RESUMO
Aqueous organic redox flow batteries (AORFBs) are regarded as a promising solution for grid-scale and sustainable energy storage, but some long-standing problems such as low energy density and cycling stability should be resolved. Herein, a highly soluble bipyridine modified with a bridging phenylene group and two quaternary ammonium terminals, namely, [(NPr)2PV]·4Cl, was synthesized and used as an ultralow-potential and two-electron storage anolyte for AORFBs. The phenylene group, which is linked but not coplanar with the two pyridinium redox centers, can thus prevent their communication and result in an exceptionally low redox potential (-0.77 V vs standard hydrogen electrode, 2e-). Moreover, the introduction of a phenylene group can warrant a certain degree of large π-conjugation effects and mitigate the intramolecular Coulombic repulsion between the two positively charged pyridinium centers, thus helping to enhance the electrochemical stability. When paired with 4-trimethylammonium-TEMPO as the catholyte, [(NPr)2PV]·4Cl enabled an exceptionally high cell voltage up to 1.71 V. The AORFB delivers outstanding battery performances, specifically, â¼89% energy efficiency, â¼100% Coulombic efficiency, and â¼99.94% capacity retention per cycle during a long-term cycling process. The two overlapped single-electron reductions of [(NPr)2PV]·4Cl from the initial cationic form to the monoradical form and then to the quinoid form during the charging process were clearly verified by a series of spectroscopic techniques, including no-deuterium nuclear magnetic resonance and electron paramagnetic resonance. This work presents a significant improvement for the construction of high-voltage AORFBs by virtue of the designability, diversity, and tunability of multiredox organic molecules.
RESUMO
Despite a great deal of gas capture strategies based on ionic liquids, reversible tuning of gas absorption by pure ionic liquids using light irradiation has never been reported. Herein, we demonstrate a novel strategy for tuning the capture of CO2 by light-responsive ionic liquids through reversible trans-cis isomerization. These light-responsive ionic liquids were constructed by tailoring the azobenzene group to the cationic moiety, which exhibited different CO2 absorption ability before and after ultraviolet (UV) irradiation. Through a combination of absorption experiments, NMR spectroscopy, differential scanning calorimetry analysis, viscosity measurement, and quantum chemical calculations, the results indicated that the significant difference in CO2 absorption capacity originated from the entropic effect, which was induced by the change in the aggregation state during trans-cis isomerization. This reversible isomerization of ionic liquids upon alternating irradiation of UV light and blue light shows the potential to control the capture and release of CO2 in an energy-saving way.
RESUMO
This work presents a new strategy for the promotion of CO2 uptake by an intramolecular proton transfer reaction in amino functionalized hydroxypyridine based anions.
RESUMO
The strong chemisorption of CO2 is always accompanied by a high absorption enthalpy, and traditional methods to reduce the absorption enthalpy lead to decreased CO2 capacities. Through the introduction of a large π-conjugated structure into the anion, a dual-tuning approach for the improvement of CO2 capture by anion-functionalized ionic liquids (ILs) resulted in a high capacity of up to 0.96â molCO2 mol-1IL and excellent reversibility. The increased capacity and improved desorption were supported by quantum chemical calculations, spectroscopic investigations, and thermogravimetric analysis. The increased capacity may be a result of the strengthened dynamic covalent bonds in these π-electron-conjugated structures through anion aggregation upon the uptake of CO2 , and the improved desorption originates from the charge dispersion of interaction sites through the large π-electron delocalization. These results provide important insights into effective strategies for CO2 capture.