Three-Dimensional Lanthanide-Based Nanoporous Metal–Organic Frameworks for High-Performance Supercapacitors

Lanthanides have been proved to be unprecedented when it comes to organized nanoporous materials with high coordination environment. In the quest to enhance the applications for energy-storage materials, three lanthanide-based metal–organic frameworks (MOFs) have been synthesized by facile hydrothermal conditions using 5-nitroisophthalic acid (H2L) as a ligand, namely, Ce–H2L, Sm–H2L, and Eu–H2L. These nanoporous MOFs consist of nine coordination sites around the lanthanide metal ion giving rise to distorted monocapped square antiprism geometry and 3D crystal structures. The electrochemical measurements demonstrate that charge storage in these MOFs occurs through faradaic redox reactions. The charge–discharge studies show that these nanoporous MOF materials deliver high specific capacity. Ce–H2L, Sm–H2L, and Eu–H2L deliver specific capacities of 625, 356, and 252 C g–1 (1389, 791, and 560 F g–1), respectively, at a current density of 1 A g–1. A symmetric supercapacitor Swagelok device has been fabricated using Ce–H2L as an electrode to further demonstrate the advantage of as-synthesized MOF. The developed symmetric supercapacitor gives a maximum specific energy of 13.6 Wh kg–1 and a maximum specific power of 7110 W kg–1 in the voltage window of 1.425 V. The energy storage trend in these nanoporous materials is Ce–H2L > Sm–H2L > Eu–H2L, which is further supported by the DFT calculations.