Sciencemadness Discussion Board - How to utilize hydrogen from electrolysis cell?

How to utilize hydrogen from electrolysis cell?

SupFanat - 23-5-2015 at 13:40

I have some theoretical interest for renewable energy.
An experiment could use any such energy source for electrolysis of water. The problem is extremely low density of produced hydrogen gas. I'd prefer to use it for some hydrogenation reaction. Is there any such reaction which can be easily catalyzed in aqueous solution? Hydrogenation of carbon dioxide to methane isn't ideal solution even if it works because methane is still gas (takes however only one-forth of original volume of hydrogen).

aga - 23-5-2015 at 13:43

UTFSE.

Unsurprisingly the electrolysis of water to make O₂ and H₂ has already been extensively researched.

Try Google for example.

www.google.com

[Edited on 23-5-2015 by aga]

The source of your Hydrogen makes absolutely no difference to how you use it.

It's still Hydrogen, and never Magic Organic Certified Hydrogen.

[Edited on 23-5-2015 by aga]

SupFanat - 23-5-2015 at 13:59

Is there any easy way to convert hydrogen to something useful with more density? Easy for beginner.
Hydrogen can be used to make some metals from oxides, for example iron from iron oxides. But such process needs some hydrogen storage which I'm not going to build anytime soon.
(The energy demand for this reaction to proceed can be fulfilled by burning of hydrogen. A part of hydrogen reacts with iron oxides, another part reacts with oxygen.)

blogfast25 - 23-5-2015 at 14:47

Quote: Originally posted by SupFanat

(The energy demand for this reaction to proceed can be fulfilled by burning of hydrogen. A part of hydrogen reacts with iron oxides, another part reacts with oxygen.)

This is chemnonsense. Some metal oxide reductions with hydrogen are Exothermic, some aren't.

aga is right: hydrogen is hydrogen is hydrogen. Even 'heavy' hydrogen (D2

has basically the same chem properties as H2.

[Edited on 23-5-2015 by blogfast25]

SupFanat - 23-5-2015 at 14:59

The reaction of iron oxides with hydrogen is slightly endothermic if water vapor is produced (but slightly exothermic if liquid water is produced).
This endothermic reaction (if iron oxides are reduced by hydrogen) can be powered by partial burning of hydrogen. That is what I know,

WGTR - 23-5-2015 at 17:26

Currently I'm under a sturdy table, in an interior room, waiting for the tornado weather to pass, while trying to iPhone type with my big thumbs. Sorry.

One way to store hydrogen is to convert it to ammonia. To store it directly, perhaps look into zeolite/molecular sieve storage. With the right pore size, more gas could be stored for a given pressure.

Molecular Manipulations - 23-5-2015 at 20:10

Electrolysis of water wont save energy, it'll waste it. Everytime. Period.
Third law of thermodynamics anyone?
WGTR yeah, I'll just run it through my backyard Habor-Bosch plant.

blogfast25 - 24-5-2015 at 05:57

Quote: Originally posted by SupFanat

The reaction of iron oxides with hydrogen is slightly endothermic if water vapor is produced (but slightly exothermic if liquid water is produced).

Nope. You don't understand how Reaction Enthalpy works. I can find examples where even with water vapour the reaction is Exothermic. The only difference between steam and water is the Heat of Vaporisation, not very large anyway.

Just find some metal oxides with really low Enthalpies of Formation. Ag2O springs to mind. There are others.

[Edited on 24-5-2015 by blogfast25]

blogfast25 - 24-5-2015 at 06:03

Quote: Originally posted by Molecular Manipulations

Electrolysis of water wont save energy, it'll waste it. Everytime. Period.
Third law of thermodynamics anyone?
WGTR yeah, I'll just run it through my backyard Habor-Bosch plant.

Exactomundo. Hence all these 'HOH fuel saving devices' being useless scams.

