Interdigitated Flow Field Research Articles

Experimental Investigation on the Performance Characteristics of Flow Fields in Redox Flow Batteries Under Various Electrode Parameters

All-vanadium redox flow battery (VRFB) is a promising energy storage technique. Flow fields play a crucial role in distributing the electrolyte into the electrode uniformly, but their performance characteristics under different electrode parameters are still unclear. In this work, taking the total pressure drop and total overpotential as performance characterizations, the influence of electrode parameters and operating conditions on the performance of serpentine flow field (SFF) and interdigitated flow field (IFF) are experimentally investigated. It is found that the battery with IFF exhibits lower pressure drop than that with SFF because of the shunt effect of IFF on electrolyte. In terms of promoting the uniform distribution of the electrolyte into the electrode, the SFF outperforms IFF when the electrode porosity is higher than 0.810, but the performance of SFF and IFF could be reversed as the electrode porosity decreases to 0.714, indicating that there may be a performance reversal between SFF and IFF when the electrode porosity decreases from 0.810 to 0.714. Moreover, the increase of current density, the decrease of electrolyte input, and the decrease of electrode thickness strengthen the performance reversal at low electrode porosity. The results well explain the debate on the superiority of IFF and SFF and the discussion on the preference between flow fields and electrode thickness in literatures and provide guidance for the selection of optimal flow field in VRFBs.

Three-dimensional modeling study of all-vanadium redox flow batteries with the serpentine and interdigitated flow fields

• A comprehensive 3-D VRFB model with different flow fields is proposed. • The SFF with smaller channel and rib widths enhances the mass transfer in the carbon paper electrodes. • The performance of the carbon paper-based VRFBs is more sensitive to channel width than rib width. A comprehensive three-dimensional (3-D) model is developed to study the performance of all-vanadium redox flow batteries (VRFBs) with both serpentine flow field (SFF) and interdigitated flow field (IFF) by using 9 cm 2 carbon paper electrodes. Thanks to the induced stronger electrolyte convection in the electrodes, the batteries with SFF have better performance than IFF, though SFF may cause a higher pressure drop, especially at high flow rates. The effect of flow field geometry of SFF on the battery performance is further studied. Decreasing the channel depth of SFF enhances the mass transfer of electrolytes in the electrode, and the battery performance is more sensitive to the change of channel depth at high current densities. In addition, the battery performance declines with the increase of SFF channel width and rib width, and the influence of channel width is more pronounced than that of rib width. Reducing the rib width increases the electrolyte convection in the electrode more evidently for SFF with a wider channel while avoiding an excessive increase in pressure drop. Therefore, in the case of high current density or low electrolyte flow rate, the SFF with small flow channel depth and small rib width is conducive to improving the performance of VRFBs.

Topology Optimization of Flow Fields for Porous Electrodes

Power-efficient energy storage is important for the successful integration of renewables into the electrical grid, and one promising storage device is the redox flow battery. In this presentation, we discuss the design of the flow field component of a redox flow battery using topology optimization. The flow field is a flow manifold that distributes and guides fluid with reactant both into and out of the reactive porous electrode. The popular two-dimensional interdigitated flow field, where a series of interlocking flow channels force fluid into the electrode, is a design that is commonly used in the lab, and we perform our optimization to improve upon this design. Specifically, we aim to minimize the electrical and flow pressure power losses, and we find that different operating conditions, i.e., flow rate and current density, lead to different optimal designs. We observe fully three-dimensional features in our optimized designs, where primary flow channels appear along with smaller branching channels that guide fluid to the electrode. This provides evidence that three-dimensional structures can provide improvement over conventional two-dimensional designs. While high power efficiency can certainly be attained using a traditional interdigitated flow field, the dimensions of the fluid channels and solid lands need to be carefully chosen for the desired operating conditions. In this presentation, we show that our method can computationally guide this design process.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-830167.

