Electrolysis of water

A couple of days, I hit upon a YouTube film where someone explained that it is possible to electrolyse water with a much smaller energy input than what science taught up to now. I for myself, thought that the energy is a fixed value for a certain amount of water. The method as described worked with something like agitating the water with a piezoelectric element. The claim was, iirc, about 15 times higher efficiency. Be it as it is, I don't really believe that.

But I wanted to see what chatGPT knows, and here are the answers:

First question
How many KWh does it need to electrolyse 1 kg water?

The amount of energy required to electrolyze 1 kg of water depends on several factors, such as the voltage and current used, the efficiency of the electrolysis process, and the temperature and pressure of the system.

However, we can make an estimate based on the standard enthalpy change of electrolysis of water at standard conditions (25°C and 1 atm pressure), which is 286 kJ/mol. The molar mass of water is approximately 18 g/mol, so 1 kg of water contains approximately 55.6 moles of water.

Therefore, the energy required to electrolyze 1 kg of water at standard conditions can be estimated as:

286 kJ/mol x 55.6 mol = 15,933.6 kJ

To convert kJ to kWh, we can divide by the number of joules in one kilowatt-hour (3,600,000):

15,933.6 kJ / 3,600,000 = 4.43 kWh

So, it would require approximately 4.43 kWh of energy to electrolyze 1 kg of water at standard conditions. Note that in practical applications, the actual energy required may be higher due to various inefficiencies in the process.

My second question;
Are there means to significantly reduce that energy?

Yes, there are several ways to reduce the amount of energy required to electrolyze water. Here are a few examples:

1. Improve the efficiency of the electrolysis process: Electrolysis involves the conversion of electrical energy into chemical energy. The efficiency of this process depends on various factors such as the type of electrode, the voltage and current used, and the temperature and pressure of the system. By optimizing these factors, it is possible to improve the efficiency of the electrolysis process and reduce the amount of energy required.

2. Use renewable energy sources: If the electricity used for electrolysis is generated from renewable energy sources such as solar or wind power, the carbon footprint of the process can be significantly reduced. This can also help to reduce the overall cost of the process.

3. Use alternative electrolytes: The traditional electrolyte used for water electrolysis is a solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH), which can be expensive and corrosive. However, there are alternative electrolytes that are cheaper and less corrosive, such as proton exchange membrane (PEM) electrolytes. Using these alternative electrolytes can reduce the overall cost of the electrolysis process.

4. Use advanced materials: There is ongoing research into developing new materials for the electrodes and other components of the electrolysis system. These advanced materials can improve the efficiency of the electrolysis process and reduce the amount of energy required.

In summary, by optimizing the various factors involved in the electrolysis process, using renewable energy sources, using alternative electrolytes, and using advanced materials, it is possible to significantly reduce the amount of energy required to electrolyze water.

What do our scientists say?

Regards,
Hans

Edited By Versaboss on 16/02/2023 22:35:10

Using AI to check the veracity of YouTube is way above my pay grade I am afraid.

I'm not a scientist, but here goes. At 100 % efficiency you'd get the same energy output by burning 1 kg of hydrogen with 16 kg of oxygen to produce 18 kg of water as it did to produce the 1 kg of hydrogen in the first place. Burning 1 kg of hydrogen produces 39.4 kWhr so to electrolyse 1kg water takes 39.4/18 = 2.2 kWhr. However the electrolysis will not be 100%efficient, so Hans's figure could well be correct. As a means of storing electricity, pumped storage is almost certainly more efficient, but I can't see us ever having enough pumped storage capacity to cope with days of no wind.

Edited By duncan webster on 16/02/2023 23:40:31

I cannot judge the chemistry mathematics but I am sceptical about the claims for agitating the water by piezoelectric transducers.

There has been work done on using such techniques for goading certain types of chemical or physical reaction into life by cavitation, using high-power, high frequency transducers to induce cavitation in the fluid, but I am not sure of their success.

It is is important to realise that "piezoelectric" describes how the tool works, not its purpose which is what matters here. Its purpose is to impart high-intensity sound fields in the water to encourage the reaction (electrolysis in this case). What it may do is help the bubbles of evolved gas break away from the electrodes, but I don't see it having any other effect; and you may obtain the same result by just spinning the electrodes.

