Intrinsic Activity Identification of Noble Metal Single-Sites for Electrocatalytic Chlorine Evolution.

Single-atom catalysts with maximal atom-utilization have emerged as promising alternatives for chlorine evolution reaction (CER) toward valuable Cl ₂ production. However, understanding their intrinsic CER activity has so far been plagued due to the lack of well-defined atomic structure controlling. Herein, we prepare and identify a series of atomically dispersed noble metals (e.g., Pt, Ir, Ru) in nitrogen-doped nanocarbons (M ₁ -N-C) with an identical M-N ₄ moiety, which allows objective activity evaluation. Electrochemical experiments, operando Raman spectroscopy, and quasi-in situ electron paramagnetic resonance spectroscopy analyses collectively reveal that all the three M ₁ -N-C proceed the CER via a direct Cl-mediated Vomer-Heyrovský mechanism with reactivity following the trend of Pt ₁ -N-C>Ir ₁ -N-C>Ru ₁ -N-C. Density functional theory (DFT) calculations reveal that this activity trend is governed by the binding strength of Cl*-Cl intermediate (ΔG _Cl*-Cl ) on M-N ₄ sites (Pt<Ir<Ru) featuring distinct d-band centers, providing a reliable thermodynamic descriptor for rational design of single metal sites toward Cl ₂ electrosynthesis.
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