How to Design a 3D Ordered Microstructure for Redox Flow Batteries: A Pore Network Modeling Study

Amid growing energy demand and the progressive contribution of intermittent renewable energy, the need for large-scale energy storage systems have become critical. Redox flow batteries can be a legitimate choice to store a huge amount of energy, subject to further improvement in their components, specifically the porous electrode. 3D printing technology is a viable method to manufacture porous electrodes with an engineered design and controllable properties. Attaining this goal requires an understanding of the effect of electrode microstructure which this study strove to provide. The effect of different parameters, including pore size, throat size, frequency of lattice units, and permeability anisotropy in the through-plane and in-plane directions were investigated in the flow-through as well as interdigitated batteries.Pore network modeling was utilized to investigate the effect of microstructure on the performance of Hydrogen-Bromine (H2-Br2) flow batteries. Simulations were carried out under steady-state conditions for electrolyte transport, species transport, and charge transport. To isolate the role of microstructure on the performance of the battery, simulations were performed at the constant flow condition in which the advective force was constant.The simulations were validated against the experimental study using an unstructured pore network, extracted from a tomography scan of a commercial carbon paper. A 3D printed ordered cubic lattice with the same permeability of the carbon paper showed a better performance. This was mainly achieved by better mass transport as a result of higher advection, diffusion, and lower tortuosity of the ordered lattice.It was found that a combination of bigger pores and smaller throats at constant permeability, facilitated the diffusion rate especially in the in-plane direction, as well as, increased the specific surface area of the network. It was also shown that a larger number of lattice units, resulted in a higher surface area, consequently a higher current generation.For both of the flow-through and interdigitated flow fields, permeability change in the through-plane direction (x-direction and y-direction) at the constant flow rate condition, almost did not affect the performance of the battery. However, the latter drastically changed the required electrolyte supplying pressure that could translate into a more economically feasible process. The permeability variation in in-plane direction reinforced or hampered the diffusion and also the current generation.Finally, an improved design of microstructure for the flow-through and interdigitated batteries were proposed and investigated. The specific surface area, permeability, and flow rate were kept constant to solely observe the role of microstructure on the battery performance. Results presented the superior performance of the improved microstructure in both flow fields. It was achieved by deviating the electrolyte main flow path, to the proximity of the membrane, where more reactions were taking place. This study took an initial step and provided insight into designing and manufacturing a porous electrode using 3D printing technologies. However, it can be continued in various paths including using complex 3D pore structures rather than simple cylindrical lattice to optimize the hydrodynamic behavior of the electrolyte and the specific surface area of the electrode.

Understanding the Interaction between Flow Field Geometries and Porous Electrode Microstructures in Redox Flow Batteries

