Tier 4 basic catylst grind

So i am doing act 4, but i really dont have good 4 stars, all of the are only rank 3, i want them to be rank 4, I have a rank 4 mordo, rank 3 killmonger, rank 3 cap america infinity war, rank 3 carnage, rank 3 airwalker all 4*, but I have 2 tier 4 basic catylsts and i want more, how do i do this, i also dont have , much energy refill.