Question

Compare and contrast the following hydrogen-storage technologies:

(1) compressed hydrogen; (2) liquid hydrogen; and (3) complex hydrides.

Answer 1

1. Compressed hydrogen is a storage form where hydrogen gas is kept under pressures to increase the storage density. Compressed hydrogen in hydrogen tanks at 350 bar (5,000 psi) and 700 bar (10,000 psi) is used for hydrogen tank systems in vehicles, based on type IV carbon-composite technology.
An innovative storage device for compressed hydrogen is based on glass capillary arrays with a honeycomb-like structure and a diameter of approximately 100 μm. This structure is mechanically stable and can manage pressures over 1,000 bar.

Composite pipes are assessed like:

• carbon fiber structure with fiberglass overlay
• perfluoroalkoxy (PFA, MFA)
• polytetrafluoroethylene (PTFE)

2. Liquid hydrogen is usually stored in horizontal or vertical cylindrical tanks. Spherical tanks are sometimes used for larger volumes. Tanks are vacuum-insulated and contain redundant pressure-relief devices as a safety precaution to prevent over pressurization.
Currently, storing hydrogen in the liquid form is being reserved for certain special applications, in high-tech areas such as space travel.
Due to Liquid Hydrogen's cold temperatures, liquid hydrogen is a hazard for cold burns. Apart from that, elemental hydrogen as a liquid is biologically inert and its only human health hazard as a vapor is displacement of oxygen, resulting in asphyxiation. Because of its flammability, liquid hydrogen should be kept away from heat or flame unless ignition is intended.

3. Complex hydrides such as Metal hydrides, chemical hydrides, Nanoporos structures are used for starge of hydrogen. These store in the interstitial structure of the complex hydrides and form defects (interstitial defects). These are very promising but are not used because of unknown thermodynamic and kinectics of the hydrides.