KARPEN PILE

[profitis]

I'm going to email you now about this one @phil.

[pomodoro]

Hi guys, I've been trying to replicate the Karpen pile for fun, using platinized platatinum electrodes and other inert electrodes.  Normally I plate a metal on one electrode and leave the other as platinized platinum. I've not been able to plate gold as yet but I've tried copper as well as a separate graphite electrode, both of which should not be touched by 1M sulfuric acid.   I've achieved over 1V unloaded with the Cu/Pt combo and about 50 microamps short circuit current for a few days with stirring and nitrogen purging, after which I turned it off. The Cu/Pt is of course simple galvanic corrosion of the copper.

Graphite/Pt gave a smaller voltage and, without stirring, the short circuit current died quickly.  I noticed bubbles around the graphite.

All I can deduce is that it is galvanic corrosion. Different potentials exist at each electrode, so when they touch and a current does flow, oxidation and reduction must occur at the electrodes to pass the current, except that Pt and Graphite (or gold) can't corrode, so H+ is slowly reduced at the more  negative terminal and water oxidized at the positive electrode. 
I still need to measure the individual potentials against AgCl/Ag of the electrodes,  but find it hard to believe that there is enough difference to decompose water electrolytically, so there is still a small mystery, for now.

[profitis]

What electrolyte did you use for the Pt/Cu and how big is your Pt size @pomodoro.

[pomodoro]

I'm using a cell with fixed electrodes about 2 inches apart. The electrodes are about 1 x 1 cm, or 2cm sq total immersed area each. Electrolyte was 1M K2SO4. I realize this setup is only appropriate for low currents but its all I have platinum wise.  The reason why I think Cu/Pt was not a good choice is because of the galvanic corrosion chart below.

[profitis]

Copper is too reactive with certain electrolytes even if below hydogen liberation potential @pomodoro but you're on the right track.try see what current you get with Pt and Ag in NaOH solut. under pure nitrogen (jewellers 925 Ag is fine etched prior in some nitric acid to make a bit of surface area) then compare under pure H2. Your graphite/Pt under vaccuum or nitrogen is capable of a tiny bit of water electrolysis at a time in bursts because the potentials of H2 and O2 buildup to a point correlating with electrode surface coverage concentration.