| Redox flow battery?RFB?is considered as the most promising large-scale energy storage technology,which has attracted more and more attention.Although the aqueous RFBs have made remarkable progress in commercial applications,these systems are mostly limited to a low energy density of 25 W h L-1 due to the narrow electrochemical window of water.Herein,it has become one of the research hotspots to develope a new generation of high energy density non-aqueous RFB.In this paper,the active species determining the energy density of RFB are our research object,and many non-aqueous RFBs have been developed.The effects of different factors on the electrolyte and battery performance have been investigated,and the charge/discharge performance of battery has also been tested.Firstly,a metal complex of[Co?phen?3]?PF6?2 was prepared by using an inexpensive ligand 1,10-phenanthroline and a non-noble metal cobalt.A non-aqueous all-cobalt RFB,using[Co?phen?3]?PF6?2 as the active species,acetonitrile as the solvent and tetraethylammonium hexafluorophosphate as the supporting electrolyte,has been studied.When using the redox couple[Co?phen?3]3+/[Co?phen?3]2+and[Co?phen?3]2+/[Co?phen?3]+as the cathode and anode respectively,the theoretical open-circuit voltage of battery reached to 1.45 V.The results showed that the graphite electrode provided a high diffusion coefficient and the change of supporting electrolyte concentration had little effects on peak current density.The coulomb efficiency was about 50-52%in a static H-type glass cell.A novel non-aqueous Fe/Co RFB employing the redox couple[Fe?phen?3]2+/[Fe?phen?3]3+and[Co?phen?3]+/[Co?phen?3]2+as the the cathode and anode respectively was proposed and investigated for energy storage application.The cyclic voltammetric results showed that the open-circuit voltage of the system reached2.1 V.The effects of charge/discharge current density on the performance of the cell were investigated.The results showed that the performance of the battery was better under the large charge current density and small discharge current density.The cycling performance showed that the battery reached a stable state after 5 cycles in flow mode.The coulomb,voltage and energy efficiencies achieved up to 80%,40%and 39%,respectively.We reported a new electroactive material benzophenone?BP?.It had low redox potential,high electrochemical reversibility and stability,and high solubility in acetonitrile.The diffusion coefficient of BP reached a maximum value of 1.43×10-5cm2 s-1?reversible state?when the concentration of the supporting electrolyte tetraethylammonium hexafluorophosphate was 0.5 M.BP was stable in a wide range of temperature,and the diffusion coefficient increased with temperature increasing.A non-aqueous organic RFB based on BP as the anolyte and 2,2,6,6-tetramethyl-1-piperidinyloxy as the catholyte was achieved with a cell voltage of 2.41 V and a theoretical energy density of 139 Wh L-1.The cycling performance in a flow battery showed a stable coulomb efficiency of 81%.We studied a high open-circuit voltage non-aqueous organic RFB employing BP and 2,5-di-tert-butyl-1,4-dimethoxybenzene as the anolyte and the catholyte,which showed a high cell voltage of 2.88 V by the measurement of cyclic voltammetry.When the electron donating methyl and methoxyl were introduced into the structure of BP molecule,the effects of chemical group on the electrochemical prosperities of BP were investigated.The results showed that the redox peak of BP moved to negative direction as the donating electron groups enhancing,which resulted in higher theoretical open-circuit voltage of 2.93 V and 3.03 V.However,the solubility of BP showed opposite trend.The cycling performance was evaluated with an in-house-designed flow battery system,and the coulomb and energy efficiency were 71.8%and 55.9%,respectively. |
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