Hysteretic order-disorder transitions of ionic liquid double layer structure on graphite. (June 2019)

• Record Type: Journal Article
• Authors: Tsai, Wan-Yu; Come, Jeremy; Zhao, Wei; Wang, Runxi; Feng, Guang; Prasad Thapaliya, Bishnu; Dai, Sheng; Collins, Liam; Balke, Nina
• Is Part Of: Nano energy. Volume 60(2019)
• Page Start: 886
• Page End: 893
• Publication Date: 2019-06
• Subjects: Ionic liquids -- Electrical double layer structure -- Atomic force microscopy -- Electrode/electrolyte interface -- Self-assembly -- Molecular dynamic simulation; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2019.04.022
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Understanding the electrical double layer (EDL) structure at the solid/liquid interface is critical towards realizing the full potential of electrochemical applications using ionic liquids. In this work, the out-of-plane and in-plane EDL structures of PYR14 -TFSI on graphite (HOPG) have been studied by in-situ electrochemical atomic force microscopy (AFM) and molecular dynamics (MD) simulation. AFM results revealed that the first adsorbed ion layer on HOPG consists of both disordered and ordered lateral domains. It has been found that the neighboring molecules in the x-y plane form intricate ordered lateral structures on length scale of hundreds of nanometers, and the out-of-plane EDL structure is independent of the in-plane structure. MD simulations under zero polarization showed that in the first adsorbed layer, cations have one preferred orientation while anions have two preferred orientations in relation to the HOPG surface, which might be the origin of the complex lateral ordering. When polarizing the surface, a hysteretic order-disorder transition of the lateral ordering in the first adsorbed layer can be observed by in-situ AFM, and the ordered domains disappear for high positive or negative voltages. Comparison with bias-dependent MD reveals that the existence of a bimodal anion distribution in the first absorbed layer can be linked to the observed transitions giving new insights into the origin of the structural domains, which can help understand unusual charge and discharge kinetics observed in similar systems. Graphical abstract: The bias-induced changes in the area coverage of structured ionic liquid at a solid interface are observed by atomic force microscopy and change hysterically.Image 1 Highlights: When in contact with graphite, 1st adsorbed PYR14 -TFSI layer forms structural domains with ordered in-plane structure up to few hundreds of nanometers in size In-plane structure can be controlled by bias showing a hysteretic order-disorder transition The bimodal anion distribution could be responsible of the lateral order-disorder transition under bias