π-Conjugated Hexaazatrinaphthylene-Based Azo Polymer Cathode Material Synthesized by a Reductive Homocoupling Reaction for Organic Lithium-Ion Batteries

Electron-Withdrawing Group Functionalized Anthraquinone Polymers for High-Performance Organic Zinc-Ion Batteries

Aqueous zinc ion batteries (AZIBs) stand out among various battery technologies for their advantages, including low cost, high safety, and green credentials. We chemically polymerized anthraquinone and triphenylamine derivatives to prepare the π-conjugated polymers poly 2-((4-(diphenylamine)benzylidene)amino)anthracene-9,10-dione (PDAH) and poly 2-((4-((4-bromophenyl)(phenyl)amino)benzylidene)amino)anthracene-9,10-dione (PDABr), as cathode materials for AZIBs. The anthraquinone-based structure's high charge storage capacity, coupled with the π-conjugated structure's strong charge transfer capability, enabled these electrode materials to exhibit excellent electrochemical performance. Among them, the electron-withdrawing group -introduced in PDABr induces a p-π interaction with the adjacent benzene ring, optimizing electron and ion migration within the battery. This enhancement improves the electrode material's stability and electrochemical activity, leading to superior battery performance, especially in rate performance, cycle life, and stability. Comparative experiments revealed that PDABr//Zn exhibited a higher specific capacity (0.1 A g-1, 210.57 mA h g-1) than PDAH//Zn (0.1 A g-1, 145.7 mA h g-1). At the same current density, PDABr//Zn also showed better cycling stability with a (capacity retention of 93% after 6000 cycles at 5 A g-1). Additionally, PDABr//Zn exhibited exceptional rate capability, maintaining its specific capacity upon returning to the initial current density. By comparing the physical and electrochemical properties of PDAH//Zn and PDABr//Zn, the relationship between the p-π conjugation effect and electrochemical performance is elucidated. This study provides a strategy for the fine-tuned, molecular design of organic electrode materials, specifically aimed at enhancing high-energy organic zinc-ion batteries.

Organic cathode with high-density active sites and extended π-conjugated structure for advanced high-performance lithium-ion batteries

Organic electrode materials demonstrate exceptional potential for sustainable rechargeable batteries due to their tunable structure, environmental friendliness and cost-effectiveness. However, their practical application in lithium-ion batteries (LIBs) is hindered by challenges such as limited capacity, poor intrinsic conductivity and significant dissolution issues in inorganic electrolytes. To address these challenges, a novel high-performance organic cathode material for LIBs, Polymeric ladder-type benzoquinone compound (PLBQ), was designed and synthesized in this work. The rational molecular design strategy imparts PLBQ with abundant active sites (CO and CN), enhancing its theoretical specific capacity. The electron-withdrawing nature of the redox-active sites (CO) and the extended π-conjugated structure lower the lowest unoccupied molecular orbital (LUMO) energy level and reduce the bandgap, thus increasing both the operational voltage and intrinsic conductivity of the PLBQ cathode. Additionally, the synergistic π-π interactions and hydrogen bonding impart remarkable solvent resistance to PLBQ, while simultaneously enhancing the stability of its molecular structure. As a result, the PLBQ cathode exhibited outstanding electrochemical performance, including long-term cycling stability (96 % capacity retention after 1000 cycles at 1 A g-1), excellent rate capability (101.3 mA h g-1 at 2 A g-1) and high reversible specific capacity (252.5 mA h g-1 at 0.1 A g-1). This work offers a novel molecular design strategy for the development of high-performance organic cathode materials for future lithium-ion batteries.

