Ion Diffusion in Porous Crystalline Materials

Solid-state proton conductors (SSPCs), which are a key component for the safety and efficiency of fuel cells, have received attention due to their broad application in electrochemical devices. In particular, porous metal-organic frameworks (MOFs) have been extensively studied as a new type of proton conductor due to their designability. During the past decade, proton-conductive MOFs have achieved high performance (&gt;10^–2 S cm^–1), comparable to the conventional material, through various synthetic strategies. The veiled conduction mechanism has been elucidated through structural analysis and spectroscopy tools such as NMR, X-ray diffraction, and neutron scattering measurement.^[1] Herein, we demonstrate a new strategy for high proton conductivity in MOF.^[2,3] Specifically, we used MOF-74 for coordinative urea insertion through post-synthetic modification and assessed the priority factor on proton conduction between the void space and pore-surface modification. Furthermore, molecular dynamics study and DFT calculation provide a comprehensive understanding of the proton conduction pathway and mechanism.<br/><b>Reference</b><br/>[1] Lim, D.-W.; Kitagawa, H. <i>Chem. Rev.</i>, <b>2020</b>, 120, 8416–8467.<br/>[2] Sarango-Ramírez, M. K.; Lim, D.-W.; Kolokolov, D. I.; Khudozhitkov, A. E.; Stepanov, A. G.; Kitagawa, H. <i>J. Am. Chem. Soc.</i>, <b>2020</b>, <i>142</i>, 6861−6865.<br/>[3] Sarango-Ramírez, M. K.; Park, J.; Kim, J.; Yoshida, Y.; Lim, D.-W.; Kitagawa, H. <i>Angew. Chem. Int. Ed.</i>, <b>2021</b>, <i>60</i>, 20173–20177.