With electrolysis a high current will, of course, work quicker but the general recommendation is to use a lower current over a longer time (less than 1 amp). You can also use plain salt as the electrolyte but this will generate hydrogen so only do it outside. Probably the safest way, if you don't want to risk affecting other metal, is to use something like Evapo-rust. It's relatively harmless and will only attack the rust.
If the pitting extends to the cutting edge there's really not much you can do about it, just sharpen it as best you can. You should end up with a tool with a bit of character.