Interdigitated Flow Field Design Research Articles

Machine-learning assisted analysis on coupled fluid-dynamics and electrochemical processes in interdigitated channel for iron-chromium flow batteries

This study explores the impact of interdigitated flow channel spacing on electrolyte distribution and flow velocity in porous electrodes, thereby affecting pump consumption and system efficiency. Utilizing a 3D electrochemical flow-coupled model, the research investigates the electrochemical performance and energy efficiency across various channel spacings, specific flow rates, and current densities. It elucidates the mechanisms by which interdigitated channel spacing influences battery performance. Through controlled trial-and-error, the optimal spacing for flow channels in Iron-Chromium Redox Flow Batteries (ICRFBs) was determined to be 4 mm. At a current density of 140 mA/cm2, the voltage efficiency reached 86.3 %, and the pump-based voltage efficiency achieved 85.9 %. To quickly and efficiently explore the impact of each individual parameter on battery efficiency and identify the optimal operating conditions, this study further developed a multi-task machine learning (ML) model. Initially trained on simulation data, the model achieved high predictive accuracy (R2 > 0.88) and effectively linked the interdigitated flow field design of ICRFBs with current density, specific flow rate, and channel spacing. The ML model was then validated through further investigation to ensure its accuracy and to achieve optimum performance efficiency as recommended by the model. This integrated approach offers a comprehensive understanding of RFBs performance under varying conditions, driving advancements in RFBs technology.

Numerical Simulation of Flow Field Structure of Vanadium Redox Flow Battery and its Optimization on Mass Transfer Performance

The structural design of the flow channel of a redox flow battery directly affects ion transport efficiency, electrode overpotential, and stack performance during charge-discharge cycles. A tapered hierarchical interdigitated flow field design that has independent flow channel structures for different levels of flow was developed in this work. Especially, the secondary branch channels are the tapered type and the corresponding cross-sections are gradually reduced along the flow direction, which is beneficial for improving the flow rate at the end of channels and enhancing mass transfer. The performances of a vanadium redox flow battery with interdigitated flow field, hierarchical interdigitated flow field, and tapered hierarchical interdigitated flow field were evaluated through 3D numerical model. The results showed that at 240 mA cm−2 and 6 ml s−1, the pump-based efficiency of the hierarchical interdigitated flow field increased by 4%-7% compared with the interdigitated flow field. Furthermore, the pump-based efficiency with tapered hierarchical interdigitated flow field increased by 1.6%-3% compared with the hierarchical interdigitated flow field. This indicates that the tapered hierarchical interdigitated flow field shows further advantages in redox flow battery applications.

Stereolithography 3D Printing As a Versatile Tool to Manufacture Porous Electrodes for Redox Flow Batteries

Redox flow batteries show potential for large-scale energy storage; yet their current costs limit widespread implementation. As the porous electrode microstructure defines the available surface area for electrochemical reactions, electrolyte transport, and fluid pressure drop [1], enhancing the electrode performance is a promising strategy to increase power density and thus reduce system costs. Conventional fibrous porous electrodes are repurposed from fuel cell gas diffusion electrodes and have not been tailored to sustain the requirements of liquid-phase electrochemistry. Therefore, new manufacturing techniques offering high control over the electrode microstructure and resulting properties need to be developed [2]. In this context, 3D printing techniques are uniquely suited to manufacture controlled and deterministic architectures, enabling the tuning of electrochemical performance and hydraulic resistance [3].In this work, we employ stereolithography 3D printing using a commercial desktop printer, followed by carbonization, to manufacture model grid structures and investigate their potential as redox flow battery electrodes. We use microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics, to evaluate the thermal behavior, manufacturing fidelity, and fluid and mass transport performance of ordered lattice structures in non-aqueous redox flow cells. We find that the flow field geometry (flow through versus interdigitated), printing orientation with respect to the printing platform, and pillar geometry (Figure 1a) influence the flow cell performance. The printing orientation impacts the surface roughness and resin spreading, which determines the electrode morphology, influencing the internal surface area, shrinking direction after carbonization, and thus the charge transfer, mass transfer, and hydraulic resistances. Moreover, mass transfer rates within the electrode are increased by altering the pillar shape to a helical or triangular design, or by using an interdigitated flow field design, providing directions to improve electrolyte mixing through the electrode. Although the commercial electrodes feature a greater internal surface area and therefore a better electrochemical performance, the area-normalized mass transfer coefficients and pressure drop can be reduced by utilizing 3D printed electrodes (Figure 1b-c). Going forward, 3D printing technologies that enable finer features combined with carbonization at elevated temperatures can be used to manufacture multi-scale electrode structures simultaneously providing excellent electrochemical performance and low hydraulic resistance. We anticipate that combining 3D printing with emerging computational topology optimization approaches could enable the bottom-up design of advanced electrode materials for electrochemical devices [4]. Acknowledgments The authors gratefully acknowledge the Dutch Research Council (NWO) through the Talent Research Program Veni (17324) and the 4TU.HTM grant for financial support.

