Impedance analysis is not an easy task. This becomes even more obvious if unusual shapes appear in the impedance diagram. Here, a low frequency hook with positive imaginary part is discussed that often leaves researchers clueless of how to handle it, especially if there is no common model for the device under test that includes the hook, which is actually true for most electrochemical systems. The low frequency hook is explained from a systems theory perspective and a very basic explanation is given of what has to happen phenomenologically for this feature to appear. The most common equivalent circuit model (ECM) for such a low frequency hook is reviewed and the relation to a general empirical low-pass filter type model is discussed. A common electrochemical example and an abstract minimal example are introduced to facilitate the interpretation of the low frequency hook for an arbitrary (photo-) electrochemical system.

阻抗分析并非易事。如果在阻抗图中出现异常形状，这将变得更加明显。在这里，讨论了带有正虚部的低频钩子，这常常使研究人员不知道如何处理它，尤其是在没有包含钩子的被测设备通用模型的情况下，这实际上适用于大多数电化学系统。从系统理论的角度解释了低频钩子，并给出了从现象学上发生什么才能使此功能出现的非常基本的解释。回顾了这种低频钩子的最常见等效电路模型（ECM），并讨论了与一般经验性低通滤波器类型模型的关系。