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

Abstract

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 -S₃ (Pt substituting the Zn site) and Pt_ads -S₂ (Pt adsorbing on the surface). In Na₂ S, the S^2- can coordinate with Pt atoms and peel them from the Pt_ads -S₂ sites, but leaves more stable Pt_Zn-sub -S₃ 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 -S₂ sites (67.18 down to 35.96 mmol g^-1 h^-1 , 52.03% drop after 6 h). Therefore, the Pt_ads -S₂ 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 -S₃ 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."

Keywords: Pt single sites; aqueous photocatalysis; collision of ions; hydrogen evolution; single-atom catalysts.