Water Transport Modeling in a Microporous Layer for a Polymer Electrolyte Membrane Water Electrolyzer Having a Gas-Liquid Separating Interdigitated Flow Field

A novel interdigitated flow field design for polymer electrolyte membrane electrolyzers (proton exchange membrane water electrolysis cells), which has oxygen exhaust channels separated from pressurized liquid water feeding channels, has been developed for ground and space applications 1), 2). This structure separates oxygen and liquid water inside the anode of the cell. Thereby it dispenses with water circulators for bubble removal from the cell and external separators by natural or centrifugal buoyancy. We thus aim to develop a numerical model for further optimization of the cell design.Finite element modeling (COMSOL Multiphysics) of water transport is three-dimensionally conducted for the anode porous transport layer coated with a hydrophobic microporous layer (MPL) (SIGRACET 29BC, SGL Carbon Inc.) assembled with the interdigitated flow field. The MPL works to separate evolved oxygen gas exhausted in the through-plane direction and pressurized liquid water injected in the in-plane direction owing to the capillary pressure 2), 3). Prominent leakage of the liquid water to the oxygen channels has not been detected.Electrochemical kinetic parameters for the model are determined by electrochemical impedance spectra. Current-voltage measurement of the cell is also performed to validate the numerical modeling.We model the current densities and the current ratio between the reactant liquid water and water vapor at the interface between the MPL and catalyst layer (CL). The model involves fractional bubble coverage of the CL with produced oxygen gas and liquid water saturation in the MPL. The vapor evaporating from the liquid water in the MPL is assumed to be mixed with the evolved oxygen for diffusive water transport. The volumetric evaporation rate is assumed as a function of the liquid water saturation in the MPL.References1) Y. SONE, O.S. HERNANDEZ-MENDOZA, A. SHIMA, M. SATO, H. NAKAJIMA, H. MATSUMOTO, Water Electrolysis by the Direct Water Supply to the Solid Polymer Electrolyte through the Interdigitated Structure of the Electrode, Electrochemistry. 89 (2021) 138–140. https://doi.org/10.5796/electrochemistry.20-00145.2) H. NAKAJIMA, V. VEDIYAPPAN, H. MATSUMOTO, M. SATO, O.S. MENDOZA-HERNANDEZ, A. SHIMA, Y. SONE, Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields, Electrochemistry. 90 (2022) 017002. https://doi.org/10.5796/electrochemistry.21-00097.3) H. Nakajima, S. Iwasaki, T. Kitahara, Pore network modeling of a microporous layer for polymer electrolyte fuel cells under wet conditions, J. Power Sources. 560 (2023) 232677. https://doi.org/10.1016/j.jpowsour.2023.232677.AcknowledgmentsThis study is based on results obtained from a project, JPNP21014, commissioned by the New Energy and Industrial Technology Development (NEDO).

