Introduction: Hoffman Apparatus for Pure Hydrogen Gas

Picture of Hoffman Apparatus for Pure Hydrogen Gas

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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


Ruslzplace (author)2015-07-26

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..

Nighthaw made it! (author)2015-05-28

I was having a problem finding a battery to use. so an inexpensive alternative that won't run down is a car battery charger, works much better as it can also produce the massive amounts of current. also I used cheaper threaded metal rods and they did start rusting, however their low cost makes them much more affordable and easier to replace

v-raze (author)2015-01-08

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.

3of5 (author)2014-10-31

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.

squiggy2 (author)3of52014-11-03

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.

eteal111 (author)2013-10-13

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)

squiggy2 (author)eteal1112013-10-13

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

RangerJ (author)2013-03-25

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.

hygicell (author)2012-05-27

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

squiggy2 (author)hygicell2012-11-09

You're 100% right. I've edited this step

hygicell (author)squiggy22012-11-09

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

TeslaBoy (author)hygicell2012-11-09


tech industries (author)2012-06-04

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.

TeslaBoy (author)tech industries2012-11-09

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

Hernando Rebolledo (author)2012-08-01

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.

nutsandbolts_64 (author)2012-07-03

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!

squiggy2 (author)nutsandbolts_642012-07-03

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.

bgoldberg1 (author)squiggy22012-07-15

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.

hogey74 (author)2012-05-28

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!

squiggy2 (author)hogey742012-05-29

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 Lap (author)squiggy22012-05-29

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.

hogey74 (author)Cat on my Lap2012-05-29

While not available now, I've been reading about work on new means of storing hydrogen using a catalyst/matrix-filled tank that won't vent hydrogen even when punctured. That's what I'm talking about - something a few years off. It's apparently safe enough that it could be built into the chassis rails of cars etc. I'm expecting that the energy density of this new type of hydrogen storage will be superior to electrical batteries and that this might tip things towards hydrogen as a fuel for mobile applications.

I've heard and thought about the compressed gas battery concept too. It maybe well be the case that new houses in future start with an excavation for storage tanks. have you also seen the British work on liquid air powered reciprocating engined cars? It's actually quite exciting the energy density they are getting and it's something that could also be done using household photovoltaics, wind etc.

Cat on my Lap (author)hogey742012-05-31

Liquid air is essentially liquid nitrogen, which is what I was suggesting. Do you have any sources for the catalyst/matrix mix they're using? Hydrogen venting isn't the only problem. Exposing the matrix to low amounts of oxygen can elicit a potent reaction.

I'm guessing they'd use MgH2 as a storage source, since it's far less pyrophoric than AlH4 or LiH. This paper seems to have some good ideas going for it--a self-sustaining reaction producing three moles of gaseous hydrogen for one mole of water once it's started. Still has the problem of having 60+ L of 300 C hydrogen gas shooting around, though.


hogey74 (author)Cat on my Lap2012-06-17

Hey nice link - never heard of that process. It's not the one I'm thinking of though - the H2 was/is stored as H2. Will keep digging...

DIY-Guy (author)Cat on my Lap2012-06-08

I like your instructable. Keep going for it! You should be the one to perfect it and place it into the public domain for the common man. Three cheers to Squiggy2 for effort and determination! And may you have many long years of life to achieve many great things.

(On a slightly discontented note; I remember how the press popularized some of these amazing things many decades ago when I was young.)
This metal hydride storage for low pressure Hydrogen gas has been announced as "just around the corner" for decades. I'm old enough to remember when this was a new idea waaaaay back when. Just where are those flying cars they also promised us?

hogey74 (author)Cat on my Lap2012-06-01

Hey now you ask, I'm trying to remember where I saw this. Might have been in a New Scientist mag? I'll do some googling and get back to you. Whatever it was, the hydrogen was not released unless a small amount of heat was applied. Not enough heat to make the process useless. I specifically remember that puncturing the container did not vent gas or create other hazards...

hogey74 (author)squiggy22012-05-29

Yeah not surprised but back then, Melbourne seemed a loooooong way away :-)

PV power really needs 4 of 5 kilowatts to power a house with spare capacity for energy storage. I like the idea of constructing a rig like yours and slowly accruing some more PV power to make a little test system with a little hydrogen tank that can run something. 10 amps? I'm about a 3rd of the way there.

