利用尿素类似物提升4-OH-TEMPO正极液容量及其在液流电池中的应用OA

4-Hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl(4-OH-TEMPO,4-HT)exhibits favorable redox reversibility as a catholyte material for aqueous organic flow batteries.However,its intrinsic solubility in neutral aqueous solutions is only about 2.1 mol/L,which severely limits the energy density of the battery.To address this issue,this study proposes the use of urea analogues,namely methylurea(MU)and ethylurea(EU),as hydrogen bond donor/acceptor additives to enhance the apparent solubility of 4-HT in the aqueous phase through intermolecular interactions,achieving physical solubilization without altering its molecular structure.The saturated solubility of 4-HT under different additive concentrations was systematically determined using ultraviolet-visible(UV-vis)spectrophotometry.The hydrogen bonding interaction mechanism between the additives and 4-HT was analyzed by proton nuclear magnetic resonance(1H NMR)spectroscopy.Combined with cyclic voltammetry,rotating disk electrode,electrochemical impedance spectroscopy,and single-cell charge-discharge tests,the physicochemical properties,electrochemical reversibility,and cycling stability of the solubilized electrolytes in actual flow batteries were comprehensively evaluated.The results showed that EU exhibited superior performance and could increase the solubility of 4-HT to 4.9 mol/L.NMR results indicated the formation of deep eutectic solution through hydrogen bonding between the additives and 4-HT,with EU showing stronger hydrogen bonding interactions than MU,which is consistent with its better solubilization effect.After solubilization,the diffusion coefficient of the electrolyte decreased slightly,but the electrochemical reversibility remained good,with the redox peak potential difference maintained at 81 mV.In full-cell tests at a current density of 20 mA/cm² over 100 cycles,the average Coulombic efficiencies of the systems with MU and EU both reached 96.5%,higher than the 96%of the blank group,while the capacity retention rates increased to 76%and 86%,respectively,significantly higher than the 17%of the blank group.This study proposes and validates a physical solubilization strategy based on urea analogues,which significantly enhances the solubility and energy density of 4-HT without compromising its electrochemical performance,providing a simple and effective technical pathway for the development of high-energy-density aqueous organic flow batteries.