Is Spillover Relevant for Hydrogen Adsorption and Storage in Porous Carbons Doped with Palladium Nanoparticles?

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• 作者：María Blanco-Rey ; J. Iñaki Juaristi ; Maite Alducin ; María J. López ; Julio A. Alonso
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 11, 2016
• 年：2016
• 卷：120
• 期：31
• 页码：17357-17364
• 全文大小：482K
• 年卷期：0
• ISSN：1932-7455

文摘

Experiments have shown that the efficiency of nanoporous carbons to store hydrogen becomes enhanced by doping the material with metallic nanoparticles. In particular, doping with palladium has been used with success. The hypothesis to justify the enhancement has been that the Pd nanoparticles dissociate the hydrogen molecules and then the hydrogen atoms spill over the carbon substrate, where the hydrogen is retained. To test this hypothesis we have performed ab initio molecular dynamics simulations of the deposition of molecular hydrogen on Pd nanoparticles (Pd₆ and Pd₁₃) supported on graphene, which is a good model for the wall of a carbon nanopore. Three channels have been identified in the simulations: bouncing off the molecule, molecular adsorption, and dissociation of the molecule in two H atoms. The relative percentage of those channels is sensitive to the size of the Pd particle. Dissociation occurs more frequently on Pd₁₃ and it generally takes place on the lateral regions of the Pd particles. However, in our simulations, we have not found a single case of H atoms or H₂ molecules spilling over the carbon substrate. We have also tested the situation when several H atoms are preadsorbed on the Pd₆ and Pd₁₃ particles and found that not a single dissociation event occurs on these H-saturated nanoparticles. These results lead us to cast strong doubts on the validity of the spillover mechanism for explaining the enhancement of hydrogen adsorption on porous carbons doped with transition metal nanoparticles.