Make Sulfuric Acid by Copper Sulfate Electrolysis




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How to make sulfuric acid by electrolysis of copper using an inert anode. Copper sulfate is very easy to obtain in large quantities at gardening and hardware stores and provides a convenient route to sulfuric acid if the appropriate anode can be obtained.


Warning: This should be done in a well-ventilated area as hydrogen gas build up is explosive. Copper sulfate is toxic and sulfuric acid is corrosive, wear gloves when handling them.


The procedure is extremely simple, just get a copper sulfate solution, insert two electrodes and run a current through them. The anode, the positive electrode, must be an inert material that can withstand extremely oxidizing conditions. Very few materials meet this condition, platinum, lead dioxide, and carbon among them. Other metals, even stainless steel, are quickly destroyed under these conditions and cannot be used. The cathode, the negative electrode, is exposed to reducing conditions so the metal requirements are must less stringent. Copper is the best choice here since it has high electrical conductivity.


When applying power, the current should be adjusted so that corrosion at the positive terminal and bubbling at the negative terminal are both minimized. The bubbling at the negative terminal is hydrogen production and that’s wasted energy that should have gone into reducing the copper sulfate.


After the solution has gone clear, filter off the particles and the clear filtrate is dilute sulfuric acid that can be boiled down to obtain concentrated sulfuric acid. It will have trace amounts of metals but for most purposes this is not an issue.



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    34 Discussions

    xue li

    2 years ago

    so the cathode and anode can be used what types of material when the electrolyte is copper sulfate ?


    7 years ago on Introduction

    once the dil sulfuric acid forms .... shouldn't i be able to dissolve more copper sulfate for further electrolysis??


    7 years ago on Introduction

    As benzeen, I would like to know if gold anodes would work for this. Gold is more electronegative than platinum. That probably means that it would be more difficult to oxidize than platinum. Am I right?

    14 replies

    but it will still dissolve. keep your voltage below 5v to minimise electrode erosion.

    all gold oxides will decompose into gold and oxygen below 160 degrees celcius. gold sulfate which somehow magically forms is too unstable and converts to gold again. but thats just gold troxide, the most stable. its likely it will form lesser oxides which decompose at lower tempuratures.

    If you have a butane torch (purchaseable on ebay for under $3), and a mould, and a source of clean copper sulfate, as well as a fiberglass or cellulose sock to put over your gold rod, you can reuse your gold over and over again!

    asuming though that no oxide drops off, going over the rod with a blowtorch or even a regular cigarette lighter, should destroy all oxide and hopefully it will stick back onto the rod!
    i personally dont know how gold will work, so try it out for yourself, i can guarantee that if you run it at 3v, your results will always be good!

    Lead on the other hand erodes about as fast. best of all the exact same proccess which erodes the lead making it brittle, converts it into lead dioxide which is more inert than platinum (if completely beta), but since it is about 50:50 alpha and beta, the alpha will slowly flake off with the bubbles. over time, but thats about it, and that will take ages!

    When i say inert, i mean inert under these circumstances. unless voltage goes too high, say over 5v, or no current passes through the anode, then it will become lead sulfate.

    I am currently proving my point by using a preused (in making copper sulfate) lead rod to electrolyze some copper sulfate completely into sulfuric acid and copper.

    Hell noo! Are you sure of that? Lead is incredibly cheap! I'll try that later. Even though it is very cheap, it is quite hard to get. At least where I live. But i'll give it a shot. I'm actually waiting for my 5v 50a psu to arrive. Would it work? The voltage is quite low, but the current is pretty high. I've heard of someone saying that lead dioxide are not very good as anodes...At least for chlorate synthesis. Just more one thing: Can I use another electrolyte other than sulfuric acid? That stuff is very hard to get here. We need tons of paper for getting our hands on that. Thank you very much.

    what i did was get some copper sulfate and electrolyze it like nurdrage did, filter it, then it was suitable to use. its only a catalyst, so only very little is needed, also your dead wrong, people i know go through allot of trouble just to get lead dioxide anodes specifically for making chlorate and perchlorate, i dont know where you heard otherwise, but it was wrong!

    Keep in mind though, the lead dioxide coated anode is only been displaced by the lead dioxide, not fully converted, in the same way copper sulfate will do to iron, it only has a surface coating, using it for anything other than electrolyzing copper or magnesium sulfate, will just not work.

    also another electrolyte you can use is nitric acid, but thats it.
    You dont need much sulfuric acid. just a 50ml solution of acid that is about as sour as lemon juice will do it. siphon a little bit from a car battery and your good to go, you can return the acid later.

    also, about that powersupply, try and use a regulator to drop the voltage to 3-4v because these kind of reactions use very little current. more amps wont to skwat!
    Ive been running mine overnight and the amperage hasnt exceeded 1A and it has a 28A potential.

