Effect Of Flow Field Design Research Articles

Correlating Electrolyte Infiltration with Accessible Surface Area in Porous Electrodes Using Neutron Radiography

Grid-scale energy storage technologies, such as redox flow batteries (RFBs), can facilitate wider adoption of wind and solar energy by leveling their fluctuating power output. The simple design and scalability of the RFB technology makes them well suited for large-scale energy storage, but significant cost reductions are necessary to meet the growing energy storage demand. Increasing the power density of the electrochemical stack is an effective strategy to reduce the overall costs while reducing the reactor footprint, which has motivated research in developing advanced electrode materials1, surface functionalization techniques2, and alternative flow field designs3. Especially for aqueous RFBs, poor wettability of the commercial porous electrodes limits the reactor performance as a fraction of the electrode surface remains inaccessible to the electrolyte. Although there is consensus that hydrophilization of electrode surfaces results in improved reactor performance4, it remains unclear how electrode area utilization is related to electrolyte infiltration under realistic flow conditions. Conventional techniques (i.e., polarization, impedance spectroscopy) can indirectly probe the accessible surface area of the electrodes but fail to provide information on electrolyte infiltration. Combining electrochemical diagnostics with imaging techniques can help overcome this limitation by tracking the electrolyte distribution within the cell5.In this work, we develop a new methodology by coupling the electrochemical diagnostic techniques with in situ neutron radiography to correlate the electrochemically accessible surface area (ECSA) to electrolyte infiltration in flow cells. We elect neutron radiography for imaging purposes as it allows minimal cell modifications and offers high contrast for water compared to other cell components. We first investigate the influence of flow rate on electrolyte infiltration with a non-convective (flow-by) flow field and show that pristine carbon paper exhibits a pressure breakthrough behavior where infiltration occurs at high electrolyte velocities (Figure 1). By changing the flow field to an interdigitated design, we show that electrolyte can access the areas under the channels at lower electrolyte velocities, however the maximum electrode saturation does not appreciably change. We correlate the neutron radiographs with ECSA values determined via cyclic voltammetry and impedance spectroscopy and find a good agreement between electrode saturation and surface area. Finally, to investigate the effect of wettability, we employ a superhydrophilic carbon paper with covalently attached taurine (2-aminoethanesulfonic acid) molecules on its surface2. The wetting of treated electrodes is nearly instant with an accompanying increase in the ECSA. Strikingly, the ECSA of treated electrodes are 10-fold higher than untreated electrodes (~300 cm2 vs ~30 cm2 per electrode), while the macroscopic saturation is similar to untreated electrodes. This reveals that pores and roughness at the finest scale can be accessed by adequately treating the electrode6. We hope that the correlation between ECSA and electrolyte infiltration informs researchers on the effect of flow field design and electrode treatment strategies for redox flow batteries and other flow electrochemical technologies. References R. R. Jacquemond et al., Cell Reports Physical Science, 3, 100943 (2022).E. B. Boz, P. Boillat, and A. Forner-Cuenca, ACS Appl. Mater. Interfaces, 14, 41883–41895 (2022).J. D. Milshtein et al., J. Electrochem. Soc., 164, E3265 (2017).B. Sun and M. Skyllas-Kazacos, Electrochimica Acta, 37, 1253–1260 (1992).L. Eifert et al., ChemSusChem, 13, 3154–3165 (2020).D. Zhang et al., Electrochimica Acta, 283, 1806–1819 (2018). Figure 1

The effects of flow field design on PEMFC

The flow field design plays a crucial role in the performance of proton exchange membrane fuel cells (PEMFCs). An efficient flow field design enhances electrochemical reactions in catalyst layers and facilitates the water removal process at the cathode. This study evaluates two PEMFC designs, rectangular and semicircle baffle flow fields, using computational fluid dynamics modeling. The models incorporate mass, heat and energy transport, electrode kinetics, and potential fields in PEMFCs. The research analyzes the hydrogen and oxygen mass flow rates and water distributions in PEMFCs at operating voltages of 0.3–1 V to determine the effect of the flow field design on performance. According to the results it is clear that flow field design has an important influence on PEMFC power density and performance. The calculated power density at 0.3 V and at 80°C for semicircle and rectangular baffle flow field PEMFCs respectively are 0.37 and 0.23 W cm−2, which indicates that PEMFC with semicircle baffle flow field has better performance in this study.

