Metal Alloys and Chemical Hydrides seem to be up there in 6 kWh/l zone though

https://www.researchgate.net/profile/Markus_Reuss/publicatio...

Not enough room? You can build a floating solar panel, that just ships over the ocean, generating charged LOHC which then is collected by a automated ship.

PS: If you look at the references of this paper you can see the BMW research that is referenced.