BTW I've been sketching an RC blimp recently that could use that hydrogen... I'm going to call it the Hoganburg

squiggy2 (author)hogey742012-05-30

ooh ooh I've been doing the same thing! An RC blimp was sort of a side reason to get this hydrogen going. When you finish it I'd love to see the plans! (assuming you're not going to patent it :P)

hogey74 (author)squiggy22012-06-01

ha ha great minds thinking alike! re - patent, nah, I'd say there's just a bit of "prior art" lol. I met a guy recently who has done world record home made helium balloons (as in, for real people) and I'm talking to him about this stuff ... I'll chuck ur details in my little hoganberg folder and flick you a message :-) I'm thinking balsa for the internal structure but it might start out as a blimp. btw lots of cheap, awesome, old-school RC gear on US ebay ...

Mykulitz (author)2012-06-09

I've been with this project before... The main reason why I didn't continue was not practical to be done... It consumed a lot of electrical energy just to produce a small amount of hydrogen gas... Why not using DC electrical motor instead... If you will use this as a fuel for stove it will very expensive unless you have your own power source... One more thing, I already heard that there's a kind of car today that can be run by using a 12v battery at the speed of 40km/h and if you run beyond that speed the gasoline engine will take over to run the car.. that one is cool... Your project was really amazing... Keep go on until you perfect it. If you can increase the production rate of the hydrogen by a minimal use of electric power that will be more amazing... Just believe for what you can do... Keep researching...

itzsnitz (author)2012-06-01

I have a thought experiment for you:

Assuming you had an infinite source of electrical energy available on vehicle (not produced by engine), how large would your device need to be in order to produce enough fuel to supply the needs of a vehicle at highway speeds?

Here are some assumptions to work from:

An energy consumption rate of 6MJ/min is required to maintain your vehicle's on highway speed (assumed be to 60MPH). The energy efficiency of your engine is around 15 MJ/kg for hydrogen fuel consumption (surely there's a better fuel specific unit, eh?).

1. How much gas must you produce per minute to keep your speed?
2. What size of electrode is required for this production rate?
3. What volume of water/acid is required for this production rate?

Your results will likely be on the order of, "Huge". The question then becomes, how can you reduce the size of your fuel cell while maintaining production rate, eliminating the need for storage system entirely?

Of course, there's still that "endless on vehicle electrical energy" problem, but I'm sure someone will figure that out! ;P

billhorvath (author)2012-05-30

The guys behind United Nuclear have been working on this problem. See

squiggy2 (author)billhorvath2012-05-31

Ah that's what they're called. I saw these guys a couple of years ago but forgot their name. It's a shame that they've been held up by the difficulty of getting the material they require. Perhaps we in Australia might be able to get our hands on them. I'm going to Nanjing in September, I'll see who I can talk to :P

HBSkirmit (author)2012-05-27

I've built several of these hydrogen generators and found that the law of physics hold true: you can never produce more power output than you put into it. You might be able to gain a few extra miles per gallon on a vehicle by using a combination of the hydrogen generator, oxygen sensor enhancers and mass air flow enhancer.
Also, the maintenance and upkeep required to keep the hydrogen tank clean and full of liquid are just not worth the effort. There are internet sites that explain the difference between hydrogen and gasoline. Gasoline has a longer "burnability" time during the combustion explosion, ascompared with the almost instant explosion of hydrogen. Someone will eventually build a great hydrogen generator, or engine that will work with it. Hope it's you Squiggy !

bac512 (author)HBSkirmit2012-05-28

See, that's the major thing holding back hydrogen generator development! 'you can never produce more power out than you put in!' Well no 'you cannot change the laws of physics!' . See my comment below.
I *DO* think most/all of the current attempts are less cost-effective than gasoline engine, I've never built one, but from what I THINK I know about them, you'd have to buy the sulfuric acid (which is a WHOLE lot more expensive than gas)... Does that REALLY last forever?
lets assume that lasts FOREVER, and you just have to add water.
Do you have to use distilled water, which costs about a dollar a gallon, but what is it's power output compared to gas? I've READ that it's MORE than gasoline (fumes for those who want to get technical) but my little 2.0L engine (800 RPM Idle) takes 28.25 CFM of air. at 14:1 compression, that means I need 2.02 CFM or fuel (compression is different for hydrogen than gas, so this figure will differ). or 4.54 CFM if I'm actually RUNNING the engine (1800RPM)... Can it produce this much (further reading says hydrogen needs 4 times the volume of gas, so 18.16 CFM)
If we use regular tap water, does the sulfuric acid need to be filtered every so often?
how much excess energy does the alternator create? can we run multiple Hoffman Apparatuses with that excess power without overloading the alternator?

squiggy2 (author)bac5122012-05-29

The idea is not to run the apparatus from the alternator - that would indeed break physics. My plan is to have it bubbling away at home from solar panels and fill up a tank, then plug that tank into my car when I come home.

1. Yes the acid really does last forever. It's about $7 per litre here in Australia from Autobarn. I just bought 1 litre, and it will be there or the life of the apparatus

2. I use rain water for my proof of concept, and I think it should be fine for large scale too, but if you wanted to you could use distilled water. 1L of water makes 24.5L of H2, so that works out to just over 4c per gallon.

