A carbonyl-rich conjugated organic compound for aqueous rechargeable Na+ storage with wide voltage window workability.

Organic compounds have become an important electrode material for aqueous electrochemical energy storage. However, organic electrodes still face poor performance in aqueous batteries due to insufficient electrochemical activity. In this work, a novel conjugated quinone compound containing a rich carbonyl group was designed. The quinone compound was synthesized by a simple dehydration reaction of pyrene-4,5,9,10-tetrone (PTO) and 1,2-diaminoanthraquinone (1,2-AQ); it contains 4 pyrazines (CN) from AQ and 4 carbonyl groups (CO), as well as a large number of active sites and the excellent conductivity brought by its conjugated structure ensures the high theoretical capacity of PTO-AQ. In the context of aqueous sodium ion batteries (ASIBs), the electrode material known as PTO-AQ exhibits a notable reversible discharge capacity of 117.9 mAh/g when subjected to a current density of 1 A/g; impressively, it maintained a capacity retention rate of 74.3 % even after undergoing 500 charge and discharge cycles, a performance significantly surpassing that of pristine PTO and AQ. Notably, PTO-AQ exhibits a wide operating voltage range (-1.0-0.5 V) and a cycle life of up to 10,000 cycles. In situ Raman and ex situ measurements were used to analyze the structural changes of PTO-AQ during charge and discharge and the energy storage mechanism in NaAC. The effective promotion of Na+ storage brought by a rich carbonyl group was obtained. The structural energy level and electrostatic potential of PTO-AQ were calculated, and the active center distribution of PTO-AQ was obtained. This work serves as a guide for designing high-performance aqueous organic electrode materials that operate across a wide voltage range while also explaining their energy storage mechanism.

Quinone-amine polymer nanospheres with enhanced redox activity for aqueous proton storage.

One of the biggest obstacles to the development of aqueous proton batteries (APBs), despite numerous optimization techniques, is the preparation and use of high-performance electrode materials. In this work, to improve the high solubility, limited capacity and poor cycle life of small organic molecules in APBs, homogeneous dispersed quinone-amine polymer nanospheres (PQANS) (average diameter: 220 nm) were synthesized by a polymerization reaction based on 3,3'-diaminobenzidine (DAB) and benzoquinone (BQ), making them suitable for proton storage in aqueous systems. As an anode for APBs, the obtained PQANS exhibits an improved reversible capacity of 126.2 mAh/g at 1 A/g after 300 cycles. The durable stable measurement of PQANS at 10 A/g was also conducted with a specific capacity of 66.8 mAh/g after 12,000 cycles. A series of in situ or ex situ measurements were used to establish the superior H+ storage mechanism of PQANS. A novel reaction mechanism of redox enhancement was revealed due to the existence of more carbonyl groups after the first cycle. Theoretical calculations were conducted to help illustrate the principle of binding protons with functional groups in PQANS. Finally, a PQANS anode-based aqueous proton full battery was constructed to demonstrate its potential application, which exhibits a specific capacity of 50.6 mAh/g at 1 A/g (600 cycles). This work provides a reference for preparing high-performance polymer-based electrode materials in aqueous batteries.

Electronic modulation and structural engineering of tetracyanoquinodimethane with enhanced reaction kinetics for aqueous NH4+ storage.

Lithium-ion batteries (LIBs) have received much attention because of their environmental, financial, and safety concerns. The advantages of aqueous electrochemical energy storage include environmental friendliness and safety, and the development of prepared electrode materials is predicted to alleviate these issues. A redox-active organic compound, 7,7,8,8­tetracyanoquinodimethane (TCNQ), is a suitable electrode for aqueous batteries. In this work, the porous and electronic interconnected structure of TCNQ is designed by electronic modulation and structure engineering. With the reduced graphene oxide (rGO) in situ homogeneous loading TCNQ by a one-step facile approach, the exquisite architecture has enhanced conductivity and connected conductive networks, favoring the storage and transportation of NH4+ or electrons in aqueous electrolytes. As a cathode, the obtained TCNQ-rGO exhibits superior performance for NH4+ batteries with an improved reversible capacity of 92.7 mAh/g at 1 A/g of quadruple capacity boosting to pure TCNQ and stable cycle life (5000 cycles at 10 A/g). The adjustment of the loading ratio of TCNQ and rGO for the cycling performance has been studied in detail. Furthermore, the superior ammonium storage mechanism of the TCNQ-rGO hybrid is thoroughly discussed by in situ Raman or ex situ measurements, which also determine the redox activity center groups of the TCNQ-rGO hybrid. Energy level calculations are conducted to help illustrate its potential as an electrode material. Our work demonstrates that electronic modulation and structural engineering of TCNQ can improve the electrochemical performance of molecular organic compound-based electrodes for aqueous rechargeable batteries in a simple and effective way.

Interface and electronic structure engineering induced Prussian blue analogues with ultra-stable capability for aqueous NH4+ storage.

Aqueous ammonium ion batteries (AAIBs) are considered potential energy storage solutions due to their faster kinetics, eco-friendliness, and high safety. Yet, appropriate electrode material for AAIBs is in continual investigation. Here, Prussian blue analogues (PBAs), Na0.73Ni[Fe(CN)6]0.88, are applied by a covalent bond assisted engineering with in situ polyaniline (PANI) polymerization. The synthesized PANI/Na0.73Ni[Fe(CN)6]0.88 hybrid (PNFF) inherited the advantages of the high conductivity of PANI and the stability of PBAs. The content of PANI had an effect on the electrochemical performance of PNFF. When served as cathode for AAIBs, the as-prepared PNFF-60 (PNFF with adjusted PANI content) delivers an enhanced reversible capacity of 92.5 mA h g-1 at 100 mA g-1 after 200 cycles. Even at a high current density of 2000 mA g-1, 95.2% capacity retention (1000 cycles) can be achieved by PNFF-60. The ammonium storage mechanism of PNFF-60 is fully investigated by in situ Raman and ex situ XPS/FTIR analysis. Moreover, an aqueous NH4+ full cell is assembled by coupling the polyimide@MXene (PI@MXene) anode, exhibiting durable cycling stability. This work adds to the understanding of constructing PBAs-based hybrid electrodes for ammonium ion storage devices.