excellent stability can provide a good choice to meet this demand. [2][3][4][5] However, the extensively studied all-vanadium RFBs suffer some long-standing problems, such as the high costs of cation exchange membranes and vanadium-based active materials and the electrolyte crossover and corrosion issues in strong acidic conditions. [6] Aqueous organic redox flow batteries (AORFBs), after being reported, [7,8] received particular attention among the existing flow battery technologies, primarily because organic redox-active materials possess numerous advantages including great natural abundance, facile structural tailorability, tunable electrochemical properties, and potentially low costs. The solutions of a number of organic active molecules, such as viologen, anthraquinone, phenazine, and azobenzene derivatives, have been investigated as the anolytes for AORFBs. And a few organic molecules are available for the catholytes, typically, 2,2,6,6-tetramethyl piperidin-1-yl)oxyl (TEMPO) and metallocene derivatives. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Considering the high redox potential of TEMPO and its derivatives (ranged from 0.8 to 1.0 V versus standard hydrogen electrode, SHE), the introduction of highly hydrophilic groups, such as the quaternary ammonium group, is a promising approach to further improve the energy density. [20,23] However, up to date, the capacity degradation mechanism on the TEMPO/viologen systems remains unclear, and a lack of appropriate spectroscopic methods was established to study the electrochemical reversibility of redox-active organic species, especially in radical involved systems.Given that the chemically stable pyrrolidinium group has an ultrawide electrochemical window and strong polarity, it has been frequently utilized as a cationic moiety of ionic liquids. [33,34] When coupled with Clion, the pyrrolidinium functionalized organic species also appear to be highly watersoluble. Herein, we report the successful synthesis of pyrrolidinium cation functionalized TEMPO and extended viologen (Pyr-TEMPO and [PyrPV]Cl 4 ), which can serve as a highlysoluble organic redox pair with high cell voltage and excellent redox reversibility in AORFBs (Figure 1). The introduction Aqueous organic redox flow batteries (AORFBs) are regarded as a promising candidate for grid-scale, low-cost and sustainable energy storage. However, their performance is restricted by low aqueous solubility and the narrow potential gap of the organic redox-active species. Herein, a highly-soluble organic redox pair based on pyrrolidinium cation functionalized TEMPO and extended viologen, namely Pyr-TEMPO and [PyrPV]Cl 4 , which exhibits high cell voltage (1.57 V) and long cycling life (over 1000 cycles) in AORFBs is reported. The intrinsic hydrophilic nature of the pyrrolidinium group enables high aqueous solubilities (over 3.35 m for Pyr-TEMPO and 1.13 m for [PyrPV]Cl 4 ). Furthermore, the interaction of nitroxyl radicals with water is observed, which may be helpful to prevent collision-induced...

Developing advanced materials, such as ionic liquids (ILs), is highly desired for post-combustion capture of carbon dioxide (CO2). In this paper, we first develop a series of chiral amino acid ILs for efficient, fast, and reversible capture of CO2. Our data reveal that the dianionic form of IL is beneficial to the formation of intramolecular hydrogen bonding, which can remarkably mitigate the viscosity increase during CO2 absorption. The enhanced absorption capacity of CO2 in the IL is mainly due to the multi-site absorption from both the amino group and the negative oxygen group. The dominating absorption pathway is that the amino group reacts with CO2 via an intramolecular proton transfer from the amino group to the negative oxygen group, leading to the formation of the intramolecular hydrogen bonding between carbamate and the protonated oxygen group. As a result, the enhanced absorption performance of amino-functionalized ionic liquids (AFILs) is achieved, especially a controllable viscosity change during the uptake, providing an important foundation for building smart absorption systems based on AFILs.

This work presents a new strategy for the promotion of CO uptake by an intramolecular proton transfer reaction in amino functionalized hydroxypyridine based anions.