CCGTs have efficiencies in the range of 60%-ish percent. bringing it up to 85% would mean that now these run almost at carnot efficiency taking adiabatic flame temperature of methane burning in air as upper and practical temperatures of heatsink (60C) as lower. this is not happening, because other cycles with lower efficiencies are used in practice

if you want to improve efficiency of power generation, just replace old junk with new kit, or better yet, build nuclear and renewables where efficiency matters less when considering emissions. you know what, damn i do think that lying box burning enough electricity to power a small country (like macedonia) could come up with this