Application Research Of Modified Carboxymethylcellulose Sodium Membrane In All Vanadium Redox Flow Battery

All-vanadium redox flow battery(VRFB)is one type of flow battery especially suitable for large scale energy storage use of electricity generating by renewable sources.The main advantages of VRFB over other energy storage devices include theoretical limitless storage capacity,flexible deign,deep discharge without any permanet damage,environment friendly,etc.,Now the biggest problem exists is the cost of the ion exchange membrane using in the VRFB.Nafion is the most widely used ion exchange membrane due to its high proton conductivity and good chemical and mechanical stability.However,Nafion fails to cope with the high vanadium ion permeability and its price can take up nearly 25% percent of the overall cost of the whole VRFB system which is unaffordable now.So,seeking alternative membranes that have low vanadium crossover and are economically affordable ion exchange membrane is an urgent call from this area of research.In this work,graphite oxide(GO)and sulfonated graphite oxide(SGO)were synthesized using an improved method.Then,GO and SGO were mixed with carboxymethylcellulose sodium(CMC)solution separately with a range of ratios to fabricate GO-CMC and SGO-CMC composite membranes via solution recast method.Water uptake,ion exchange capacity,vanadium ion permeability and proton conductivity and ion selectivity behavior of the modified carboxymethylcellulose sodium membrane was studied by various characterization techniques.The results indicated that when the doping ratio was 7% with SGO,the composite membrane exihibted the best ion selectivity property.To further decrease the vanadium ion permeability of 7%SGO-CMC,layer-by-layer self-assembly of PDDA and PSS polyelectrolytes onto the surface of 7%SGO-CMC membrane through alternative dipping method.The best ion selectivy was obtained after two coating layers.The VRFB single cell test of 7%SGO-[PDDA/PSS]2 recorded highest coulombic efficiency which was 98.49% when the current density was 60 m A·cm-2,after 50 charge-discharge cycle tests,its capacity still remained 84.28%,Both values were far more higher than Nafion under identical settings.Through the work I completed,modified carboxymethylcellulose sodium membrane can suppress the vanadium ion permeability and showed better VRFB sigle cell test compared to Nafion.Besides,carboxymethylcellulose sodium is readily commercially available for over three hundred of years.From this point of view and the results obtained,the modified carboxymethylcellulose sodium membrane can be considered as a promising candidate for future possible use in VRFB.