Ammonia is probably the most scalable medium for energy storage. It doesn't need to be pressurized, and doesn't leak as easily as hydrogen does. You can also turn it into fertilizer, which is a huge advantage that gasoline doesn't have. It's going to be the go to solution for ocean container ships and many companies are already working on large scale marine ammonia engines.
More Discussion of ammonia's potential over here: https://news.ycombinator.com/item?id=38053586