Recent advancements in defect engineering have significantly improved catalysis by modulating the electronic structure and enhancing the intrinsic abilities of catalysts. However, establishing a clear structure-property relationship at the atomic level remains a challenge due to the inherent polydispersity of catalysts, which hinders a comprehensive understanding of the defect catalysts. Atomically precise metal nanoclusters can serve as model catalysts because of their perfect monodispersity and well-defined structure. While, the understanding about defects in atomically precise metal nanoclusters is insufficient. This review encompasses various types of defects (such as heteroatom incorporation, vacancies, ligand deficiencies, etc.) in atomically precise coingage metal clusters, characterization methods, and their applications within the realm of catalysis. At the conclusion of this review, we propose several prospects, including the controllable construction of defects, further enhancement of the performance of clusters with defects, and monitoring the in-situ evolution of defects in clusters during catalysis. The purpose of this review is to deepen the understanding of defects in atomically precise clusters, establish the relationship between defect structure and catalytic performance, and offer valuable insights for the designing and developing of efficient defect-rich cluster catalysts.

Nickel sulfide exhibits excellent catalytic activity in the electrochemical 2,5-hydroxymethylfurfural oxidation reaction (HMFOR). However, due to the polydispersity of nanoparticles, it is difficult to establish a clear structure-activity relationship at the atomic level. In this work, we have successfully synthesized atomically precise Ni₆(PET)₁₂ and Ni₄(PET)₈ clusters (PET: 2-phenylethanethiol) for HMFOR. Ni²⁺ and S^2- with atomic ratio of 1:2 were mainly existed in Ni₆(PET)₁₂ and Ni₄(PET)₈ to form Ni-S bond. The electrochemical test results have suggested both Ni₆(PET)₁₂ and Ni₄(PET)₈ displayed outstanding electrocatalytic ability for HMFOR. The Ni₆(PET)₁₂ exhibited better electrocatalytic ability than Ni₄(PET)₈ with higher current density, lower overpotential and faster reaction kinetics. The superior electrochemical ability of Ni₆(PET)₁₂ may be due to the enhanced adsorption towards HMF molecule with strong interaction towards hydroxyl group and furan ring. Moreover, it  found that the Ni²⁺ species in Ni₆(PET)₁₂ could rapidly oxidized into Ni³⁺ species, which could spontaneously capture electron and proton from HMF for oxidation. The theoretical calculation demonstrated that the Ni₆(PET)₁₂ process lower free energy barrier than Ni₄(PET)₈ to display excellent electrocatalytic performance. This work is of great significance for designing efficient electrocatalysts for HMFOR.