3. If you just swapped your petrol tank for a hydrogen gas tank, you would get about 85% the power of petrol, compared to propane which puts out about 75% power.
However, if you go to the effort to install a direct injection system, power output can be increased to up to 15% more than petrol

im3733 (author)squiggy22012-05-29

It may be worth pointing out that the reason that the sulfuric acid lasts (theoretically) forever is because it does not actually participate in the electrolysis, it merely acts as a catalyst, lowering the activation energy of the water, allowing it to react easier.

When you stated using "high chromium stainless steel plates", what grade were/are you referring to? I'm woefully unfamiliar with steel grades and what they mean.

Also, what is your theory on using both the oxygen and the hydrogen as fuel? Both are flammable, would the resulting energy output be really any different? Obviously the result of burning both simultaneously would be water vapor, and some condensation is guaranteed, which could be problematic eventually.

im3733 (author)im37332012-05-29

Correcting myself here. " merely acts as a catalyst, lowering the activation energy of the water, allowing it to react easier" isn't quite right.

What the acid actually does is increase the conductivity of the water, because pure H2O is not a conductor, it only can conduct electricity because of impurities, which is accomplished through the addition of sulfuric acid.

However, my previous statement, that the acid is not actually used up in the reaction, still stands.

That said, it would be better to use distilled water than tap water, because tap water (in the US, at least) is treated with chlorine and other nasty chemicals that you do not want to end up coming in contact with in any quantity (the little bit dissolved in water is harmless, usually).

squiggy2 (author)im37332012-05-29

That's right, the sulphuric acid is just an electrolyte to allow the flow of current through water. Other electrolytes, however, like salt, are preferred in the electrolysis reaction and split instead of the water.

I use rain water to avoid things like chlorine and fluorine in tap water, but if you wanted to do it absolutely you should use distilled water.

To be honest I don't know much about steel grades either as far as naming and production and things, but I do know the effects of alloying elements to steel. The chromium is what stops stainless steel from rusting. Officially "stainless" means at least 12% chromium composition, but this is the bare minimum and will still rust under extreme conditions. Medical grade stainless is up around 30% chromium. This would cost a bomb if you wanted to buy a couple of plates, but use your discretion to get something in between. The higher the chromium content, the less it wiil corrode

squiggy2 (author)squiggy22012-05-31

Ah I must correct you there.
One of the greatest misconceptions about oxygen is that it is flammable. Oxygen is not flammable. Oxygen facilitates combustion of fuels, but if you apply heat to pure oxygen, nothing will happen. If you apply oxygen to an already burning fuel, it will increase the rate of combustion - sometimes dangerously so - but that does not mean it itself is flammable.

That aside, your question was "why don't you use both the hydrogen and oxygen together?"
You're right, I could use both, which would give me a perfect stoichiometric ratio and best efficiency. But to do that I would need to compress and carry 2 fuel tanks. twice as much fuel. The air all around us is 21% oxygen - why not use that?
And we do. That's what cars use to combust their fuel.

The main losses in energy come from the electrical resistance of the system and overvoltage required to split the water molecules. Not the fact that i'm only using half the product, so to carry oxygen really is more effort than it's worth when there's plenty of it in the atmosphere

bac512 (author)squiggy22012-05-30

I missed how much volt/amperage this device took, but no, running it from the alternator would NOT be breaking physics. Breaking physics would be if you used only sulfuric acid in the tank, and could run the this thing forever, with it's only power being itself. You're adding water ('fuel'), so you've got some extra input there. Storing hydrogen is kinda dangerous...

1) good to know, but I do believe your plates are slowly 'disappearing' (for lack of the correct term.) also...

2) how FAST does it generate the H2?

Now mind you, I am *NOT* against this idea. I've always thought this sounded like a good idea, I'm just currently too lazy to build one/lack an engine to 'adapt'.. I'm just trying to point out to all the people who say 'you can't get more out than you put in' that THAT IS NOT THE CASE. you're using the energy in water, and (I'm pretty sure) your plates will degrade. It SHOULD be possible to generate MORE ELECTRICITY than you put in (again, because you're using additional fuel (I say that over and over to again, try to drive that point home to those who don't understand that MORE is coming from the other sources, not being 'magically created'))

ronv2 (author)2012-05-30

I understand using platinum (etc.) as electrode material catalyses the electrolysis and so less waste heat is produced. This of course is pretty expensive, but does anyone have any experience with using material from an automobile catalytic converter (from a wreck?) in this sort of application?

