Revealing how alkali cations affect the electrical double layer structure of stainless steel in alkaline aqueous environments

The core components of nuclear power plants are composed of stainless steel and other effectively passivated alloys as primary structural materials. However, the properties of the passivating oxide films are profoundly influenced by the coolant chemistry, and the breakdown of the passive films, e.g., due to pitting or stress corrosion cracking, which renders these alloys susceptible to hyperbolic failure and inconsistent with the leak-before-break criterion. Herein, atomic force microscopy (AFM) is used to examine a negatively charged stainless steel surface. The interaction between hydrated alkali cations (i.e., K⁺, Li⁺) and the passivated steel substrate affects the structure of the electrical double layer (EDL) as revealed by analysis of AFM interaction forces. As a result, a more disrupted EDL is indicated in the presence of Li⁺ relative to K⁺. Hence, the cation species present in the coolant can potentially have impact on degradation of alloy components in nuclear power plants. These findings also provide insights into EDL behaviors in batteries and other electrochemical devices.