I am really experienced about this subject. now let me give experienced of mine. first of all HB, 2B and B. the most abundant graphene layer is located on the 2B pencil leads. however, although HB include less graphene but more pressed and is more orginized that 2B. according to the conductivity of this pencil leads; HB is closer glassy carbon electrode than 2B. to obtain a proper CV results, their conductivity is lesser than fabricated commercialized electrodes so you have to carry out a pretreatment such as you can clean them electrochemically in 1M H2SO4 from -1,2V to 1,2V by using CV until you get superficial cycles , or modified them conducting polymers or other molecules. other problem is modification you can find SEM pictures of pencil leads on the internet but 2B has rough structure therefore adsorption is very easy by using 2B leads especially some conducting polymers or mediators. I believe ıt seems 2B is more useful than HB. of course it depends on your experiments. I hope these informations'll help you.

I guess, you use the pencil as a counter electrode? I have no experience with cyclic voltammetry, but the softer the pencil, the higher is the graphite content and the conductivity. Try 6B, 8B or even softer (if available).

Thanks for the comment .... Some articles have mentioned the harder the lead the better.... others have just used HB .... I have different results with different brands cant really explain why there is so much diversity

I used 0.5 mm HB leads, as working electrodes for sensing purpose. I ran CV by using these electrodes, no noise was observed..

I am really experienced about this subject. now let me give experienced of mine. first of all HB, 2B and B. the most abundant graphene layer is located on the 2B pencil leads. however, although HB include less graphene but more pressed and is more orginized that 2B. according to the conductivity of this pencil leads; HB is closer glassy carbon electrode than 2B. to obtain a proper CV results, their conductivity is lesser than fabricated commercialized electrodes so you have to carry out a pretreatment such as you can clean them electrochemically in 1M H2SO4 from -1,2V to 1,2V by using CV until you get superficial cycles , or modified them conducting polymers or other molecules. other problem is modification you can find SEM pictures of pencil leads on the internet but 2B has rough structure therefore adsorption is very easy by using 2B leads especially some conducting polymers or mediators. I believe ıt seems 2B is more useful than HB. of course it depends on your experiments. I hope these informations'll help you.

Why do you want to use pencil graphite? Is this because it is cheaper?

Is it more convenient to clean between use than alternative electrodes?

I am asking because it is easy to make your own microwire electrodes for instance using carbon, or gold, fibres. You can seal one in a pipette tip. these are cheap too, but give very good sensitivity.

Stan

I agree with Constant M. G. van den Berg of using pipette tip filled with carbon paste mixed with paraffin oil, and a wire such as Ag/AgCl can be used for connection. Suitable electrolyte should be used, while pencil can be used as carbon graphite.

Common pencils (HB) are good enough. We use them for the connection between salt bridge of reference electrode and solution.

I have had good results with the carbon rods that can be obtained from Zn carbon batteries. These need to be cut out from the battery so be careful, wear gloves. Once cleaned with water by sonication these work well as both counter and working electrodes. I also had very good results using CD and DVDs to make silver and gold working electrodes.

I have tried carbon paste mixed with paraffin oil but couldnt obtain a good peak in CV .... am not sure if there is a problem with the pretreatment process or just not using the correct amounts of the mixture ....

Constant M. G. van den Berg could you provide me with more information about the technique please

Kevin Honeychurch .... how can I just extract the rods ?????

You will need to cut open the battery with a suitable saw (care!). Once you have exposed the inner Zn/carbon/electrolyte mixture you can dig out the carbon rod with a spatula or similar. Be careful as this very acidic (gloves). When you have removed the rod from this, clean it in water (sonication) and it is ready to be used. Be care with sawing and the acidic nature of the internal material. Only zinc/carbon batteries have this carbon rod.

Patricia Khashayar: I dont wish to push you in the direction of wire electrodes. If you wish you work with paste electrodes, that is very interesting too. But, you asked how we make the electrodes: take a polypropylene or polyethylene pipette tip, 100 microL type, and push through the hole in the end a gold wire of 10 or 25 micrometer thickness, about 3 cm long. about 1 mm should stick outside. then heat the end of the tip, whilst holding the wire at the back-end so it does not fall out. You need to heat to about 200 oC, can with a soldering iron or a slow-blowing heating gun. that will melt the end of the tip and the wire will be sealed in place. Then you push an electrical cable into the back end of the tip to make a connection. That is all there is to it.

You can read about this in our papers on micro wire electrodes, which include vibrated wires which have even better sensitivity. We mostly use gold wires, but you can of course use carbon fibre or silver wires.

best of luck, Stan

..........however, I think that Stan's method above is properly the better way forward.

You can also have a look at the silver electrodes I made from compact discs and DVDs.

http://eprints.uwe.ac.uk/20905/1/UPD%20Pb%20at%20Ag%20CD-R%20electrode.pdf

Patricia, You can use graphite brush electrodes used to repair two phase DC electric motor.

If you uses pencil graphite you must use HB that has less stone sand.

Graphite from pencils has also some sulphur, then you must burn it using a lighter. I do it usually.

Is there any place I can buy graphite brush electrodes or can I make them in the lab ???

You can buy in RS-international (located at India):

http://in.rsdelivers.com/catalogue/category/variac-brushes/9863.aspx

Tanx :)

While I was using pencil, I had problem developing similar electrodes .... Even when I bought a pencil of a single brand, the result was different .... Didnt u had a similar problem in ur experience?

Graphite is a semiconductor, a little contamination modify the resistivity. The temperature has also great influence.

I used tungsten electrodes used for soldering. They withstands high currents, high temperatures and they resist very well chemical products. It is not needed to use lantanated ones because the result is similar but the cost higher.

If you still need use graphite, use the same product serial. Remember that you should burn them to remove sulphur

http://www.saiweldindia.net/tungsten-electrode.htm

Can I use these electrodes for biomedical research as well as they seem industrial

Titanium is used usually in implants, but I did not used them as electrodes. You should look for biomedical compatibility of both metals

The electrode surface area might be different..... I have used glassy carbon electrode from same manufacturer with 3 mm dia. and these are supposed to be optimized for repeatability. But I found big variability when u test them. An alternative would be to use smaller electrode area....u could mask portions of electrode using tape to get similar geometric surface area.

As I said carbon is a semiconductor, where conductivity vary a lot due a few ions different in one piece from another. The temperature introduces also a great variation in conductivity. I recommend a metal if repeatability is important.

I know this QA line is old, but I would like to point out you to our fresh paper dealing with pencil graphite electrode.

http://dx.doi.org/10.1016/j.jelechem.2016.11.030

Hi Jan

Thats an interesting article. But didnt you have anyproblem with the reproducibility of the results when using these pencils?

Hi Patricia, it depends on what you consider acceptable. For me, the reproducibility was quite OK from electrode to electrode and box to box. For ferricyanide, the EPs were scattered ca 5 mV, not more.