Hi
It seems , based on this paper, that Nickel is only 10-15% less efficient than Platinum for water disassociation
In other words, we really dont need expensive platinum electrodes to crack water into hydrogen and oxygen - just Nickel.
Reference here :
http://www.engr.psu.edu/ce/enve/logan/publications/2010-Selembo-etal-IJHE.pdf
"The MEC performance in terms of coulombic efficiency, cathodic, hydrogen and energy recoveries were similar using Ni or Pt cathodes, although the maximum hydrogen production rate (Q) was slightly lower for Ni"
Now this is small scale tests with powdered anodes/cathodes, however the principal should still hold for larger plate electrodes in HHO cells.
Apparently Titanium is also good for water disassociation ( electrolysis splitting of water ). I have seen youtube videos of dry cells that apparently more efficiently than stainless steel ones.
I got my nickel electrodes from a school/college science supplies online store.
I'm sure someone would be able to source bigger nickel plate if they hunted around.
I found a source for nickel 735 which is a copper, zinc, nickel alloy. I have no idea of its worth but its fairly inexpensive as compared to pure nickel.
One note: I talked to an electro-chemist on this. He stated that nickel is naturally poisonous to humans. And it must be placed in I believe he stated the anodes position to prevent it leaching itself into the water.
I tried aircraft grade titanium in a test bowl and saw little results myself. Id like to see more on these titanium cells to see what theyve done, and what grade of titanium they are using.