Hydrogen sorption in palladium doped microporous materials

This research investigated “hydrogen spillover” which has been suggested to improve the hydrogen uptake of bridged and chemically doped porous materials at room temperatures. XRD, Temperature Programmed Desorption and hydrogen sorption measurements were used to characterise the as-received and palladium doped porous materials. The hydrogen uptakes of as-received Maxsorb (activated carbon), Black Pearls (carbon furnace black) and MOF-5 (metal organic framework) were all very low (<0.16 wt.%) at room temperature and 16 bar. Bridging the Black Pearls and Maxsorb carbon samples with 5 wt.% Pd/C resulted in fractionally higher hydrogen uptakes (0.01 wt.%). These results bore a closer resemblance to a physical mixture of Pd and carbon which suggested that the bridges had not been formed and spillover was not occurring. A higher wt.% Pd chemically doped carbon showed an initial rapid hydrogen uptake (0.03 wt.% at <1 bar) followed by a shallower near linear uptake above this pressure. The hydrogen uptake seemed more consistent with palladium and carbon sorbing independently, rather than hydrogen spilling over from palladium to carbon giving enhanced uptake. However, good contact between Pd and carbon must be established and the result must be replicated to confirm its validity in the face of much contrary literature.