High pressure (could be up to 200 bars) water electrolysis increases the efficiency of this process. That is why, there are two types of water electrolyzers, namely: atmospheric (which has lower efficiency) and high-pressure (which has the highest efficiency).

Hope this helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

Thank you Professor

To reach 200 bars we must use expensive devices (compressors ...etc), therefore hydrogen produced by such process will not be economically reliable...

If there is another process or a new technique using nanoparticles or semiconductors (photocatalytics) or others ???

Thanks again 

Hello Sellami,

First, you not need to reach 200 bars pressure. I'm just providing the range.

There is another state-of-the-art methodology for water splitting at room temperature using the so-called artificial leaf. My colleague at Harvard University (Dan Nocera) has developed this technology using a special catalyst that he developed.

You can go to Harvard.edu and search for Daniel Nocera's research on the artificial leaf.

Professor Yehia Khalil, Yale University

Prof Khailil,  I agree that Prof Nocera's work on the artificial leaf is very promising:

http://news.mit.edu/2011/artificial-leaf-0930

http://nocera.harvard.edu/Publications2016

but its not quite ready yet.

High pressure electrolysis is also very interesting.  It still can't compete with steam methane reforming because most of the energy input is electricity and it take about 2 Cal of fuel or more to make every Cal of electricity you produce but it is still a huge step in the right direction.  Pumping water instead of compressing H2 and O2 is a big advantage of the process.  I think the key to success may be finding an application where both the high pressure H2 and the high pressure O2 are put to good use.

Thanks prof  Yehia Khalil and Rick Manner for your interesting comments and useful contributions.

Regards.