A team from MIT and other institutions has analysed the performance of a class of materials considered a promising candidate for hydrogen storage.
The new activated carbon materials incorporate a platinum catalyst, so hydrogen atoms can bond directly to the surface of carbon particles and then be released when needed.
‘You have to be able to pump the gas in [at room temperature] and release it when you need it to burn,’ said MIT’s Sow-Hsin Chen, senior author of a paper describing the new method.
Such a storage system could avoid the cost and weight associated with conventional hydrogen storage.
Current approaches either liquefy the gas, requiring energy-intensive systems and heavy insulation to maintain a temperature of -423°F; or store it under high pressure, requiring powerful pumps and robust tanks to withstand 5,000 to 10,000 pounds per square inch (psi) of pressure.
Bonding the hydrogen to a highly porous, sponge-like material, such as a metal hydride or activated carbon, makes it possible to use ambient pressure and room temperature in storage tanks that could be lighter, cheaper and safer.
The tricky part of designing such systems is finding a storage medium that bonds the hydrogen atoms tightly enough to prevent them leaking away, but not so tightly that they cannot break free when needed.
According to MIT, activated carbon has been proposed as a possible storage medium that could work by bonding dissociated hydrogen atoms, but previously there was no good way of analyzing the material’s behavior and optimizing its storage capability.
The team analyzed the activated carbon’s storage of hydrogen using inelastic neutron scattering, which they say is capable of determining whether the hydrogen in the sample exists as individual atoms or H2 molecules. This approach can also assess the gas’s interaction with the storage material.
Using this method, they were able to provide evidence that hydrogen moves into the material as a result of the spillover effect, in which atoms — thanks to the presence of platinum particles as a catalyst — split off from their molecules and diffuse through the carbon, where they bond to its surface.
The new analysis method should make it possible to fine-tune the properties of the activated carbon material to increase its storage capacity, Chen said.
Their findings were reported in a paper published online in the Journal of Physical Chemistry Letters in August.