Ions in Electrically Conductive and Insulating Metal-Organic-Frameworks: Transport and Energy Storage

Abstract

Ion transport in metal-organic frameworks (MOFs) is attracting increasing attention since ions can be easily incorporated into porous MOF structures as guest species, promising a variety of possible applications. While electronically insulating but ionically conductive MOFs show great potential as solid electrolytes, the precise structure and tunability of MOFs also enables rational combination of electronic and ionic conductivity to create intrinsic mixed conductors. The combination of both conduction pathways is highly relevant for energy storage applications where ions interact with and insert into electronically conductive electrode active materials. This thesis first explores ion transport in an anionic MOF electrolyte, conducting mono- and divalent cations. Transport studies give insight into how MOF structure and ion-related variables impact ionic conductivity and activation energy. Studies on this material paint a picture that furthers our understanding of fundamental ion transport mechanism in MOF electrolytes. Incorporating electronic transport as an additional layer of complexity, new mixed proton-electron conductive two-dimensional MOFs based on aromatic azaborine ligands are synthesized. Their dual conductive nature is confirmed by separating the ionic and electronic contributions to the overall transport. Lastly, a family of triazatruxene-based two-dimensional electronically conductive MOFs are explored as pseudocapacitors. Here, the diffusion of ions inside the pore network as well as their interaction with MOF active sites depending on the interlayer spacing are investigated for their impact on capacitance.