Intrinsic Chlorine Evolution Kinetics Revealed by Impedance Spectroscopy in a Water-Free Electrolyte

A long-standing challenge in chlorine electrocatalysis is the lack of experimental access to intrinsic elementary-step kinetics, owing to the unavoidable chemical complexity of aqueous electrolytes, including catalyst oxidation, competing oxygen evolution, and chlorine hydrolysis. Here, we establish a chemically controlled, water-free electrochemical environment that eliminates these parasitic processes and enables platinum to operate as a pristine model catalyst for the chlorine evolution reaction (CER). By integrating steady-state polarization with operando electrochemical impedance spectroscopy (EIS), we develop a multiresponse kinetic framework that allows simultaneous and independent extraction of the rate constants of the Volmer, Heyrovský, and Tafel steps, together with their equilibrium parameters and surface coverage evolution. This approach provides the first unperturbed kinetic description of CER. Strikingly, we find that, in the absence of aqueous perturbations, the rate-determining step (RDS) of CER does not shift with overpotential, in sharp contrast to the long-standing interpretation derived from aqueous systems. These findings redefine the mechanistic understanding of CER and establish a general strategy for interrogating halogen-involved electrocatalysis under chemically idealized conditions.