    Will the process get screwed if I use that psu? I'll buy a 3v 1a. I'm not sure of what I'm thinking is correct, but that is okay....Erm....The idea of making lead dioxide coated anodes from lead is just oxidizing it using an electrolysis that generate oxygen gas on the anode, right? There is a large number of electrolytes that, if electrolysed, will release oxygen at the anode. Electrolysis of aqueos sodium bicarbonate will release oxygen at the anode. Can I use that? Electrolysing a solution of copper sulfate will actually release oxygen at the catode as well...That would probably be able to oxidize lead to lead dioxide, right? Would it work?

    since youll never get a current draw over 1A/100ml, a good resistor will work fine to cut down the voltage.

    What i find happens, is that if there is too much bubbling at the cathode, like nurdrage says, you will loose sulfate ions, which generally form sulfur trioxide!.

    Many a time i have detected sulfur like smells coming off my electrolysis , at 5V!

    Also, the answer is no, no other electrolytes short of a few very strong acids harder to get than sulfuric acid.
    it isnt the fact there is oxygen bubbling out. This type of reaction is fairly unique between lead and sulfuric acid, even more so because its the cathode which is going to oxidize, which eventually does though, into lead tetroxide, in carbatteries and such.
    Another thing, dont touch the lead dioxide coating, its alpha and weak, so much bubbling such as with 5v, which rip off the Lead dioxide.

    at 5v i calculated, i lost 30% of the sulfuric acid that there should have been there! at 3.5v i lost almost none!
    just get a 3.5v regulator or proper resistor, dont pass up on the PSU.
    regulator chips only cost $2-3 and thats in packs of 10!

    By the way, the lead dioxide coating, i find i have to reapply once ever day or two, which is ok since it only takes about 5 minutes in a solution of sulfuric acid made from 50ml saturated copper sulfate!
    On 3v, i havent once had to reapply, which is good since i dont have any acid right now!

    how can lead get oxidize at the cathode? Is there any way to avoid lead dioxide oxidize to lead tetroxide? using 3v 1a would reduce its erosion? how would that work? i am really trying to understand the process, but it sounds really confusing....

    I wouldnt bother learning how it works, i didnt.

    Also, lead tetroxide, is Pb2O3, which is NOT a higher state of oxidization, despite having more oxygen.
    PbO2 --- 2 oxygen per Lead
    Pb2O3 ---1.5oxygen per lead

    PbO2 is the higher oxide, and in a cell will not decompose into teroxide, despite what you may see occur when you run the electrolysis. Lead on its own will convert to teroxide, any exposed lead, for obvious reasons will form orange-brown teroxide.

    What happens in a car battery, is, when the battery becomes discharged, the acid , with the aid of the electron flow, can react with the lead, now, both electrodes become lead sulfate coated.
    This will happen automatically even if there is no lead sulfate to begin with, it is really just skipped when there is no sulfate. anyway, imagin it does form sulfate,
    here is the reaction that occures.
    Anode Reaction: PbSO4(s) + H+(aq) + 2e− → Pb(s) + HSO−
    Cathode Reaction: PbSO4(s) + 2H2O(l) → PbO2(s) + HSO−
    4(aq) + 3H+(aq) + 2e−

    In an ideal reaction, no oxygen or hydrogen will escape , which is the case with my current electrolysis, though a small bit of hydrogen is escaping as the copper sulfate levels drop, and it burns my lungs every time i breath in without the fan on (breathing in hydrogen gives a false burning feeling in the lungs much like chlorine, or hydrochloric acid, but not in the nose).

    the reaction that goes on is very unique in the case of sulfuric acid and lead .
    Its best you not worry about it.

    both the anode and cathode are reacting with the acid, the only difference is that the cathode is using oxygen from the water to complete the sulfate - ions, rather than the two which made up the sulfate to begin with

    okay then.... but to coat the electrodes with the lead dioxide, both electrodes are supposed to be lead? oneof the electrodes will become lead dioxide and the other one will become lead sulfate? what current should be applied?

    actually as i said before, it will become coated in lead dioxide, not made of it. neither will become lead sulfate , its hard to explain. its like its constantly forming sulfate and at that moment, converts back, when electrolysing , behaving as if it was sulfate, without ever actually changing. I myself know little about the deep mechanics of all this, i just know whats happening and have an understanding why.

    Also, current limiting is no real problem , just try to keep the voltage below 5v, and let the current do whatever if you are electrolysing less than 200ml water, otherwise try to keep the current under 2A/100ml all asuming youve dissolved as much copper sulfate as possible . no fancy equiptment needed for that though, just move your anode and cathode further apart to lower the current!

    the requirements change with the situation. most often only as much current is drawn that is needed, not as much as the power supply can supply. for example. my powersupply can deliver 28A, but the load is only taking 500mA.

    as a general rule. if its bubbling violently , reduce current or space out the electrodes. no bubbling should be occuring at the cathode. and very little should be occuring at the anode. If you can manage it, use 5v and sace the electrodes really far apart so that the cathode is not bubbling at all. the cell resistance will be cutting the voltage down to about 4v anyway.
    The cathode bubbling is fine though in the first 6 hours or so. after that, try and prevent it, or risk loosing acid. which you can tell by the stench of burning rubber (sulfur dioxide/trioxide).

