A rational design of efficient trifunctional electrocatalysts derived from tailored Co2+-functionalized anionic metal-organic frameworks

Recent advances in the metal-organic framework-based electrocatalysts for trifunctional electrocatalysis

The sustainable energy technology is in great demand due to the depletion and the risks associated with the use of fossil fuels. Various energy technologies like regenerative fuel cells, zinc-air batteries, and overall water-splitting devices have a huge scope in the growth of green energy. The efficiency of these devices is reliant upon the multifunctional electrocatalysts, which include both bifunctional and trifunctional electrocatalysts. Among the different categories of the materials used for such multifunctional electrocatalysis, metal-organic-frameworks (MOFs) occupy a very consolidated place because of their high surface area, porosity, and many other unique physicochemical properties. However, the use of MOFs for the trifunctional electrocatalytic applications is in the budding phase and needs to be explored more. Further, most of these MOF-based trifunctional electrocatalysts are derived by pyrolyzing MOFs at high temperatures. Therefore, there is a need to develop more conductive MOFs which can be directly utilized for the trifunctional applications. In this frontier article, we present the latest reports on the MOF-based materials for trifunctional applications. The material design strategies of the MOF-based materials for trifunctional electrocatalysis have been discussed. The progressive improvements made with MOFs in electrocatalytic applications have been provided with emphasis on the structural, active site and compositional requirements. Finally, the challenges and viewpoints on the future development of the MOF-based materials for trifunctional electrocatalysis have been provided.

Ultrafast Universal Fabrication of Metal-Organic Complex Nanosheets by Joule Heating Engineering

Two-dimensional metal-organic complex (MOC) nanosheets are of great interest in various areas. Current strategies applied to synthesize MOC nanosheets are suffering from low yield, usage of large amounts of environmentally unfriendly organic solvent, are time and energy consuming, and cumbersome steps for 2D nanostructures. In this work, a novel joule heating mechanism is proposed to fabricate MOC nanosheets about 5 nm in thickness with tunable metal compositions (i.e. M = Co, CoNi, and CoFe) within 60 s. Small amount of water is used as the only solvent. Under the intense irradiation of the microwave, fast heating via ionic conduction loss is realized, and urea is catalytically condensed into the long-chain organic ligands rich in N atoms that are capable of coordinating with metal ions to form the stubborn MOC framework, which is simultaneously puffed into an ultrathin nanosheet structure by the intensive release of gas. As a proof of concept, the as-synthesized Co-MOC nanosheet exhibits a superior lithium storage performance of 360 and 330 mA h g^-1 after 1200 and 2300 cycles at a current density of 500 and 1000 mA g^-1 , respectively.

Crystal structures and the ferroelectric properties of homochiral metal-organic frameworks constructed from a single chiral ligand

MOFs have proven to be promising candidates for designing ferroelectric materials. Herein, two new homochiral MOFs, Co-MOF-1 and Co-MOF-2, have been synthesized using the chiral ligand, HL (HL = phenyl-((pyridin-4-ylmethyl)-amino)-acetic acid), and Co(NO₃)₂·6H₂O. Co-MOF-1 was obtained via a two-step synthetic route involving a hydrogel to Zn-MOF conversion and a dissolution-recrystallization process. Co-MOF-2 was directly synthesized by a coordination reaction between chiral ligand, HL, and Co(NO₃)₂·6H₂O under hydrothermal conditions. We investigate the correlation between the ferroelectric properties of the samples and their crystal structures. The ferroelectric properties of Co-MOF-1 and Co-MOF-2 are drastically different. Indeed, Co-MOF-2 shows an obvious hysteretic behavior, while a clear electric hysteresis loop was not observed for Co-MOF-1. These significant disparities may be attributed to the different molecular dipole moments in Co-MOF-1 and Co-MOF-2. The different octahedral coordination units in the molecular structures of the Co-MOFs may alter the dipole moments of the molecules, resulting in the absence of a hysteresis loop for Co-MOF-1.