Re: energy need to produce one litre of hydrogen?
- From: hhc314@xxxxxxxxx
- Date: Tue, 1 Jul 2008 09:01:45 -0700 (PDT)
On Jun 29, 11:13 pm, Robert Adsett <s...@xxxxxxxxxxxxxxxxxxxxx> wrote:
In article <54b51682-4c0e-4391-9a9c-4bda0e1c2893@
I won't defend the original poster. You are posting through Google
groups I'll let you research it. It is in this thread, you can take it
up with them. I merely quoted it as an indication that the question
that was asked was indeed answered explicitly more than once.
Bob, please explain the connections that exists between posting
through Google to Usenet Newsgroups has anything at all to do with
reseraching a subject? You lost me with that statement. (First,
realize that sci.energy.hydrogen is not a "Usenet Newsgroup". Second,
if you are using the Google search engine to reserach any scientific
or engineering topic, you run the risk on encountering some good
information and other information posted by laymen and sometimes
crackpots. Consequently, to validate the credibility of any scientific
information posted on the Newsgroups or equally on the Web, you have
to research it using an authoritative textbook or scientific paper. In
this case, the science involved is described in any excellent text on
the subject of "Physical Chemistry", a subject that addresses all
alspect of this case starting with the perfect gas laws, electrode
potentials, the physical nature of electrolysis, and every parameter
affecting the process. Failing this, by simply surfing the Newsgroups
and Websites that Google or any good search engine will surface, you
are kidding yourself thinking that that is real reseach into a
subject, and attempting to "take it up" with the sources of most of
the incorrect data is not really worth the effort. I prefer simply to
cite corrections to erroneous information by pointing to a legitimate
and recognized source of correct information.
In this case I would cite: "Elements of Physical Chemistry", Samual
Glasstone and David Lewis, D. Dan Nostrand Company, Inc., Princeton
New Jersey, Toronto, London, and New York.
There are a number of excellent textbooks on the subject, and I only
cite this particular publication because it an older reference on the
subject, is avalable in most university and larger public libraries,
plus I still have my copy from my undergraduate college years. Another
good place to start serious reserach would be the "The Journal of
Electochemistry". Also, any professinal paper published on the
subject of water electrolysis will usually contain a hundred or more
citations of related scientific papers and topical publications.
Generally speaking, this is how any professional researches a topic in
science or engineering.
The electrolysis of water to liberate hydrogen and oxygen is not a new
subject to science, and the methods for achieving it was well
documented and have been so for over 100 years. As a consequence, the
methods of achieving it and optimizing its yield efficiency are quite
well understood. Still, it should be noted that the electrolysis of
water has only a limited number practical applications, unlike the
electrolysis of other fluids.
I also note the the electrolysis of water can produced any number of
undesirable gases other than hydrogen and oxygen unless the non-
conductive pure water is converted into an electrolyte though the
addition of a very carefully selected salt or acid. Otherwise the you
will no obtain the expected stochiometric ratio of hydrogen and
oxygen, since the gas produced by the electrolysis will also contain
other gasses which are usually noxious, toxic, or corrosive such as
chlorine, flourine, bromine, sulfur dioxide...just to name a few.
Well, it is a gas and at STP I would expect it to act pretty close to an
ideal gas so around 22.4 would be my initial guess. Like you to be sure
I'd have to check references to get an exact number but do you really
expect it to be far enough from an ideal gas to make much of a
difference?
You are of course correct that pure hydrogen is as close at you can
get to an ideal gas, and have a molar volume of 22.4 (give or take a
but I have never heard of anyone producing anything close to pure
hydrogen though the use of electrolysis. Unless laboratory methods are
employed to dry and purify the hydrogen, it will always contain a
significant amount of other gases including water vapor, some oxygen,
and gases produced from the substance added to the water to permit it
to conduct an electric current.
Still, I would have to agree for the accuracy of the usualy garage
conducted experiment, the passage of 1-Farraday of charge through a
water bases electrolyte will produce roughly 22.4 liters of gas at
STP. Consequently, a very simple anwer to the OP's question is that it
would take 1-Faraday/22.4 passing through the electrolyte to produce 1
liter of hydrogen gas.
Now you can worry about real world practical efficiencies that will
further limit the available energy due to, as you noted, such things
conductivity and electrode overvoltages.
Oops, forgot to mention ion or charge migration rates in the
electrolyte! :-) (My old p.chem prof would hit me for that!)
Bob, you give me too much credit for having that degree of ambition!
An accurate analysis of the enegy losses in the process, as you note,
are set by at least six different considerations. I simply thought it
would benefit some readers to know how physical chemistry views
electrolysis and how/why it works as it does. For no reason other
than to throw cold water of some of the crackpots that claim
miraculous results though the use of pulsed waveforms, high
frequencies, and other magic tricks that simply cannot work because
they are inconsistent with known science.
Harry C.
.
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