Oxygen(O_(2))is an abundant material with its highly positive redox potential,making it a cost-effective choice for the cathodic active material of aqueous flow batteries(AFBs).However,utilizing O_(2)as an active mate...Oxygen(O_(2))is an abundant material with its highly positive redox potential,making it a cost-effective choice for the cathodic active material of aqueous flow batteries(AFBs).However,utilizing O_(2)as an active material may induce a high overpotential issue for oxygen reduction reaction(ORR).To address this problem,this study proposes a new AFB system employing iron-2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol complex(Fe(BIS-TRIS))and O_(2)as redox couple and cobalt(triisopropanolamine)complex(Co(TiPA))as the redox mediator.Co(TiPA)can mitigate ORR overpotential through a mediated electron transfer(MET)mechanism.More specifically,during the charging step,in the catholyte,Co(II)(TiPA)s are oxidized to Co(III)(TiPA)s at the cathode,while HO_(2)-s are oxidized in the electrolyte tank,producing O_(2).During the discharging step,Co(III)(TiPA)s are reduced to Co(II)(TiPA)s.The resulting Co(II)(TiPA)then chemically reacts with O_(2)in the electrolyte tank,regenerating Co(III)(TiPA).Namely,this cycle ensures that Co(III)(TiPA)is electrochemically reduced to Co(II)(TiPA)at the cathode,while the reduced Co(II)(TiPA)is chemically re-oxidized in the electrolyte tank,effectively mediating electron transfer between electrode and oxygen.This process facilitates ORR without direct electrochemical reaction at the cathode,thereby alleviating its overpotential.UV-Vis spectroscopic analysis verifies that Co(TiPA)spontaneously reacts with O₂and mediates ORR.Fe(BIS-TRIS)-O_(2)AFB maintains 79.1%of its initial capacity over 170 h,demonstrating the feasibility of Co(TiPA)as the redox mediator.However,its structural degradation under oxygen evolution reaction is observed,limiting the long-term stability of Fe(BIS-TRIS)-O_(2)AFB.Thus,its structural modifications or development of alternative redox mediators are required.展开更多
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2023R1A2C2002444).
文摘Oxygen(O_(2))is an abundant material with its highly positive redox potential,making it a cost-effective choice for the cathodic active material of aqueous flow batteries(AFBs).However,utilizing O_(2)as an active material may induce a high overpotential issue for oxygen reduction reaction(ORR).To address this problem,this study proposes a new AFB system employing iron-2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol complex(Fe(BIS-TRIS))and O_(2)as redox couple and cobalt(triisopropanolamine)complex(Co(TiPA))as the redox mediator.Co(TiPA)can mitigate ORR overpotential through a mediated electron transfer(MET)mechanism.More specifically,during the charging step,in the catholyte,Co(II)(TiPA)s are oxidized to Co(III)(TiPA)s at the cathode,while HO_(2)-s are oxidized in the electrolyte tank,producing O_(2).During the discharging step,Co(III)(TiPA)s are reduced to Co(II)(TiPA)s.The resulting Co(II)(TiPA)then chemically reacts with O_(2)in the electrolyte tank,regenerating Co(III)(TiPA).Namely,this cycle ensures that Co(III)(TiPA)is electrochemically reduced to Co(II)(TiPA)at the cathode,while the reduced Co(II)(TiPA)is chemically re-oxidized in the electrolyte tank,effectively mediating electron transfer between electrode and oxygen.This process facilitates ORR without direct electrochemical reaction at the cathode,thereby alleviating its overpotential.UV-Vis spectroscopic analysis verifies that Co(TiPA)spontaneously reacts with O₂and mediates ORR.Fe(BIS-TRIS)-O_(2)AFB maintains 79.1%of its initial capacity over 170 h,demonstrating the feasibility of Co(TiPA)as the redox mediator.However,its structural degradation under oxygen evolution reaction is observed,limiting the long-term stability of Fe(BIS-TRIS)-O_(2)AFB.Thus,its structural modifications or development of alternative redox mediators are required.
