| With the depletion of global fossil energy and environmental issues,it is imperative to develop large-scale energy storage equipment?vanadium redox flow battery,VFB?for renewable energy.Membrane is one of the key components in VFB and has great influence on battery efficiency,cost and lifetime.There are multi-ionic transports across membrane under electric field dragging force and electrolytes concentration gradient.Therefore,the ideal membrane should have good ion transmission capability,high ion selectivity,stable chemical properties,and low cost.Due to the low cost of the rigid phenyl ring of sulfonated poly?ether ether ketone??SPEEK?,the large steric hindrance can essentially prevent the cross-contamination of vanadium ions.Unfortunately,the aromatic backbone also limits the hydrophilic/hydrophobic microphase separation of ion-conducting channels and lower ion conductivity.In this work,SPEEK membranes and MWCNT/SPEEK composite membranes were prepared by electrospinning,construct a more open proton conduction channel,after the microscopic morphology is regulated,a more open proton conduction channel is constructed by regulating its microscopic appearance and excellent battery performance is obtained.Firstly,SPEEK nanofiber mats with smooth surfaces were prepared by electrospinning,then the electrospun SPEEK membranes were prepared by controlling the membrane formation conditions of the nanofiber mats.The results showed that the SPEEK nanofiber mats with smooth surface and smooth surface were prepared when the mass fraction of SPEEK spinning solution was 18 wt.%and the voltage was 20 kV,and the diameters were distributed around180 nm.Then,SPEEK membrane with dense and nanofiber morphology was prepared by hot pressing at 140°C and 5 MPa for 30 minutes.Then,through electrospinning and hot-pressing,dense SPEEK membranes with visible interconnected nanofiber network are fabricated,which induce long range ionic conductive pathways.The results of SPEEK membrane prepared by comparative casting method show that the performance of SPEEK membrane?Spun-54?is optimal,and the proton conductivity of Spun-54 is 23.8%higher than that of cast film?Cast-54?with the same degree of sulfonation;The swelling resistance and mechanical properties of electrospinning membranes are greatly enhanced due to the interaction of nano-networks.At the current density of 100 mA cm-2,the voltage efficiency?VE,86.0%?and energy efficiency?EE,84.2%?of Spun-54 are 10.3%and8.8%higher than that of Cast-54,respectively;Moreover,there is a significant advantage over the EE?74.9%?of the commercial Nafion211.Finally,multi-walled carbon nanotubes?MWCNT?/SPEEK composite membranes were prepared by electrospinning.The MWCNTs were aligned along the axial direction of the SPEEK nanofibers under high electric field,which resulted in good dispersion of MWCNTs in SPEEK nanofibers.It aligns along proton conductive pathways,the oxygen-containing groups on MWCNT could participate the formation of hydrogen bond networks and proton hopping.While vanadium ions could not transport by hopping,the blocking and non-swelling nature of MWCNT restricts vanadium ions permeation through the hydrophilic proton conductive domains.When the MWCNT doping amount was 0.5 wt.%,the vanadium ion permeability coefficient of the electrospinning membrane?Spun0.5?was significantly reduced by 67.6%compared to the pure electrospinning membrane.The excellent ion selectivity and anti-swelling performance make Spun0.5 film show excellent efficiency?Coulombic efficiency 98.1%,energy efficiency 86.2%?at a current density of 100 mA cm-2,which is higher 16.6%and 15.1%than that of Nafion211.In addition,100 long-cycle cycles at a current density of 100 mA cm-2showed that Spun0.5 exhibited superior stability performance,with a capacity decay of only0.47%/cycle and less than Nafion211?0.84%/cycle?. |
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