Water Transport Modeling in a Microporous Layer for a Polymer Electrolyte Membrane Water Electrolyzer Having a Gas-Liquid Separating Interdigitated Flow Field

A new interdigitated flow field design for polymer electrolyte membrane electrolyzers has been developed for ground and space applications. It internally separates oxygen and liquid water, eliminating the water circulators to remove the bubbles and external gas-liquid separators with buoyancy. The capillary pressure in the hydrophobic microporous layer(MPL) of the anode porous transport layer enables the internal separation of oxygen gas and pressurized liquid water. A finite element model (COM-SOL Multiphysics) simulates water transport in the MPL. Electrochemical impedance spectra determine the electrochemical kinetic parameters for the model. The model accounts for the oxygen bubble coverage of the CL, liquid water saturation in the MPL, and the current ratio between liquid water and water vapor at the MPL-CL interface. The vapor from liquid water in the MPL mixes with oxygen for diffusion. The water evaporation rate based on liquid water saturation in the MPL is introduced.

A parametric numerical study on the performance of polymer electrolyte membrane fuel cell with intermediate‐blocked interdigitated flow field designs

AbstractFlow field design is crucial for achieving higher performance in polymer electrolyte membrane fuel cells (PEMFCs). This study uses a two‐phase, multi‐component, and three‐dimensional model to simulate the performance of PEMFCs that use interdigitated flow field design with intermediate blocks on the cathode side. A detailed parametric study is presented to investigate the effects of various geometric and operational parameters. Of the parameters studied, inlet mass flow rate, relative humidity, and rib width had the greatest impact on cell performance. The results show that increasing the cathode stoichiometric ratio resulted in higher fuel cell performance for blocked interdigitated designs compared to parallel designs. In addition, using cathode channels with higher height values resulted in lower PEMFC performance for all flow fields. Higher values of rib/channel width ratio resulted in lower cell performance due to liquid water accumulation in the rib regions. However, at higher rib/channel width ratios, the positive effect of using interdigitated flow designs was more pronounced. Moreover, at a low relative humidity of RH = 25%, a 10.4% higher performance was obtained for the interdigitated type II compared to cases with RH = 100%, due to more effective over‐rib convection and higher water removal.

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

CFD modeling of residence time distribution and experimental validation in a redox flow battery using free and porous flow

Abstract The successful use of clean energy sources will rest, in part, on the availability of efficient energy storage systems. Thus, the present work examines two critical factors (flow patterns and residence time distribution, RTD) affecting the performance of one of the most promising energy storage systems: redox flow batteries (RFBs). The goal is to develop a methodology for analyzing the hydrodynamic and mass transport behavior within a commercial redox flow battery (CRFB). This methodology includes modeling of the flow behavior as well as its experimental validation with RTD. The CRFB consisted of a square geometry with an interdigitated flow field design. Experimental residence time distribution curves for this device were obtained at four different flow rates using the stimulus-response technique with step signal. Theoretically, the flow behavior within the CRFB was approximated by an axial dispersion model (ADM), and a plug dispersion exchange model (PDE), as well as by solving the hydrodynamic equations (Navier–Stokes and Brinkman equations) and the mass transport equation (convection-diffusion) using COMSOL Multiphysics® 5.3. The calculated RTD curves are in good agreement with the experimental RTD curves. Our theoretical and experimental analysis resulted in better approximations of the axial dispersion, and the presence of stagnant zones, and channeling and by-pass (i.e., preferential flow) effects at low and intermediate Reynolds numbers (Re). The experimental RTD curves show that the liquid flow pattern in the CRFB deviates considerably from the axial dispersion model at low Re, conditions under which the CRFB exhibits significant channeling effects, as well as stagnant and dead zones. The PDE model was able to describe the deviation from ideal flow pattern caused by channeling, recycling, or by the presence of stagnant regions in the CRFB. The mass transport in the CRFB was determined by measuring the distribution of tracer molecules at different time points after the initial (step) tracer injection. The interdigitated flow field geometry exhibited a homogeneous flow distribution, featuring an increased mean electrolyte velocity inside the electrode. This simulation allowed locating stagnant zones that would locally affect the mass transport properties and globally lead to a reduction of the RFB conversion efficiency.

