Hydrogen Fuel Cells: Current Status and Potential for Future Deployment
This chapter provides an overview of fuel cell technology. The basic principles of fuel cells have been described along with their three main application areas including transportation, portable power and stationary power. Hydrogen is the lightest of gases, so its storage density is low even when it is pressurized to 700 bar or stored as a cryogenic liquid. Hydrogen is typically produced by steam reforming natural gas. The reformate stream contains substantial amounts of CO, which must be removed by the shift reaction to make the hydrogen suitable for polymer electrolyte membrane (PEM) fuel cells. In the case of PEM fuel cells, practical stack efficiencies are about 50 percent. Direct methanol fuel cells suffer from higher activation and ohmic losses than PEM fuel cells and can therefore produce practical efficiencies of around 30 percent. Solid oxide fuel cells exhibit low activation losses due to very high operating temperatures resulting in efficiencies of around 60 percent.