Really? I literally read dozens of papers about it a decade ago, at least... I guess I don't work adjacent to there so maybe no one else does either. Odd, I never have heard a reason why they were all that much worse than alternatives other than for corrosion and licensing costs, I am surprised that such a well defined problem just stopped being studied.

I suppose at some point it's not competitive with solar so what's the point. Maybe we reached that threshold recently.