Comparative study of conventional and unconventional designs of cathode flow fields in PEM fuel cell

The choice of an appropriate flow field distributor is crucial to circumvent mass and charge transfer resistance-related issues in proton exchange membrane fuel cells (PEMFCs). In this work, incorporating all the anisotropic nature of the gas diffusion layers (GDLs), a three-dimensional, multiphase CFD model is built to perform a comparative study of several types of cathode flow field designs. Three conventional (i.e. parallel, serpentine and interdigitated) and two recently-introduced (i.e. parallel with blocks and the metal foam) flow field designs were considered for the cathode side. The results showed that the best fuel cell performance is obtained with the metal foam flow field as it induces the lowest water saturation, the lowest values and more uniform distribution of current density and temperature as well as relatively medium pressure drop. Compared with the parallel flow field case, the peak power density increases by about 50% when using the metal foam flow field and by about 10% when using the other three investigated flow fields (i.e. serpentine, interdigitated and parallel with blocks). The parametric analysis reveals that the metal foam outperforms other designs at intermediate and high humidity conditions whereas the interdigitated flow field design outperforms other designs at low humidity conditions.

Flow field design pathways from lab-scale toward large-scale flow batteries

Current demonstration projects show that the power capacity of redox flow batteries can span a large range from kW- to MW-scale. The large-scale, especially MW-scale, flow battery system can usually benefit from cell's large active area, due to that a large cell can reduce the required number of cells and thus assembling difficulties. However, the lack of practical pathways for scaling-up lab-scale toward large-scale flow field designs has been one of the barriers to the commercialization of flow batteries. The present study investigates the interdigitated flow field design for a large-scale (900 cm2 active area) vanadium redox flow battery cell, based on a three-dimensional, multi-physical model. Four pathways for scaling up the flow field are investigated, including (i) geometric similarity, (ii) channel length extension, (iii) same pressure drop, and (v) split-interdigitated flow field. The relation between the width and length of the channel and the concentration overpotential is formulated. The results show that the split-interdigitated flow field outperforms the other scaling-up methods in terms of the overall energy efficiency, while at the cost of the increased pressure drop. To alleviate the high pressure drop, the design can be improved by widening the main channels or adding one extra flow inlet.

A hierarchical interdigitated flow field design for scale-up of high-performance redox flow batteries

The pumping loss of redox flow batteries increases dramatically when scaling up to large-area cells, and becomes a key limiting factor for engineering high-performance cell stacks. This work proposes a hierarchical interdigitated flow field design that has independently regulated distribution/collection channels to lower pumping loss and enhance mass transport: a small quantity of primary branch channels with larger section area is engineered to transport the electrolyte across the length of the entire electrode with a relatively low pressure drop, while a large number of secondary branch channels with smaller section area serve to inject the electrolyte into the adjacent porous electrode with a relatively high velocity to ensure good mass transport. The analytical and experimental methods are combined to understand the mass transport phenomena in the presented flow field. It is shown that the hierarchical interdigitated flow field can significantly reduce the pumping loss by 65.9% and increase the pump-based voltage efficiency from 73.8% to 79.1% at 240 mA cm−2 and 3.0 mL min−1 cm−2 compared with the conventional interdigitated flow field, which demonstrates that the hierarchical interdigitated flow field presents a promising solution for scaling up the high-performance redox flow batteries.

Three-dimensional CFD modeling of direct ethanol fuel cells: evaluation of anodic flow field structures

Mathematical modeling and simulation are widely applied to investigate the fluid dynamics properties in fuel cells. Flow field design determines how effective the fuel is distributed along the diffusion layers and the catalyst. The computational fluid dynamics modeling approach allows an effective investigation of different flow field designs through examining concentration profiles in the porous regions, velocity profiles, and pressure drop in the flow channels of fuel cells. In this work, mathematical models considering both complete oxidation of ethanol and partial oxidation with by-products in Pt-based catalysts were implemented in a three-dimensional geometry using the ANSYS CFX software. Laminar flow in the flow channels, steady-state operation, isothermal, and non-isothermal conditions was assumed. Commonly used flow field designs were investigated: serpentine, double serpentine, parallel, interdigitated, and spot. The interdigitated flow field design presented the best results in the isothermal simulations, whereas in the non-isothermal simulations the double serpentine presented the best results.

