Hoffman Apparatus for Pure Hydrogen Gas




About: I study Aerospace Engineering at RMIT, in the hope that one day I will be able to bring about the return of intercontinental airship cruises. Until then I like to make stuff in the shed, and surf instructables

I’m sick of hydrocarbons. There are way better gasses out there that do the same job.
Did you know – the original engine by Rudolf Diesel was made to run on peanut oil, and the original T-model Ford was designed for ethanol fuel?
Anyway, enough of that. Before I can think about alternative automobile fuels, I need an efficient way of creating said alternative.

Hydrogen gas has already been used by a number of people and companies as an alternative to petrochemical fuels. The one commonly appearing in the media is the hydrogen fuel cell, whose appearance is similar to a battery (though the inner workings are very different) and produces electricity to power an electric motor.
This, however, requires a whole new car designed specifically for use with a fuel cell.
Unfortunately little known to the wider public, BMW actually has a fleet of cars – regular petrol cars only very slightly modified – running off hydrogen gas as a combustion fuel. They use exactly the same mechanism as if they were running off petrol, but it’s not petrol.

This got me thinking. My car runs on petrol. Perhaps I too could use hydrogen gas and have a car that produces absolutely no CO2 emissions. So this is my first step (don’t get too excited, it’s just a baby step) towards that future.

A Hoffman voltameter, or Hoffman apparatus, uses electrolysis to produce hydrogen and oxygen gasses from water.
By passing a DC electric current through the water (with an electrolyte solute to improve conductivity), energy is put into the water – enough so that the chemical bonds within H2O are broken and it splits and reforms into H2 and O. The O then finds another O that split from another molecule of water and forms O2. Hydrogen gas (H2) forms as bubbles at the negative cathode and oxygen gas (O2) at the positive anode, so if the two electrodes are kept slightly separate, the two gasses can be collected separately and used for good, or evil, depending on personal preference.

The following instructable contains some dangerous chemicals;

- Hydrogen gas (obviously) is a colourless, odourless, highly explosive gas. Never have a naked flame, or anything hotter than 600°, anywhere near your working area. Until you’re ready for the fun part, of course.

- Sulphuric acid is a wonderful electrolyte, but horribly dangerous if handled irresponsibly. It will burn skin and tables and faces, so always handle with the utmost care and always wear safety glasses and natural rubber (not latex) gloves.

- PVC should not be used for any purpose involving compressed gasses. It has a tendency to shatter and splinter when put under pressure. The PVC used in this instructable is simply used as feet for the apparatus and does not come into contact with any kind of pressures above atmospheric.

Step 1: Materials

All of the materials below have been chosen for their resistance to sulphuric acid. If you want to change some of the components in your own design, check the new material for its resistance to H2SO4.

5 mm thick Perspex sheet – around 500mm * 300mm of the stuff

2 high chromium stainless steel plates, 140mm*120mm, bent at 90° 20mm in from the long end. Don’t skimp on quality, you need the high chromium stuff or it will go rusty in minutes.

4 Stainless steel bolts and corresponding nuts ~30mm long and 10mm in diameter

4 Hose clamps – you know, the ones you screw with a screwdriver to tighten

8 Aluminium L bracket 100mm in length

An old bicycle tyre inner tube or other thin natural (not neoprene) rubber sheet

Scrap PVC pipe ~20mm diameter

The end of a PVC pipe threaded on the outside, and corresponding screw cap 50-80mm diameter

And 2 more threaded pipes + caps ~20mm diameter
~1m really thick wire. We’re talking 2+mm diameter of the copper, not including insulation

Two of those battery connectors that you crimp onto the wire, or alligator clamps.

