I've been researching hydrophilic electrodes. What we want is an electrically conductive electrode that is stable in water, and has a bandgap that is as close as possible to equal to the dissociation constant of H3
Graphene-doped metal appears to be the way to go. Graphene is an atomic-scale honeycomb lattice of graphite (carbon). It's 100 times stronger than steel and conducts electricity efficiently. It's too bad we can't yet buy graphene in large, thick sheets... it'd be the ideal electrode.http://www.ncbi.nlm.nih.gov/pubmed/23240759
Superhydrophilic graphene-loaded TiO2
It's got charge separation already owing to its conduction band between the graphene and TiO2
, and since it's superhydrophilic, the water attempts to attach to it, scouring off any fouling. And it's highly conductive.http://journal.insciences.org/wp-content/files_mf/1664_171x_1_2_80.pdf
"Spin-polarized DFT calculations show that adsorption of water molecules on graphene plays the role of defects which facilitates the tunability of the bandgap and results in opening a large bandgap of ~ 2 eV."
You'll note that's larger than the 1.8 eV dissociation constant of H3
. So there would be a slight cost over the 1.8 eV required to dissociate H3
alone... but keep in mind that it's the hydrophilic surface that forces water to reorient into H3
in the first place, thereby increasing the efficiency of dissociating it.
But good news... the thicker the graphene sheet, the lower the bandgap:https://www.me.utexas.edu/news/pdfs/Graphene_Ruoff.pdf
"Angle-resolved photoemission spectroscopy (ARPES) studies suggested that this gap decreased as the sample thickness increased and eventually approached zero when the number of layers exceeded four"
ZnO / graphene oxide also appears to be a good material.http://pubs.acs.org/doi/abs/10.1021/am403149g
"When the amount of graphene oxide added is 10 mg, the graphene–ZnO quasi-shell–core composite possesses the optimal photocatalytic degradation efficiency and the best photoelectrochemical performance."
You can purchase small sizes of graphene 'foam':http://graphene-supermarket.com/White_Papers/Graphene%203D-%20free%20standing-flyer.pdf
But attaching electrodes to a graphene 'foam' might prove problematic.
How to dope the base with graphene?http://iopscience.iop.org/0022-3727/46/2/025301/pdf/0022-3727_46_2_025301.pdf
You mix 416.75 ml acetone (99.9% pure), 88.25 ml deionized water, 1.5 grams (high purity 5 micron to 45 micron) graphite, put it into a sealed jar. Then you high speed blend the solution for 12 hours (this is where a high speed pulse motor powering a large stirring magnet would come in handy, it needs to blend at about 15000 RPM) or in a sonic cleaning machine (like you use for jewelry) for 12 hours (if you use this method, fill the sonicator with water, then set your jar with the water/acetone/graphite mix into the water, and be sure to keep the sonicator cavity topped off with water as it'll evaporate pretty quickly, and you might have to drop ice cubes into the water in the sonicator cavity because it'll heat up). You can also put it into a paint mixer (the kind that shakes the paint can back and forth), but you'd have to run it for as much as 24 hours.
That'll give you a liquid solution of graphene that is stable in liquid solution and will remain so for weeks. Let it sit and settle for about a week. Then you put a working amount in a test tube and centrifuge it at 1000 RPM for an hour to separate out any heavier graphite particles. Then you suck out the liquid, leaving behind the heavier graphite particles that didn't get broken up.
Next, you polish your plates to a mirror finish to remove the oxide layer. Now, it has to be said here that graphite contributes to pitting corrosion on some forms of stainless steel (Nichrome, Inconel, Inconel X, Inconel 702, 304, 310, 316, 330, 347), and induces galvanic corrosion on aluminum.
Here's the corrosion potentials of a variety of metals, from most anodic to most cathodic:http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm
Mg alloy AZ-31B
Mg alloy HK-31A
Zinc (hot-dip, die cast, or plated)
Beryllium (hot pressed)
Al 7072 clad on 7075
Al 218 (die cast)
Al 5456-0, H353
Al A360 (die cast)
Stainless steel 430 (active)
Stainless steel 410 (active)
Copper (plated, cast, or wrought)
Stainless steel 310 (active)
Stainless steel 301 (active)
Stainless steel 304 (active)
Stainless steel 430 (active)
Stainless steel 410 (active)
Stainless steel 17-7PH (active)
Niobium (columbium) 1% Zr
Brass, Yellow, 268
Uranium 8% Mo.
