Re: As I can know the efficiency of my catalyst and .........?

Dear William,

I think that others have performed similar experiments before you.  Please 
follow the links at the end of this answer.  Use the MadSci Search Engine for 
more information.

You do not give the identity of your catalyst, but it must be a good 
conductor.  Ionic salts are added to water to speed the electrolysis of 
water since pure water is a poor conductor.  You already have NaCl in the 
solution (Na+ & Cl-)which is already a good conductor.  I suspect that one 
or both of your electrodes is copper and is responsible as the source of 
the copper hydroxide.  

SAFETY NOTE:  
chloride salts are not recommended as electrolytes since chlorine gas 
is liberated at the anode!


Since the quantity of hydrogen liberated is not an indicator of the 
efficiency of the catalyst (merely the product of the total current 
passed) it is the speed or rate of liberation which characterizes a 
catalyst.  You know the efficiency of the catalyst from the increase in 
rate in the manner that you have already observed.

Similar observations have been presented to MadSci Network 
before..."How can I electrolyze water so I don't get an oxide on my anode?"
Find the answer here 
and "Weird electrolysis results" were explained here 
.

Best regards and SAFE experimenting!!