A car battery or something else capable of supplying 12 volts DC an a lot of current. A computer power supply is not suitable, as the amount of current the Hoffman apparatus draws will (and did) blow up the power supply. 12 volts is an arbitrary number, but H2O requires a minimum 5 volts to split, and the higher the voltage, the faster your reaction, but the more heat will be generated. I tried a 50 volt DC converter, but the wires leading from the wall to the converter got unnervingly hot.
1 – 3 litres of sulphuric acid. This is marketed as car battery acid or electrolyte. Sometimes it is sold as industrial strength acid drain cleaner, but so is hydrochloric acid, and you MUST NOT USE HYDROCHLORIC ACID. Instead of the electrolysis producing hydrogen gas and oxygen gas, it will prefer hydrogen and chlorine. Chlorine gas was used in the First World War because it burns soft, moist flesh like lungs and eyes. It was subsequently banned from warfare and labeled inhumane. Go for battery electrolyte. If you get drain cleaner make sure you know for sure it is sulphuric acid.
I say 1-3 litres because, depending on your finances and level of clumsiness, you can choose to buy 1 litre and dilute it with 2 litres of water, or buy 3 litres. Optimum performance comes at a concentration of 31% sulphuric acid by weight. Any more or less and the electrical resistance of the system increases, though not by a huge amount. I diluted my acid to make it safer and cheaper, and ended up with about 12% acid by weight, and I produce (very) roughly 2-3 litres per minute of hydrogen gas.
Other people use safer electrolytes like salt or bicarb soda, but these have drawbacks. Using salt also produces chlorine gas, and bicarb produces carbon dioxide, nullifying the idea of green energy. The other drawback is that these electrolytes are consumed and must be topped up every so often. Sulphuric acid is not consumed in the reaction, so once you’ve bought it, it’s there forever unless you spill it. Therefore, as long as it is handled responsibly, in my opinion, sulphuric acid is the best electrolyte to use.
Sulphuric acid is a colourless liquid when you buy it, but trace amounts of rust from inferior stainless steel have discoloured my batch.

Silicone bathroom sealant (must be silicone, not polymer sealant)

Looooots of araldite (or other) 2 part epoxy glue

----- Things which I used but would suggest NOT using -----
Gas taps from a camping stove. I thought it would be good to be able to turn the gas flow on and off, but it just ended up in me forgetting they were closed, building up too much pressure and bursting a hole in the body of the apparatus. I would suggest open PVC pipes.

Jug plugs. I wanted the wires to be removable to make everything neater when not in use, but the plugs actually turned out to be the weakest link, having the highest resistance of the whole thing and heated up too much. I have since revised the design and clamped the thick wire directly to the electrode bolts. The plugs still pop up in some of the photos though.

Case clamps. I tried to have a removable lid, so I bought some case clamps and tried a number of different gaskets including silicone sealant, inner tube rubber, neoprene gasket, bits of yoga mat, camping mat + inner tube rubber, and then gave up because the clamps couldn’t provide enough force to seal properly and I couldn’t stop it leaking.
I ended up gluing the lid on. Perhaps you could try bolting the lid on evenly all around the edges.

Step 2: Production

NB. This is not an account of the exact process I went through, but rather a list of all the successful steps I took. As such there may be some discrepancies with the pictures, and things like bits of yoga mat or case clamps attached to the apparatus, which I didn’t mention. You can ignore those as in they end they didn’t work and don’t do anything on the final product. The pictures are just there to provide a visual aid and clarification of the written instructions.

This is the cad drawing a made up. It’s not so useful for you, because you can just skip to the end of this instructable to see what it looks like, but it was good for me to get an idea of where to go. I’ve included the  file here as a .STP and .3DXML.

Step 3: Step 1: Main Body

First I cut the Perspex into 4 of 145*140mm rectangles, and 2 of 150*150mm squares. This is to take into account the 5mm thickness, and give me a volume of 140*140*140mm = 3L.
I drilled 4 bolt holes – exactly the same size as the bolts to make a tight fit – into one of the 150*150mm squares that would be the bottom.
After sanding the edges and making everything smooth, I glued the 4 rectangles together using the araldite epoxy so that each side had its 140mm side vertical, and was attached to one other rectangle at its edge and one other on its face. Does that make sense? See the pictures for clarification. Then I glued the bottom on.

To keep the hydrogen and oxygen gasses separate; I added a septum (a sliver of Perspex about 20mm wide) which I glued to the top of the sides. This must be flush with the top of the sides, as it will also glue to the lid to create two separate chambers – one above each electrode.

Step 4: Step 2: Reinforcement and Sealing

I glued on the aluminium L brackets to provide some additional strength to the structure, and sealed the inside edges with silicone sealant.
Pro tip: if you cover your fingers in washing detergent, the sealant will stick to the Perspex but not your fingers! Otherwise it’s very difficult and messy.
*Ignore the silicone around the top of the apparatus in the last photo – that shouldn’t be there

Step 5: Step 3: Outlet Pipes

At this point I used gas taps, but I would suggest NOT using anything that would prevent gas escaping. The apparatus can withstand enough pressure to blow up a balloon, even so much that I cannot break it with all the pressure I can create from my trumpet-playing lungs, but If you prevent the gas escaping completely and forget about it, enough pressure will build up to cause a rupture.