Three-dimensional model for stacks of tubular high temperature proton exchange membrane fuel cells incorporating a thin layer approach for the membrane electrode assembly

A three-dimensional, non-isothermal, steady state model for stacks of tubular high temperature proton exchange membrane fuel cells (HT PEM FCs) is developed. It is based on a thin layer approach for the membrane-electrode assembly while retaining Butler-Volmer kinetics, concentration and Ohmic losses on both electrodes. It solves for flow, temperature and concentration fields as well as locally resolved current densities for multiple cells. Single cell results for the polarization curve compare well with experimental data for single tubular HT PEM FCs. The model allows for efficient simulations of stacks of multiple tubular HT PEM FCs with a shared air channel in which the interactions between local FC performance and flow, temperature and concentration fields pose a major design challenge. The effects of flow field design, flow rate and cell distance in a stack of 7 tubular cells are investigated and basic approaches for the design of such stacks are derived.

Design and Development of Open Cathode PEM Fuel Cell – Flow Analysis Optimization by CFD

AbstractAir‐cooled polymer electrolyte membrane fuel cells (PEMFCs) have emerged as a potential power generation source, due to its simple construction and operation. Flow‐field designing for the efficient distribution of reactants is of paramount importance in air‐cooled PEM fuel cells. The requirement of flow fields with uniform distribution amounting to minimal pressure drop across the flow area is necessary for high gas utilization and easy removal of water. Thus, the present work deals with the design of land and pillar flow field type for cathode, and further optimization of its flow pattern. A 3‐D computational fluid dynamics analysis tool for modeling fluid flow was used for simulating the reactant distribution profile and finalizing the flow field design. The effect of flow field design, inlet velocity and inlet ports dimension were studied in order to obtain flow pattern with uniform distribution. The optimized configuration showed higher percentage of flow area (76%) with outlet velocities ranging from 3.0–5.5 m s−1 in relation to inlet velocity of 4.4 m s−1. From the results it was inferred that, with the increase of air inlet velocity and modified flow design, the non‐uniform areas occurring in flow field are reduced leading to uniform air distribution throughout the flow volume.

Experimental study of the effect of flow field design to PEM fuel cells performance

Fuel cells are one of the most important sources of alternative energy in generating electricity with a wide range of applicability. One of the most prominent of the challenges that effect on the performance of the fuel cells is the designs of flow field plate which are responsible on distributing reactant gases evenly throughout the cell, removing excess water efficiently, and supplying a conduction route for the electrons from the external circuit. In this study, the effect of gas flow fields design on fuel cell performance investigated experimentally. Polymer electrolyte membrane fuel cell (PEMFC) with 20 W (2.38 A × 8.4 V) were used. Where eight graphite plates with various flow field or flow channel designs (Parallel-Z flow field, Serpentine-Z flow field, Serpentine-2Z flow field, Serpentine-3Z flow field, Serpentine-S flow field, Serpentine-2S flow field, Serpentine-W flow field, and Novel serpentine- modified W flow field) were used for the PEM fuel cell assembly. From acquired results showed that Novel serpentine-modified W flow field design is superior compared with other proposed flow field designs in the current study. The reason of the modified Serpentine-W gives the better cell performance is that it extends over the entire surface, thus it generates a better and uniform distribution of the reactant gases. Therefore, an appropriate and uniform distribution of current over the electrode surface is produced, which increasing the pressure forces of the species to transfer during the sideways, resulting in more a uniform distribution of species through the (GDL).

Effect of flow field design and channel/header ratio on velocity distribution: An experimental approach

In this paper, an investigation was carried out to observe the effect of flow field design on flow distribution uniformity and its effect on a fuel cell performance. The research followed two methodologies; the first examined the effect of several flow field plate designs (Single Serpentine, parallel Z, 2Z, U, and 2U) on distribution uniformity of flow velocity. The second methodology involved studying the effect of header/channel area ratio on flow velocity distribution in “Parallel Z and U- type” flow fields in an attempt to obtain a more uniform distribution of flow velocity. Results acquired from first research methodology showed that using the serpentine flow field design resulted in a very small non-uniformity coefficient of flow velocity distribution of nearly 0.0271 which indicates uniform flow velocity distribution with highest pressure drop, while the U-type yielded the highest non-uniformity coefficient (0.246–0.249) which represents non-uniform distribution of flow velocity with lowest pressure drop. The results obtained from the second research methodology while using a fixed header area and variable channel area for both parallel Z and U-type channels; showed a decrease in non-uniformity coefficient with decreasing header/channel area ratio with increasing overall pressure drop in both types of flow channel design.

