Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu₆ Clusters

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu₆, abbreviated as LnCu₆-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu₆-IM (Ln = La and Nd; IM = Imidazole), and LnCu₆-IDA (Ln = Nd; H₂IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu²⁺ ions around one Ln³⁺ ion in LnCu₆, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu₆ clusters exhibit different OER activities with remarkable turnover frequency of 135 s^-1 for NdCu₆-AC, 79 s^-1 for NdCu₆-IM and 32 s^-1 for NdCu₆-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.