Hydrogen Storage

The following is a case highlight from a paper that can be read here.

As the need for cleaner forms of energy grows, metal hydrides look to be a promising way to store enough hydrogen to meet future energy requirements. A complex metal hydride storage medium of 2LiBH₄-MgH₂ was proposed as an optimal candidate for hydrogen storage based on its cost, availability, and energy density. However, the thermodynamic and heat transfer properties of the system need to be understood in order to design proper storage tanks for the material.

The effective thermal conductivity of the complex metal hydride was measured at different temperatures in both the absorbed and desorbed states using C-Therm’s Modified Transient Plane Source (MTPS) sensor.

Thermal conductivity as a function of temperature for both the absorbed and desorbed state of the complex metal hydride

This graph shows that while the absorbed state has a higher thermal conductivity, both exhibited quite low thermal conductivities compared to other common materials. This provided insight for the design of a thermal management system; since the hydride itself would be insufficient at dissipating enough heat, other solutions must be found such as additives or active cooling.

The following is a case highlight from a paper that can be read here.

Magnesium hydride is an attractive material for hydrogen storage due to availability and energy density; however, it does have a high temperature of operation and slow reaction kinetics. Heat transfer issues prove to be one of its most significant draw backs, as poor heat transfer could result in the melting of the magnesium, or the stopping of the reaction during desorption.

One proposed solution was to press the powder into pellets to achieve higher thermal conductivity and doping the hydride with vanadium catalysts to improve thermal conductivity. Vanadium compounds were added by first ball milling the compound, reducing its particle size. The thermal conductivity of pure magnesium hydride powder was found to be 0.092 W/mK, however this decreased for all the trials after ball milling had taken place. The results for pressed magnesium hydride powders can be seen below:

Thermal conductivity of magnesium hydride pellets, with differing particle sizes and additives

This shows that while pressing the powder did have a large increase on thermal conductivity (about 20x), the addition of vanadium or vanadium oxide on a catalyst had little impact, meaning that larger particle size should be prioritized over the use of additives.

The following is a case highlight from a paper that can be read here.

As metal hydrides receive more research and funds, more effort goes into characterizing them. In this particular experiment, a sealed stainless-steel vessel has been used to stored the metal hydride in either powder or pellet form. However, it is important to characterize a wide range of metal hydrides to understand how much heat needs to be put into the stainless-steel vessel in order to release a given amount of hydrogen gas.

The thermal conductivities of metal hydrides in both powder and pellet form were tested using the Modified Transient Plane Source (MTPS) sensor. Due to the reactive nature of metal hydrides, they were all tested in an inert atmosphere glove box. The results of various metal hydrides can be seen below:

A graph showing the thermal conductivities of common metal hydride materials, both as a powder, and compressed pellet

These results allow for better control of hydrogen release based on energy input, depending on the type of hydride or solid state used.