A research team at Imperial College London is working on a new series hybrid drivetrain based on the ZEBRA sodium nickel-chloride battery and a solid oxide fuel cell. While pretty much all of the fuel cell-powered vehicles currently being developed use proton exchange membrane (PEM) fuel cells that run on hydrogen gas, this system uses a solid oxide stack that runs at higher temperatures. The heat generated by the stack could be used to power a fuel reformer that could use alternative fuels to generate hydrogen on the fly.
Unfortunately that heat that is given off comes at the cost of power density which is lower than PEM stacks. Solid oxide stacks also don't like to cycle on and off either which makes them better suited to an application like a series hybrid where they aren't the primary power source. The Zebra batteries that the team is using also have good operating characteristics as far charging and discharging efficiency, they don't drain while sitting and they have long life and good safety. The problem is they also need to operate at high temperatures on the order of 520-570F.
The researchers have been testing a bench-top system working with compressed hydrogen, propane and natural gas as fuels. Due to storage issues the hydrogen has the lowest range. The propane and natural gas are used with an on-board reformer but still result in CO2 emissions. Because of the heat generated by both the fuel cell and battery, such a system is not likely to be usable in smaller vehicles although it could be workable in larger vehicles like transit buses.