Motif Editing Reveals Hidden Active Sites in Atomically Precise Metal Nanoclusters for Enhanced Electrocatalysis

Metal nanoclusters offer atomically precise platforms for catalysis but often require bulk molecular motifs to achieve cluster stability. Here, we assess how these motifs block access to active sites and quantify trade-offs between structural integrity and catalytic performance. Based on this, we designed a motif-by-motif surface editing strategy to expose catalytic sites with atomic precision while preserving the kernel integrity of the cluster. Using [Au₂₅(pMBA)₁₈]^- nanoclusters (pMBA = para-mercaptobenzoic acid) as a model system, we selectively replace sterically bulky Au₂(pMBA)₃ motifs with compact Cu-(pMBA)₃ units, yielding [Au₁₃Cu₄(pMBA)₁₂]^3- nanoclusters with a symmetric, open-surface architecture. In situ absorption and mass spectrometry reveals a stepwise motif exchange mechanism distinct from conventional coreduction or ligand displacement, which enables surface reconstruction without kernel distortion. The resulting clusters deliver a 180-fold enhancement in hydrogen evolution turnover frequency (18.8 s^-1), compared to the parent [Au₂₅(pMBA)₁₈]^- (0.1 s^-1), attributed to increased Au₃ facet exposure and improved hydrogen binding, as suggested by spectroscopy and density functional theory. This work offers a generalizable route to programmable surface engineering in metal nanoclusters, contributing to advance in the longstanding paradox between atomic precision and catalytic accessibility.