Kaveevivitchai, Watchareeya

DOE OSTI2023

Mixed‐Valence Cu I /Cu III Metal–Organic Frameworks with Non‐innocent Ligand for Multielectron Transfer

Abstract We report two novel three‐dimensional copper‐benzoquinoid metal–organic frameworks (MOFs), [Cu 4 L 3 ] n and [Cu 4 L 3 ⋅ Cu(iq) 3 ] n (LH 4 =1,4‐dicyano‐2,3,5,6‐tetrahydroxybenzene, iq=isoquinoline). Spectroscopic techniques and computational studies reveal the unprecedented mixed valency in MOFs, formal Cu(I)/Cu(III). This is the first time that formally Cu(III) species are witnessed in metal–organic extended solids. The coordination between the mixed‐valence metal and redox‐non‐innocent ligand L, which promotes through‐bond charge transfer between Cu metal sites, allows better metal‐ligand orbital overlap of the d‐π conjugation, leading to strong long‐range delocalization and semiconducting behavior. Our findings highlight the significance of the unique mixed valency between formal Cu(I) and highly‐covalent Cu(III), non‐innocent ligand, and pore environments of these bench stable Cu(III)‐containing frameworks on multielectron transfer and electrochemical properties.

Fu, Shang‐Yuan↗

DOE OSTI2023

Mixed‐Valence Cu I /Cu III Metal–Organic Frameworks with Non‐innocent Ligand for Multielectron Transfer

Abstract We report two novel three‐dimensional copper‐benzoquinoid metal–organic frameworks (MOFs), [Cu 4 L 3 ] n and [Cu 4 L 3 ⋅ Cu(iq) 3 ] n (LH 4 =1,4‐dicyano‐2,3,5,6‐tetrahydroxybenzene, iq=isoquinoline). Spectroscopic techniques and computational studies reveal the unprecedented mixed valency in MOFs, formal Cu(I)/Cu(III). This is the first time that formally Cu(III) species are witnessed in metal–organic extended solids. The coordination between the mixed‐valence metal and redox‐non‐innocent ligand L, which promotes through‐bond charge transfer between Cu metal sites, allows better metal‐ligand orbital overlap of the d‐π conjugation, leading to strong long‐range delocalization and semiconducting behavior. Our findings highlight the significance of the unique mixed valency between formal Cu(I) and highly‐covalent Cu(III), non‐innocent ligand, and pore environments of these bench stable Cu(III)‐containing frameworks on multielectron transfer and electrochemical properties.

Fu, Shang‐Yuan↗

DOE OSTI2022

A nitrogen- and carbonyl-rich conjugated small-molecule organic cathode for high-performance sodium-ion batteries

Organic-based cathode materials have attracted considerable attention for sustainable Na-ion batteries due to their great promise to overcome the issues arising from the insertion of large Na + into the rigid structures of conventional transition-metal-containing inorganic electrodes. The structural flexibility as a result of weak intermolecular interactions and simple electron- and ion-storage mechanisms found in organic compounds ensure facile and reversible transport of Na ions. In order to address the general drawbacks of small-molecule organic electrodes such as material dissolution in commonly used organic electrolytes and poor electronic conductivity, we report the use of a nitrogen- and carbonyl-rich highly extended π-conjugated small molecule, hexaazatrianthranylene (HATA) embedded quinone (HATAQ), as a cathode for sodium-ion batteries. The unique hydrogen bonds between highly functionalized conjugated HATAQ molecules allow supramolecular graphite-like 2D layered arrangements in the solid state which help facilitate the structural stability during long-term cycling and promote charge transfer. The compound delivers a capacity as high as 460 mA h g -1 at 500 mA g -1 and an excellent capacity retention of 99% (~138 mA h g -1 ) after 5000 cycles at an extremely high rate of 60 A g -1 . The reaction kinetics and redox mechanism of the material have been elucidated by several characterization techniques together with density functional theory (DFT) studies. The insights gained in this work could pave the way for ultra-high-performance small-molecule organic cathodes for sustainable energy storage.