In any case the efficiency gain in using such a system might well be wiped out by the electricity needed by the appropriate signal-generator and amplifier driving the transducers at the required frequency and power - whatever these may be for the specific electrolyser.

Most exciting. We must be on the verge of a perpetual motion machine that actually outputs useful energy as well!

There's a level of efficiency saving that can be realised relative to established technologies by modifying the surface-chemistry at the electrodes to provide favourable conditions, an optimisation which is done in much the same way that catalysts for various industrial processes work.

ITM power (local to me), and several other electrolyser companies have had a great deal of success finding better electrochemical pathways to increase H2 production efficiency.

So in that regard, the video may be credible, and ChatGPT has given an overview of some of the optimisation strategies used in a sort of garbled, word-salad-y kind of way (as well as very confidently listing renewable energy, which is fundamentally wrong, as that doesn't reduce energy consumption just carbon emissions, exposing the language model's relative fallibility).​

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As to piezoelectric vibration, without reviewing the source material I don't find it particularly credible, but there's also some very interesting papers on out there on sonochemistry (initiating and controlling chemical reactions using sound) in niche scenarios which wouldn't make it entirely ridiculous.

It would be important to understand if they're accurately accounting for the mechanical energy provided by the ultrasound (and the efficiency of the sound generator) or not in their calculations.

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However, we all know that it is simply not possible to produce more energy from burning H2 and O2 than was expended in producing them in the first place.

If someone is showing an electrolyser which recieves 4kW of energy, but produces enough hydrogen and oxygen to produce 5kW of energy then:

• the most generous interpretation is that they're drawing the system boundaries incorrectly, and failing to account for another energy source, such as mechanical energy input or the chemical energy in a reagent or catalyst which is expended during the process and will eventually need to be replenished or regenerated.

• A much more likely one is that they're a charlatan and they know it.

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Their maths would probably be the deciding factor for me:

If they're claiming it is 15 times more efficient than a process which runs at an efficiency of 80-85% on an industrial scale (e.g. 15 * 85% = 1275% ), then they're exceeding unity and it's absolute tosh.

If they're trying to create an impressive headline number by using a deliberately weird way to calculate the multiplier, such as comparing their efficiency to existing approaches in terms of energy lost relative to a theoretical maximum (e.g. existing losses: 1kW * [1-0.85] = 0.15kw lost, our new process: 1kw * [1-0.99] = 0.01kw lost, and 0.15/0.01 = 15 thus our new process is 15 times more efficient)...

Then they're just being awful at science (and mathematical) communication, quite possibly on purpose to grab attention.

Edited By Jelly on 17/02/2023 16:43:03

What's missing from the Youtube claim is the baseline. 15 times higher efficiency than what?

Big money opportunity coming up! I've invented a synthetic rubber that lasts 10 times longer and has 50 times the grip. Mortgage your house to buy shares in Duff Rubber, because the new material obviously makes all existing tyres obsolete. The profits will be enormous.

Unfortunately my baseline was a rotten banana skin. Compared with an ordinary car tyre, my invention is completely hopeless.

Dave

Everything said about base lines is true and helpful. Of course it breaks the rules of physics.

However it can be remarkably successful. You, as an investor, buy shares in the company and then the company disappears. Scammers don't need computers.

Just a thought, if governments invest in controlled fusion research are they being scammed? It is very difficult to know.

JA

Edited By JA on 17/02/2023 18:44:16

Edited By JA on 17/02/2023 18:52:54

Is electrolysis the source of the hydrogen that will power the super clean motors?

Reply to JA , if the ITER Project doesn't work , then yes, we are being well and truly scammed.

Very easy to bamboozle politicians.

First for Old Mart - yes, the main process for 'producing' hydrogen is electrolysis.

Now for the main argument.
Hans has carefully set out the theory - how much energy is needed. Good science. But then he goes on to ask how we could improve on that figure. What he seems not to appreciate is that science is about what happens. No fairy stories, if you do this, you get that. So what we could reasonably be asking, instead, should be, I suggest:
Ok, what do we need to do to get as near to that theoretical figure as possible?

