CO2 emissions from the transportation sector are now the largest source of greenhouse gas emissions in many parts of the world, including the U.S.. Hydrogen fuel cell technology offers the promise of a zero emissions footprint, but with several drawbacks. Hydrogen molecules are extremely light, requiring high pressure (700 bar, or 300x the pressure of car tires) to densify the energy needed to support vehicle range requirements. High pressure storage drives fuel tank and refueling infrastructure costs, and poses added safety risks.