Azopyridine Aqueous Electrochemistry Enables Superior Organic AZIBs

Azo compounds (AZO), such as azobenzene, are classic organic electrode materials featuring a redox potential close to Zn/Zn2+. Recent studies show that azobenzene could work as a cathode in aqueous zinc-ion batteries (AZIBs), providing a voltage output of around 0.7 V. However, the energy storage mechanism of AZO cathodes in AZIBs remains unclear, and their practical usage in AZIBs is hindered by the low voltage. In this study, azopyridine isomers, the hydrophilic analogues of azobenzene, were adopted as cathodes for AZIBs, and the energy storage mechanism was unveiled through aqueous electrochemical studies. Through in situ electrochemical characterizations and theoretical computations, we reveal that both the electron-withdrawing effect of the pyridyl group and the H+-involved -N = N-/-NH-NH- redox reaction uplift the redox potential of the azopyridine cathodes. These findings led to the first AZO-based AZIB, providing a voltage output of 1.4 V. The proposed air-stable AZIBs deliver a high energy/power density and a capacity of around 200 mAh g-1. This work discovers different azopyridine electrochemistry in aqueous and organic electrolytes and enabling AZIBs to outperform its competitors from the AZO family.

Ionic Covalent-Organic Frameworks Composed of Anthryl-Extended Viologen as a Kind of Electrochemiluminescence Luminophore

Nowadays, covalent-organic frameworks (COFs) integrated with the electrochemiluminescence (ECL) behavior are highly desired owing to the significant advantages including multifunctionality, high sensitivity, and low background noise. Here, two ionic COFs (iCOFs) consisting of the anthryl-extended viologen as the backbone were designed and synthesized via the Zincke reaction. It is found for the first time that the as-prepared iCOFs accompanied by potassium persulfate as the coreactant can provide a clear ECL response in a water-bearing medium. The maximum ECL emissions of the iCOFs were in agreement with the photoluminescence spectra. Besides, cyclic voltammetry and electron paramagnetic resonance measurements reveal that the pyridinium unit was electrochemically reduced to afford the free radical. Then, it reacted with SO4·- to generate the excited-state [iCOF]*. Finally, [iCOF]* quickly returned to its ground state coupled with a clear ECL emission, yielding a maximum ECL quantum efficiency of 23.4% compared with tris(2,2'-bipyridyl) ruthenium(II) as the benchmark. In brief, the current study opens a way to develop a kind of ECL emitter that holds great potential in sensing, imaging, and light-emitting devices.

Flexible Aqueous Supercapacitors for Long Cycle-Life Using Electrode with Multiple Active C═S Sites

Even though a few organic materials have attracted considerable attention for energy storage applications, their dissolution in the electrolyte during the charging-discharging processes presents a formidable challenge to their long-term performance. In this work, according to the principle of like dissolves like, non-polar trithiocyanuric acid (TCA) can effectively inhibit dissolution in an aqueous electrolyte, hence prolonging the cycle life. Moreover, theoretical calculations suggest that TCA lowers lowest unoccupied molecular orbital (LUMO) energy level, thereby promoting reaction kinetics. The CV curves of TCA maintain a rectangular structure even at a high scan rate of 1000 mV s‒1 and exhibit a remarkable capacitance retention rate of 93.1% after 50,000 cycles. Asymmetric flexible supercapacitors utilizing the TCA exhibit an impressive energy density. Moreover, they maintain 94.2% of their capacitance after undergoing 80,000 cycles. Their integration with perovskite solar cells to facilitate the rapid storage of photogenerated charges enables efficient solar energy utilization, providing a practical solution for capturing and storing renewable energy.

A redox-active organic cage as a cathode material with improved electrochemical performance

Organic cages offer numerous opportunities for creating novel materials suitable for a wide range of applications. Among these, energy-related applications are beginning to attract attention. We report here the synthesis of a [3 + 6] trigonal prismatic cage constituted by three redox-active dibenzotetraazahexacene subunits. Cathodes formulated with the organic cage show enhanced performance compared to those formulated with the individual subunits, showing improvements in terms of electrochemical stability, lithium-ion diffusivity, and cathode capacity.

