H2 can be dissociated by an electric arc into monatomic hydrogen, which can in turn be trapped in that state in the crystalline structure of certain metals (Palladium is one, if I recall). This technology has existed for a long time, but it has had no industrial application that I know of). By creating a colloidal suspension of fine particles of these metals, with high surface area/volume ratios, in cryogenic fluids (like H2 or O2) it might be possible to cold-stabilize large amounts of monatomic hydrogen for use as a fuel enhancer, greatly increasing power and thrust in engines of conventional chemical rocket design. There are other diatomic gases this could be tried with, too.

As the cryogenic fuel and oxidizer met in the engine and conventional combustion took place, the metallic particles would vaporize releasing the H1 which would rapidly react to return into its diatomic state, releasing enormous amounts of energy. Has anyone ever looked into this?

I can see a lot of places where this chain of events might break down, but I can't believe someone hasn't experimented with this. The energy available in monatomic hydrogen has been a dream of rocketeers for decades, it is the most energetic chemical reaction known, potentially giving specific impulses several times that of 2H2+O2 -> 2H2O. I first read about it in one of G Harry Stine's books in the early 60s.