Redox flow batteries are a promising technological option to integrate the growing supply of renewable energies into the electricity grid, however their deployment is hampered by high costs. To increase cost competitiveness, research efforts have targeted design of new electrolytes, high performance materials, and alternative electrochemical reactor concepts [1]. One powerful strategy is to increase the overall efficiency of the electrochemical stack, which can be achieved by improving the electrochemical performance and reducing the pumping power requirements. Selecting and optimizing the flow field design and electrode microstructure is crucial to accomplish an optimum trade-off. Drawing inspiration from polymer electrolyte fuel cells, current flow battery technologies leverage flow-through, interdigitated and serpentine flow field designs [2]. However, while functional, these designs have not been tailored for the specific requirements of redox flow batteries where single-phase reactive flows are sustained. Recent studies have investigated the influence of the channels and ribs dimensions [3], branched channel geometries [4], as well as the electrode microstructure on the reactor performance [5]. However, the interaction between the flow field geometries and the electrode microstructure determines the accessible surface area, mass transfer phenomena, and pressure drop; but remains poorly understood. With this in mind, we are poised to answer the following scientific question: What is the optimal combination of flow field and electrodes in redox flow batteries? In this work, we evaluate the interaction between geometrically diverse flow field geometries and porous electrode microstructures. We study seven different flow field designs in combination with two commonly used fibrous electrode structures – a carbon paper and a cloth (Figure 1). Flow-through, serpentine, and multiple variations of interdigitated flow fields were designed and fabricated by graphite milling. We employ a suite of polarization, electrochemical impedance spectroscopy, capacitance, and pressure drop measurements to elucidate structure-property-performance relationships. We find that the interdigitated designs perform better with high density of channels (i.e. shorter rib-channel width), even though this leads to higher pressure losses. Interestingly, pressure drop measurements show a similar relative contribution of the flow field and the electrode to the pumping losses, which motivates engineering of flow field geometries and electrode structures in tandem. Mass transfer overpotentials and pressure losses in cloth electrodes are reduced when using flow field geometries that force electrolyte flow into an in-plane direction in the electrode (i.e. parallel to the membrane plane), such as flow-through and interdigitated designs with wider ribs between channels. On the contrary, carbon paper electrodes perform better with interdigitated designs that force electrolyte flow into the through-plane direction (i.e. perpendicular to the membrane plane). Based on these findings, we have undertaken the engineering of innovative flow fields designs by combining interdigitated and branched patterns using 3D-printing, obtaining promising results that will be discussed in the final part of my talk.Figure 1. Polarization results for the combination of cloth and paper electrodes with three different flow field designs, at 5 cm·s-1 in the electrode. References Sánchez-Díez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, Journal of Power Sources, 481, 228804 (2021).D.Milshtein, K.M.Tenny, J.L.Barton, J.Drake, R.M.Darling and F.R.Brushett, J. Electrohcem. Soc., 164, E3265-E3275 (2017).R.Gerhardt, A.A. Wong, M.J. Aziz, J. Electrohcem. Soc., 165, A2625-A2643 (2018).Zeng, F. Li, F. Lu, X. Zhou, Y. Yuan, X. Cao, B. Xiang, Applied Energy, 238, 435-441 (2019).Forner-Cuenca, E.E. Penn, A.M. Oliveira, F.R.Brushett, J. Electrohcem. Soc., 166, A2230-A2241 (2019). Acknowledgments This work has been partially funded by the Agencia Estatal de Investigación (PID2019-106740RB-I00 and RTC-2017-5955-3/AEI/10.13039/501100011033). Figure 1

Characterization and scale-up of serpentine and interdigitated flow fields for application in commercial vanadium redox flow batteries

Vanadium redox flow batteries constitute a promising option in the field of stationary energy storage especially with respect to long-duration and large-scale duty scenarios. Indeed, although having numerous beneficial characteristics in the design and operation of vanadium redox flow batteries, their low power density is hindering their penetration into the energy storage market. Flow-field design and flow rate optimization are effective ways to improve battery power density. There are numerous studies in published literature on serpentine and interdigitated flow fields with deeper flow channels on thick bipolar plates. This paper deliberates the characterization of laboratory cells of size 100 cm2 equipped with serpentine and interdigitated flow fields on thin bipolar plates which generally employ in commercial stacks. The experimental results of charge-discharge life cycles and polarization measurements have been interpreted with the help of computational fluid dynamics simulations. The simulations are then extended to a cell size of 625 cm2. The results revealed an interesting characteristic on the variability of geometrical scale-up in each flow-field to obtain desired electrolyte distribution at minimal pressure drop.

Numerical simulation of the polymer electrolyte membrane fuel cells with intermediate blocked interdigitated flow fields

The main purpose of this paper is to study fuel cell performance using an interdigitated flow field with intermediate channel blocks on the cathode side. Application of an intermediate block in the middle of the interdigitated flow channel is a very new idea aimed at increasing the performance of polymer membrane fuel cells, which in practice result in novel arrangements of interdigitated flow channels. A middle block is desirable because the change in flow channel is minimal, the cost of fabricating bipolar plates does not increase, and it leads to an increase in the transfer rate of reactants into the gas diffusion layer due to enhanced over-rib flow pattern and direction. In this work, a three-dimensional, isothermal, and two-phase model is used to simulate the performance of such fuel cells. The polarization curves, the distribution of reactants on the cathode side, the distribution of liquid water, and the induced transverse flow were analyzed for three type of interdigitated flow fields along with parallel flow fields at reference conditions. The results showed that interdigitated flow fields with middle blocks lead to an increase in reactant transfer to the catalyst layer, an increase in reaction rate, and better removal of the resulting liquid water within the fuel cell. In the reference condition, in terms of maximum power density, the type I interdigitated flow field (without intermediate block) increased the net power by 8.2% compared to the parallel flow field, and the type II and III interdigitated flow fields also increased the power by 12.58% and 9.03%, respectively. At high current density, the type II interdigital flow field had the best performance in terms of enhancing the transfer of reactants to the catalyst layer and the expulsion of liquid water from that layer.