    Also yes, both electrodes must be lead when making the lead dioxide coating.
    when you are using your lead dioxide coated electrode to electrolyze copper sulfate solution, you should use the lead dioxide coated cathode, as an anode, and copper wire as the cathode.

    one last tip. cover up the container you plan to use!
    I just finished my electrolysis, and i have sulfuric acid spattered everywhere, and sulfuric acid doesnt just dry up like water does. it becomes stronger and stronger, as water evapourates, and then once it hits about 50%, it sucks water from the air (being hygroscopic), and stays that way for a long time! it evaporates at the same rate as vegetable oil, so dont expect it to go anywhere fast!
    also protect your electrical connections, acid is corrosive.....duh!

    fear not, in a few days you'll have an example to copy off!

    Ohh... Electrochemistry is amazing. I'll try that later. I've bought a 3v 1a for this. I was using a 12v 5a and I got bubbling at the cathode that was actually scaring me. I've bought platinum coated electrodes and MMO electrodes. I'll use them to make sulfuric acid and then make the lead dioxide electrode for the time the platinum and the MMO gets weak. Just more one thing. To concentrate sulfuric acid, can I set up a fractional distillation apparatus? Would it yield a good concentration of acid? Which temp should I keep it?

    MMo...oh dear :(

    I dont think the MMO will hold out well against the acid, though platinum will work. and so long as you dont exceed 3v, the platinum will last forever.

    you know how i made my lead dioxide coated anode?
    I got a carbon rod and electrolysed copper sulfate into a 3% solution of sulfuric acid. then i filtered it, and electrolysed the lead and BAM done.

    The reason i use lead with an oxidized layer of lead dioxide is because i dont want to get platinum, if you have platinum, then you dont really need to worry about using lead!
    But if you do want to use lead as an anode, you can tell when all the lead dioxide that can form, has formed, when it turns completely black. having said that, try to keep your amperage very low when making the lead dioxide layer because it is alpha, the weak form of lead dioxide (not like beta, which is what proper lead dioxide anodes are made of). once an hour slightly wipe of the lead dioxide that forms, and eventually you get lead dioxide pores forming which will hold it better.

    To concentrate sulfuric acid, just boil it.
    it boils at 300 celcius,
    i wouldnt risk distilling it because allot would decompose at that heat.
    water boils at 100c, sulfuric acid boils at 300.
    use glass, on an electric stove and youll be fine.

    I've received my platinum electrode today. I'm running the electrolysis with 150g of copper sulfate dissolved in 500ml of distilled water, using aluminum cathode and the platinum anode, runing it on 1.5v 1a. Almost no bubbling on the anode...That is good, right?

    aluminium shouldnt be used, only copper or graphite for the cathode.
    and yes, this is good. more bubbling can be expected as the reaction goes on.

    be sure though to cover up the container the reaction is going on in, since you get acid mist setting everywhere around, even though you cant see it, its happening.

    Aluminium undergoes a displacement reaction with copper that replace aluminium metal with copper metal, and you end up with copper coated aluminium and aluminium sulfate. later as the acid strengthns, it will eat away the aluminium.

    no gas means near 100% effeciency, so yes, it is good.


    it might look like a normal copper plating reaction, its actually not!

    copper sulfate reacts with all more reactive metals (lead, iron, zinc, magnesium, aluminium, potassium, sodium ect), in a displacement reaction, which exchanges the copper in copper sulfate, with the reactive metal, which means you get the surface coated in copper, and a reactive metal in solution will be likely to ruin the anode, as well as affecting the cell current load capacity.
    use copper wire as the cathode, or anything less reactive that iron, excluding all forms of steel!
    nothing but copper , lead or graphite should be left in the cell while it is off.

    take the aluminium out immediately, also, word of warning. this will happen eventually, the solution will bubble a

    that was cool, any hints or tips, on the electoode? would silver work? or can you make a platnium one/ buy it. and how do you make a lead oxide electrode?
    and how could you do this to get magnesium out of magnesium sulphate??

    2 replies

    It won't work with magnesium electrodes. Don't even try it. If any magnesium metal goes into the solution, it will displace copper ions. You will get a deposity of copper metal on the magnesium electrode, and your solution will fill up with magnesium ions. And the idea is that the metal ions are removed from the solution, and so does the hydroxide ions. You will be left with a solution with hydrogen ions and sulfate ions. If you use magnesium sulfate, the magnesium ions won't be reduce, since hydrogen is discharged preferentially. And even if they were discharged, magnesium metal reacts promptly with the sulfuric acid, and goes back do magnesium sulfate. It would not work.

    you can make lead dioxide by electrolysing a lead rod with sulfuric acid. the negative will get coated in black lead dioxide, this is enough to protect it form erosion, so long as current is flowing through and your volage does not exeed 5v. do not use 5v or it will die, you must use 5v or less. 3.5v is best though.