ScholarWorks@성균관대학교

초록

Aqueous multivalent metal ion capacitors are very attractive owing to their high capacitance, low cost, environmental benignity, and safety. Herein, hierarchically structured, conductive lanthanide metal-organic frameworks (MOFs) assembled by nanorods for ultrastable flexible magnesium ion capacitors (MICs) is designed. Three MOFs, consisting of lanthanide metals (La, Ho, and Yb) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), are structurally stabilized through the covalent bonds and electronically conductive due to π-d conjugation. Among 3 MOFs, Ho-HHTP electrodes in a full-cell system achieved long-term cyclic stability with a high capacitance retention of 65.0% after 12 000 cycles and a high Coulombic efficiency of 96.9%. Furthermore, flexible pouch cells are fabricated using Ho-HHTP as anode, reduced graphene oxide as cathode, and poly(vinyl alcohol) (PVA)/Mg(ClO4)2 as gel electrolyte, demonstrating a low capacitance decay rate of 0.00444% per cycle during 10 000 cycles owing to the hierarchical structure and intrinsic electronic conductivity. As indicated by density functional theory and spectroscopic characterizations, Mg2+ ions are faradaically stored in the catechol part of the ligand, and Mg2+ inserted into the vacant Ho sites contributes to structural stability. Furthermore, operando 2D correlation Raman spectroscopy identified how Mg2+ ions interact with the ligand of Ho-HHTP and demonstrated the sequential change of peak change. © 2024 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbH.

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