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

铂的电化学氧化和形成的超薄氧化膜的还原导致铂的溶解和表面重构，这是燃料电池中铂催化剂降解的主要原因。虽然Pt氧化的研究已经进行了很长时间，但到目前为止，对其原子尺度机制的更详细的了解只针对致密的Pt（111）表面。对于伴随的铂溶解，甚至完全缺乏微观模型。在本项目中，我们将系统地研究Pt单晶电极的氧化、氧化还原和溶解，重点研究Pt（001）、Pt（110）和Pt（310）表面。原位表面x射线散射技术将用于澄清精确的原子和纳米级表面结构，电化学质谱法将用于确定阳极和阴极溶解的电位和时间依赖性速率。我们将具体研究(i)氧化初始阶段氧和Pt表面原子之间位置交换的机制、动力学和可逆性，（ii）形成的Pt氧化膜的结构和结构演变，（iii）氧化/还原循环引起的表面重组，以及（iv）所有这些如何影响Pt溶解。质谱测量将涵盖广泛的氧化参数，包括电位时间程序、溶液组成（阴离子种类、pH值、O2含量）和温度，从而确定对催化剂稳定性具有特别基本兴趣或实际意义的情况。通过x射线散射，我们将获得更有限氧化条件范围内的详细结构数据，其选择将由溶解数据指导。与合作小组的密度泛函理论计算一起，这些结果应该提供微观原子尺度机制的详细见解。作为第一个测试，我们开发的模型是否可以应用于理解真实催化剂的稳定性，我们还将对中间模型系统进行补充研究——在平面碳载体上具有定义facet的形状控制Pt纳米晶体。

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.