Optimization of an Electrochemical Gas Separation and Inerting System

Aircraft fuel tank inerting is typically accomplished by supplying nitrogen enriched air (NEA) into the ullage (volume of air above the fuel level in the tank). We have developed a novel on-board electrochemical gas separation and inerting system (EGSIS) to generate NEA for fuel tank inerting. EGSIS is an electrically powered system that functionally combines a proton exchange membrane (PEM) fuel cell cathode with an electrolyzer anode. Water management is important in such a PEM-based system because proton transfer requires proper hydration of the membrane. Extremes of both dryout and flooding conditions should be avoided for optimal EGSIS performance. Previous single-cell EGSIS experiments revealed that supplying liquid water at the anode will maintain sufficient membrane hydration even when the system is operated under dry cathode conditions. However, it was difficult to avoid flooding at low cathode air stoichiometries when parallel flow field channels were employed. Here, we implement various strategies to optimize EGSIS performance such as using serpentine and interdigitated flow field channels, as well as a double-layer gas diffusion layer with graded hydrophobicity to mitigate flooding and improve water management. We also present a theoretical analysis of various stack configurations for a practical EGSIS module.

Topology Optimization of 3D Flow Fields for Flow Batteries

As power generated from renewables becomes more readily available, the need for power-efficient energy storage devices, such as redox flow batteries, becomes critical for successful integration of renewables into the electrical grid. An important aspect of a redox flow battery is the planar flow field, which is usually composed of two-dimensional channels etched into a backing plate. As reactant-laden electrolyte flows into the flow battery, the channels in the flow field distribute the fluid throughout the reactive porous electrode. We utilize topology optimization to design flow fields with full three-dimensional geometry variation, i.e., 3D flow fields. Specifically, we focus on vanadium redox flow batteries and use the optimization algorithm to generate 3D flow fields evolved from standard interdigitated flow fields by minimizing the electrical and flow pressure power losses. To understand how these 3D designs improve performance, we analyze the polarization of the reactant concentration and exchange current within the electrode to highlight how the designed flow fields mitigate the presence of electrode dead zones. While interdigitated flow fields can be heuristically engineered to yield high performance by tuning channel and land dimensions, such a process can be laborious; this work provides a framework for automating that design process.

Model-based optimization for combined interdigitated and serpentine flow field in redox flow batteries

ABSTRACT Interdigitated flow field and serpentine flow field are widely adopted in redox flow batteries, but their superiority cannot be determined independently of the operating conditions, electrode properties, and electrolyte properties. Matching the flow field to the operating conditions can effectively improve the efficiency of flow cells. To this end, the present study proposes a model-based optimization method to promote the system energy efficiency of flow cells by combining the interdigitated and serpentine flow channels and considering the heterogeneous distribution of reactants. The fluid dynamic model, electrochemical model, and genetic algorithm are integrated into an optimization framework in the present study to obtain the novel interdigitated-serpentine flow field. Simulative results show that compared to the interdigitated or serpentine flow field, the optimized interdigitated-serpentine flow field yields increments in the system energy efficiency ranging from 2% to 20% under varying operation conditions.

