As a fuel to power engines, hydrogen may realize the possibility of very low emissions—and potentially zero emissions. Hydrogen fuel can be converted electrochemically into electric energy using a fuel cell or burned in a hydrogen combustion engine. The fuel cell is one of the most promising clean-energy technologies, while the hydrogen combustion engine provides another option for carbon-free hydrogen fuel.
Hydrogen does not commonly occur in its diatomic form on Earth and, thus, it is not so much an energy resource as it is a synthesized carrier, made from other resources. Today, hydrogen is commonly generated from natural gas with about 80 percent efficiency. Hydrogen is also extracted from water using electricity to power an electrolysis reaction.
Storing hydrogen fuel onboard a vehicular poses challenges. Although hydrogen is environmentally friendly, particularly at its point of use, it is not as dense as conventional fossil fuels and requires large, reinforced and pressurized storage tanks to achieve practical driving distances. This presents space constraints for vehicle designs and potential safety concerns.
The U.S. Department of Energy Hydrogen Program technical plan calls for the development and commercialization of economical hydrogen production, generation, and distribution technology by 2015 and market incorporation by 2020.
To support this goal, LLNL researchers have designed, built, and demonstrated a hydrogen-storage tank on a conventional vehicle that can hold 10 kilograms of liquid hydrogen—enough for 500+ miles of driving. Livermore Laboratory is also examining the use of exotic microbes as biological hydrogen generators. For use in hydrogen fuel production, the most promising microbes are Pyrococcus furiosus. P. furiosus can consume extracts of starchy plant matter, digesting the carbohydrate in a way that not only provides energy but also releases hydrogen gas.
In addition, Livermore Laboratory researchers designed a hydrogen-storage tank for a hybrid vehicle that can hold liquid hydrogen for six days without venting. This is a significant increase compared to other tanks capable of holding hydrogen for merely two to four days. Such a vehicle could become competitive in the marketplace when fuel tank technology is improved upon and ecomonical hydrogen production methods are discovered.
This Science & Technology Review article describes a conceptual design of a hydrogen hybrid vehicle that features a large fuel tank for pressurized hydrogen. It has a gasoline-equivalent fuel efficiency of 80 mpg and a driving range of 380 miles (608 kilometers).
This document describes one concept to circumvent the challenges of fueling up with hydrogen by harnessing the ability of naturally existing microbes to create the fuel in the vehicle's powertrain.