The generic volcano plot is a widely employed practical tool to display and compare the activity of different electrocatalysts in dependence of a small number of descriptors. It is known that the apex of the volcano curve shifts with applied potential. However, the trend of the potential-dependent shift of the volcano apex has remained unclear. Herein, we address this question for a two-step electrocatalytic reaction. With the transfer coefficient assumed as 1/2, our analysis reveals that the adsorbate coverage at the volcano apex equals 1/2 regardless of potential. We present a criterion to predict the direction and magnitude of the apex shift as a function of the activation energies of the two steps. Thereafter, the criterion is extended to the oxygen reduction reaction. The influence of the transfer coefficient and the potential of zero charge on the volcano plot is revealed. Implications of the presented criterion for targeted design of electrocatalysts are discussed.

通用火山图是一种广泛使用的实用工具，可根据少量描述符显示和比较不同电催化剂的活性。众所周知，火山曲线的顶点随着施加的电位而移动。然而，火山顶点的潜在依赖移动的趋势仍不清楚。在这里，我们针对两步电催化反应解决了这个问题。假设转移系数为 1/2，我们的分析表明，无论潜力如何，火山顶点的吸附物覆盖率都等于 1/2。我们提出了一个标准来预测顶点偏移的方向和大小，作为两个步骤的激活能量的函数。此后，该标准扩展到氧还原反应。揭示了转移系数和零电荷电位对火山图的影响。讨论了所提出的电催化剂目标设计标准的含义。