If you extract sea water, and filter it, would it be suitable as an input for green hydrogen production? From an electrochemical perspective, would this be the only process step required?
Hydrogen production from water occurs through water splitting 2 H2O -> 2 H2 + O2. Seawater has a high concentration of chloride anion, which is good because you always need an electrolyte for electrochemical reactions. However, Cl(-) is much more easier to oxidize than water. Therefore, the reaction 2 H+ + 2 Cl- -> H2 + Cl2 will proceed. This is a commercial process to produce Cl2. However, it can't be a source of H2, because it would result to overproduction of Cl2. At the same time, hypothetically it might be possible to develop a water oxidation catalyst, which can tolerate the presence of Cl-
Hydrogen production from water occurs through water splitting 2 H2O -> 2 H2 + O2. Seawater has a high concentration of chloride anion, which is good because you always need an electrolyte for electrochemical reactions. However, Cl(-) is much more easier to oxidize than water. Therefore, the reaction 2 H+ + 2 Cl- -> H2 + Cl2 will proceed. This is a commercial process to produce Cl2. However, it can't be a source of H2, because it would result to overproduction of Cl2. At the same time, hypothetically it might be possible to develop a water oxidation catalyst, which can tolerate the presence of Cl-
Yurii V Geletii thank you for your super fast answer. In terms of quantity of products produced, would the chlorine gas would be small by comparison?
There is no shortage of freshwater for electrolysis, but not where cheap electricity can be obtained from solar energy. One can, of course, desalinate sea water, and then conduct electrolysis, only who will buy such expensive hydrogen. In turn, with the electrolysis of seawater, it is similar to the transesterification of oils. In the case of transesterification, there is a problem with glycerol, and here with chlorine, which additionaly is not only poisonous but also a strong oxidant. So getting hydrogen in large amounts from seawater is a pipe dream so far.
Dear John Patrick O'Connor , seawater have a quite large amount of salts, mainly NaCl (31-38 g/kg) but also many other cations and annions, which make difficult to design a catalyst to deal with the whole matrix of seawater, furthermore it is full of microscopic marine life and rests of organic matter.
With respect to your second question, chlorine gas would be important and if not recovered for some application, the "green" hydrogen would be in fact green but due to the colour of the Cl2 gas. Cl2 is toxic, irritant and it would be a worst problem than CO2 released by burning oil, gas or coal.
Probably the best option would be filtering the seawater and working with that filtered water to produce green H2. Filtering consumes energy and probably you end up with some concentrated brine as byproduct, that could cause some ambiental problems too. This is what desalination plants do, filter the seawater by forced osmosis to get a fraction of fresh water and another of brine.
Hope it helps.
" would the chlorine gas would be small by comparison? " It depends on numerous factors, first on the activity of water oxidation catalyst.
"the "green" hydrogen would be in fact green but due to the colour of the Cl2 gas. Manuel Gómez , H2 and O2/Cl2 are formed in different compartments of electrolyzer. H2 can't be contaminated with Cl2
I know Yurii V Geletii , what I mean is that you end up with a byproduct. Cl2 has also lots of industrial applications but may be it would be too much to be managed by industry, if seawater is the source of H2.
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