgCl does not form by direct combination of Ag+ and Cl−, rather through the transformation of soluble species AgCln + 1–n (0 ≤ n ≤ 3) first formed from the combination of the Ag+ and Cl− into the solid AgCl phase.

The Nernst equation below shows the dependence of the potential of the silver-silver(I) chloride electrode on the activity or effective concentration of chloride-ions: The exact standard potential given by an IUPACreview paper is +0.22249 V, with a standard deviation of 0.13 mV at 25 °C.

A porous (or fibrous) filter located at/near the tip of the reference electrode allows to establishing a liquid contact between the solution to be measured and the electrolyte solution in equilibrium with the silver chloride (AgCl) coating the Ag(s) surface.

An insulated electrical wire connects the silver rod with the measuring instrument.

Silver chloride electrodes are also used by many applications of biological electrode systems such as biomonitoring sensors as part of electrocardiography (ECG) and electroencephalography (EEG), and in transcutaneous electrical nerve stimulation (TENS) to deliver current.

An important component of the operation is the electrolyte gel applied between the electrode and the tissues.

At the same time, the chloride anions (Cl−) present in the electrolyte solution travel towards the anode (positively charged electrode) where they are precipitated as silver chloride (AgCl) as they bond with the silver cations (Ag+) present onto the Ag(s) electrode surface.

[11][12] When there is an uneven distribution of cations and anions, there will be a small voltage called half-cell potential associated with the current.

In seawater or chlorinated potable water they are usually directly immersed with no separate electrolyte.