Dual Electronic and Li + Ion Conducting Ytterbium–Hexaazatrinaphthalene Metal–Organic Framework and Its Carbon Nanotube Composites

Despite spectacular recent advances in electronic metal–organic frameworks (MOFs) that exhibit either electronic or ionic conductivity, mixed ionic–electronic conducting (MIEC) MOFs with dual electron and ion transport capabilities are rare yet crucial for future energy storage and electrochemical applications. Here, we present a modular design strategy for MOF-based MIEC materials by combining a Li+-ion-conducting ytterbium–hexahydroxy-hexaazatrinaphthalene (Yb–HOHATN) framework based on an N-heteroaromatic ligand with electrically conductive multiwalled carbon nanotubes (CNTs), yielding Yb–HOHATN@CNT composites with impressive dual conduction properties. The Yb–HOHATN MOF features hexagonal channels decorated with Lewis basic N-sites that facilitate Li+ ion binding and transport, generating excellent ionic conductivity (7.3 × 10–5 S/cm), while the ligand π-stacks support through-space charge transfer, leading to modest electrical conductivity (9.8 × 10–8 S/cm). Solvothermal growth of Yb–HOHATN MOF on electrically conducting multiwalled carbon nanotubes (CNTs) yielded porous, crystalline Yb–HOHATN@CNT composites that displayed significantly improved electronic conductivity (5.4 × 10–3 S/cm). The Li+-doped Yb–HOHATN@CNT composite simultaneously exhibited impressive electronic and ionic conductivities (1.1 × 10–2 and 4.03 × 10–6 S/cm, respectively), emerging as an effective MIEC. This work not only presents an intriguing dual ionic–electronic conducting MOF@CNT composite but also provides a generalizable blueprint for crystalline MIECs that seamlessly combine the Li+ ion-transport capabilities of heteroatomic ligand-based MOFs with the electronic conductivity of CNTs, thereby unveiling MOF@CNT composites as a promising platform for advanced energy storage and electronic technologies.