Nanochannel Engineering in Metal-Organic Frameworks by Grafting Sulfonic Groups for Boosting Proton Conductivity

Constructing highly proton-conducting metal-organic frameworks (MOFs) remains a difficult challenge. Hence, we developed an effective nanochannel engineering strategy by grafting sulfonic-abundant benzene-1,3,5-trisulfonic acid (BTSA) onto the Zr-6-clusters of PCN-222 to act as a proton-conducting intensifier. Although the introduced BTSA dramatically reduced the pore volume, the resultant MOF (PCN-222-BTSA) exhibited strong water affinity and thus significantly enhanced water uptake at low RH values, reaching up to an almost equivalent water adsorption capacity at a high RH value compared with the capacity of pristine PCN-222. Benefiting from the enhanced water adsorption behavior and the proton-donating capability of sulfonic groups, PCN-222-BTSA displayed 2-3 orders of magnitude higher proton conductivity than pristine PCN-222. Our work is the first to report on postsynthetic modification in the nanochannel of MOFs for proton conduction, which demonstrates a strategy to design functional MOFs with abundant sulfonic groups and provides a bright avenue for constructing proton-conducting materials.