Abstract
We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored.
Highlights
Energy and climate concerns have led to the development of new renewable energy sources including wind, solar and biofuels
The cyclic voltammogram (CV) of these two types of catholytes are shown in profiles are similar to the CV profile measured previously using the solution with 0.01M V(acac)[3] in acetonitrile with 0.5 M TEABF4 supporting electrolyte[6]
The Coulombic efficiency are ~100% after the 2nd cycle, suggesting that the gradual decay in the capacity is likely related to the decay of the catalytic activities because of the loss of the Bi nanoparticles on the carbon electrode and/or aggregation of the Bi nanoparticles. In this proof-of-concept study, we have introduced a new concept of hybrid Na-based flow batteries (HNFBs) with a floating liquid Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane
Summary
Energy and climate concerns have led to the development of new renewable energy sources including wind, solar and biofuels. This Na90Cs10 alloy is composed of solid Na particles dispersed in a molten Na-Cs alloy at temperature above −8 oC40, making it a floating anode at −8 oC or higher Such a molten anode can be paired with a flowing catholyte to offer a hybrid flow battery with ultrahigh volumetric and gravimetric energy densities while still maintaining the advantage of RFBs in decoupled design of power and energy. Because of the use of molten Na alloys at the anode (which has an electrochemical potential of − 2.7 V vs SHE), the cell voltage can be increased to 3 volts or higher, depending on the catholyte chemistry This further increases the energy density of HNFBs by a factor of 3 in comparison with conventional RFBs using an aqueous media for both the anolyte and catholyte. This specific energy (480 Wh/kg) is 18 times the specific energy provided by conventional all vanadium RFBs (~25 Wh/kg)[2]
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