Hani M. El-Kaderi

Covalent organic frameworks (COFs) have emerged as promising sulfur hosts for lithium-sulfur batteries; however, most studies rely on conventional two-dimensional cast cathodes, which restrict practical sulfur loading levels and areal capacity. Here, we report a 3D direct ink writing (DIW) strategy for fabricating metal-free, redox-active COF-based cathodes that enable electrodes with practical sulfur loadings essential for achieving high areal capacity. This study addresses the long-standing processing challenges associated with COF-based DIW to fabricate sulfur cathodes by carefully optimizing the ink rheology, printing parameters, and postprocessing conditions. A porous anthraquinone COF (DAAQ-TFP), synthesized via a scalable terracotta method, was used as the sulfur host and further formulated as a printable ink with shear-thinning behavior suitable for DIW. The free-standing 3D-printed cathodes delivered high sulfur loadings (up to 10 mg cm–2) and areal capacities (up to 11.1 mAh cm–2) at 0.05 C. Furthermore, battery cycling studies of a 5.1 mg cm–2 sulfur-loaded cathode-based coin cell demonstrated good cycling stability over 300 cycles with >95% Coulombic efficiency. These results support advancement in battery technology by offering promising solutions to improve active-site accessibility and enhance performance and reliability in metal-sulfur batteries under higher loading conditions.

Bimetallic NiCo-MOFs are grown in situ on nickel foam and their supercapacitor activity is investigated in three- and two-electrode configurations.

The optimization of the properties of laser-induced graphene (LIG) is crucial for advancing flexible supercapacitor electrodes. This study examines how varying interline (hatch) spacing, 200 µm, 300 µm, and 400 µm, during femtosecond (fs) laser writing on polyimide tape, affects the resulting LIG structure and electrochemical performance. Comprehensive characterization using scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) revealed that the LIG prepared with 300 µm line spacing (S#2) exhibited the most favorable combination of physicochemical and electrochemical characteristics. S#2 showed the lowest structural disorder (I_D/I_G = 0.324 ± 0.014), the highest graphitic ordering (prominent (002) XRD peak), and the lowest electrical resistance (34 Ω cm⁻¹). Interestingly, S#2 also demonstrated the highest water contact angle, indicating greater hydrophobicity, yet delivered the best electrochemical performance, suggesting a more complex relationship between surface wettability and charge storage. In a three-electrode configuration with 1 M KOH, S#2 achieved an areal capacitance of 166.6 mF cm⁻² at a scan rate of 5 mV s⁻¹ and a specific capacitance of 73.1 mF cm⁻² at a current density of 0.5 mA cm⁻², along with superior charge–discharge behavior and a low impedance R_ct value (44.36 Ω). It also demonstrated excellent cycling stability, retaining ∼100% of its capacitance over 5000 cycles at the current density of 4 mA cm⁻², and maintained stable performance under bending, confirming its potential for flexible and wearable energy devices. Furthermore, a flexible symmetric supercapacitor device fabricated using S#2 delivered a specific capacitance of 45.4 mF cm⁻² and an energy density of 4.0 µWh cm⁻² at 0.5 mA cm⁻². These results identify line spacing as a key laser parameter governing the structural, chemical, and electrochemical characteristics of LIG and suggest that surface hydrophobicity may play a beneficial role beyond conventional hydrophilic designs.

The work demonstrates the necessity of monomer purification prior to COF synthesis and monomer impurities contributing to catalytic activity.

The practical deployment of lithium–sulfur batteries (LSBs) is hindered by fundamental limitations in conventional slurry-cast cathodes, including poor sulfur utilization, sluggish ion transport, and low areal capacity, particularly in thick electrodes required for high energy density. To address these challenges, we present direct ink writing (DIW) as an additive manufacturing strategy to fabricate advanced current-collector-free, 3D-printed sulfur cathodes (3DP S@CoNi-DSACs/NC) with hierarchically porous architectures that enhance lithium-ion diffusion, promote electrolyte penetration, and reduce interfacial resistance. The synergistic effects of Co/Ni dual-atom sites accelerate redox kinetics and mitigate polysulfide shuttling. As a result, the optimized 3DP cathode with a sulfur loading of 5.4 mg cm⁻² demonstrated excellent rate capability, delivering a high reversible capacity of 1041.4 mAh g⁻¹ at 1C with 85.5% capacity retention after 1000 cycles, significantly outperforming its cast counterpart. Remarkably, even at a higher sulfur loading of 8.1 mg cm⁻², the 3DP cathode maintains outstanding performance, achieving a discharge capacity of 1538.4 mAh g⁻¹ and an areal capacity of 12.5 mAh cm⁻² at 0.1C. This study not only demonstrates the functional integration of catalytically active materials into 3D printable sulfur cathode architectures but also offers a scalable and transformative platform for building high-performance LSBs beyond conventional electrode manufacturing methods.

Ion transport and storage in porous materials play a vital role in numerous energy storage and conversion technologies, such as batteries, capacitors, and fuel cells. In this study, molecular dynamics simulations are used to investigate the structure–property–function relationship of lithium and sodium ion transport and storage in highly porous and π-conjugated Aza-linked covalent organic frameworks (COFs). The simulations reveal that the diffusion coefficients of free lithium ions are significantly higher than those of free sodium ions across all of the COF structures, highlighting the influence of ion size on mobility in the absence of solvent molecules. The presence of nitrogen atoms in the imidazole and phenazine rings of the framework of BCOF-1, referred to throughout this article as Aza-COF, was found to significantly decrease the diffusion coefficients of the metal ions due to the significant electrostatic attraction between the ions and the lone pairs of the nitrogen atoms. Replacing the nitrogen atoms with carbon atoms led to increased diffusion coefficients, suggesting that the lone pairs and π-electrons of the frameworks play critical roles in ion binding. Pore decoration of the frameworks with glycol side chains dramatically reduced ion mobility due to increased electrostatic interactions. This indicates that the ether groups in these side chains create a more restrictive environment for ion movement. Overall, the simulations reveal that the electronic properties and chemical functionality of the pore walls, the free volume of the pores, and the solid-state packing of the COF structure significantly impact the ion transport and storage within the framework. This understanding paves the way for the rational design of new COF materials with tailored ion transport and storage properties for potential use as electrodes and solid-state electrolytes in sustainable batteries.

Covalent organic frameworks (COFs) have emerged as a versatile class of materials owing to their well-defined crystalline structures and inherent porosity. In the realm of COFs, their appeal lies in their customizable nature, which can be further enhanced by incorporating diverse functionalities. Postsynthetic modifications (PSMs) emerge as a potent strategy, facilitating the introduction of desired functionalities postsynthesis. A significant challenge in PSM pertains to preserving the crystallinity and porosity of the COFs. In this study, we aim to investigate the intricate interplay between PSM strategies and the resulting crystalline and porous structures of the COFs. The investigation delves into the diverse methodologies employed in PSMs, to elucidate their distinct influences on the crystallinity and porosity of the COFs. Through a comprehensive analysis of recent advancements and case studies, the study highlights the intricate relationships among PSM parameters, including reaction conditions, precursor selection, and functional groups, and their impact on the structural features of COFs. By understanding how PSM strategies can fine-tune the crystalline and porous characteristics of COFs, researchers can harness this knowledge to design COFs with tailored properties for specific applications, contributing to the advancement of functional materials in diverse fields. This work not only deepens our understanding of COFs but also provides valuable insights into the broader realm of PSM strategies for other solid materials.