Novel Obstructed Flow Field Designs for Improved Perfomance in Vanadium Redox Flow Batteries

One of the major challenges that limits the widespread commercialization of vanadium redox flow batteries (VRFBs) is their relatively low power density, which often results in higher cost [1]. In recent years, significant effort has been put on understanding the effect of flow field design on the power density performance of VRFBs [2-3]. Flow fields play a crucial role in effective delivery and removal of active species from the electrode surface and hence they can significantly alter the power output of the VRFBs. Due to inherent similarities between fuel cells and redox flow batteries, flow field designs for VRFBs have been limited to previously studied conventional flow designs such as parallel, serpentine, and interdigitated. Though significant effort has been placed on analyzing which design performs better and how certain parameters can result in higher performance; investigation of novel flow designs outside the fuel cell research has remained much unexplored. Although conventionally utilized flow field designs have very different flow paths for delivery of the electrolyte in two dimensions; the channel depth seems to remain constant for the flow field studies reported so far. Considering the porous electrodes lie in parallel with the channel floors in most of the VRFB cell fixtures, it is believed that alterations of the channel depth throughout the length of the flow channels can help facilitate better transport of active species to the electrodes. Motivated by this, various forms of channel obstructions and ramped flow field designs have been investigated to understand the effect of channel depth and delivery of electrolytes on the power density of the VRFBs. Results have shown significant improvements in power density (up to 90%) with the addition of alterations to the channel depth with minor (10%) or no change in pumping losses. These findings suggests that engineering of the flow field designs in all three dimensions can help further improve the power density of VRFBs.

The Influence of Flow Field and Electrode Design on Crossover of Ions in All-Vanadium Redox Flow Batteries

Among the many types of redox flow batteries (RFBs), the all-vanadium redox flow battery (VRFB) is one of the most viable chemistries for commercialization 1. One of the key factors obstructing the commercialization process of VRFBs is the high cost of these systems, resulting from relatively poor performance 2. Flow field and electrode design are considered to be key optimization factors in VRFBs that can enable high battery performance and resultant market competitiveness 3. The flow field and electrode designs are known to directly affect the mass transport, performance, capacity utilization, and parasitic pressure losses 4. Much experimental and modeling work has been done to understand the combined effect of flow field design and electrodes on mass transport behavior and performance of VRFBs 5 and other electrochemical systems 6. However, neither modeling nor experimental approaches targeting the direct effect of flow fields and electrodes on vanadium crossover has been reported. In this work, we will present experimental data in which different flow fields, along with different electrode materials, have been tested from multiple perspectives including overall cell performance, pressure drop and vanadium crossover. A UV-Vis spectroscopy setup has been implemented to quantify vanadium crossover under different operating conditions. The results of this study should provide more in-depth insight to optimize VRFBs for enhanced performance and reduced vanadium crossover and pressure drop. Fig.1 : The effect of the different flow plate design on the VRFB systems (a) Performance (b) Image of the solution at the end of experiment for different cell configurations

Performance enhancement of iron-chromium redox flow batteries by employing interdigitated flow fields

Abstract The catalyst for the negative electrode of iron-chromium redox flow batteries (ICRFBs) is commonly prepared by adding a small amount of Bi3+ ions in the electrolyte and synchronously electrodepositing metallic particles onto the electrode surface at the beginning of charge process. Achieving a uniform catalyst distribution in the porous electrode, which is closely related to the flow field design, is critically important to improve the ICRFB performance. In this work, the effects of flow field designs on catalyst electrodeposition and battery performance are investigated. It is found that compared to the serpentine flow field (SFF) design, the interdigitated flow field (IFF) forces the electrolyte through the porous electrode between the neighboring channels and enhances species transport during the processes of both the catalyst electrodeposition and iron/chromium redox reactions, thus enabling a more uniform catalyst distribution and higher mass transport limitation. It is further demonstrated that the energy efficiency of the ICRFB with the IFF reaches 80.7% at a high current density (320 mA cm−2), which is 8.2% higher than that of the ICRFB with the SFF. With such a high performance and intrinsically low-cost active materials, the ICRFB with the IFF offers a great promise for large-scale energy storage.

Effects of flow field design on water management and reactant distribution in PEMFC: a review

The performance of a proton exchange membrane fuel cell (PEMFC) stack is affected by many factors, including the operating conditions, flow field and manifold design, and membrane performance. To achieve the desired PEMFC performance, the reactant must be uniformly distributed and effectively diffused into the catalyst layer for the electrochemical reaction. Water management and reactant distribution in fuel cells are crucial because they affect the distribution and diffusion rate of the reactant. This paper reviews the important research results reported in recent years related to the effects of water and reactant distribution on the performance and life span of PEMFC stacks.

Effects of Straight and Serpentine Flow Field Designs on Temperature Distribution in Proton Exchange Membrane (PEM) Fuel Cell

Proton exchange membrane fuel cells or sometimes called as polymer electrolyte membrane (PEM) fuel cells is a device for energy transformation in a changing process from one form of energy to another form of energy. It became as an alternative especially for future use in stationary and vehicular applications. PEM fuel cells provide high efficiency and power density with null emission, low operating temperature, quickly start and long life. One of the aspects that are crucial in optimizing the PEM fuel cells performance is a flow field geometry. In this paper, a simulation case of PEM fuel cells was simulated to determine effects of a straight and serpentine flow field on temperature distribution in PEM fuel cells. ANSYS Fluent software was used to simulate 3-dimensional models of single PEM fuel cells in order to determine the effects of changes in the geometry flow field on temperature distributions. Results showed that the serpentine flow field design produces a better temperature distribution along the membrane. The simulation result shows a good agreement with the experiment, thus boost a higher confidence in the results to determine the effectiveness of the flow field design in PEM fuel cells.

