Polymer electrolyte membrane (PEM) fuel cells are a promising technology for automotive applications. To achieve the cost versus durability required for the commercialization of this technology, material production and its associated challenges have gained much interest. To reduce the production time per fuel cell stack, it is important to increase the number of units produced. A time-consuming step in the production of stacks is the activation, also known as break-in, which is necessary to carry out a subsequent factory-acceptance-test. The state-of-the-art studies found in literature are mainly tailored towards investigating various break-in procedures without taking into consideration the possible mechanisms behind the performance increase during the initial operation. This interconnection between break-in procedures and physical phenomena is hence missing. In this review, we describe the optimized state for the membrane and catalyst layer in regards to their morphology and composition. We compare this to the known state after production and discuss which mechanisms change the initial state. This information is then used to put into perspective the mechanisms that improve the cell performance and the time scale on which they will take place. Despite the high dependency of the activation behavior on the production steps and the material used, we can conclude that the main sluggish activation mechanisms for state-of-the-art CCMs are the removal of solvents from production and changes in the catalyst layer ionomer and at the membrane surface. Membrane bulk protonic conductivity and changes in platinum structure are expected to have a subordinate role in the activation process. High humidities or even liquid water in the cell and the cycling between oxidizing and reducing conditions at the electrodes accelerate the activation process. Thus, this review serves the development of “smart” and “fast” break-in procedures.

聚合物电解质膜（PEM）燃料电池是汽车应用中的一项有前途的技术。为了实现该技术商业化所需的成本与耐用性，材料生产及其相关挑战引起了人们的极大兴趣。为了减少每个燃料电池堆的生产时间，重要的是增加生产的单元数量。堆叠生产中一个耗时的步骤是激活（也称为闯入），这是进行后续工厂验收测试所必需的。文献中发现的最新研究主要针对调查各种闯入程序而设计，而没有考虑初始操作期间性能提升背后的可能机制。因此，缺少闯入程序和物理现象之间的这种相互联系。在这篇综述中，我们描述了膜和催化剂层的形态和组成方面的优化状态。我们将其与生产后的已知状态进行比较，并讨论哪些机制会更改初始状态。然后，此信息用于透视改善电池性能的机制及其发生的时间尺度。尽管活化行为对生产步骤和所用材料的依赖性很高，但我们可以得出结论，目前最先进的CCM的主要活化机理是从生产中除去溶剂以及催化剂层离聚物和催化剂的变化。在膜表面。膜的整体质子传导性和铂结构的变化预期在活化过程中起次要作用。电池中的高湿度甚至液态水以及电极在氧化和还原条件之间的循环都会加速活化过程。因此，此审查有助于开发“智能”和“快速”侵入程序。