Effect of Contacts in Assemblies of Nanoparticles on Hydrogen Adsorption and Kinetics

Numerous studies have demonstrated a strong coupling between the lattice strain and catalytic activity of platinum group elements. Understanding the strain–activity relationships require creating new types of strained nanoscale materials. Here, we investigate strain distribution in assemblies formed by attachment of metastable Pt and Pd nanoparticles. Through the formation of coherent and incoherent interfaces at the particle-particle contacts, these systems give rise to unusual coordination environments and strain states that may affect their catalytic activity. Transmission electron microscopy observations suggests that octahedral nanoparticles form preferentially face-to-face, corner-to-corner, and corner-to-face contacts. We use classical molecular dynamics to simulate the nanoparticles attachment process leading to the formation of particle-particle contacts and to create plausible atomistic models of these contacts depending on the relative orientation of the nanoparticle. Characteristics of the atomic sites in the vicinity of the contacts regions, including coordination number and local interatomic distances, allow us to relate the structure of the particle-particle contacts and the corresponding strain distributions to their ability to bind and accumulate hydrogen species. These predictions are then validated against <i>ab initio</i> simulations and further linked to the local electronic properties of the interfacial atoms. This study deepens our mechanistic understanding of the role of nanoparticle contacts in hydrogen adsorption and provides suggestion on a viable path towards rational design of hierarchical structures with a high affinity to hydrogen.