Single Serpentine Flow Field Research Articles

Multivariate efficiency assessment and optimization of unitized regeneration proton exchange membrane fuel cell based CCHP system

Targeting the shortcomings of low round-trip efficiency (RTE) in unitized regeneration proton exchange membrane fuel cell (UR-PEMFC), a model incorporated combined cooling, heating, and power (CCHP) technology for UR-PEMFC was proposed, which integrated a three-dimensional two-phase flow field model with a zero-dimensional system model. Additionally, a multi-criterion evaluation system was introduced for the URFC-CCHP system, which encompasses three decision-making methods. To illustrate the applicability of the model, the assessments of four typical flow field configurations were utilized as case studies and presented their rankings. The results reveal that, compared to a system focused on electrical power output, the system exhibited a remarkable enhancement in RTE, increasing from 35.96 % to 76.67 %. Notably, during the cold season, the RTE surpassed that of the warm season by 8.74 %–10.62 %. Operating under a cyclic condition of fast charging and slow discharging proved to be conducive to maintaining the optimal RTE of the system. Furthermore, the computational outcomes of the three decision-making methods in the multi-criterion evaluation system exhibited consistency, unanimously identifying the optimal flow field as the three-serpentine flow field, while designating the single-serpentine flow field as the least favorable. It aims to present a novel technology for enhancing the RTE of UR-PEMFC.

Comprehensive evaluation of the influence of PEM water electrolyzers structure on mass transfer performance based on entropy weight method

The proton exchange membrane water electrolyzer (PEMWE) has broad prospects in hydrogen production due to its green and efficient advantages. This paper comprehensively analyzes the performance and water-gas transport characteristics of PEMWE with different cell structures, in which polarization curves, flow velocity distribution, oxygen concentration, temperature, liquid water saturation, and pressure are investigated. Simultaneously, the study explores the effects of variations in inlet velocity, inlet temperature, porosity, and thickness of the anode porous transport layer (APTL) on the four flow fields. Finally, the technique for order preference by similarity to ideal solution (TOPSIS) based on entropy weight method is employed for a comprehensive evaluation of the flow fields. The results indicate that, compared to parallel flow field (PFF), sinusoidal wave flow field (SWFF), intercepted flow field (ICFF), and single-serpentine flow field (SSFF) exhibit stronger exhaust capabilities, with temperature uniformity increasing by 83.65 %, 59.24 %, and 70.15 %, respectively. However, the longer flow channel of SSFF results in a high pressure drop and lower liquid water saturation. An increase in inlet velocity leads to a decrease in temperature, causing an increase in voltage, as higher temperatures reduce activation and ohmic overpotentials. Additionally, an increase in the porosity and thickness of APTL deteriorates the polarization performance of PEMWE. The research results of this study can provide valuable assistance for the future design of PEMWE.

Control of Liquid Water Transport in Cathode of PEFC Using Wettability-Patterned Electrodes

During the operation of polymer electrolyte fuel cells (PEFCs), the product water that accumulates in the cathode electrode blocks the oxygen transport to the reaction sites and causes severe performance degradation. This phenomenon, known as “flooding,” is one of the critical issues to be solved for achieving high efficiency and high power density. To alleviate water flooding, it’s necessary to design an electrode/channel structure that could actively remove liquid water from the porous electrode. Zhang et al. [1] reported that the wettability patterning of a gas diffusion layer (GDL) enables it to provide the liquid water pathway in the cathode electrode. Furthermore, Nishida et al. [2] demonstrated that the hydrophilization of cathode channel walls promotes water removal from the GDL to the flow channel. This study fabricated a wettability-patterned GDL impregnated with a hydrophilic silica-based solvent and newly proposed an electrode/channel structure combining the patterned electrode and hydrophilized flow channel. The effect of its structure on the liquid water distribution within the cathode GDL of an operating PEFC was also investigated using X-ray imaging.The authors fabricated the experimental fuel cell with an effective electrode area of 1.8 x 1.6 cm2. The membrane electrode assembly (MEA) was sandwiched between two carbon separators with a single-serpentine flow field (number of channels: 7, channel width: 1.0 mm, depth: 1.0 mm, total length: 88.5 mm). Fig. 1 shows the regions measured by X-ray imaging in the cross-sectional view of the cathode. Since the cathode GDL is irradiated with an X-ray beam in the in-plane direction, the through-plane distributions of water can be observed in the GDL. The measurement regions were set under the 4th channel and under the land between the 3rd and 4th channel. The GDL in the cathode was impregnated with the silica-based solvent in the range of 0.3 mm width x 10 mm length x 0.1 mm depth. The hydrophilized region was positioned along the right sidewall of the 4th channel. The channel walls of the cathode were also coated with the same hydrophilic solvent. Fig. 2 represents the distribution of water saturation in the (a) uncustomized and (b) wettability-patterned GDL. The current density was increased stepwise from 0.14 to 1.02 A/cm2 for 8 min at room temperature and non-humidified condition. All images were captured at t=6 min after starting the operation. Dry hydrogen (stoichiometry: 1.5@2.0A/cm2) and oxygen (stoichiometry: 3.0@2.0A/cm2) were supplied to the anode and cathode, respectively, in a counter-flow arrangement. As shown in Fig. 2(b), it was noted that the water saturation around the hydrophilized region was effectively reduced due to the in-plane water suction. The patterned GDL partially impregnated with the highly hydrophilic solvent enables to induce the product water from the hydrophobic to hydrophilic region, resulting in the reduction of flooding. To further accelerate the through-plane water transport from the hydrophilized region in the GDL to the channel sidewall, it’s essential to introduce a difference in their wettability and optimize their combinations.

