I did a search to find such devices.  I didn't but came up with this
interesting article:

http://www.feer.com/articles/2000/0012_21/free/p056innov.html

Do you know where you saw the aftermarket devices?

Ed

-----Original Message-----
Dave said:

I've seen them (catalysts) sold as an aftermarket add on for wet cells used
in solar
storage applications however (catalyst replacement caps).

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