There is another question: do these figures represent the end of the road for progress in this matter? Well, perhaps not, but that is again what science is about. You work out other possible theories, and you try them out, and you calculate carefully what goes into the process, and what comes out, and you hope that the answer is better. And if you succeed, (and only then) you publish your results*, with two objects in mind - first, you hope that others will try your new method, and come up with similar, better results, and benefits all round. Second, you hope someone will get together the finance to make your new process available more widely, so that money, and other benefits, will accumulate for them, and for you.
* and at this point, you need to consider a patent.

If, however, you 'invent' a new process which you claim to be much better, and don't show your working, and if you do, you get the sums wrong, you are no better than a million others who have convinced folk to change their ways, and no real benefit results. Whether it is called snake oil or religion, the outcome is the same.

I don't believe in fairy stories; neither should you.

Regards, Tim

Most hydrogen is produced by reacting methane with steam. By product is of course CO2. Until we have plentiful excess electricity the hydrogen economy is a non starter. It can be a means of using wind power produced in the early hours of the morning when no-one else wants it, but I can't see that being significant. Open to bring corrected of course.

Not for the first time am I moved to quote perhaps my favourite source of wisdom:-

"“If you can’t dazzle them with brilliance, baffle them with bullshit.”

W.C. Fields

The Wikipedia article on Hydrogen production gives some figures:

• Efficiency by electrolysing water : 70 to 80%
• Efficiency by steam reforming Natural Gas: 70% - 85%

Very similar, and the efficiency of both processes is already high.

Electrolysis of water has some system efficiencies that reduce the cost. It can soak up overproduced green energy, basically using every spare watt that would otherwise be lost. And if an industrial process produces a lot of waste heat, less electricity is needed to electrolyse hot water, potentially reclaiming energy that would otherwise go up a cooling tower or into an estuary.

Dave

My claim for electricity was based on an understanding that petro-chemicals were on the way out. A process that produces carbon dioxide as a byproduct is not helpful, but one that produces oxygen is exactly the opposite. And I was relying on details from Orkney and and Norway, where electrolysis is used.

Tim

Someone is working on a process which turns methane into hydrogen and carbon dust (soot). If it works it's neat, but of course we would still then be depleting our oxygen when we burned the hydrogen, no one seems bothered about that.

The simple answer is yes, but many a slip t'wixt cup and lip.

The cheapest way of making Hydrogen at the moment is chemically from fossil fuels. Historically cheaper to burn methane to generate high-pressure high-temperature steam, that breaks more Methane into Carbon Dioxide and Hydrogen, than it is to electrolyse water with electricity generated electricity by burning methane in a gas turbine.

Apart from wasting methane which is valuable for other purpose, the process produces large quantities of Carbon Dioxide. Cleaner alternatives are desirable!

Hydrogen from electricity becomes cost effective whenever a cheap source of electricity is available, and renewables offer just that.

Renewables already provide about 40% of UK electricity, most of it from wind. The problem with wind is it doesn't blow consistently, so some days, it can't deliver. On the other side of the coin, the wind blows round the clock, and is available to generate electricity more or less continually. At the moment, when we're all asleep, demand drops, and wind turbines are allowed to spin uselessly. Rather a lot of power is available, but no-one wants it. Fairly easy I think to connect Electrolysis plant to the grid that only consumes unwanted power whenever it is available. The Hydrogen could be collected for vehicles, or more likely as a first step, fed into the existing gas network to beef up diminishing natural gas supplies. Nothing new here: good old Coal Gas was about 50% Hydrogen.

Dave

I think the first large scale production of Hydrogen, for filling baloons over 220 years, was by passing steam though a bundle of red hot Iron rods. This reaction may be exothermic and does not directly need a carbon based fuel. If Aluminium is used instead of Iron it would certainly be exothermic. Both metals are very energy expensive.

JA

This process was used in the GDRass hydrogen over ironoxide and thus reduce it to metallic iron and in reverse pass steam over iron and reduce h2o to H2. A method of storing hydrogen,being investigated for industrial use nowadays

h