(Invited) Stability of Platinum-Electrolyte Interfaces
Authors: Cherevko Serhiy , Briega Martos Valentin , Qiu Yunsheng , Reichmann Ina , Lauf Pascal 
Published: December 2024

Platinum-liquid electrolyte interfaces are one of the most studied in electrochemistry. Still, until very recently, knowledge of the interfacial changes during platinum oxidation and reduction remained elusive. This information is crucial for any electrochemical applications in which platinum is used as a catalyst as it allows its more economical utilization. For instance, if excursions to destructive higher anodic potentials are avoided in proton exchange membrane fuel cell (PEMFCs) cathodes, significantly lower platinum amounts can be used, still providing the required long-term operation. It is an example of so-called operational mitigation approaches. Material science solutions are often cheaper and more versatile. This work gives an overview of our research and literature on the stability of different platinum-electrolyte interfaces aiming at the development of more robust catalysts following both material science and operational approaches.

Because of its application in PEMFCs, platinum is best studied in liquid acidic electrolytes, which is the starting point of this presentation. Transient anodic and cathodic platinum dissolution concepts are explained using polycrystalline, single crystalline, and nanoparticulated platinum electrode systems. Further, different case studies are presented for each listed system. Thus, the effect of pH, temperature, reactive gases, and electrolyte composition on Pt dissolution is investigated using Pt electrodes with extended surfaces.1, 2 Single crystals are used in a combined on-line inductively coupled plasma mass spectrometry (ICP-MS) and high energy X-ray diffraction (HE-XRD) study to reveal the atomistic picture of the surface processes during oxidation/reduction.3, 4 Both systems are further explored by applying surface modifiers, e.g., protective porous metal oxides, surface melamine overlayer, graphene, etc., to suppress dissolution.

Since Pt/C nanoparticulated catalyst is used in real PEMFCs, a series of studies have taken into account the specific interface present in applied devices, spanning from solid-liquid to solid-solid (ionomer) electrolyte. For this, gas diffusion electrode (GDE) setups,5, 6 which allow on-line dissolution studies from real fuel cell anodes, are used. The primary outcome of this later study is the importance of Pt mass transport processes on the equilibrium of the dissolved species near the electrode and the overall stability of platinum.7 Hence, in developing more advanced catalyst layers, besides stabilizing the catalyst-electrolyte interfaces, the fate of the dissolved species in the electrolyte must not be overlooked. While platinum-electrolyte interfaces are considered in this work, the obtained knowledge is more general as experimental methods and gained insights on interface stabilization can also be applied to other systems.

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