Sulaiman - 24-5-2015 at 06:22

I agree that some small scale useful way of utilising small scattered sources of 'clean' power is required,
I doubt that electrolysis is the answer due to equipment and storage requirements, and potential explosions etc.
plus you shpuld also utilise the other half of the energy that went into splitting the water, the oxygen.
Pure oxygen to compete with oxygen from liquefied air for example,
or just to enable the easier combustion of renewable hydrocarbons etc.

Something low level such as electrolytic refining in remote areas?
Water pumping and purification?
Pure H2 and O2 seems more like a farm for a rocket launching facility !

[Edited on 24-5-2015 by Sulaiman]

blogfast25 - 24-5-2015 at 06:27

Quote: Originally posted by Sulaiman

plus you shpuld also utilise the other half of the energy that went into splitting the water, the oxygen.

Energetically the problem is that the energy you expend to carry out the electrolysis is never the same as the energy you get back by recombining the H2 and O2. The former process is by definition not 100 % energy efficient, so energy is effectively lost. Driving the motors directly with current is thus more energy efficient.

With electrolysis there are ALWAYS Ohmic losses.

Hydrogen fuelled motors have their uses, of course, but not in the field of energy conservation.

[Edited on 24-5-2015 by blogfast25]

WGTR - 24-5-2015 at 07:17

I'm not sure where people are getting the idea that the OP wants to break thermodynamic laws, but perhaps I'm missing an earlier thread/post.

The idea of a liquid hydrocarbon's total synthesis from basic things like H₂, C, CO₂, etc., was a personal obsession for a couple of years. It was, in fact, what initially got me interested in chemistry. The idea wasn't to make something from nothing, but to convert electrical energy (solar, etc.) into an energy dense form such as a liquid hydrocarbon. It happens that liquid hydrocarbons are easy to transfer from one container to another, and offer high energy density storage for things like automobile transportation, etc.

Impractical as it might be on a benchtop scale, I think conversion to ammonia is going to be the most direct way of storing hydrogen as a R.T. (although slightly pressurized) liquid. The bonus is that the hydrogen can be recovered pretty easily with a heated catalyst.

Another method is to make acetylene directly from carbon and hydrogen in an electric arc, or via calcium carbide. This can be directly hydrogenated to ethane at mild temperatures. Ethane is the simplest alkane that can remain a liquid at room temperature, although its critical temperature is about 32C at 700 PSI. Propane would be even better in this way, and Mg₂C₃ can be used as a starting point for this. Anyway, here is some reading for those interested:

Attachment: de96001664_rpt38.pdf (926kB)
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blogfast25 - 24-5-2015 at 08:37

Quote: Originally posted by WGTR

I'm not sure where people are getting the idea that the OP wants to break thermodynamic laws, but perhaps I'm missing an earlier thread/post.

I don't think anyone is saying that.

Up to and including now, N2 + 3 H2 == > 2 NH3 requires Born-Haber, an energy inefficient process. Then reverting that back to H2 would also be energy intensive.

A VERY expensive way to store energy, if you ask me.

WGTR - 24-5-2015 at 16:17

Quote: Originally posted by SupFanat

I have some theoretical interest for renewable energy.
An experiment could use any such energy source for electrolysis of water. The problem is extremely low density of produced hydrogen gas. I'd prefer to use it for some hydrogenation reaction. Is there any such reaction which can be easily catalyzed in aqueous solution? Hydrogenation of carbon dioxide to methane isn't ideal solution even if it works because methane is still gas (takes however only one-forth of original volume of hydrogen).

I think the questions are fair. It can be difficult to search for these things online if one is unfamiliar with the proper search terms. I would like to apologize to the OP for not answering more directly before.

I don't know of any hydrogenation reaction that can occur through direct catalysis in aqueous solution, at least not ones that are useful for energy storage. There is an electrolytic process involving the reduction of CO₂ in aqueous solution, however. The reference that I'm going to post is somewhat dated, and better references may be available. However, it should provide some ideas.

Attachment: Electrocatalytic activity of Cu electrode in electroreduction of CO2.pdf (365kB)
This file has been downloaded 756 times

This wiki link should provide some general information:

http://en.wikipedia.org/wiki/Electrochemical_reduction_of_ca...

