Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H 2 O 2 Production.

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn-N ₂ O ₂ moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn-N ₂ O ₂ -S). Systematic analyses demonstrate that the synergetic effects between the N ₂ O ₂ species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O ₂ reduction to H ₂ O ₂ . Remarkably, the Zn-N ₂ O ₂ moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H ₂ O ₂ generation. Consequently, the Zn-N ₂ O ₂ -S SAC exhibits impressive electrochemical H ₂ O ₂ production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm ^-2 in the flow cell, it shows a high H ₂ O ₂ production rate of 6.924 mol g _cat ^-1  h ^-1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.
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