"Spontaneous Ionic Polarization in Ammonia-Based Ionic Liquid"

Ki-jeong Kim: Hongtao Yuan, Hoyoung Jang, Bongju Kim, Donghoon Seoung, Yasuyuki Hikita, Harold Y. Hwang, and Jun-Sik Lee; ACS Applied Energy Materials, 06/25/18.

Additional Authors: Hongtao Yuan, Hoyoung Jang, Bongju Kim, Donghoon Seoung, Yasuyuki Hikita, Harold Y. Hwang, and Jun-Sik Lee

Abstract:

Ionic liquids and gels have attracted attention for a variety of energy storage applications, as well as for highperformance electrolytes for batteries and supercapacitors. Although the electronic structure of ionic electrolytes in these applications is of practical importance for device design and improved performance, the understanding of the electronic structure of ionic liquids and gels is still at an early stage. Here we report soft X-ray spectroscopic measurements of the surface electronic structure of a representative ammonia-based ionic gel (DEME-TFSI with PS-PMMA-PS copolymer). We observe that, near the outermost surface, the area of the anion peak (1s Ncore level in TFSI) is relatively larger than that of the cation peak (N+ in DEME). This spontaneous ionic polarization of the electrolyte surface, which is absent for the pure ionic liquid without copolymer, can be directly tuned by the copolymer content in the ionic gel, and further results in a modulation in work function. These results shed new light on the control of surface electronic properties of ionic electrolytes, as well as a difference between their implementation in ionic liquids and gels.