General Efficacy of Atomically Dispersed Pt Catalysts for the Chlorine Evolution Reaction: Potential-Dependent Switching of the Kinetics and Mechanism

The electrochemical chlorine evolution reaction (CER) is a key anodic reaction in the chlor-alkali process for Cl2 production, on-site generation of ClO–, and Cl2-mediated electrosynthesis. Although Ru-based mixed metal oxides have long been used as CER catalysts, they suffer from a selectivity problem due to the competing oxygen evolution reaction. To overcome this shortcoming, we have developed a new CER catalyst composed of atomically dispersed Pt–N4 sites on carbon nanotubes (Pt1/CNT). In this study, we demonstrate that the catalytically active Pt–N4 sites can be constructed from H2PtCl6·6H2O and an ionic liquid via a bottom-up approach and a Pt-porphyrin-driven top-down method. Both catalysts exhibit excellent CER activity and remarkable selectivity, demonstrating the general efficacy of Pt1/CNT for the CER. The electrochemical and in situ X-ray absorption spectroscopy analyses reveal that Pt1/CNT catalysts show a reaction order of ∼1.8 in the low overpotential regime, where the Volmer step is reconciled with the rate-determining step (RDS). Interestingly, in the high overpotential region, the CER over Pt1/CNT proceeds with a lower reaction order and the RDS switches to the Heyrovský step. These unprecedented kinetic insights are clearly distinguished from the oxide-based CER catalysts with the opposite sequence of the RDS.