Electrically driven first-order phase transition of a 2D ionic crystal at the electrode/electrolyte interface.

Area of Science:

• Physical Chemistry
• Materials Science
• Electrochemistry

Background:

• Liquid electrolytes at metal electrode interfaces exhibit complex structures distinct from bulk.
• Electrode potential is a key factor in disorder-order and order-order transitions within adsorbed layers.
• Microscopic mechanisms and free energy changes during these transitions are not well understood.

Purpose of the Study:

• Investigate the crystallization process of adsorbed layers at molten salt-metal interfaces.
• Elucidate the stages and driving forces behind electrolyte ordering on electrode surfaces.
• Characterize the free energy variations and interfacial capacitance changes during transitions.

Main Methods:

• Simulated a prototypical molten salt-metal interface.
• Analyzed the transition from disordered to ordered adsorbed structures.
• Utilized finite-size effects analysis to determine transition order.

Main Results:

• Observed a two-stage transition: initial preordering into polycrystalline structures, followed by abrupt monocrystalline ordering.
• Preordering effects showed characteristics of a continuous transition.
• Finite-size analysis confirmed the first-order nature of the transition to a monocrystalline state.
• Increasing system size shifted the onset voltage and significantly raised the free energy barrier.

Conclusions:

• Electrolyte ordering on metal electrodes is a multi-stage process driven by electrode potential.
• Interfacial capacitance peaks sharpen with increasing system size, reflecting the free energy barrier.
• Understanding these transitions is crucial for controlling interfacial properties in electrochemical systems.