General Efficacy of Atomically Dispersed Pt Catalysts for the Chlorine Evolution Reaction: Potential-Dependent Switching of the Kinetics and Mechanism
Taejung Lim, Jae Hyung Kim, Jinjong Kim, Du San Baek, Tae Joo Shin, Hu Young Jeong, Kug‐Seung Lee, Kai S. Exner, Sang Hoon Joo
Abstract
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.