Storage hydrides

Consider a chemical reaction, which may be described in the form 

For near-ideal multi-component gases, it is possible to use macroscopic average variables in a thermodynamical description, and write the change in the Gibb s free energy G as 

Introducing the enthalpy from the definition H = G + TS, the temperature dependence of the quantities in (2.56) can be expressed by van t Hoff s equation 

In integrated form this reads (using AH = AG + TAS to fix the integration constant) 

Finally, with use of Pj = X P the equilibrium conditions, one can rewrite (2.58) in the form (given in a slightly different way by Morse, 1964 Schlapbach and Ztittel, 2001) 

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The use of hydrides as a means of storing hydrogen is not yet (ca 1994) of commercial importance. Hydride storage has been used in demonstrations, eg, to power automobiles (206). Hydride formulations and properties are available (131,207—209). 

One of the problems with early hydride systems was decrepitation of the alloy. Each time the metal hydride storage tank was recharged the particles would break down and eventually the particles became so small that they began to pass through the 5-p.m sintered metal filter which kept the hydride inside the tank. Addition of 0.5% manganese, which caused the decrepitation process to cease once the particles reached a size of about 10 p.m, solved this problem. 

One of the principal advantages of hydrides for hydrogen storage is safety (25). As part of a study to determine the safety of the iron—titanium—manganese metal hydride storage system, tests were conducted in conjunction with the U.S. Army (26). These tests simulated the worst possible conditions resulting from a serious coUision and demonstrated that the metal hydride vessels do not explode. 

K. C. Hoffman and co-workers, "Metal Hydride Storage for MobUe and Stationary AppUcations," SAE Fuels andUubricants Meeting St. Louis, Mo., 1976. 

Conclusively, hydrogen has been used and stored safely in the industry for quite a long time as compressed gas or liquefied hydrogen, and it seems that metal hydride storage will be equally safe or even safer. Consideration of future hydrogen applications reveals no safety problems in the industrial and commercial markets. Although hydrogen safety... 

Toyota and Honda have been experimenting with both methanol and metal-hydride storage of hydrogen. Honda has built several test cars, in 1999 a Honda FCX-V1 (metal-hydride hydrogen) and FCX-V2 (methanol) were tested at a track in Japan. The Ballard powered version-1 was ready, but proved to be a little sluggish and noisy. The other car suffered from a noisy fuel cell. Both Honda fuel cell test cars were built on the chassis of the discontinued EV Plus battery electric. Honda used a different and more aerodynamic body. 

Waste heat from the fuel cell is used to reverse the reaction and release the fuel. In 2005 GM and Sandia National Laboratories launched a 10-million program to develop metal hydride storage systems based on sodium aluminum hydride. 

Several storage systems can be implemented, making up water splitting. The electrochemical NiOOH/MH metal hydride storage process has been implemented in a bipolar AlGaAs/Si cell [104],... 

Compressed gas and liquid storage are the most commercially viable options today, but completely cost-effective storage systems have yet to be developed. The safety aspects with all storage options, particularly the novel hydride storage options, must not be underestimated (Schlapbach and Ziittel, 2001). 

Hydrocell - Develops alkaline fuel cells and metal hydride storages. 

Cross-cutting R D efforts in the area of metal hydride storage systems. 

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