Electrically Driven First-order Phase Transition of a 2D Ionic Crystal at the Electrode/Electrolyte Interface by Dr Sara Bonella

07 May 2026 09.30 AM - 10.30 AM MSE E-Studio (N4.1-B2-02) Alumni, Current Students

NTU MSE Seminar Hosted by Prof Li Shuzhou

Abstract

Liquid electrolytes adsorbed at the surface of metallic electrodes display a multitude of structures that can largely differ from the parent bulk system, both in terms of composition and local organization. In particular, the existence of disorder–order or order–order transitions has been increasingly reported in experimental and simulation studies, and the electrode potential identified as the corresponding driving force. The microscopic mechanisms and the stages of the process are, however, poorly understood, and the free energy variation during the transition remains insufficiently characterized. To fill this gap, we investigate the crystallization of the adsorbed layer in a prototypical molten salt–metal interface. We demonstrate that the transition from the disordered to ordered structures proceeds in two stages. Preordering effects are observed across a wide range of potentials, resulting in the formation of a polycrystalline structure on the electrode surface, before an abrupt ordering transition finally occurs. The preordering displays signature of a continuous transition. On the other hand, finite-size effects analysis proves the first-order character of the transition toward the monocrystalline state. Upon increasing the system size, a shift in the onset applied voltage is observed, accompanied by a dramatic increase in the free energy barrier. The latter reflects in the interfacial capacitance, which displays a peak that sharpens with increasing system size.

Biography
Dr Sara Bonella
Deputy Director (CECAM)
EPFL

Sara Bonella graduated in Physics from the University of Rome “La Sapienza” and obtained her PhD from Boston University. After a post-doc at the Scuola Normale Superiore in Pisa, she returned to “La Sapienza” where she became a member of faculty (Ricercatore a Tempo Determinato) in 2008. In 2014 she moved to Lausanne to become permanent Deputy Director of the Centre Européen de Calcul Atomique et Moléculaire (CECAM) and Maitre d’Enseignement et Recherche at EPFL. Her responsibilities at CECAM include teaching and research, fostering activities and collaborative projects in the CECAM network, and the development of strategic initiatives. Her main scientific interests currently are the development of methods for simulations of condensed phase systems, with focus on the inclusion of quantum nuclear effects, and molecular dynamics with applications in first principles calculations and classical polarizable models for supercapacitors. She is the author of 70+ papers and a member of several international scientific panels.

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