AndyPipkin (author)2012-05-27

You don't get something for nothing, your car engine makes the electricity to run the cell in the first place, using more fuel and also puts load on the alternator and wears that out too. Charge batteries off a solar panel and you are getting there I guess. Don't get me wrong here, not knocking it, it's all interesting to me!

bac512 (author)AndyPipkin2012-05-28

In actuality, an alternator always puts out the same voltage/current at (whatever RPM). it produces MORE energy than it needs, and the regulator turns that into heat. So, USING that excess energy to create more 'fuel' is going to keep the alternator cooler, and extend it's life. (Does this make it 'perpetual'? Or 'Over-unity'? No. There's still fuel involved, which he says the sulfuric acid will stay 'forever', you still have to add water. Plus the inertia of the car moving also decreases the energy used by the engine.) people want to argue that this IS NOT as 'efficient' as gasoline, or even all-electric cars. Maybe not. But it is 'greener' (no emissions from charging or running it). Input is water, which covers 80% of the earth, plus the engine output is steam (and/or water) which eventually makes it back to water PLUS, it's cleaner. So, efficiency is not really an issue.
FYI-- HEAT is the END RESULT of ANY ACTION. So, is it really any wonder the earth is heating up?

Linksep (author)bac5122012-05-29

You're confusing a permanent magnet generator with an alternator. A permanent magnet generator will output a fixed wattage for a given RPM, however an alternator puts out variable wattage based on load. When there is very little electrical load the regulator reduces the power going to the rotor which reduces the strength of the magnetic field which reduces the alternators output as well as the power required to spin the alternator. As electrical demand increases (voltage drops) the regulator increases the power going through the rotor which increases the strength of the magnetic field which causes higher wattage output (and more input power required to turn the alternator). If you don't believe me and you have a car with a small engine: While the engine is idling with every electrical load turned off that you possibly can; turn on every electrical accessory you can simultaneously (might need a helper to flip switches)... High-beam headlights, rear window defroster, seat heaters on high, HVAC fan to max speed (without the AC on, just the fan).... your engine speed will decrease momentarily (until the idle speed controller adjusts) due to the increased load on the alternator. In my little 4-cyl car I can hear and feel the engine bog down for a second just from turning on the rear window defroster alone (20 Amps draw @14.4 volts = 288 watts; 746 watts per horsepower means it takes 0.4 HP extra just to run my defroster).

Jakwiebus (author)2012-05-25

this is a awesome build,
but not any old hydrogen producing machine is a Hoffman apparatus. I suggest you change the title to "hydrogen fuel cell for pure hydrogen gas"
'cause thats what this is. a fuel cell, not a advanced chemical apparatus capable of collecting accurate volumes of hydrogen.

don't understand me wrong, as a person who likes green energy sources I say this is awesome.
as a chemist I say: this is a fuel cell. ;-)

squiggy2 (author)Jakwiebus2012-05-26

But is it still a fuel cell if it converts electricity to chemical energy? I thought a fuel cell was only chemical energy to electricity

I'm jumping in, so forgive me if I'm repeating what has already been said.

A fuel cell is a electrochemical cell that produces electricity using redox reactions. The difference between standard electrochemical cells is that they are "refilled" with the chemicals to be reduced and/or oxidized.

A rechargeable cell (battery) is (generally) sealed and contains all reactants electrolytes and eventual reaction products and reacharges by applying an electrical current, pushing products of the reaction back towards reactants.

A primary cell is (generally) sealed and cannot be reacharged, generally due to design limitations.

Burning hydrogen utilizes heat to start the chemical reaction (in this case) between hydrogen and oxygen.  It is less efficient (because it is a heat engine - c.f. Carnot) than a fuel cell, but is much easier to construct, because you don't have to figure out the ion exchange mechanism necessary to keep the reaction going.

This is none of these.  It is a hydrogen generator.  I think that, given it's configuration, and use of H2SO4 as an electrolyte, it is reasonable to call this a Hofmann Generator.

Jakwiebus (author)squiggy22012-05-26

you are intending to use the hydrogen as a fuel so you're making. But it's named like that all over the Internet and that is not wrong since it's like a rechargeable battery, what you're doing is the charging, and the discharging happens while burning, but there instead of producing energy in the form of electricity again, you make water vapor and warmth. (but that you probably already knew).

but if you're uncomfortable by changing the name of your project, with Hoffman apparatus you're making yourself also clear, it's just not exactly scientifically accurate, but I can live with that since you collect the hydrogen and the oxygen separately ;-)

ps: if you're planning on filling a bottle with a hydrogen and oxygen mixture and shooting it like a rocket, I suggest you don't use the stoichiometric correct 2:1 ratio but rather a 4:1 ratio of H2 and O2. that will give the loudest bangs and furthest launches. (experimentally proven :P )

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