Preconditioning Operation of Membraneless Vanadium Micro Redox Flow Batteries

Abstract

Development of a Membraneless Vanadium Micro Redox Flow Battery (MVMRFB) with an automated closed-loop control, using micro actuators and micro sensors, is presented for the first-time during electrolyte preconditioning operation in recirculation mode. The progress of preconditioning is tracked with UV-vis spectroscopy by 3D printed micro flow cuvettes. Influence of flow rate, reactor internal resistance, and presence of side reactions in the preconditioning process are studied. Optimal flow rate ratio between negative and positive electrolytes is determined and significant performance improvements achieved by operating at lower flow rates are obtained. Influence of reactor internal resistance, which is directly related with the maximum power density, is evaluated demonstrating that operating at a high-power density can be a source of inefficiency due to the presence of side reactions. Finally, presence of side reactions is evaluated through a dual measurement of electrolytes concentrations in both negative and positive side, and it is demonstrated to be a cause for charge imbalance between the two half-cells. This work lays a solid foundation for the successful implementation of a charge-discharge cycle in MVMRFBs operating in recirculation mode.