Teaching Metal-Organic Frameworks to Conduct: Ion and Electron Transport in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are an expansive class of extended solids formed by coordination bonding between metal ions/clusters and organic ligands. Although MOFs are best known for their intrinsic porosity, they are now also emerging as an unusual set of porous, electrical, and ionic conductors that could address a number of applications in energy storage and generation. In this review, we focus on intrinsic ionic conductivity in MOFs and outline approaches for achieving high ionic conductivities. First, we highlight the use of noncoordinating acidic groups to integrate anions into MOF organic linkers. Next, we discuss the use of open metal sites to anchor anions and generate mobile ions. Then, we discuss the use of postsynthetic modifications to graft anions onto ligands and defect sites. Finally, we outline several unexplored approaches to improving ionic conductivity in MOFs and highlight several potential new applications. Expected final online publication date for the Annual Review of Materials Research, Volume 52 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.