Structural Fusion‐Induced Activity Suppression in Copper Nanoclusters for Electrocatalytic Nitrate Reduction

ABSTRACT Understanding how structural evolution influences catalytic behavior is a central challenge in chemistry. We establish an atomically precise platform to directly probe the catalytic consequences of structural fusion in copper nanoclusters and uncover a counterintuitive anti‐emergent phenomenon, wherein increased structural complexity leads to suppressed activity. By integrating thiacalix[4]arene with an ortho‐hydroxyl‐substituted alkynyl ligand, we enable the in situ generation and directional templating of C 2 2 − dianions, achieving controlled fusion of two Cu 17 units into a well‐defined supercluster, {(C 2 ) 6 @Na 2 Cu 40 (TC4A) 6 (3‐HOhexC≡C) 6 } ( Cu 40 ). Precise regulation of the hydroxyl position allows selective isolation of the monomeric counterpart {NaCu 17 (TC4A) 3 (6‐HOhexC≡C) 6 } ( Cu 17 ), providing a closely matched model pair to disentangle fusion effects. The generality of this C 2 2 − ‐templated fusion pathway is further supported by the isolation of Cu 22 and Cu 43 clusters. Comparative electrocatalytic analysis shows that, despite similar topological architectures, Cu 40 exhibits markedly inferior nitrate‐reduction activity relative to the Cu 17 and Cu 22 monomers. Notably, Cu 17 delivers an optimal NH 3 Faradaic efficiency of 98.45% with a production rate of 2.91 mol·h −1 ·g −1 at −1.0 V. In situ spectroscopic experiments combined with DFT calculations reveal that fusion preserves the intrinsic nature of Cu active sites but reduces surface accessibility and perturbs local electronic environments, thereby suppressing interfacial *H formation and hindering hydrogenation of *NO intermediates.