Experimental investigation on a polymer electrolyte membrane fuel cell (PEMFC) parallel flow field design with external two-valve regulation on cathode channels

Parallel/interdigitated/serpentine flow field PEM fuel cells have similar performance under low overvoltage operation. At higher overvoltage, interdigitated/serpentine flow field performance may exceed parallel flow field designs due to better water removal and more uniform reactant distribution by convective reactant flow in the GDL under land area, i.e. cross flow. However, serpentine flow field design suffers from high pumping losses and the risk of local flooding at channel U-bends. Additionally, interdigitated flow field designs may have higher local flooding risk in the inlet channels and relatively large pumping requirement at low current densities. In this study, a novel parallel flow field design with external two-valve regulation on the cathode was presented. Two valves introduced continuous pressure differences to two separate manifolds in the cathode that induce cross flow across the land areas. Moreover, both valves remained partially open to maintain a good water removal from flow channels. Comparative test results showed the proposed design surpasses performance of both parallel and interdigitated flow field design at operation current density of 0.7 A cm−2 or higher. The performance enhancement is 10.9% at peak power density point (0.387 W cm−2 @ 0.99 A cm−2) compared to parallel flow field taking into account pumping losses.

Influences of operational factors on proton exchange membrane fuel cell performance with modified interdigitated flow field design

This paper presents a novel design of the rectangular parallelepiped within the interdigitated flow field to augment the performance of a PEM fuel cell by simulation and experiment. The numerical results indicate that the performance is enhanced with increasing the rectangular parallelepiped number because of stronger obstructing reactant gases through the channel to enter catalyst layers. In addition, the novel design is numerically obtained for the interdigitated flow field. The operational parameters are then determined by the Taguchi method on the experiment according to the novel design. The net power obtained is 26% greater for the novel design at the optimum parameter combination of A2B3C2D2E2 than for the smooth-walled channel at the A2B2C2D3E3.

The dew point temperature as a criterion for optimizing the operating conditions of proton exchange membrane fuel cells

In this article an analytical method to calculate the dew point temperatures of the anode and cathode exit gas streams of a proton exchange membrane fuel cell is developed. The results of these calculations are used to create diagrams that show the dew point temperatures as function of the operating pressure, the stoichiometric flow ratios and the net drag coefficient of water through the membrane. Then, computational modeling results obtained with a previously published model are analyzed and compared with the dew point charts, and it is demonstrated how cell flooding or membrane dry-out can be predicted a priori with the aid of these diagrams. Finally, guidelines for the desired cell operating temperature based on the expected dew point temperatures are developed. In the current work these guidelines are limited to the interdigitated flow field design, and they are likely to be different for conventional flow field plates. The diagrams presented here are created for completely dry inlet gases, but they can be easily corrected for a non-zero inlet relative humidity.

Low stoichiometry operation of a proton exchange membrane fuel cell employing the interdigitated flow field – A modeling study

A multiphase fuel cell model based on computational fluid dynamics is used to investigate the possibility of operating a proton exchange membrane fuel cell at low stoichiometric flow ratios (ξ < 1.5) employing the interdigitated flow field design and using completely dry inlet gases. A case study of two different operating temperatures and two different operating pressures is presented. In all cases the cathode side stoichiometric flow ratio was varied from ξc = 1.5 to 1.2, and the anode side varied to as low as ξa = 1.05. It is found that operating at ambient pressure leads to a generally dryer cell, and the only possibility to prevent membrane dry-out is to operate at or below 70 °C. The cell is generally better humidified at an elevated pressure, and here it is found that the cathode channels will become flooded when the operating temperature is too low, e.g. 70 °C, while membrane hydration levels of λ = 7–10 can be achieved at 80 °C. Operation at stoichiometric flow ratios as low as ξ = 1.2 at the cathode side and ξ = 1.05 at the anode side appear feasible. If this can be verified, it would allow open-ended anode operation without recirculation or flow shifting, thus significantly reducing system complexity and cost.

