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Synthetic Generality of Atomically Dispersed Pt Catalysts and Their Electrochemical Kinetics for the Chlorine Evolution Reaction

Lim, TaejungKim, JinjongJoo, Sang Hoon
Issued Date
128th KCS Meeting
Electrochemical chlorine evolution reaction (CER) is a major anodic reaction for Cl2 production or on-site HClO generation. Although Ru-based mixed metal oxides have been used as commercial CER catalysts for the past half century, their oxide active sites also catalyze a parasitic oxygen evolution reaction (OER). Recently, we have developed a new class of CER catalysts based on atomically dispersed Pt–N4 sites on carbon nanotubes (Pt1/CNT). In this work, we demonstrated the synthetic generality of Pt–N4 sites for catalyzing CER and identified potential-dependent kinetics of Pt–N4 sites for CER. We prepared two types of Pt1/CNT catalysts using H2PtCl6∙6H2O and ionic liquid via a bottom-up approach [Pt1/CNT(Cl)] and using Pt-porphyrin via a top-down approach [Pt1/CNT(P)]. Both the two Pt1/CNT catalysts comprised Pt–N4 active sites and exhibited similarly high CER activity (10 mA cm–2 @ 1.4 V vs. RHE), and ~100 % CER selectivity in OER-predominating 0.1 M NaCl electrolyte (pH 1), demonstrating the general nature of Pt–N4 as an effective catalytic site for CER. The analyses of Tafel slope, reaction order, and in situ X-ray absorption near edge structure (XANES) revealed pre-adsorbed Cl– before equilibrium potential of CER (1.36 V vs. RHE), indicating a unique CER behavior that commenced with Pt–Cl species. At low overpotential, the Pt1/CNT catalysts showed a reaction order (R) of ~1.8 and an average oxidation number (Ox.) of ~2.8 for CER evidencing the dominance of Volmer adsorption as the rate-determining step (RDS), which was clearly distinguished from the oxide-based CER catalysts (R ~ 1). As overpotential increases, CER over Pt1/CNT catalysts proceeds with decreasing reaction order and Ox. of ~3.9, indicating a switch to the Heyrovský discharge as the RDS.
Korean Chemical Society


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