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<p>Electrochemical interfaces between polymer electrolytes and electrodes are central to electrochemical devices in the global transition towards renewable energy. Here we show that the adsorption and desorption of sulfonates in Nafion on Pt(111) involve distinct elementary steps, with the latter proceeding through a coupled cation–electron transfer. Adsorbed sulfonates not only block a fraction of surface Pt sites but, more importantly, generate two additional types of surface adsorbate, OH<sub>Nafion</sub> and O<sub>Nafion</sub>, which exhibit distinct kinetic properties from adsorbed OH and O on bare Pt(111), respectively. The impact of the adsorption of sulfonate groups in Nafion on the activity of the oxygen reduction reaction (ORR) on Pt cannot be rationalized by existing thermodynamic descriptors. The reduced ORR activity on the Nafion-covered Pt(111) is caused by the kinetically hindered *O→*OH conversion and *OH reduction on sites close to adsorbed sulfonates.</p><p></p>

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Coupled cation–electron transfer at the Pt(111)/perfluoro-sulfonic acid ionomer interface and its impact on the oxygen reduction reaction kinetics

  • 期刊论文

  • 发表日期：

    2025年1月13日

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  • Kaiyue Zhao,
  • Mingchuan Luo,
  • Yongfan Zhang,
  • Xiaoxia Chang,
  • Bingjun Xu

摘要

Electrochemical interfaces between polymer electrolytes and electrodes are central to electrochemical devices in the global transition towards renewable energy. Here we show that the adsorption and desorption of sulfonates in Nafion on Pt(111) involve distinct elementary steps, with the latter proceeding through a coupled cation–electron transfer. Adsorbed sulfonates not only block a fraction of surface Pt sites but, more importantly, generate two additional types of surface adsorbate, OHNafion and ONafion, which exhibit distinct kinetic properties from adsorbed OH and O on bare Pt(111), respectively. The impact of the adsorption of sulfonate groups in Nafion on the activity of the oxygen reduction reaction (ORR) on Pt cannot be rationalized by existing thermodynamic descriptors. The reduced ORR activity on the Nafion-covered Pt(111) is caused by the kinetically hindered *O→*OH conversion and *OH reduction on sites close to adsorbed sulfonates.