Unveiling the influence of ion-specific interactions on the electrochemical wettability alteration of Cu-CuOx surfaces

This study explores the effect of ionic species and the ion-specific interactions on the dynamic wettability change of the copper-copper oxide (Cu-CuO x ) surfaces induced by the electrochemical reactions . Utilizing an electrolyte droplet as an electrochemical cell placed on a superhydrophobic Cu-CuO x surface, we examined the impact of electrochemical reaction on the evolution of the droplet shape with electrolytes containing varying cations (Na + , K + , Mg 2+ ) and anions (SO 4 2- , Cl - , NO 3 - ). This droplet shape evolution signified the wettability change and was quantified using the changes in the contact angle and baseline size. Our results show that while all electrolytes induce wettability change under reduction potential, the magnitude of change depends on the cation and anion present in the electrolyte. The magnitude of the wettability change under similar potentials follows the order Mg 2+ < K + < Na + for cations and NO 3 - < Cl - < SO 4 2- for anions. Electrochemical analysis shows that trends obtained for the effect of ions on the wettability change align with electrochemical reaction parameters, specifically charge transfer resistance and areal capacitance, indicating a causal relationship. Furthermore, we obtain that the reaction occurring near the three-phase contact line plays a significant role in the droplet shape change. A detailed discussion on the causal interdependence of the electrochemical reaction parameters and the wettability parameters is presented. The findings offer mechanistic insights into electrochemical systems and the role of ion-dependent electrochemical wettability change, which has potential applications in electrocatalysis and energy storage.