Mixed Ionic and Electronic Conductivity in a Tetrathiafulvalene-Phosphonate Metal-Organic Framework

Mixed ionic-electronic conductors have great potential as materials for energy storage applications. However, despite their promising properties, only a handful of metal-organic frameworks (MOFs) provide efficient pathways for both ion and electron transport. This work reports a proton-electron dual-conductive MOF based on tetrathiafulvalene(TTF)-phosphonate linkers and lanthanum ions. The formation of regular, partially oxidized TTF stacks with short S<middle dot><middle dot><middle dot>S interactions facilitates electron transport via a hopping mechanism, reporting a room-temperature conductivity of 7.2 x 10-6 S cm-1. Additionally, the material exhibits a proton conductivity of 4.9 x 10-5 S cm-1 at 95% relative humidity conditions due to the presence of free -POH groups, enabling efficient proton transport pathways. These results demonstrate the potential of integrating electroactive building blocks along with phosphonate groups toward the development of mixed ionic-electronic conductors.