On the hydrogen adsorption and dissociation on Cu surfaces and nanorows

Abstract

Here we present a thorough density functional theory study, including and excluding dispersive forces interaction description, on the adsorption and dissociation of H2 molecule on the low-index Miller Cu (111), (100), and (110) surfaces and two different surface Cu nanorows, all displaying a different number of surface nearest-neighbours, nn. The computational setup has been optimized granting an accuracy below 0.04 eV. Surface and nanorow energies ¿for which a new methodology to extract them is presented¿ are found to follow the nn number. However, the adsorption strength is found not to. Thus the adsorption energies seem to be governed by a particular orbital↔ band interaction rather than by the simple nn surface saturation. The van der Waals (vdW) forces are found to play a key role in the adsorption of H2, and merely an energetic adjustment on chemisorbed H adatoms. No clear trends are observed for H2 and H adsorption energies, and H2 dissociation energy with respect nn, and no Brønsted-Evans-Polanyi, making H2 adsorption and dissociation a trend outlier compared to other cases. H2 is found to adsorb and dissociate on Cu(100) surface. On the Cu(111) surface the rather smaller H2 adsorption energy would prevent H2 dissociation, regardless is thermodynamically driven to. On Cu(110) surface the H2 dissociation process would be endothermic, and achievable if adsorption energy is employed on surpassing the dissociation energy barrier. On low-coordinated sites on Cu nanorows, vdW plays a key role in the H2 dissociation process, which otherwise is found to be endothermic. Indeed dispersive forces turn the process markedly exothermic. Nanoparticle Cu systems must display Cu(100) surfaces or facets in order to dissociate H2, vital in many hydrogenation processes.