As expected, the feature concept car being shown by Mercedes-Benz at Frankfurt this year was the F 125! But Merc isn't actually calling it a concept, rather a "research vehicle" that will help the company work toward a gasoline-free future. In this case it's a hydrogen-filled future, with this car running on compressed gas and so giving off only water vapor and oxygen as emissions. But, it's also a plug-in, meaning you can charge this thing up on your garage in addition to topping off the tank at your local H2 filling station -- at some point in the future when you actually have an H2 filling station. Read on for more details.