Warning: Hydrogen is a flammable gas.
Sodium bisulfate is corrosive, wear gloves when handling it.
Additionally, safety alarms are very loud by design.
Wear hearing protection when performing this experiment.
Greetings fellow nerds.
Detectors for carbon monoxide as well as natural gas like this one have become increasingly popular to warn against such gases.
They're manufactured on such a large and competitive scale that the free market has made them very inexpensive..
You can even get combination units like this one that can sense both carbon monoxide and natural gas.
Some high end models will even give readouts to give you a rough indication of the concentration.
Although you should not rely on the readout for accuracy since they're not calibrated to laboratory grade standards.
Anyway, both of these sensors will detect their respective gases, but a lesser advertised feature is that they are both sensitive to hydrogen gas.
So let's demonstrate that.
First i'm going to make a very crude hydrogen generator by getting a acid solution of sodium bisulfate.
I used about 10g in 90mL of water but the exact amount is not critical.
Then i drop in a piece of zinc metal which will react with the acid and generate hydrogen gas.
You can also use aluminum metal but i prefer zinc since i find the hydrogen evolution slower and more steady.
Now all we do is place the detector over the hydrogen source and wait.
It takes some time for the gas to diffuse into the sensor so be patient.
I fast forwarded a good minute until i had a reaction.
And there we go, the reading changed.
The detector thinks it's detecting carbon monoxide and is giving a reading but it's actually reacting to hydrogen.
Oh there we go, the alarm has been set off.
Interestingly enough the long beep and even the display indicates it was the natural gas sensor that was tripped, not the carbon monoxide sensor.
Both sensors were activated but the circuitry considers the natural gas sensor as taking priority.
Let me take it away from the gas so it resets and i'm going to try it again.
I'm trying to orient the detector so the hydrogen just saturates the carbon monoxide detector.
Hmmů still detecting gas.
Oh there we go.
The carbon monoxide sensor is now generating such a strong signal that the circuitry now considers that the higher priority signal and raises the four beep alarm sound.
You can also see the display for carbon monoxide is off the scale.
Now at this point you might be asking why do these sensors even have the ability to detect hydrogen and why isn't that listed anywhere.
Well the ability to detect hydrogen isn't a design feature, it's just a side effect of how the sensors work.
Let me open up my detector to show you what's inside.
Now i don't know enough about electronics to tell you how the circuit works,
but i can tell you this large cylinder that looks like a battery is actually the sensor for carbon monoxide.
It works by oxidizing carbon monoxide along with moisture in the sensor at the anode of an electrochemical cell.
The protons generated dissolve and move through the electrolyte to the cathode where they close the circuit and pass a current.
The current generated is measured and correlates to the carbon monoxide concentration.
But if you add in hydrogen gas it can also be oxidized and will also generate protons and pass a current just like carbon monoxide, giving you a false positive reading.
The sensor is still much more selective and sensitive to carbon monoxide though.
Hydrogen has a much weaker response so the true value is much greater than what you're seeing here.
You could read 50 ppm carbon monoxide but actually have a thousand parts per million of hydrogen in the air.
Now this tiny little easy to miss component here is the combustible gas sensor, and can sense things like propane, methane, natural gas and so on.
It works by a heating semiconductor element of tin oxide.
This saturates with oxygen from the air and in turn increases the resistance of the tin oxide.
When it when it comes in contact with a reducing gas like propane, the high temperature element essentially burns the gas with the oxygen inside the tin oxide and depletes it of oxygen.
The loss of oxygen from the tin oxide makes it conductive and lowers the resistance.
The change in current flow can be used to determine gas concentration.
So it's essentially a destruction of oxygen sensor rather than a combustible gas sensor.
Although when you really think about it, most gases that can destroy oxygen from a sensor are combustible so the label is still accurate.
Hydrogen is also combustible, so it does the same thing as natural gas and reacts with oxygen in the sensor depleting it, giving a positive reading.
The sensor is doing exactly what it was intended to do, detect a combustible, oxygen destroying gas.
Now you might be wondering if this sensor can be used to detect low oxygen concentrations, vacuums, or oxygen free environments since it relies on lack of oxygen in the sensor.
It cannot reliably be used that way because you still need to destroy the oxygen already absorbed into the sensor.
So it truly is a destruction of oxygen sensor, rather than a lack of oxygen sensor.
As a side note this large round object here is the piezoelectric alarm.
It's not in itself a sensor, although i see a lot of websites that inaccurately mislabel it as such.
So now that we know our carbon monoxide sensors can also detect hydrogen, what can we do with this knowledge?
Well it's feature or a flaw depending on your application.
If you are working with hydrogen gas like an analytical lab that uses a hydrogen carrier gas for their gas chromatograph,
a carbon monoxide detector can be a nice cheap leak detector.
In this case it would be a useful feature.
But in some cases hydrogen interference can be a bad thing.
Like if you're in an industry that uses both gases then not being able to tell the difference when the alarm goes off can severely hamper your efforts in finding and stopping the true cause.
Better sensors that are specific to carbon monoxide or hydrogen do exist, but they are expensive and not cost effective for domestic applications.
Especially since one of them, hydrogen, is very rarely encountered in dangerous concentrations.
Nonetheless, for you amateur chemists that want a cheap hydrogen detector, now you have one.
Before i go, i should mention something about lifespan.
Electrochemical sensors have limited lifespans as their elements break down.
As this happens the response to actual carbon monoxide will decrease and eventually stop entirely,
giving you a false zero reading even though there is carbon monoxide or hydrogen everywhere.
So they need to continually be replaced every few years according to the manufacturer's instructions.
Anyway, thanks for watching.
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