Hybrid Pd₃₈ nanocluster/Ni(OH)₂-graphene catalyst for enhanced HCOOH dehydrogenation: First principles approach

Hydrogen energy is a potential next-generation energy source for fossil fuel replacement. The development of high-efficiency materials and catalysts for storage and transportation of hydrogen energy must be achieved to realize hydrogen economy. Recently, catalyst systems such as Pd nanoclusters (Pd NCs) supported on nickel hydroxide (Ni(OH)2) have been reported to have advantages, including effective suppression of CO production and efficiency enhancement of HCOOH dehydrogenation. However, the reaction mechanism and multi-metallic interface system design of such systems have not been elucidated. Therefore, various Ni(OH)₂ surfaces supported on a graphene system were designed through density functional theory calculations, and the support material was combined with Pd₃₈NC (Pd₃₈NC/Ni(OH)₂-G). Subsequently, the adsorption behavior of HCOOH dehydrogenation intermediates was analyzed. We found a new adsorption configuration in which HCOOH* (where * and a single underline indicates the adsorbed species and adsorbed atom, respectively) was adsorbed in a more stable manner (adsorption energy, E_ads= −1.22eV) on the system than HCOOH* (E_ads=−1.10eV) owing to the presence of Ni(OH)₂-G. This affected the next step in HCOOH dehydrogenation, i.e., formation of HCOO* species, and showed a positive effect on the HCOOH dehydrogenation. To fundamentally understand this phenomenon, electronic structure (d-band center and density of states) and stability (vacancy formation energy) analyses were performed.