Dissolution of a platinum catalyst is a major degradation mechanism of fuel cells, but the exact reaction mechanism has remained unclear. Here, electrochemical ambient pressure X-ray photoelectron spectroscopy (EC-APXPS) was utilized to provide direct information on chemical species on a single-crystal Pt(111) electrode under extremely low pH conditions. Measurements were conducted using a novel condensed electrolyte film electrochemical cell applying work function measurement as a loss-free probe for electrochemical potential. We show that platinum can dissolve chemically as Pt²⁺ ion during potential cycling and redeposit as Pt²⁺ at the onset potential for cathodic reactions. The dissolution of Pt does not require electrochemical oxidation via oxide place exchange. In contrast, the adsorption of oxygenated species (OH* or O*) at the onset potential for anodic reactions is a sufficient prerequisite to the dissolution. These results provide new insight into the degradation mechanism of Pt under extremely low pH conditions, predicted by the Pourbaix diagram, having practical applications to the durability of Pt-based catalysts in electrochemical energy conversion devices.

中文翻译：

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用Operando X射线光电子能谱研究在负pH条件下电位循环过程中Pt（111）的化学溶解

铂催化剂的溶解是燃料电池的主要降解机理，但是确切的反应机理仍不清楚。在这里，电化学环境压力X射线光电子能谱（EC-APXPS）用于在非常低的pH条件下提供有关单晶Pt（111）电极上化学物种的直接信息。使用新型的冷凝式电解质膜电化学电池进行测量，将功函数测量用作电化学电势的无损探针。我们表明，铂在潜在的循环过程中可以化学溶解为Pt ²⁺离子，并重新沉积为Pt ²⁺发生阴极反应的潜力。Pt的溶解不需要通过氧化物位置交换进行电化学氧化。相反，在阳极反应的起始电势下，含氧物质（OH *或O *）的吸附是溶解的充分先决条件。这些结果提供了对在极低pH条件下Pt降解机理的新见解，这是根据Pourbaix图预测的，对电化学能量转换设备中基于Pt的催化剂的耐久性具有实际应用价值。