Real-time Characterization of Chemical Structure and Dynamics of Electrical Double Layer at Electrode-electrolyte Interfaces

The chemisorption of species from supporting electrolytes on electrode surfaces is ubiquitous in electrochemical systems and affects the dynamics and mechanism of various electrochemical reactions. The understanding of chemical structure and property of the resulting electrical double layer is vital but limited. In this work, we operando probed the electrochemical interface between a gold electrode surface and a common supporting electrolyte, phosphate buffer, using our newly developed in situ liquid secondary ion mass spectrometry during dynamic potential scanning. We surprisingly found that on the positively charged gold electrode surface sodium cations coexisted within the inner Helmholtz layer to form ion pairs with the accumulated phosphate anions, resulting in a strong and dense adsorption phase which was further revealed to retard the electro-oxidation reaction of ascorbate. This finding addressed one major gap in the fundamental science of the electrode-electrolyte interface that where and how the cations exactly reside in the double layer to impose effects on electrochemical reactions, providing insights into engineering of better electrode-electrolyte interfaces in a wide range of fields such as electrochemical conversion and storage of energy, electrocatalysis, and electrodeposition.