(330c) On the Importance of the Electric Double Layer Structure in Electrocatalysis

Electrochemistry, the fundamental basis of sustainable energy conversion technologies, studies the interconversion of electric-chemical energy at heterogeneous interfaces. The electrochemical reaction mainly occurs at the solid-liquid (or electrode-electrolyte) interface, where a characteristic liquid structure, i.e., an electric double layer (EDL) is formed. Since the early 1900s, when the concept of EDL was first proposed, unremitting efforts have been made to identify EDL structural changes depending on the applied potential, but only a few molecular details have been disclosed to date. One famous example is EDL capacitance, an indicative quantity of the EDL structural change, which shows two characteristic peaks in a dilute electrolyte, but no molecular theory of liquid structure has fully explained them. To address this century-long debate, we develop a molecular simulation method to model the electrified interfaces based on quantum mechanical electronic structure theory and energetics – a density functional theory in classical explicit solvents (DFT-CES). Using DFT-CES, we find unprecedented liquid structural changes and phase transitions of the EDL, which originate two capacitance peaks at the same potentials to the experiment. Furthermore, we envisage a new perspective for developing better electrochemical systems by tailoring the interface; there’s plenty of room in between.