Metal Hydride Technology
Hydrogen (H2) is the most abundant element in the universe. It has the highest energy per unit of weight of any chemical fuel and is non-polluting since it produces only water when combusted (equation 1).

2 H2 + O2 --> 2 H2O + HEAT DH = -286 kJ per mole of water formed (1)

Hydrogen are normally stored as a compressed gas or cryogenic liquid. Both are extremely volatile and requires thick and heavy storage container. The discovery of metal hydride presents a new way to store hydrogen. Metal hydride are special transition metal alloy that has a special capability to reversibly store and release hydrogen (equation 2).

M + x/2 H2 <--> M-Hx + HEAT (2)

Hydrogen charging and discharging process using metal hydride storage

In the forward reaction, heat is required for the absorption of hydrogen to form a metal hydride. When this happens, hydrogen is distributed compactly throughout the metal hydride lattice.  The reaction is reversible and its direction is determined by the pressure of the hydrogen gas. If the pressure is above the equilibrium pressure of the hydrogen gas, the reaction proceeds to the right to form a metal hydride (Stage 2/graph1); if the pressure drops below the equilibrium, hydrogen is liberated and the alloy returns back to its original state. This equilibrium pressure is dependent on temperature - it increases with inceasing temperature and vice versa. Metal hydrides is thus able to adsorb and release hydrogen reversiblily without significant deterioration.

Graph 1: Hydrogen is adsorbed at pressures higher than 5 atm and desorb at lower pressure

In the metal hydride, the hydrogen is distributed compactly throughout the metal hydride lattice. Even though conventional metal hydride (AB5) stores up to 1.6% of usable hydrogen by weight, hydrogen storage product using metal hydride has a high volumetric hydrogen storage capacity compared to conventional hydrogen storage which requires heavy pressurised cylinder.

Storage
State
Medium
Method
Storage Vs Gas
Density (kg/m3)
Storage Vs Weight
Efficiency (%)
Gas
Stainless steel tank
( 150 atm )
Compression
12.1
1.5
Liquid
Stainless steel tank
Compression
@ -220
46.9
13

Aluminium Tank
Compression
@ -220
46.9
23.7
Solid
Stainless steel tank
Diffusion
47.0
1.4 - 1.65

Advantagous of AB5 metal hydride for hydrogen storage:
  • Hydrogen is stored in safe and reliable metal hydride
  • High volumetric hydrogen density at low pressure - compact storage
  • No boiled off effects like compressed hydrogen gas
  • Hydrogen discharges and absorbs at normal atmospheric pressure and temperature
Our range of metal hydride (Ab5) hydrogen storage systems.