A Liquid-Liquid Interfacial Strategy for Construction of Electroactive Chiral Covalent-Organic Frameworks with the Aim to Enlarge the Testing Scope of Chiral Electroanalysis

Although electroactive chiral covalent-organic frameworks (CCOFs) are considered an ideal platform for chiral electroanalysis, they are rarely reported due to the difficult selection of suitable precursors. Here, a facile strategy of liquid-liquid interfacial polymerization was carried out to synthesize the target electroactive CCOFs Ph-Py+-(S,S)-DPEA·PF6- and Ph-Py+-(R,R)-DPEA·PF6-. That is, a trivalent Zincke salt (4,4',4″-(benzene-1,3,5-triyl)tris(1-(2,4-dinitrophenyl)pyridin-1-ium)) trichloride (Ph-Py+-NO2) and enantiopure 1,2-diphenylethylenediamine (DPEA) were dissolved in water and chloroform, respectively. The Zincke reaction occurs at the interface, resulting in uniform porosity. As expected, the cyclic voltammetry and differential pulse voltammetry measurements showed that the tripyridinium units of the CCOFs afforded obvious electrochemical responses. When Ph-Py+-(S,S)-DPEA·PF6- was modified onto the surface of a glassy carbon electrode as a chiral sensor, the molecules, which included tryptophan, aspartic acid, serine, tyrosine, glutamic acid, mandelic acid, and malic acid, were enantioselectively recognized in the response of the peak current. Very importantly, the discriminative electrochemical signals were derived from Ph-Py+-(S,S)-DPEA·PF6-. The best peak current ratios between l- and d-enantiomers were in the range of 1.31-2.68. Besides, a good linear relationship between peak currents and enantiomeric excess (ee) values was established, which was successfully harnessed to determine the ee values for unknown samples. In a word, the current work provides new insight and potential of electroactive CCOFs for enantioselective sensing in a broad range.

Stable Hexaazatrinaphthalene-Based Planar Polymer Cathode Material for Organic Lithium-Ion Batteries

Organic materials have garnered intensive focus as a new group of electrodes for lithium-ion batteries (LIBs). However, many reported organic electrodes so far still exhibit unsatisfying cycling stability because of the dissolution in the electrolytes. Herein, a novel azo-linked hexaazatrianphthalene (HATN)-based polymer (AZO-HATN-AQ) is designed and fabricated by the polymerization of trinitrodiquinoxalino[2,3-a:2',3'-c]phenazine (HATNTN) and 2,6-diaminoanthraquinone (DAAQ). The abundant redox-active sites, extended π-conjugated planar conformation, and low energy gap endow the AZO-HATN-AQ electrode with high theoretical capacity, excellent solubility resistance, and fast Li-ion transport. In particular, the fully lithiated AZO-HATN-AQ still keeps the planar structure, contributing to the excellent cycling stability. As a result, AZO-HATN-AQ cathodes show high specific capacity (240 mAh g-1 at 0.05 A g-1), prominent rate capability (98 mAh g-1 at 8 A g-1), and outstanding cycling stability (120 mAh g-1 after 2000 cycles at 4 A g-1 with 85.7% capacity retention) simultaneously. This study demonstrates that rational structure design of the polymer electrodes is an effective approach to achieving excellent comprehensive electrochemical performance.

High-Rate Organic Cathode Constructed by Iron-Hexaazatrinaphthalene Tricarboxylic Acid Coordination Polymer for Li-Ion Batteries

The sluggish ion-transport in electrodes and low utilization of active materials are critical limitations of organic cathodes, which lead to the slow reaction dynamics and low specific capacity. In this study, the hierarchical tube is constructed by iron-hexaazatrinaphthalene tricarboxylic acid coordination polymer (Fe-HATNTA), using HATNTA as the self-engaged template to coordinate with Fe2+ ions. This Fe-HATNTA tube with hierarchical porous structure ensures the sufficient contact between electrolyte and active materials, shortens the diffusion distance, and provides more favorable transport pathways for ions. When employed as the cathode for rechargeable Li-ion batteries, Fe-HATNTA delivers a high specific capacity (244 mAh g-1 at 50 mA g-1 , 91% of theoretical capacity), excellent rate capability (128 mAh g-1 at 9 A g-1 ), and a long-term cycle life (73.9% retention over 3000 cycles at 5 A g-1 ). Moreover, the Li+ ions storage and conduction mechanisms are further disclosed by the ex situ and in situ characterizations, kinetic analyses, and theoretical calculations. This work is expected to boost further enthusiasm for developing the hierarchical structured metal-organic coordination polymers with superb ionic storage and transport as high-performance organic cathodes.