Acyclic Tripodal Receptors as Ultrahigh Superprotonic Conductors

Abstract

Abstract Solid‐state proton‐conductors (SSPCs) with high conductivity and excellent chemical stability are the key requirements for proton exchange membrane fuel‐cell systems. Herein, inspired by the acyclic supramolecular chemistry, we inaugurate a new class of proton‐conducting tripodal receptor based hydrogen‐bonded platforms, namely, Tripod‐COOH‐P and Tripod‐NO 2 ‐P, with differently functionalized tails. The receptors act as anchors for the intrinsically crystallized proton carriers (H 3 PO 4 and H 2 PO 4 − ) through multiple host‐guest interactions and thus eventually address leaching issues with externally doped phosphoric acid from SSPCs. Distinct variation in structural engineering through “ complementary docking strategy ” coupled with striking variation in H‐bonded architectures (continuous versus closed loops) marked for three orders higher proton conductivity of Tripod‐COOH‐P (1.5 × 10 −2 S cm −1 ) than that for Tripod‐NO 2 ‐P (3.08 × 10 −5 S cm −1 ) at 80 °C under 80% RH. Quantum‐chemical simulation revealed a smaller proton transfer energy barrier (E PT ) in Tripod‐COOH‐P (13.7 kcal mol −1 and 1.7 kcal mol −1 for channel‐ a and b , along with an energetically favourable “ quantum tunnelling effect ” in channel‐b) than in Tripod‐NO 2 ‐P (24.9 kcal mol −1 ). Such a unique framework engineering served as an effective tool for flaunting tripodal receptor Tripod‐COOH‐P as a new zoner ultrahigh proton conducting platform (beyond > 10 −2 S cm −1 ).