Why it works
Quoting from the article:
They found that hydrogen binding initiated a domino effect, with structural changes propagating from the sample’s surface through all the carbon layers underneath, turning the initial graphite-like structure of planar carbon sheets into an arrangement of carbon atoms that resembles diamond … [T]he scientists discovered that hydrogen binding resulted in the formation of chemical bonds between graphene and the platinum substrate.
How to instantly turn ‘pencil lead’ (graphite) into diamond | KurzweilAI
This illustration shows four layers of transformed graphene (single sheets of graphite, with carbon atoms represented as black spheres) on a platinum surface