Brass, Naval, 464
Muntz Metal 280
Nickel-silver (18% Ni)
Stainless steel 316L (active)
Stainless steel 347 (active)
Molybdenum, Commercial pure
Stainless steel 202 (active)
Bronze, Phosphor 534 (B-1)
Stainless steel 201 (active)
Carpenter 20 (active)
Stainless steel 321 (active)
Stainless steel 316 (active)
Stainless steel 309 (active)
Stainless steel 17-7PH (passive)
Silicone Bronze 655
Stainless steel 304 (passive)
Stainless steel 301 (passive)
Stainless steel 321 (passive)
Stainless steel 201 (passive)
Stainless steel 286 (passive)
Stainless steel 316L (passive)
Stainless steel 202 (passive)
Carpenter 20 (passive)
Titanium 5A1, 2.5 Sn
Titanium 13V, 11Cr, 3Al (annealed)
Titanium 6Al, 4V (solution treated and aged)
Titanium 6Al, 4V (anneal)
Titanium 13V, 11Cr 3Al (solution heat treated and aged)
Noble (Less Active, Cathodic)
The closer together the two metals in the list above, the less chance of galvanic corrosion. Since we want to use graphene on the cathodes to force H2
O into an H3
configuration, our best bet would be to use gold (prohibitively expensive), silver (prohibitively expensive), AM350 (only for non-acidic conditions), Titanium 75A (which would make an excellent electrode, and is currently in use in desalination plants), or 202 SS (which can be electrochemically polished in preparation for graphene coating, and has good corrosion properties due to being passive). These would make good cathodes.
Now I just have to figure out how to get the graphene to attach to the plate surface... I'm not sure if it's as simple as painting it on the surface and letting the carbon in the graphene molecularly attach to the metal as the acetone / water dries, then buffing with a soft cloth and heavy pressure to ensure a uniform layer. I can't find much info.
For the anodes, we have to find a metal that's at the other end of the scale, yet is tough enough to stand up to electrolysis. This will give us the largest electrochemical potential (and thus reduce the amount of electricity we have to supply to accomplish dissociation), while still giving good electrode life. So in this case, we'd want to use something like SS434, which is SS430 with molybdenum for enhanced corrosion protection.
This report shows nickel borate makes a good electrolysis anode, as a replacement for cobalt-based anodes:http://www.gizmag.com/electrode-materials-hydrogen-fuel/15118/
Also, Cobalt / Oxygen / Flourine catalytic anodes to reduce dissociation overpotential:http://www.google.com/patents/US8192609
I intend to try something different... I'll use magnesium hexahydrate in the water itself to force it into the hexagonal configuration. It's formally notated as Mg[H2
, but more accurately would be notated as Mg[H2
. Then I'll try hitting it with different forms of energy resonantly (magnetism, light, RF, x-ray, electricity). I'll also try sound, adding PVDF-TFE to the water to act as a piezoelectric. The surfaces of the dissociation chamber will be hydrophilic to further help water change its configuration to H3
If we could find pure barium, it'd be even better. The technically correct chemical notation of pure barium in water would be Ba[H2
. You can see that it's so reactive that it splits the water into OH and O from the outset. The problem is, it's so reactive it's a fire hazard even in air (it has to be stored in noble gasses or under mineral oil), so introducing it to the water would be problematic, and it corrodes quickly to barium oxide in air.
For the plates, since the H3
exclusion zone is only on the order of 10-15 microns or so, and therefore the plates have to be that close or thereabouts so that only H3
is between the plates, not H2
O, how about very thin beads of silicone caulk run at regular spacing down one side of the plates... the voltage will exert a force that tries to pull the plates together. When they hit the silicone caulk, they can't move anymore, thus they can't short out.
That problem solved, we'd have to come up with some way of accurately applying a 10-15 micron high bead of silicone caulk