However

There's an upper limit to what elements will fuse and give off energy. Making the larger elements actually takes energy, and splitting them is what gives off energy. That's why we use Uranium in fission and hydrogen in fusion.

IIRC (but physics long time ago), iron is the highest element you can fuse and still get energy out of it. I've heard Lithium is the best bet for a fusion reactor, but I can't remember where, so take that with a grain of salt.