Cathodes

The Cathode has a relatively non demanding job to do in the Chlorate or Perchlorate cell. The reactions that must happen at the Cathode occur easily and most metals are protected by the fact that they are connected to the minus of the supply, (Cathodically protected).
Two unwanted reactions that happens at the Cathode in the Chlorate cell are Hypochlorite and to a lesser extent Chlorate being reduced ie.converted back into Chloride. This is undesirable as it wastes current by destroying the wanted products. Keeping the current density high on the Cathode will decrease the amount of Cathodic reduction of Hypochlorite, therefor Cathodes of excessively large surface area should not be used. (Ullman page 9) Use similar surface area to Anode or smaller and cover the backs of the Cathodes. Using smooth surfaced material helps reduce actual surface area.
Using Titanium metal stops the reduction of Chlorate unlike Iron which reduces Chlorate. Chromates added to the cell also stop Cathodic reduction as do Yttrium(III) compounds. Flourides and Persulphates also. Transition metal ions are responsible for the catalytic reduction of Hypochlorite in the bulk of the cell solution in a Chlorate cell. Therefor it is best to avoid Nickel, Copper, Zinc, Cobalt, etc as a Cathode material.

Cathodes
Titanium	This is a good Cathode material if you can get it. It won't corrode and contaminate the product. The metal and it's hydrides have electro catalytic effect similar to Mild Steel for the evolution of Hydrogen. It also has the advantage of not reducing Chlorate. It lasts about 2 years in commercial cells with Hydrogen embrittlement ending its life. Use Grade 1, 2, 3 or 4. The Grades containing Al are inclined to warp especially at high temperatures. There are reports of thin sheets of Grade one Ti becoming brittle and breaking soon after they are installed in a cell. Use sheets that are at least 1mm thick.
Stainless steel	There are many types of stainless steel. Food grade works good, some of the other grades will corrode a small amount and give your solution a yellow colour. The yellow colour is colloidal Iron and Chromium. The Chromium is bad news when you are using a Lead Dioxide anode as it forms a thin layer on the Anode and drastically reduces the current efficiency. Use a grade that will not corrode at all. Protect exposed surfaces of the SS at the top of the electrolyte using plastic or such like. Don't leave the cathodes in the electrolyte with the power switched off. Grades of SS that are OK are type 347, 316 and food grade SS. Other alloys that are OK are Durimet 20, Hastelloy HB-1, Hastelloy HC-3, Hastelloy C. Don't leave in a cell that is not operational.
Mild steel	This is cheap but it will corrode if you don't have Chromate in the electrolyte to help protect it. You can't use chromate's if you are using Lead Dioxide anodes and as Chromate's will lower current efficiency. Some of the Cathode will have to come up above the solution level so as to get a connection to it. This part should be protected with a plastic sleeve or something similar to stop it corroding in all cells Chromate's or not. The corrosion products are not detrimental to the Chlorate product but you may have a yellow colour (colloidal Iron) that need extra work to get rid of. You must not leave the steel in the cell if it is turned off or it will corrode even more. According to JES Vol.105. No.3 (1958) [bottom of last page] using mild steel drastically reduces current efficiency?. It has been used in industry.
Copper	Copper is OK if you are going to use your Chlorate for bleaching! For all other uses of Chlorate it should be ruled out completely.
Nickel	Nickel can be used as a cathode if you can get it but it will corrode if you don't have Chromate's in the electrolyte for to protect it. It leaves a black mess in the Chlorate cell. It has been used in Perchlorate production. You can't use Chromate's with Lead Dioxide as the current efficiency will be low. You may be able to get Nickel welding rods as a free sample from your welding supply store. In a report from a home producer of Perchlorate, Nickel welding rods when used in a cell that went all the way from Chloride to Perchlorate suffered corrosion. Don't leave in a cell that is not operational. Since it is a transition metal, it's ions will help to reduce Hypochlorite in the solution bulk of a Chlorate cell which is undesirable.
Graphite	Graphite can be used for a Cathode but will blacken your product a small amount in the long run. Leaving them sitting in a cell when it is turned off causes it to corrode somewhat and they shred a bit when the current is turned back on. They make good cathodes if you take them out of the cell when they are not in use and give them a wash. They are a good choice for the Amateur as they will not contaminate your cell with Chromate's if you are using a Lead Dioxide anode. Graphite rods are available as gouging rods from the welding supply store. Remove the copper coating (if they have any) by peeling. Then run in a small cell for a short period and dump contents. This gets rid of all Copper that may have been on the rods after peeling.
Lead metal	Lead has never been used in industrial setup's but would make an easily fabricated Cathode
Lead dioxide	Lead dioxide should NEVER be used as a Cathode as it will dissolve in a short space of time
Platinum	You can use Platinum as a Cathode of you so wish.

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