Mircea Dincă’s research while affiliated with Massachusetts Institute of Technology and other places

Sodium-ion batteries (SIB) attract considerable attention, but their practical implementation continues to suffer in large part from the limited energy density of current SIB cathode materials. In principle, redox-active organic materials can tackle this challenge because of their high theoretical energy densities. However, electrode-level energy densities of organic electrodes are compromised due to their poor electron/ion transport and severe dissolution. Here, we report the use of a low-bandgap, conductive, and highly insoluble layered metal-free cathode material for SIBs. It has a high theoretical capacity and enables a practical-level active material content, achieving an electrode-level energy density of 606 Wh kg–1electrode and long cycle life. It allows for facile two-dimensional Na+-ion diffusion, which enables high intrinsic rate capability. In-situ growth of the active cathode material with carbon nanotubes, which improves charge transport and charge transfer kinetics, further enhances the power performance. Altogether, these allow the construction of full SIB cells built from an affordable, sustainable organic small molecule, which provide a cathode energy density of 472 Wh kg–1electrode when charging/discharging in 90 seconds, a top specific power of 31.6 kW kg–1electrode.

Metal‐organic frameworks (MOFs) are promising materials for gas sensing but are often limited to single‐use detection. A hybridization strategy is demonstrated synergistically deploying conductive MOFs (cMOFs) and conductive polymers (cPs) as two complementary mixed ionic‐electronic conductors in high‐performing stand‐alone chemiresistors. This work presents significant improvement in i) sensor recovery kinetics, ii) cycling stability, and iii) dynamic range at room temperature. The effect of hybridization across well‐studied cMOFs is demonstrated based on 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11‐hexaiminotriphenylene (HITP) ligands with varied metal nodes (Co, Cu, Ni). A comprehensive mechanistic study is conducted to relate energy band alignments at the heterojunctions between the MOFs and the polymer with sensing thermodynamics and binding kinetics. The findings reveal that hole enrichment of the cMOF component upon hybridization leads to selective enhancement in desorption kinetics, enabling significantly improved sensor recovery at room temperature, and thus long‐term response retention. This mechanism is further supported by density functional theory calculations on sorbate–analyte interactions. It is also found that alloying cPs and cMOFs enables facile thin film co‐processing and device integration, potentially unlocking the use of these hybrid conductors in diverse electronic applications.

Two-dimensional conductive metal–organic frameworks (2D cMOFs) are an emerging class of crystalline van der Waals layered materials with tunable porosity and high electrical conductivity. They have been used in a variety of applications, such as energy storage and conversion, chemiresistive sensing, and quantum information. Although de-signing new highly conductive 2D MOFs and studying their composition/structure-property relationships have at-tracted significant attention, there are still very few examples of 2D cMOFs that exhibit room-temperature electrical conductivity above 1 S cm–1. When such high conductivities are achieved, Ni-diamine linkages are often involved, yet Ni-diamine MOFs remain difficult to access. Here, we report two new 2D cMOFs M3(HITT)2 (M = Ni, Cu; HITT = 2,3,7,8,12,13-hexaiminotetraazanaphthotetraphene). Ni3(HITT)2 exhibits electrical conductivity of as high as 4.5 S cm–1 at 298 K, much higher than that of its copper analogue Cu3(HITT)2, 0.05 S cm–1. Spectroscopic analysis reveals that Ni3(HITT)2 exhibits significantly stronger in-plane π-d conjugation and higher density of charge carriers com-pared to Cu3(HITT)2, accounting for the higher electrical conductivity of Ni3(HITT)2. The present work provides a deeper understanding of the influence of metal nodes on the electrical conductivity of cMOFs.

Two-dimensional conductive metal–organic frameworks (2D cMOFs) are an emerging class of crystalline van der Waals layered materials with tunable porosity and high electrical conductivity. They have been used in a variety of applications, such as energy storage and conversion, chemiresistive sensing, and quantum information. Although de-signing new highly conductive 2D MOFs and studying their composition/structure-property relationships have at-tracted significant attention, there are still very few examples of 2D cMOFs that exhibit room-temperature electrical conductivity above 1 S cm–1. When such high conductivities are achieved, Ni-diamine linkages are often involved, yet Ni-diamine MOFs remain difficult to access. Here, we report two new 2D cMOFs M3(HITT)2 (M = Ni, Cu; HITT = 2,3,7,8,12,13-hexaiminotetraazanaphthotetraphene). Ni3(HITT)2 exhibits electrical conductivity of as high as 4.5 S cm–1 at 298 K, much higher than that of its copper analogue Cu3(HITT)2, 0.05 S cm–1. Spectroscopic analysis reveals that Ni3(HITT)2 exhibits significantly stronger in-plane π-d conjugation and higher density of charge carriers com-pared to Cu3(HITT)2, accounting for the higher electrical conductivity of Ni3(HITT)2. The present work provides a deeper understanding of the influence of metal nodes on the electrical conductivity of cMOFs.

Electrically conductive metal‐organic frameworks (MOFs) are promising candidates for electrochemical capacitors (EC) due to their high specific surface areas and potential for redox activity. To maximize energy density, traditional inorganic pseudocapacitors have utilized faradaic processes in addition to double‐layer capacitance. Although conductive MOFs are usually comprised of redox active ligands which allow faradaic reactions upon electrochemical polarization, systematic studies providing deeper understanding of the charge storage processes and structure‐function relationships have been scarce. Here, we investigate the charge storage mechanisms of a series of triazatruxene‐based 2D layered conductive MOFs with variable alkyl functional groups, Ni3(HIR3‐TAT)2 (TAT = triazatruxene; R = H, Et, n‐Bu, n‐Pent). Functionalization of the triazatruxene core allows for systematic variation of structural parameters while maintaining in‐plane conjugation between ligands and metals. Specifically, R groups modulate interlayer spacing, which in turn shifts the charge storage mechanism from double‐layer capacitance towards pseudocapacitance, leading to an increase in molar specific capacitance from Ni3(HIH3‐TAT)2 to Ni3(HIBu3‐TAT)2. Partial exfoliation of Ni3(HIBu3‐TAT)2 renders redox active ligand moieties more accessible, and thus increases the dominance of faradaic processes. Our strategy of controlling charge storage mechanism through tuning the accessibility of redox‐active sites may motivate further design and engineering of electrode materials for EC.