Identification of the Stable Pt Single Sites in the Environment of Ions: From Mechanism to Design Principle.

For single-atom (SA)-based catalysis, it is urgent to understand the nature and dynamic evolution of SA active sites during the reactions. In this work, an example of Pt SA-Zn 0.5 Cd 0.5 S (Pt SA-ZCS) is found to display interesting phenomena when facing the Brownian collision of ions in aqueous photocatalysis. Via synchrotron radiation, surface techniques, microscopy, and theory calculations, the results show that two kinds of Pt sites exist: Pt Zn-sub -S 3 (Pt substituting the Zn site) and Pt ads -S 2 (Pt adsorbing on the surface). In Na 2 S, the S 2- can coordinate with Pt atoms and peel them from the Pt ads -S 2 sites, but leaves more stable Pt Zn-sub -S 3 sites, bringing a low but stable catalytic activity (19.40 mmol g -1 h -1 ). Meanwhile, in ascorbic acid, the ascorbic acid ions show less complex ability with Pt atoms, but can decrease the migration barrier of Pt ads -S 2 sites (67.18 down to 35.96 mmol g -1 h -1 , 52.03% drop after 6 h). Therefore, the Pt ads -S 2 sites gradually aggregate into nanoclusters, bringing a high but decayed catalytic activity. Moreover, a Pt SA-ZCS-Sulfur composite is designed mainly covered by Pt Zn-sub -S 3 sites accordingly (max: 79.09 mmol g -1 h -1 , 5% drop after 6 h and QE: 14.0% at 420 nm), showing a beneficial strategy "from mechanism to design principle."