Thermal conductivity of hydrogen sorbent materials for onboard storage applications

Measuring the thermal conductivity (TC) of H₂-physisorption storage materials under system conditions are critical in designing the most practical onboard H₂ storage vessels. Furthermore, knowing the TC helps understanding how the heat associated with the sorption/desorption of H₂ is distributed throughout the storage material.
In this work, we will show that the thermal properties of the powder materials can differ significantly from those of the bulk materials as heat transfer within a powder mainly occurs via: a) conduction through the solid particles and the gas within the interstices; and b) convection through the gas. To this end, we measured the TC on pellets of MOF-5 and powder Cu-MFU-4l with our state-of-the-art TC apparatus. We studied the behavior under He and H₂ pressures ranging from 0.03 - 80 bar, at temperatures ranging from 40 K - 380 K, and for different degrees of powder compaction. We will discuss that we measure an effective thermal conductivity that depends on the TC of the powder particles, on the powder compaction, the TC of the surrounding gas, the number of binding sites occupied, and the possible expansion or contraction of sorbents during the gas sorption/desorption which in turn all depend on temperature and pressure.