Oh, that's weird. They missed all the other noble metals besides silver too. No platinum, rhodium... those things have really really interesting orbital structures, I'm surprised they're worth leaving out of something so tricky when it might be important. Strange.
The only thing I can think of is that they did it and know that those noble metals don't work very well, and so they're getting everyone else to follow a wild goose chase down a very expensive rabbit hole while they already have a better approach.
... but the tech doesn't look that developed. Very strange.
