Single-atom catalysts offering intriguing activity and selectivity are subject of intense investigation. Understanding the nature of single-atom active site and its dynamics under working state are crucial to improving their catalytic performances. Here, we identify at atomic level a general evolution of single atom into a near-free state under electrocatalytic hydrogen evolution condition, via operando synchrotron X-ray absorption spectroscopy. We uncover that the single Pt atom tends to dynamically release from the nitrogen-carbon substrate, with the geometric structure less coordinated to support and electronic property closer to zero valence, during the reaction. Theoretical simulations support that the Pt sites with weakened Pt-support interaction and more 5d density are the real active centers. The single-atom Pt catalyst exhibits very high hydrogen evolution activity with only 19 mV overpotential in 0.5 M H 2 SO 4 and 46 mV in 1.0 M NaOH at 10 mA cm −2 , and long-term durability in wide-pH electrolytes.

Atomically dispersed metal catalysts maximize atom e ciency and display unique catalytic properties compared to regular metal nanoparticles. However, achieving high reactivity while still preserving high stability at high loadings remains as a grand challenge. Here we solve the challenge by synergizing strong metal-support interactions and spatial con nement, which enable to fabricate highly loaded (3.1 wt%), active and stable atomic Ni and dense atomic Cu grippers (8.1 wt%) on a graphitic C 3 N 4 support.For semi-hydrogenation of acetylene in excess of ethylene, the fabricated catalyst shows 11 times higher activity than the atomic Ni alone, high ethylene selectivity (90%), and high stability against both sintering and coke formation for 350 h. Comprehensive microscopic and spectroscopic characterization and theoretical calculations reveal the active site of the bridging Ni con ned in two hydroxylated Cu grippers, whose structure changes dynamically by breaking interfacial Ni-support bonds upon reactant adsorption and making these bonds upon product desorption. Such a dynamic effect confers high activity/selectivity and high stability, providing an avenue to rational design of e cient, stable, highly loaded, yet atomically dispersed catalysts.

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Controlling the chemical environments of the active metal atom including both coordination number (CN) and local composition (LC) is vital to achieve active and stable single-atom catalysts (SACs), but remains challenging. Here we synthesized a series of supported Pt 1 SACs by depositing Pt atoms onto the pretuned anchoring sites on nitrogen-doped carbon using atomic layer deposition. In hydrogenation of para-chloronitrobenzene, the Pt 1 SAC with a higher CN about four but less pyridinic nitrogen (N pyri ) content exhibits a remarkably high activity along with superior recyclability compared to those with lower CNs and more N pyri . Theoretical calculations reveal that the four-coordinated Pt 1 atoms with about 1 eV lower formation energy are more resistant to agglomerations than the three-coordinated ones. Composition-wise decrease of the Pt−N pyri bond upshifts gradually the Pt-5d center, and minimal one Pt−N pyri bond features a high-lying Pt-5d state that largely facilitates H 2 dissociation, boosting hydrogenation activity remarkably.