Performance evaluation on full-scale proton exchange membrane fuel cell: Mutual validation of one-dimensional, three-dimensional and experimental investigations

The coupling of multiple physical processes such as gas multi-component transport, gas–liquid multiphase flow, and electrochemical reactions within the proton exchange membrane fuel cell (PEMFC) makes its hydrothermal management exceptionally complicated. Therefore, the complex heat and mass transfer processes in the full-scale PEMFC are investigated in single cell with single channel serpentine flow field (FF). Firstly, the reliability of the proposed three-dimensional (3D) computational fluid dynamics (CFD) numerical model is verified by using the experimental test results of a single cell. Among them, the trend of simulation and experiment performance curves is consistent, and the minimum error of current density is 0.665%. Secondly, the ionomer model of cathode catalyst layer (CCL) is considered in CFD simulation, which is closer to the actual working condition of fuel cell (FC). The resistance of ionomer film and liquid water film mainly affects the diffusion rate of oxygen in CCL, resulting in a decrease in both current density values and power density values. Subsequently, the electrochemical reaction platform of one-dimensional (1D) FC is constructed, and the performance curves of multi-scale FCs are analyzed. The results demonstrate that the error of stack level is the largest, followed by single cell and single channel is the smallest. Finally, the 1D numerical model and the 3D PEMFC multiphase flow CFD model are utilized to investigate the cell voltage losses in the bionic spider flow field, the variable path flow field, and the serpentine flow field, respectively, under different operating conditions.

Behavior analysis of PEMFC with geometric configuration variation during multiple-step loading reduction process

Load shedding could be a solution to water accumulation alleviation during the operation of proton exchange membrane fuel cell (PEMFC) engines. In this paper, multiple-step loading reduction strategies based on two laboratory-scale (25 cm2) single PEMFCs (assembled with triple-serpentine and single-serpentine flow field plates on the both electrodes and thus named after cell TS and cell SS respectively) are experimentally discussed and evaluated. The real-time pressure evolution and HFR are recorded, compared and analyzed to characterize water transfer phenomenon among the components. The investigation results suggest that: 1. From the perspective of output voltage and power after load reduction, the number of reduction step has little effect on the output performance; 2. Cell TS exhibits better homogeneous trend of pressure drop although with less water removal quantity comparing with that of cell SS, which is resulted from multi-channel configuration; 3. The cathode pressure drop of cell SS decreases obviously throughout the experiment, indicating the convinced water removal capability of single-serpentine configuration; 4. Constant increase of HFR reflects membrane dehydration when the loading reduces. This paper demonstrates the possibility of removing accumulated liquid water by reducing the load of PEMFCs.

Experimental study and optimization of flow field structures in proton exchange membrane fuel cell under different anode modes

As one of the critical components in the proton exchange membrane fuel cell (PEMFC), the flow field is crucial to the improvement of cell performance. However, the current research on flow field structure lacks consideration of the influence of different anode modes, which makes the existing flow field structure rules have limitations in the practical application of PEMFC. In this paper, the PEMFC characteristics of parallel flow field, S-shaped flow field, multi-serpentine flow field and single-serpentine flow field at the cathode side are compared experimentally in the dead-end anode (DEA) mode and hydrogen circulation anode (HCA) mode, respectively. Especially, the spatial current density distribution and parasitic power of different flow field structures are measured. The results show that the performance trends of different flow field structures change with the DEA and HCA anode modes. In DEA mode, the PEMFC is prone to flooding, and the flow field with high gas velocity in the channel has better drainage ability, which can obtain higher cell performance. The HCA mode is helpful for the discharge of water in the PEMFC, which effectively alleviates the adverse impact of water accumulation on the overall performance, and the mass transport ability of the flow field structure plays a leading role in the cell performance improvement. In addition, although the high gas flow velocity has better drainage ability in the flow field, it may lead to a decrease in the current density distribution uniformity and PEMFC net output power density. Based on the comprehensive consideration of the experimental results, the multi-serpentine flow field is more suitable for DEA mode, and the S-shaped flow field is more suitable for HCA mode.