25 ENERGY STORAGE↗

DOE OSTI2022

Proton-enabled biomimetic stabilization of small-molecule organic cathode in aqueous zinc-ion batteries

Small-molecule organic cathode materials offer flexible structural design features, high capacity and sustainable production. Nonetheless, the stability decrease due to the high solubility of the electrode materials especially under electrochemical cycling conditions limits their wide-range applications in energy storage technologies. Here we describe a nature-inspired strategy to address cathode stability via introduction of transient vinylogous amide hydrogen bond networks into the small-molecule organic electrode material hexaazatrianthranylene (HATA) embedded quinone (HATAQ). Thanks to the proton-enabled biomimetic mechanism, HATAQ exhibits unparalleled cycling stability, ultra-high capacity and rate capability in aqueous zinc-ion batteries, delivering 492 mA h g -1 at 50 mA g -1 and a reversible capacity of 199 mA h g -1 , corresponding to 99% retention at 20 A g -1 after 1000 cycles.

25 ENERGY STORAGE↗

DOE OSTI2022

Superior performance enabled by supramolecular interactions in metal-organic cathode: the power of weak bonds

Metal–organic-based electrode materials are increasingly appealing because both metal and organic linker are capable of undergoing redox processes, thus offering a high specific capacity. High porosity which can be achieved by the rational design of these materials is generally perceived as one of the major criteria for high rate performance. However, while Li-ion transport may be possible, oftentimes the counteranions (e.g., PF 6 - ) and solvent molecules are co-inserted into the porous host lattice, potentially hindering Li-ion diffusion pathways. Here, in this study, we propose the concept of close-packed metal–organic cathode stabilized by multiple supramolecular interactions as a viable solution for exceptional electrochemical performance. This is illustrated in a modularly designed redox-active [CuL(Py) 2 ] n (LH 4 = 1,4-dicyano-2,3,5,6-tetrahydroxybenzene, Py = pyridine). The mechanistic studies and DFT calculations confirm that the supramolecular interactions between its close-packed chains are the key to the flexible host lattice which only allows desolvated Li + to intercalate, while these weak bonds also stabilize the inserted Li in the preferred hopping sites, creating optimal diffusion paths. The performance observed in this work is found to be among the best ever reported for metal–organic cathodes with a capacity as high as 255 mA h g -1 at 65 mA g -1 (0.25C) and a reversible capacity of 59 mA h g -1 at ~26 A g -1 (100C) corresponding to 81% retention after 1000 cycles. These findings reveal a potential new strategy towards metal–organic-based electrodes with high performance and enhanced cycling stability.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Supramolecular Self-Assembled Multi-Electron-Acceptor Organic Molecule as High-Performance Cathode Material for Li-Ion Batteries

Organic electrode materials possess many advantages such as low toxicity, sustainability, and chemical/structural tunability toward high energy density. However, to compete with inorganic-based compounds, crucial aspects such as redox potential, capacity, cycling stability, and electronic conductivity need to be improved. Herein, a comprehensive strategy on the molecular design of small organic electron-acceptor-molecule—hexaazatrianthranylene (HATA) embedded quinone (HATAQ) is reported. By introducing conjugated quinone moieties into the electron-deficient hexaazatriphenylene-derivative core, HATAQ with highly extended π-conjugation can yield extra-high capacity for lithium storage, delivering a capacity of 426 mAh g -1 at 200 mA g -1 (0.4C). At an extremely high rate of 10 A g -1 (19C), a reversible capacity of 209 mAh g -1 corresponding to nearly 85% retention is obtained after 1000 cycles. A unique network of unconventional lock-and-key hydrogen bonds in the solid-state facilitates favorable supramolecular 2D layered arrangement, enhancing cycling stability. To the best of the authors’ knowledge, the capacity and rate capability of HATAQ are found to be the best ever reported for organic small-molecule-based cathodes. Finally, these results together with density functional theory studies provide proof-of-concept that the design strategy is promising for the development of organic electrodes with exceptionally high energy density, rate capability, and cycling stability.

25 ENERGY STORAGE↗