Simple “Directional Trimming” Strategy Engineered Platinum Atomic Clusters with Controllable Coordination Numbers for Efficient Hydrogen Evolution

The coordination number (CN) in atomic cluster (AC) catalysts endows their catalytic performance with flexible tunability. However, the quantitative relationship between the CN and catalytic activity of atomic cluster catalysts remains ambiguity. Herein, inspired by the gardeners trimming plants branches to obtain ornamental value shape, we propose a “directional trimming” strategy to obtain a series of AC catalysts with wide range of Cl CN and establish an inverted volcano curve to explain the effect of CN on hydrogen evolution reaction (HER). Moreover, Pt/CB-90 (moderate Cl CN of 3.7) exhibits the lowest overpotential of 22.94 mV at 10 mA cm⁻² and outstanding mass activity (25 times to commercial Pt/C). This proposed synthesis strategy fully utilizes the precursor atoms and is widely applicable. The reaction liquid can be reused up to 20 times to obtain 1130 mg catalysts without introducing any other chemicals. Additionally, theoretical calculations highlight the appropriate Cl CN benefits the HER on Pt₂ ACs. This fundamental understanding of the role of CN in catalytic activity offers valuable guidance to promote performance in various catalytic reactions. © 2025 Wiley-VCH GmbH.