Low Stoichiometry Operation of a Polymer Electrolyte Membrane Fuel Cell Employing the Interdigitated Flow Field Design

Fuel cell operation on dry reactant gases under low stoichiometry conditions employing the interdigitated flow field is investigated using a multi-fluid model. It is assumed that the MEA contains a water uptake layer which facilitates water absorption to the membrane and hence prevents the anode gas phase from drying out. It is shown that the membrane humidity increases with decreasing stoichiometric flow ratios to values of λ ≈ 7. Operating the cathode side at a stoichiometric flow ratio of 1.2 appears feasible under steady state conditions, while our simulations suggest that the anode stoichiometry may even be as low as 1.05. The effect of operation pressure and temperature on the membrane water content is studied. Finally, experiments are suggested to determine the kinetic absorption coefficient and the specific surface area of the electrolyte inside the catalyst layers.

Low Stoichiometry Operation of a PEM Fuel Cell Employing the Interdigitated Flow Field Design

not Available.

Design, Optimization, and Fabrication of Slotted-Interdigitated Thin Metallic Bipolar Plates for PEM Fuel Cells

Thin metallic sheet bipolar plates (BPPs) with sustainable coating are promising candidates to replace conventional graphitic or machined thick metal plates due to their lightweight and low cost. Interdigitated flow field design is easier for two stamped thin metallic sheets joined together to compose reactant flow fields in both sides and serpentine coolant flow field in the middle. Unfortunately, this kind of BPP inevitable brings two main defects: rupture of material during forming process and uneven flow distribution in practical operation. First, we propose a slotted-interdigitated configuration of the flow field for proton exchange membrane fuel cell with consideration of the characteristics of the metallic sheet forming process. In order to relieve the uneven flow distribution, an analytic model is introduced to analyze the reactant gas flow based on the similarity between the gas flow and the electrical current. Furthermore, an optimization model is proposed. The depth of the slot on the channel rib is optimized to eliminate the uneven flow distribution to obtain high reaction performance. Second, we studied the BPPs from the manufacturability perspective because it is also another important factor that should be considered in the design stage. The key geometric dimensions of flow field section, where the rupture occurs, are extracted and parametrized. Finite element analysis model is established to analyze the formability of BPP by flexible forming process (FFP). In addition, different dies with various flow channel sections are prepared and experiments are performed. Some design principles about material selection and key geometric dimension definition are proposed to improve the formability of BPPs. In the end, based on the design principles and experimental results, the dies are carefully design and fabricated experimental setup for FFP is prepared and practical experiments are performed. High quality metallic BPPs are achieved eventually by FFP.

A study of multi-phase flow through the cathode side of an interdigitated flow field using a multi-fluid model

This work presents a study of multi-phase flow through the cathode side of a polymer electrolyte membrane fuel cell employing an interdigitated flow field plate. A previously published model has been extended in order to account for phase change kinetics, and a comparison between the interdigitated flow field design and a conventional straight channel design has been conducted. It is found that the parasitic pressure drop in the interdigitated design is in the range of a few thousand Pa and could be reduced to a few hundred Pa by choosing diffusion media with high in-plane permeability. The additional compressor work due to the increased pressure loss will only slightly increase, and this may be offset by operating at lower stoichiometries as the interdigitated design is less mass transfer controlled, which means that the overall efficiency of the interdigitated arrangement will be higher. In the interdigitated design more product water is carried out of the cell in the vapor phase compared to the straight channel design which indicates that liquid water management might be less problematic. This effect also leads to the finding that in the interdigitated design more waste heat is carried out of the cell in the form of latent heat which reduces the load on the coolant. Finally we see that the micro-porous layer might help keep the gas diffusion layer substrate dry due to a potentially higher evaporation rate caused by a combination of the Kelvin effect and a larger specific surface area compared to the diffusion layer substrate.