Abstract
A low-pressure drop stack design with minimal shunt losses was explored for vanadium redox flow batteries, which, due to their low energy density, are used invariably in stationary applications. Three kilowatt-scale stacks, having cell sizes in the range of 400 to 1500 cm2, were built with thick graphite plates grooved with serpentine flow fields and external split manifolds for electrolyte circulation, and they were tested over a range of current densities and flow rates. The results show that stacks of different cell sizes have different optimal flow rate conditions, but under their individual optimal flow conditions, all three cell sizes exhibit similar electrochemical performance including stack resistivity. Stacks having larger cell sizes can be operated at lower stoichiometric factors, resulting in lower parasitic pumping losses. Further, these can be operated at a fixed flow rate for power variations of ±25% without any significant changes in discharge capacity and efficiency; this is attributed to the use of serpentine flow fields, which ensure uniform distribution of the electrolyte over a range of flow rates and cell sizes.
Highlights
Precise compensation of balance between the electricity generation and consumption requires effective energy storage system
The serpentine flow field, when attached to a porous substrate, exhibits certain desirable flow features that are beneficial for an electrochemical reaction occurring in the porous substrate [44,54]
Detailed computational fluid dynamics (CFD) simulations show that this split happens right at the inlet channel itself and the part going through the substrate will flow towards the outlet channel with partial mixing with the electrolyte flowing in the channels
Summary
Precise compensation of balance between the electricity generation and consumption requires effective energy storage system. The principal focus of the present study is on the performance characteristics of the kWscale VRFB stacks equipped with serpentine flow fields and cell sizing for application in large-scale energy storage To this end, three stacks made of 410, 918 and 1500 cm cell nominal active areas have been studied to obtain data of electrochemical parameters including cell/stack resistivity and pressure drop while operating at current densities from to 120 mA.cm−2 and over a range of electrolyte flow rates. Three stacks made of 410, 918 and 1500 cm cell nominal active areas have been studied to obtain data of electrochemical parameters including cell/stack resistivity and pressure drop while operating at current densities from to 120 mA.cm−2 and over a range of electrolyte flow rates Results show that these stacks have the advantage of low pressure drop and negligible shunt losses compared to the flow frame design. Materials, methods, characterization and results are discussed below
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