Interdigitated flow field impact on mass transport and electrochemical reaction in high-temperature polymer electrolyte fuel cell

The enhanced performance of Polybenzimidazole (PBI) based high-temperature polymer electrolyte fuel cell (HT-PEFC) with interdigitated flow field over the other flow fields can be a consequence of higher average pressure developed on the flow field due to dead end in the channels or faster mass transport due to pressure-driven convection in the gas diffusion layer (GDL). In the present study, the effect of average pressure on the flow field and mass transport mechanism in the GDL on the HT-PEFC performance have been systematically decoupled. Three-dimensional simulation validated by experimental studies confirm that the enhanced performance in case of the interdigitated flow field is due to faster mass transport in the GDL and not due to higher average gas pressure. The simulation studies are performed on the interdigitated flow field and compared against the parallel flow field to have an insight into the effect of key operating and geometric parameters. There exists an optimum value for channel to rib ratio and current density saturates after an air stoichiometry of 4 which is validated by experiments.

Electrolyte circulation effects in electrochemical performance for different flow fields of all‐vanadium redox flow battery

AbstractA comparative study of electrochemical performance and hydrodynamic effects on a single cell for all vanadium redox flow batteries has been investigated in the present study. Electrochemical performance of a cell has been conducted with an active area of 414 cm2fitted with serpentine, interdigitated, and enhanced cross‐flow split serpentine (ECFSS) flow fields. The effects of electrolyte circulation rates on the electrochemical performance have been investigated for each flow field, and stable energy efficiency was achieved in 20 charge/discharge cycles for all three flow fields. Higher coulombic, voltage, and energy efficiencies in the serpentine flow field were achieved to be 96%, 82%, and 79%, respectively. The maximum peak power density values for the serpentine, ECFSS, and interdigitated flow field were found to be 158.2, 152.5, and 136.8 mW·cm−2, respectively, at a flow rate of 345 mL·min−1. Furthermore, detailed flow analysis was simulated by using computational fluid dynamics, and these studies postulated the reasons for the higher performance of the serpentine flow field compared to other flow fields.

Effect of compression of microporous and gas diffusion layers on liquid water transport of PEMFC with interdigitated flow field by Lattice Boltzmann method

In this study, a multi-component multiphase pseudopotential Lattice Boltzmann method with multi relaxation time (MRT) collision operator is used to investigate liquid water transport in the compressed microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells with interdigitated flow field. In this simulation, in order to achieve the real physical conditions of liquid water and air, such as viscosity ratio and high-density ratio, the forcing term is improved. Effect of parameters such as PTLs compression, intrusion thickness of the MPL, and operating temperature are studied.By studying four different compression levels (one without compression), when the PTL compression level is 85%, the water removal time is in the optimum state. Therefore, further increasing of compression level does not result in reduced water removal time. The simulation results indicated by rising temperature from 30 to 80 degrees The maximum level of saturated water is reduced by a factor of 5. Also, when the MPL thickness increases, the liquid water content is reduced in the PTL.

Development of innovative flow fields in a vanadium redox flow battery: Design of channel obstructions with the aid of 3D computational fluid dynamic model and experimental validation through locally-resolved polarization curves

Distribution of the electrolyte over the porous electrode is a critical issue limiting the power density of vanadium redox flow batteries. The flow field design involves a trade-off among high battery performance, low pressure drops, reduced electrolyte imbalance and thus the understanding of the physical phenomena regulating mass transport of the electrolyte is crucial to develop improved flow fields. This work firstly presents the development of a 3D computational fluid dynamic model that couples fluid dynamic analysis of the electrolyte with the electrochemistry of the reactions involved. The model simulates the influence of both single serpentine and interdigitated flow field. After extensive validation with respect to local polarization curves in symmetric cell with both positive and negative electrolyte, the model is used to design flow fields with two different channel obstructions: the first one is located at the channel wall, while the second one is placed close to electrode interface. Both obstructions create a localized pressure difference between adjacent channels, enhancing electrolyte permeation through porous electrode. Finally, model predictions are verified experimentally: considering cycling operation at different operating current densities, the second obstruction is more effective in obtaining a good trade-off among performance, pressure drops and evolution of exchanged capacity.

Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields

Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields

An Identification Size of The Interdigitated Flow Field on Pressure Loss Effects and Efficiencies in Vanadium Redox Flow Battery

In vanadium redox flow battery (VRFB), the active area for charge-discharge plays an important role on the optimization of the system. In this work, the optimum flow rate and current density of Nafion 117 membranes were examined and compared using 5cm2 and 25cm2 size of interdigitated flow field to operate VRFB at maximum efficiencies and discharge capacity. During discharge, flow field 25cm2 showed the highest discharge capacity of 367.5mAh at 10mAcm-2 as compared to 5cm2 flow filed which gave 221.9mAh. For battery efficiencies, three different parameters showed significant effects on different size of interdigitated flow field. 25 cm2 size of interdigitated flow field gave higher efficiencies than 5.0 cm2 up to 98%. This research offers fundamental understandings that bigger active area is needed to fully utilize the performance of VRFB.

A novel cooperative design with optimized flow field on bipolar plates and hybrid wettability gas diffusion layer for proton exchange membrane unitized regenerative fuel cell

Proton exchange membrane unitized regenerative fuel cell (PEM-URFC), as a novel electrochemical device which combines fuel cell (FC) and water electrolyzer (WE), is gradually being recognized as promising power source with reduction of size and cost. Unsatisfying mass transfer ability under the two adverse modes is the main factor hindering the commercialization of URFC, which calls for a bifunctional cell structure. In this study, a novel cooperative design with interdigitated flow field on bipolar plate (BPP) and a hydrophilic-hydrophobic alternative gas diffusion layer (GDL) is proposed to compose a new means of mass transfer under both working modes. Cells made up with different combinations of BPPs and GDLs are tested to confirm the usefulness of the new design. The cell with the optimized structure shows great progress in performance. The current density increases by 11.5% under FC mode and 4.8% under WE mode. EIS test and GDL's structure measurement are also carried out to further explain the working principle of the positive effect made by the new system on the cell. It is also found that the novel design of the URFC in this study has great adaptability to various operating conditions based on the stability test.

Experimental and Numerical Studies of Enhanced Interdigitated Flow Field for PEM Fuel Cells

AbstractThe presence of blockages in the flow field (FF) of proton exchange membrane fuel cells (PEMFCs) increases the mass transport of reactants toward the catalyst layer regions and improves cel...

Flow field designs developed by comprehensive CFD model decrease system costs of vanadium redox-flow batteries

Different flow field designs are known for vanadium redox-flow batteries (VFB). The best possible design to fulfil a variety of target parameters depends on the boundary conditions. Starting from an exemplary interdigitated flow field design, its channel and land dimensions are varied to investigate the impact on pressure drop, channel volume, flow uniformity and limiting current density. To find a desirable compromise between these several partly contrary requirements, the total costs of the VFB system are evaluated in dependence of the flow field’s dimensions. The total costs are composed of the electrolyte, production and component costs. For those, the production technique (injection moulding or milling), the pump and nominal power density as well as depth of discharge are determined. Finally, flow field designs are achieved, which lead to significantly reduced costs. The presented method is applicable for the design process of other flow fields and types of flow batteries.Graphical abstract

Numerical comparison between conventional and interdigitated flow fields in Proton Exchange Membrane Fuel Cells (PEMFCs)

The recent trend towards the decarbonization of the energy system has renewed the scientific community's interest in fuel cells. These devices have the potential to eliminate, or greatly reduce, the production of greenhouse gases. Polymeric Electrolyte Membrane Fuel Cells (PEMFC) are among the most promising technologies in this regard, being suited for various applications in stationary power plants, vehicles, and portable power devices. The critical issues in PEMFC are the limitation of oxygen transport through the air cathode and water management at high current density operation, which could be largely limited by modifying the design of the reactant supplier channels. In this paper, a three-dimensional CFD approach is used to compare straight and interdigitated flow fields, focusing on the increased current density and improved water management in the diffusion and catalyst layers for the interdigitated design. The simulation results show that the fluid is forced to flow through the porous layers, promoting a convection-type transport, leading to better water removal from the porous layers as well as to increased transport rates of reactants/products to/from the catalyst layers. This leads to reduced concentration overpotentials, and it shows the potential of simulation-driven design for high energy density PEMFC systems.