Effect of different flow field designs and number of channels on performance of a small PEFC

An improper designed flow field of a polymer electrolyte fuel cell (PEFC) can cause the maldistributions, resulting in the reduction of PEFC performance and lifetime. Although there are several researches investigating the effect of flow field design, the parallel in series flow fields have, however, received a very low attention. In this study, a numerical investigation on the distributions in six different flow field designs over 5 cm2 PEFC has been systematically carried out using CFD techniques via ANSYS FLUENT software to study the effect of different flow field configurations and number of channels. The results revealed that, for a small-size PEFC, the flow fields with less number of channels provided both a better uniformity and cell performance. Although the number of channels affects the small-size PEFC performance much greater than the flow field geometric configurations, the further investigation revealed that the influence of configurations will be greater as the number of channels increases. In addition, with the same number of channels, the parallel in series flow fields performed better than the multi-channel serpentine flow fields in both uniformity and water management aspects as their geometry provided higher reactant flow velocity.

Effects of flow field design on the performance of a PEM fuel cell with metal foam as the flow distributor

In this work, we report the improvements made on the PEM fuel cell with metal foam as the flow distributor. The comparison in polarization curve is made between the PEM unit cell with different metal foam flow field designs and the PEM unit cell with graphite bipolar plate as flow distributor. The experimental results show that after using improved metal foam flow field designs, the fuel cell's performance increases. Our results show that, in the PEM unit cell with single zone metal foam, the convection is weak at side corners. Dividing the metal foam into multiple regions and using multiple inlets effectively improves gas distribution. AC impedance measurement was also performed to study impedance characteristics. The Nyquist and Bode plots confirmed that Ohmic resistance, activation resistance, and mass transfer resistance of metal foam fuel cell are all smaller than that of conventional PEM unit cell.

Effect of flow field design on performances of high temperature PEM fuel cells: Experimental analysis

Among all types of fuel cells, attention is being drawn lately on high temperature Polybenzimidazole (PBI) PEM because their operative temperature range (120–180 °C) increases the tolerance to carbon monoxide. This feature allows working with low quality hydrogen produced by hydrocarbon reformation. Most of the literature on PBI PEM deals with membrane and MEA related issues, however, cell efficiency and specially, commercial feasibility are conditioned by other fuel cell components as bipolar plates. In the present study the focus is on the effect of the flow field geometry of high temperature PBI PEM composite bipolar plates on the overall performance of the cell. For this purpose, three different channel geometries are studied: two serpentine flow fields and parallel channels flow field. Results show that serpentine geometry yields higher performance though it introduces higher pressure drop along the cell as well.

Effect of Flowfield Design on Solid Oxide Fuel Cell Performance

not Available.

Effect of flow field design on the performance of elevated-temperature polymer electrolyte fuel cells

In our previous work, operation of polymer electrolyte fuel cell (PEFC) at 95°C was investigated in detail and it was found that dry operation of PEFC at elevated temperatures makes the parallel flow field design a viable design option for high temperature applications such as for automobiles. In this work, a three-dimensional, non-isothermal PEFC model is used to compare the performance of a 25 cm2 fuel cell with serpentine and parallel flow field design operated at 95°C under various inlet humidity conditions. Numerical results show that the parallel flow field provides better and more uniformly distributed performance over the whole active area which makes the parallel flow field a better design compared to the serpentine flow field for PEFCs operated at elevated temperature and low inlet relative humidity. Copyright © 2006 John Wiley & Sons, Ltd.

Effect of Flow Field Design and Voltage Change Range on the Dynamic Behavior of PEMFCs

Data are presented to show that the dynamic behavior of a proton exchange membrane fuel cell (PEMFC) subjected to rapid changes in the voltage depends on the type of flow field and on the voltage range of the voltage change. These data consist of the responses of the current density when the flow rates are constant and at levels that result in operation between fuel stoichiometries of 1.2 and 1.1 (see Ref. 1 and 2 for other stoichiometries). The data expand an understanding of the previously observed pseudo-second-order dynamics of the current responding to a change in voltage. The results show that the undershoot of the final steady-state current that follows the resulting overshoot was observed with a standard triple-path serpentine flow field (SFF) but not with a single-path SFF. The results also show that the dimensionless peak current and the percentage of the overshoot current depend on the starting cell voltage and on the range of the voltage change. Evidence is presented to indicate that these peak heights are limited primarily by oxygen mass transfer, even though the PEMFC is operating at close to fuel-starved conditions.