Abstract
In this study, we have proposed a novel concept of hybrid flow batteries consisting of a molten Na-Cs anode and an aqueous NaI catholyte separated by a NaSICON membrane. A number of carbonaceous electrodes are studied using cyclic voltammetry (CV) for their potentials as the positive electrode of the aqueous NaI catholyte. The charge transfer impedance, interfacial impedance and NaSICON membrane impedance of the Na-Cs ‖ NaI hybrid flow battery are analyzed using electrochemical impedance spectroscopy. The performance of the Na-Cs ‖ NaI hybrid flow battery is evaluated through galvanostatic charge/discharge cycles. This study demonstrates, for the first time, the feasibility of the Na-Cs ‖ NaI hybrid flow battery and shows that the Na-Cs ‖ NaI hybrid flow battery has the potential to achieve the following properties simultaneously: (i) An aqueous NaI catholyte with good cycle stability, (ii) a durable and low impedance NaSICON membrane for a large number of cycles, (iii) stable interfaces at both anode/membrane and cathode/membrane interfaces, (iv) a molten Na-Cs anode capable of repeated Na plating and stripping, and (v) a flow battery with high Coulombic efficiency, high voltaic efficiency, and high energy efficiency.
Highlights
Energy and climate concerns have led to the development of new renewable energy sources including wind, solar and biofuels
The second group is composed of carbonaceous materials because they have been widely used for vanadium redox batteries (VRBs) with good electrocatalytic activities [12,13,14,18,19,20,21,22,23]
The study of cyclic voltammetry reveals that the positive electrodes made of precious metals, carbonaceous materials, or Nb2 O5 - and WO3 -decorated carbonaceous materials do not provide symmetric electrocatalytic activities for oxidation and reduction of the triiodide/iodide redox couple in aqueous solution
Summary
Energy and climate concerns have led to the development of new renewable energy sources including wind, solar and biofuels. RFBs in separation of power and energy, dendrite growth of the Li anode, ion crossover, self-discharge, and high manufacturing costs of flow batteries Another concept of hybrid flow batteries with a molten Na-Cs alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane and operated at room temperature has been proposed [39,40,41]. This hybrid Na-based flow battery (HNFB), as shown schematically, has the potential to offer many unmatched advantages over VRBs. the utilization of molten Na90 Cs10 alloys at room temperature allows the specific capacity of the anode (~1050 mAh/g) to approach the theoretical capacity of pure Na (1166 mAh/g) while still maintaining the advantage of RFBs in decoupled design of power and energy.
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