There's potentially some merit there, since the expense of the catalyst (and its decontamination process) is a significant barrier to the use of hydrogen fuel cells. That said, I'd expect it to be dramatically less efficient than a fuel cell system.

They have a fuel cell vehicle - https://www.toyota.com/mirai/

I have my doubts that hydrogen combustion will ever be viable for consumer vehicles. The energy output is far too low, and storage is vastly too problematic.