Hydrogen gas by electrolysis

[Walter M]

Does hydrogen formed by electrolysis have a specific isotopic signature?

With other words; does hydrogen undergo isotopic fractionation during the process?

[Enthalpy]

Hi Walter M, welcome here!

 

As far as I know, every method to prepare deuterium begins by enrichment of heavy water, then reduction to hydrogen, and at last anrichment of deuterium.

 

Because hydrogen reduction demands much energy, it's done as late as possible, when water contains already much deuterium. Electrolysis is one convenient means. Hydrogen diffusion then separates the isotopes efficiently thanks to the big mass ratio.

 

Electrolysis itself doesn't seem to contribute much to the separation. It must be about as efficient as one single step of gaseous diffusion, but it will reduce protium (¹H) first, which is exactly the undesired effect since enrichment's goal is deuterium (²H). The reason being that the lighter protium is more mobile than deuterium.

 

I've read conflicting reports about it, but even deuterium production in Norway for Germany during WWII was the reduction step, not intended for enrichment, and was not the only step in enrichment. Enrichment by electrolysis only would need to

- Electrolyse all the natural water, instead of the enriched fraction of it;

- Repeat it many times with successive concentrations, despite gaseous diffusion does the rest as efficiently and at a low energetic cost, once hydrogen is reduced.

 

So while some separation occurs, it's the wrong direction, and far worse than competing means.