Effect of flow field on the performance of an all-vanadium redox flow battery
Introduction
There is increasing interest in redox flow batteries because of the requirement for large scale electrical energy storage in a world where increasing share of electricity is being generated from renewable energy sources such as wind and solar photovoltaic systems. Among various flow battery systems, the all-vanadium redox flow batteries (VRFB) are among the most studied owing to a number of desirable features such as quick response, tolerance to deep discharge, long cycle life, high energy efficiencies of over 80% in large installations and active thermal management [1], [2], [3], [4]. VRFBs employ VO2+/VO2+ as the positive electrolyte and V+2/V+3 redox couple in sulphuric acid as the negative and positive half-cell electrolytes, respectively [2]. VRFBs have been under development for the past three decades. Much of the recent research has focused on materials for electrodes, catalysts, new electrolytes or additives to increase energy density and range of operating temperature, cheaper ion exchange membranes and separators as alternatives to Nafion. Due to the need for larger cell and stack sizes and to improve efficiency further, a number of studies have focused on electrolyte circulation and especially on the configuration of the flow field which can be an important factor in determining the performance of a redox flow battery (RFB). A well-designed flow field will minimize the pressure drop required for circulating the electrolytes for charging and discharging the battery while maintaining proper distribution of the reactants over the cell and carrying reactants convectively into the reaction zone through cross-flow in the porous substrate [5]. Under-the-rb cross-flow occurs due to the pressure difference between adjacent parallel channels [6]. It has two consequences, both beneficial from the point of view of the flow battery. Firstly, it reduces the flow in the serpentine thereby reducing the pressure drop. Secondly, it feeds the reaction zone with reactants convectively, which enables a higher reactant flux than what is possible with diffusion only. It therefore reduces concentration overpotential and increases the electrochemical energy conversion. The importance of this is well-recognized in the fuel cell literature [7], [8], [9], [10] and new configurations of flow fields have been proposed in the literature [11], [12] to enhance it in a serpentine flow field. Its importance to flow battery applications has also been underscored in recent literature [5], [13]. Electrolyte distribution has been identified as one of the key factors that affect the performance of RFB [14], [15].
Several in-situ experimental studies have been reported on the role of flow field configuration on the electrochemical behaviour and performance of RFBs [16], [17], [18]. Chen et al. [16] made a comparative study of parallel and serpentine flow fields and concluded the latter to be preferable due to the non-uniformity that could arise in parallel flow fields. Aaron et al. [17] proposed zero gap cell architecture with serpentine flow field which showed significantly higher power density than the conventional cell structure. Tsushima et al. [18] studied the influence of cell geometry and operating parameters on performance of redox flow battery with serpentine and interdigitated flow fields and found better performance with interdigitated flow field in VRFB than with the serpentine flow field. However, most of these studies have been performed in small cells with active area of 25 cm2 or less and the effect of the flow field may not have had an impact on the overall performance. The effect of electrolyte circulation rate has also not been studied systematically. The aim of present work is to redress these gaps by conducting comparative and systematic experimental studies in which the hydrodynamic and electrochemical performance is measured in an all-vanadium redox flow battery of about 100 cm2 cell size fitted with conventional, interdigitated and serpentine flow fields.
Section snippets
Details of the experimental studies
The single-cell VRFB consisted of a proton exchange membrane (Nafion 117, 0.18 mm thickness - Alfa Aesar), electrodes, electrolyte distributors, Cu current collectors of 2 mm thickness and Perspex end plates of 15 mm thickness. Graphite plates (SGL Grade R7510, 10 mm thickness), engraved with either serpentine or interdigitated flow fields over a 10 cm × 10 cm active area, served as electrolyte distributors. The electrodes on the anode and the cathode sides were made of one-layer of carbon felt
Typical results
Charge-discharge curves are widely used to evaluate the electrochemical behaviour of VRFBs [1]. Typical results obtained from the present experiments are given in Fig. 2; these have been obtained for the interdigitated flow field. Fig. 2a shows the charge-discharge curves for over 50 cycles. The current density during charging and discharging was maintained at 50 mA cm−2 and the electrolyte flow rate maintained at 58 ml min−1. Excellent stability can be seen in the charge-discharge curves over
Discussion and conclusion
Direct comparison of the electrochemical performance of the conventional flow field with other flow fields has not yet been reported in the open literature. The consistent and stable performance data obtained in the present study provide two useful insights:
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A comparison of the polarization characteristics of serpentine and interdigitated flow fields has been made by the present authors [6] in a smaller cell of 80 mm × 51 mm size. The present results in a larger cell are in contradiction with
References (24)
- et al.
Characteristics and performance of 1kW UNSW vanadium redox battery
J. Power Sources
(1991) - et al.
Redox flow cells for energy conversion
J. Power Sources
(2006) - et al.
Effect of channel-to-channel cross flow on local flooding in serpentine flow fields
J. Power Sources
(2008) - et al.
Interaction between the diffusion layer and the flow field of polymer electrolyte fuel cells—experiments and simulation studies
J. Power Sources
(2003) - et al.
Experimental studies on optimal operating conditions for different flow field designs of PEM fuel cells
J. Power Sources
(2006) - et al.
A new flow field design for polymer electrolyte based fuel cells
Electrochem. Commun.
(2007) - et al.
An improved serpentine flow field with enhanced cross-flow for fuel cell applications
Int. J. Hydrogen Energy
(2011) - et al.
Distribution of incompressible flow within interdigitated channels and porous electrodes
J. Power Sources
(2015) - et al.
An optimal strategy of electrolyte flow rate for vanadium redox flow battery
J. Power Sources
(2012) - et al.
Numerical investigations of flow field designs for vanadium redox flow batteries
Appl. Energy
(2013)
Ex-situ experimental studies on serpentine flow field design for redox flow battery systems
J. Power Sources
Cycling performance and efficiency of sulfonated poly (sulfone) membrane in vanadium redox flow battery
Electrochem. Commun.
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