RESUMO
Theoretical calculations are performed to elucidate the adsorption behaviors and poisoning effects of CO gas on the ZrCo surface, which drastically limits its application in hydrogen isotopic storage. Specifically, the ionic Zr-Co bond on the surface leads to unique CO adsorption structures on different sites. The CO molecule tends to prefer a tilted adsorption configuration on the Co-Co bridge site. The electronic structures, charge distributions, and bonding characteristics are further explored to study the CO adsorption properties, which obey the electron density donation and back-donation mechanism. For different CO coverages, the stepwise adsorption energies of CO increase with the increasing of coverage, reaching the saturated coverage at nCO = 11. Then, the effects of temperature and partial pressure on CO coverage are evaluated using atomic thermodynamics. The computed phase diagram shows that the ZrCo(110) surface has a stable coverage of nCO = 6 at ambient temperature under ultrahigh vacuum conditions. The pre-adsorbed CO molecules lead to the charge redistribution and the d-band center downshift on the surface, which significantly affect hydrogen adsorption and dissociation. Our results provide insights into the poisoning mechanisms of the impurity gas on ZrCo alloys, which can be beneficial for designing high-performance ZrCo-based alloys with improved poisoning tolerance.
RESUMO
Extensive research has been devoted to developing metal nanoparticle (NP) doped porous materials with large hydrogen storage capacity and high hydrogen release pressure at ambient temperature. The ultra-sound assisted double-solvent approach (DSA) was applied for sample synthesis. In this study, tiny Pd NPs are confined into the pore space of HKUST-1, affording Pd@HKUST-1-DS with minimizing the aggregation of Pd NPs and subsequently the formation of Pd NPs on the external surface of HKUST-1. The experimental data reveal that the obtained Pd NP doped Pd@HKUST-1-DS possessed an outstanding hydrogen storage capacity of 3.68 wt% (and 1.63 wt%) at 77 K and 0.2 MPa H2 (and 298 K and 18 MPa H2), in comparison with pristine HKUST-1 and impregnated Pd/HKUST-1-IM. It is found that the storage capacity variation is not only ascribed to the different textural properties of materials but is also illustrated by the hydrogen spillover induced by different electron transport from Pd to the pores of MOFs (Pd@HKUST-1-DS > Pd/HKUST-1-IM), based on X-ray photoelectron spectroscopy and temperature desorption spectra. Pd@HKUST-1-DS, featuring high specific surface area, uniform Pd NP dispersion and strong interaction of Pd with hydrogen in the confined pore spaces of the support, displays the high hydrogen storage capacity. This work highlights the influence of spillover caused by Pd electron transport on the hydrogen storage capacity of metal NPs/MOFs, which is governed by both physical and chemical adsorption.