Use PVC pipe with a screw cap or something else that is obvious when closed.

Edit: So you can close the pipes when not in use to prevent acid spills, but make sure they are open when in use!!

I drilled 2 holes in the last piece of Perspex (square) and glued on the gas taps.

Step 6: Step 4: Electrodes

To make sealing washers, I cut 4 circles out of the tire inner tube, and then cut out the centres. Putting these on the outside, between the bolt head and the Perspex bottom, I bolted on the electrodes, L side facing out, so that the electrodes were as close to each other as possible. The bolt holes in the Perspex were 40mm away from each edge. There should only be washers between the bolt head and Perspex, not between nut and electrode, as this is where the electrical connection is made.

Step 7: Step 5: Wire

But how to get the electricity IN there? I crimped the thick wire at one end to battery connectors, and the other end I stripped about 100mm from the end. Winding it around and through, I used the hose clamps to clamp it as tightly as I could to the bolt heads.
Don’t get your wires/bolts mixed up or you will have a short circuit and blow something up. One whole electrode is positive and one is negative, NOT one side of each electrode to each polarity.

At this point you might like to add in a switch or something (as long as it’s a chunky, 10+ amp switch). I just used a clamp to hold the wire on the battery because you need to take it on and off quickly and often.

Step 8: Step 6: Finishing Touches

Finally I drilled a hole and glued on the large threaded pipe as a place to pour in and out the acid. I put it on the bottom so I didn’t expose the brass gas taps to more acid than necessary when filling and emptying, but it didn’t really work anyway. If you’re not using gas taps, you can put it anywhere you like, but if it’s in a corner, it will be easier to pour ALL the acid out.
I also made some legs out of scrap PVC pipe so the bolts don’t touch the ground.

Once I was sure I had done absolutely everything else, and the electrode bolts were done up nice and tightly, I glued on the lid.

Step 9: Step 7: Testing

Now comes the fun… er… calm, composed, and purely scientific…. part.
All in the name of research, it was now time to test the properties of the Hoffman apparatus.
Namely, the explosive properties of the hydrogen produced. In the video below you can see the fruits of my labour, and the power of hydrogen gas. Imagine if all this energy could be harnessed and used for productive purposes (not that what I’m doing isn’t productive) like transport, heating and energy production.
At the moment the car battery I use is charged from power coming out of the wall, but the end goal is to run the Hoffman apparatus on solar or wind energy to be completely green.


Thanks to:

- Iain for helping here and there with bits and bobs, and being the ignition technician during the testing phase, when I wasn’t game enough to stand that close to a litre of highly explosive gas with a lighter in my hand.

- The neighbours for not calling the police

- Dad for supplying the necessary adhesives and fasteners
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115 Discussions


3 years ago on Introduction

squiggy2 Not trying to get off subject, but as far as your output goes, I have made a smaller version of the generator using s\s light switch covers that I got at the hardware store, and increased the output by simply setting the system on top of a speaker with just a hum of soundwaves coming from it. I was thinking perhaps some sort of sonic resonance could help with yours also.. Good Luck. Great post, BTW..


4 years ago on Introduction

Thank you for making a well planned, working device using quality materials and methods. I will keep this instructable as a resource in my own projects. Also, great video, dubstep is indeed amazing.


4 years ago

It shouldn't be co2 you are to worry about, plants take care of that, what you should be worried about is co3 and unburnt fuel.

1 reply

Reply 4 years ago on Introduction

What? CO3 is only produced in things like corona discharges. It's extremely unstable and lasts less than a second. What has it got to do with anything?

Plants do take care of CO2, but not fast enough. We are cutting down all the trees, and producing far to much CO2 for the remaining ones to handle. Have you been following the news over the last decade?

Unburnt fuel lowers the efficiency of your car, but it's not a huge environmental factor at the levels we get today.


