As I stated in the last sentence of my previous reply, it is not necessary to leave a portion of the Ag uncoated with AgCl. It is fine to coat the entire Ag surface with AgCl.

Hi Abu

I am not sure if I understood your question.

By the title it sound like you want to know how to make it:

https://www.youtube.com/watch?v=xM-YsiFnJ1I

http://pubs.acs.org/doi/abs/10.1021/ed077p97

And other ways like polarization in 0.1M HCl.

But if you are asking what is the AgCl for, so this is the "junction" that determine the potential, + if you do not have silver the electrode is just almost insoluble highly insulating salt so it is not mch of an electrode any more.

As titled in your question, it is a Ag/AgCl reference electrode and therefore silver metal is a required component of the electrode. Thus it is necessary to be present to form the electrode couple and also to serve as the electron conductor. If you tried to completely convert all of the silver to the chloride, it would probably disintegrate since silver chloride would not have  support from the metal. In addition, if used in a 3-electrode amperometric system, or potentiometrically, there is negligible current flow through the reference electrode and thus little conversion of the Ag or AgCl occurs. Finally, you do not need an unchloridized portion of the silver wire because the AgCl is sufficiently porous that the solution will make contact with the Ag.

Thank you

I think the title is misleading- sorry for that. It should have been "Is it necessary to leave a portion of Ag not coated with AgCl in Ag/AgCl reference electrode? Or it is fine to coat the whole Ag?"

As I stated in the last sentence of my previous reply, it is not necessary to leave a portion of the Ag uncoated with AgCl. It is fine to coat the entire Ag surface with AgCl.

Correct.  The Ag portion outside of the solution need not be coated; especially the portion where electrical connection is made.

The silver should be immersed in silver chloride solution, which can be housed in a small test tube

Richard Durst knows all. It is good to see his name here.  If you just stick a silver wire in a solution containing chloride, you will have such a reference electrode that is good enough for many analytical purposes (voltammetry), but not good enough for potentiometry or other thermodynamic purposes.   There are many issues to deal with if the solution contains nonaqueous solvents, other halides, cyanide ion, or the temperature is uncontrolled.  Most of this is well described in standard texts. There are further problems if the circuit draws current via a very small surface area electrode such as one implanted in biological tissue or even a single cell.

Silver-silver halide reference electrodes were nicely covered in the 1961 book by Ives and Janz. I don't have a copy at  hand but I noted in my thesis that it was chapter 4, pages 179-230. Might be worth seeing if you can get hold of a copy.

https://books.google.fi/books/about/Reference_Electrodes_Theory_and_Practice.html?id=9PUhMwEACAAJ&redir_esc=y

I found that book helpful as I used Ag/AgCl pseudo-reference electrodes in my postgrad studies, I prepared them by anodising coiled 1mm diameter silver wires against a Pt mesh in sat. KCl soln. using a small battery (9V as I recall). The silver surface darkens and gets a dull, matt finish.

As others said, you don't need to leave silver exposed for the immersed part of the electrode, just at the other end where you will make your electrical connection.

When you test the potential with a voltmeter against an SCE in KCl the difference should be around 40mV (off the top of my head - in my thesis I told that Ag/AgCl wire electrodes were prepared "as described elsewhere" and referenced Ives & Janz).

I just checked your library catalogue, you have a copy of Ives & Janz

https://troy.lib.sfu.ca/search~S1?/aives/aives/1%2C92%2C1051%2CB/frameset&FF=aives+david+j+g&2%2C%2C2

While the chapter by Janz in the book you cited is excellent, another more-recent book worth consulting is Roger Bates' 1973 book, "Determination of pH, Theory and Practice", which has a very detailed section on Ag/AgCl reference electrodes.  Back in the day, every analytical chemist had, or should have had, this monograph.

There are few under 70 who understand how a pH meter works. Perhaps none at the level of Roger Bates.  :)  Roger was not distracted by LinkedIn, Twitter or Research Gate.. He was able to concentrate on the science.

Point well taken, Pete.  Perhaps we should discontinue this discourse and get back to the lab bench.  ;-)

Hi all, Thank you for your help. Being a Mechanical Engineer graduate, it is pretty hard for me to deal with the chemical and chemistry stuff. I really appreciate your time.

Dear Mr. Abrar, we recently published an article about manufacturing of a solid-state reference electrode based on Ag/AgCl particles for potentiometry. It is an alternative method. The electrode worked very well. You can download the paper in my profile or on link: http://www.j-sens-sens-syst.net/4/53/2015/jsss-4-53-2015.pdf. However, the best review about subject is: Guth, U., Gerlach, F., Decker, M., Oelßner, W., and Vonau, W.: Solid-state reference electrodes for potentiometric sensors, J.Solid State Electrochem., 13, 27–39, 2009. I hope this answer helps you. Kind regards. 

Hi! Michael,

As you said "The silver surface darkens and gets a dull, matt finish.", do you mean a kind of purple coating?

I tried anodising a Ag wire in KCl a.q. (Pt plate as the counter electrode) and saw the purple coating. Usually AgCl is white. What is the purple coating?

After a period of using the home-made Ag/AgCl electrode, the color changed from purple to light yellow to white. What occured during this process?

And, I ever tried anodising a Ag wire in HCl a.q. and saw opaque white precipitate falling off the surface of Ag wire. I think the white substabce should be the AgCl which seems could not adsorb firmly on the Ag wire.

Has anyone any success with SSRE solid state reference electrodes? i've tried a few and they are never anywhere near a standard ag/agcl KCL filled ref

some success, we use it on our biosensor for example - https://www.zimmerpeacocktech.com/products/electrochemical-sensors/oxygen-sensors/