Ligands Affect Hydrogen Absorption and Desorption by Palladium Nanoparticles

We report herein in situ X-ray diffraction experiments that show that surface ligands affect the rates of hydrogen absorption and desorption in octahedral palladium nanoparticles. This observation was made possible by: (i) using a UV-driven photolysis and ozonolysis treatment to convert the ligand-stabilized palladium nanoparticles to pristine (i.e., ligand-free) nanoparticles while maintaining the size and shape of the core; and (ii) tracking in situ the phase transformation under a hydrogen environment. Our experiments revealed that pristine nanoparticles absorb and desorb hydrogen 10-fold faster than the corresponding ligated samples. This finding is supported by comparing octahedral nanoparticles stabilized by two different types of ligand coatings that both show faster hydrogen absorption and desorption after ligand removal. The data indicate that in addition to nanoparticle shape, surface structuring, and size, the ligand shell must be taken into account when examining hydrogen absorption and desorption in palladium nanoparticles.