5 years ago

I've done this with KOH, and got results, but you could also do this with any salt (although NaCl is crazy hazardous when broken apart)

1 reply

Reply 5 years ago on Introduction

I used to use salt water from the beach, and that's fine for small quantities, but as you said, if you want to do more than a balloon-full, you're in danger of toxic chlorine gas.
Any salt will work, but I like sulphuric acid because it isn't consumed in the reaction. Eventually you will have to replace KOH as the O evolves into oxygen gas, but sulphuric acid lasts forever


6 years ago on Introduction

SInce you are dealing with sulphuric acid, which, as you point out, is a colorless liquid, I thought I might add this bit of wisdom, by that great poet, Anon Y. Mous:

Little Willie was a chemist,
Little Willie is no more.
What he thought was H2O
was H2SO4.


7 years ago on Step 5

do not EVER use PVC wit a gas !! it will burst and splinter ! exteremely dangourous !!

3 replies

Reply 6 years ago on Introduction

Please put not one, but several warnings in your text, so people know the risks for their other projects. The use of PVC is probibited for any gas,even for compressed air

tech industries

7 years ago on Step 6

You may want to consider using inert carbon rods (which can be found inside "super heavy duty" carbon-zinc dry cells) rather than the metal bolts you have posted above. Eventually, no matter the composition of the bolts, if they are metal, the anode will corrode and wind up deposited on the cathode. This is also the reason why batteries use carbon instead (in carbon-zinc ones)- while being excellent conductors, they won't corrode.

1 reply
TeslaBoytech industries

Reply 6 years ago on Step 6

This is not true, Carbon reacts with the oxygen being produced forming carbon dioxide,
And not all metals are reactive.

Amigos el solo hecho de agregar oxigeno a nuestro medio ambiente, es fantástico, el producir hidrógeno por este medio tiene sus riesgos pero aun así tiene sus ganancias, yo estibe trabajando con un generador a base de hidróxido de potasio y ese si que generaba hidrógeno para enfriar un generador eléctrico de 50 MW Mega vatios con 70 amperios y con hidróxido de potasio al 6% con un voltaje de 7 a 12.

Does heating the water (perhaps, using green sources) aid in hydrogen production? Adding energy into the water /may/ cause the bonds to be a bit... weaker, but then, of course, heating is very dangerous near highly flammable gases, like hydrogen!

2 replies

Yep heating would help. But you're right you don't want to have too many hotspots when you're dealing with hydrogen :P The other thing is you don't want the water to evaporate. I actually need to cool my apparatus after extended periods because the water gets close to boiling and I end up collecting small amounts of steam.


Reply 7 years ago on Introduction

If your apparatus were pressurized, the boiling point of the water would be higher, and less cooling, or no cooling, would be needed, to avoid steam production.


7 years ago on Introduction

Mate, love this. A couple of comments:
1. I wanted to do that course in the early 90s but I was too chicken to move to Melbourne from North Queensland lol. I'm now doing an aviation degree in Brisbane - years later!
2. I've got a couple of brief-case style solar panels that supply about 1 - 1.5 amps @ 12v - I reckon they're what I'd run this with, maybe through a regulator.
3. Now that the storage problem is being solved, I reckon hydrogen will be huge, especially as photovoltaics get cheaper. I can see a bigger version of this setup in everyone's house. Maybe outside.
4. Thanks for the instructable!

2 replies

Reply 7 years ago on Introduction

I dunno how it was back then, but these days you would be alone. There are a couple of kids in my class form townsville and longreach.

You could do something with controlling the resistance of the system, but my apparatus draws close on 10 amps, so you'd need a few panels to be able keep the volts up, I'm in the same situation so that's what I'm working on now - i'll post result when I have some.

I'm very much looking forward to hydride storage tanks, and hopefully the decriminalisation of the materials used in them. I'm can't wait until everyone is producing there own fuel at home!
Thank YOU for your support

Cat on my Lapsquiggy2

Reply 7 years ago on Introduction

Hydride storage at home? They're some of the most dangerous chemicals on the planet--explosions even in advanced laboratories are routine. Compressed or liquid hydrogen would probably be safer, albeit marginally.

I think compressed nitrogen is a decent route for energy storage. Sets of tanks can power tesla turbines to generate electricity to produce H2 on demand. Storing large amounts of flammable or reactive compounds is going to elicit an implacable--and warranted--NIMBY response.