This skips the step of producing hydrogen as an intermediate product, although it will likely be produced at the same time as the desired product. Producing C2 and greater hydrocarbons is somewhat of the "holy grail" of these electrosynthesis techniques for reasons that you mention. Methane is easier to store than hydrogen, but it still requires high pressures and/or low storage temperatures. One option is to explore the use of high surface area materials to facilitate methane storage. I've included one such reference below:

Attachment: Methane storage in zeolite-like carbon materials.pdf (2MB)
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As blogfast25 and others have alluded to, poor efficiency will likely rear its ugly head. This may or may not be a concern for your current situation. In some papers on electroreduction of CO₂, hydrogen is left out of the efficiency calculations, although it may be a sizeable proportion of the overall products. Keep that in mind.

Finally, are you thinking up an entry for the current Hackaday competition? A lot of your questions seem to be related to this year's topic.

[Edited on 5-25-2015 by WGTR]

blogfast25 - 24-5-2015 at 17:22

WGTR:

All these 'exotic' electrochemical thingymejibs are 'interesting' but rarely lead to anything practical. Just look how sophisticated both types of Li batteries are!

[Edited on 25-5-2015 by blogfast25]

SupFanat - 25-5-2015 at 09:21

Quote: Originally posted by Sulaiman

Pure H2 and O2 seems more like a farm for a rocket launching facility !

[Edited on 24-5-2015 by Sulaiman]

It's a good idea for a rocket launching facility. Rockets should use renewable fuels as well. It may be the same fuels which are used today but from renewable sources.

Molecular Manipulations - 25-5-2015 at 23:46

Quote: Originally posted by SupFanat

Rockets should use renewable fuels as well. It may be the same fuels which are used today but from renewable sources.

Getting hydrogen from water is less 'renewable' than current methods. Sure, we wont run out of water, but where do you think the electricity comes from? Unless you live in France it's probably from fossil fuels. The additional steps of carrying electricity through wires, through an inefficient cell, and storing the product wastes more.

SupFanat - 26-5-2015 at 02:26

Who says it must be electricity from grid?
Only local renewable power plant makes sense.

blogfast25 - 26-5-2015 at 07:10

Quote: Originally posted by SupFanat

Who says it must be electricity from grid?
Only local renewable power plant makes sense.

Sure, you could use a wind farm (e.g.) to generate the electricity for electrolysis. So what?

vmelkon - 26-5-2015 at 07:12

Quote: Originally posted by blogfast25

Up to and including now, N2 + 3 H2 == > 2 NH3 requires Born-Haber, an energy inefficient process. Then reverting that back to H2 would also be energy intensive.

A VERY expensive way to store energy, if you ask me.

I don't know how energy intensive the process for making NH3 is, but for the later part, it is NOT necessary to break down NH3 back to the elements. You can just burn NH3 in a combustion engine and you get N2 + H2O.

Apparently, there was one canadian who did that in the 1970s. The video of the interview is on Youtube.

Molecular Manipulations - 26-5-2015 at 07:13

Exactly. Regardless of the source, there's much better ways to store energy.

blogfast25 - 26-5-2015 at 07:52

Quote: Originally posted by vmelkon

Apparently, there was one canadian who did that in the 1970s. The video of the interview is on Youtube.

If it is then it should be easy to find or to find references to that invention. I'm deeply sceptical about that route.

[Edited on 26-5-2015 by blogfast25]

SupFanat - 27-5-2015 at 04:16

I could use a small wind turbine but it's useless thing without some energy storage. Inefficient electrolysis is still better that 0% efficiency.

Zyklon-A - 12-6-2015 at 07:18

This doesn't increase efficiency much, but a safer way to harness electricity from recombining hydrogen and oxygen than 'simple' burning is a schmantic fuel cell. This was employed in the Apollo Moon lander, during the day, solar panels powered the lander as well as split water and stored the constitute gaseous elements in cylinders. When solar power is unavailable (at night) the stored fuel was recombined using a schmantic fuel cell. Not sure what advantage this has over rechargeable batteries though.