Hydrogen-mediated enhancement of Ag₄ cluster activity and stability for CO₂ electroreduction

Electrochemical CO_2 reduction to CO (CO_2RR) is a sustainable carbon utilization route. Silver is widely recognized for its high CO selectivity and favorable cost-performance compared to gold, but nanostructured Ag catalysts suffer from stability issues during prolonged operation. Using the IM^2ODE inverse-design algorithm and density functional theory calculations, we identify the large-pore N-doped graphene (NG) supported regular tetrahedral Ag_4 cluster (r-Tet) as thermodynamically stable and CO_2RR-active. Substituting its apical Ag atom (Ag_3M@NG; M = \rm Cu, Ru, Rh, Pd, Ir, Pt, Au) shows that coinage metals (Cu, Au) preserve stability but lack activity, whereas other metals cause loss of the initial tetrahedral geometry due to excessive CO binding (-2.63 eV to -3.20 eV). To resolve this, we introduce a hydrogen atom at the hollow site (Hollow-H) of r-Tet, which concurrently activates the Ag_4 cluster for CO_2RR and strengthens interfacial Ag-N bonding. The H-activated catalyst proceeds via a two-stage mechanism with H activation (0.80 eV) as the potential-determining step (PDS). Crucially, Hollow-H acts as a dual-purpose electronic promoter: It localizes the apical Ag atom orbital for CO_2 activation while simultaneously transferring charge to prevent cluster deformation from an imbalanced charge distribution. This work establishes hydrogen-activated engineering as a general strategy for enhancing both the activity and stability of supported cluster electrocatalysts.