Density Functional Theory Studies of Size and Doping Effects on Hydrogen Evolution Catalysis by Ag and Cu Nanoclusters

Turning nonprecious metals into efficient catalysts for the hydrogen evolution reaction (HER) presents both fundamental challenges and significant technological implications. Metal nanoclusters (MNCs) exhibit considerable potential to achieve this objective due to their quantum size effects and low-coordination environments. In this study, we comprehensively investigate the size and doping effects of silver (Ag) and copper (Cu) clusters using first-principles density functional theory (DFT). Our findings indicate that the adsorption free energies of hydrogen on both Cu and Ag clusters are enhanced compared to those on their periodic surface counterparts, leading to significantly improved HER performance. Specifically, for Cu clusters, Cu55 demonstrates the best HER performance with a hydrogen free energy (ΔGH) of only −0.03 eV at hollow sites. In contrast, Ag13 exhibits the best HER performance among Ag clusters, with a ΔGH of −0.08 eV at bridge sites. The incorporation of nickel (Ni) and platinum (Pt) weakens the hydrogen adsorption energy of the Cu13 cluster, resulting in improved HER performance for Cu13. Partial density of states (PDOS) analysis reveals that as we transition from bulk materials to clusters, the density of states around the Fermi energy increases due to quantum confinement effects, thereby enhancing hydrogen binding ability. Also, the doping of Ni and Pt in Ag and Cu clusters can effectively shift the position of the d-band center and tune the hydrogen binding ability. Furthermore, Bader charge analysis indicates that charge accumulation on the Pt- and Ni-doped clusters increases with cluster size. This research provides valuable insights into optimizing catalytic activity for hydrogen adsorption across different cluster sizes, as well as in Ni- and Pt-doped Cu and Ag nanoclusters in the context of HER.