The Effect of Channel Tapering on the Performance of Vanadium Redox Flow Batteries

Abstract

The recent growth of intermittent renewable energy sources, such as wind and solar, requires a simultaneous growth of grid-scale energy storage facilities to provide energy resilience and reliability. Redox flow batteries (RFBs) are electrochemical devices that stand out as potential candidates for the storage of large amounts of energy in an economical and flexible way due to their ability to decouple power and energy capacity. However, one of the main drawbacks that hinders the widespread adoption of RFBs is their relatively low power density, which results in large stack size and high system cost. In recent years, the optimization of engineering aspects, such as electrode materials and cell architectures, has become a key element on the roadmap towards high-performance and cost-effective RFBs. For example, flow fields are critical components for the transport of active species to/from the electrochemically active area of the electrode (i.e., the surface area of the fibers) and, therefore, their design significantly affects the power output and efficiency of the system. In this work, the effects of interdigitated channel tapering on the performance of aqueous vanadium RFBs are examined experimentally, theoretically and numerically. Critical performance metrics, such as peak power density, limiting current density, round-trip efficiencies and pressure drop are obtained experimentally using flow cells with the tapered flow fields and compared to the ones obtained with the conventional (i.e., non-tapered) flow fields. To establish a fundamental understanding, the experimental results are further examined by means of a macroscopic multiphysics model. The initial results show that the use of novel flow-field designs can be an effective way to develop RFBs with superior performance, while maintaining pumping losses in acceptable levels. A mechanistic understanding on the transport behaviors and their coupling to the electrochemical performance will be provided.