Abstract
Isolated single-site catalysts (ISSCs) have emerged as promising materials for energy conversion and storage. However, current approaches for inorganic nanocatalysts are often ineffective in achieving precisely ordered periodic atomic arrangements of active sites, often leading to a random distribution of active-site motifs on an inorganic substrate. In this work, we introduce a novel partial-coverage-assembly strategy, leveraging graphdiyne-derived fragment ligands, to synthesize a unique Cu nanocluster catalyst with an ordered periodic arrangement of isolated single-metal Cu sites [Cu(4)(TFA)(4)(DPBD)(2), Cu-SMS], while maintaining identical atomicity and a homogeneous coordination microenvironment. This strategic approach significantly enhances the electron transport capability by incorporating graphdiyne-inspired bridging ligands as compared to non-coverage-assembled Cu-MMS (MMS: multiple-metal site). As a result, the Cu-SMS nanocluster catalyst exhibited superior performance in electrocatalytic nitrate reduction to ammonia, achieving a Faradaic efficiency exceeding 99%, surpassing all previously reported atomic precise metal nanocluster catalysts. Through a combination of in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, electrochemical mass spectrometry and density functional theory calculations, we unraveled a detailed mechanistic pathway of nitrate reduction on Cu-SMS, highlighting the role of key intermediates (*NO(2), *NO, *NHO, *NHOH, *NH(2)OH, *NH(2)) and identifying the rate-determining step. In all, these findings present a novel methodology for synthesizing periodic SMS catalysts, emphasizing the emergent catalytic behaviors of precisely ordered metal clusters in heterogeneous catalysis.