Mechanisms of the electrochemical oxidation, restructuring, and dissolution of platinum

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The electrochemical oxidation of platinum and the reduction of the formed ultrathin oxide films result in Pt dissolution and surface restructuring, which is a main origin of Pt catalyst degradation in fuel cells. Although Pt oxidation has been studied for a long time, a more detailed understanding of their atomic-scale mechanisms has up to now been obtained only for the close-packed Pt(111) surface. For the accompanying Pt dissolution, microscopic models are even lacking completely. In this project we will systematically study the oxidation, oxide reduction, and dissolution of Pt single crystal electrodes, focusing on the more open Pt(001), Pt(110), and Pt(310) surfaces. In situ surface X-ray scattering techniques will be employed for clarifying the precise atomic and nanoscale surface structure, electrochemical mass spectrometry for determining the potential- and time-dependent rates of anodic and cathodic dissolution. We will specifically investigate (i) the mechanisms, kinetics, and reversibility of the place exchange between oxygen and Pt surface atoms in the initial stages of oxidation, (ii) the structure and structural evolution of the formed Pt oxide film, (iii) the surface restructuring caused by oxidation/reduction cycles, and (iv) how all of this influences Pt dissolution. The mass spectrometry measurements will cover a wide range of oxidation parameters, including the potential-time program, solution composition (anion species, pH, O2 content), and temperature, allowing to identify cases that are of particular fundamental interest or practical relevance for catalyst stability. With X-ray scattering we will obtain detailed structural data for a more restricted range of oxidation conditions, whose selection will be guided by the dissolution data. Together with density functional theory calculations by collaborating groups, these results should provide detailed insights on the microscopic atomic-scale mechanism. As a first test whether the developed models can be applied for understanding the stability of real catalysts, we will additionally perform complementary studies for an intermediate model system – shape-controlled Pt nanocrystals with defined facets on planar carbon supports.