(Digital Presentation) Effect of Compression Pressure on Water Removal and Power Generation Performance of PEFC with Modified Electrode/Channel Structure

Water flooding in cathode electrodes of polymer electrolyte fuel cells (PEFCs) is a critical issue that must be solved for achieving high efficiency and high power density operations. To alleviate this problem, it is necessary to design the optimum electrode/channel structure for actively removing liquid water from the porous media to the flow channel. In the previous studies, Okuhata et al. [1] revealed that the introduction of penetration holes to gas diffusion electrodes (GDEs) effectively promotes the water discharge and improves the limiting current density. Nishida et al. [2] investigated the effect of channel hydrophilization on the water behavior in the cathode of an operating cell using the cross-sectional visualization technique. It was found that the hydrophilization of cathode channels encourages the water suction from the gas diffusion layer (GDL) to the channel and enhances the oxygen diffusibility to the catalyst layer (CL). Our research group has proposed a novel hybrid electrode/channel structure combining the electrode perforation and channel hydrophilization and has investigated its effect on the improvements of water drainage and cell performance. In this study, we directly visualized the liquid water distribution in the cathode GDL of a customized PEFC with the hybrid electrode/channel structure using X-ray imaging and evaluated the transient response of cell voltage under the constant-current operations. Furthermore, the influence of compression pressure on the water behavior in the perforated GDL and the performance characteristics of the customized cell was also examined.For the X-ray investigation, we fabricated a specialized miniature fuel cell with the effective electrode area of 2.88 cm2. The membrane electrode assembly (MEA) was sandwiched between two carbon separators with a single-serpentine flow field (number of channels: 7, channel width: 1.0 mm, depth: 1.0 mm, total length: 88.5 mm). Fig. 1 shows a schematic cross-sectional view on the cathode side of the experimental cell. Since the cathode GDL is irradiated with X-ray beam in the in-plane direction, the through-plane distributions of water can be observed in the GDL under the 4th channel and under the land between the 3rd and 4th channel. To promote the water discharge from the fine porous media, a penetration groove (width: 300 μm, length: 11 mm) was installed into the GDL, MPL and CL and positioned along the right sidewall of the 4th channel. The channel walls on the cathode side were coated with the silica-based hydrophilic solvent. The contact angle of water on the hydrophilized channel is 9.8o. In the hybrid electrode/channel structure, liquid water accumulated in the CL and MPL is firstly discharged into the large groove in the in-plane direction. Subsequently, water droplets gathered in the groove are grown up and attached to the hydrophilized channel walls. The droplets are spread out on the hydrophilic sidewalls and the liquid films are moved upward. Fig. 2 presents the distributions of water saturation in the perforated GDL of the customized cell assembled under two different compression pressures of 0.5 and 1.0 MPa. The current density was increased stepwise from 0.14 to 1.02 A/cm2 for 8 min under the room temperature and non-humidification condition. All images were captured at t=8 min after starting the operation. Dry hydrogen (stoichiometry: 1.5@2.0A/cm2) and oxygen (stoichiometry: 3.0@2.0A/cm2) were supplied to the anode and cathode in the counter-flow arrangement. It was found that the introduction of the hybrid structure effectively decreases the water saturation around the groove due to the in-plane water discharge. The reduction of saturation under the land is much less than under the channel because the strong mechanical compression crushes the pore structure under the land regions and suppresses the water transport. In addition, the low-saturation region of 28% or less around the groove is enlarged with a decrease in compression pressure. The low compression pressure maintains the relatively large porosities in diffusion media and facilitates the water removal.

Numerical simulation analysis of the performance on the PEMFC with a new flow field designed based on constructal-theory

The design of the flow field structure has an important impact on the performance of PEMFC. An excellent design of the flow field will optimize the gas-liquid distribution inside the fuel cell, and enhance the diffusion of the reactant gases while reducing problems such as water flooding or uneven mass transfer of reactants, thus improving the overall performance of the cell. A new form of flow field based on the design ideas of Constructal-theory and Murray's Law was proposed in this paper. In this study, the PEMFC with the new and conventional flow fields were compared under the same conditions, and it is proved that the cell with the new flow field has a more balanced performance on output power and global pressure drop in contrast with conventional flow fields. In this study, the output power density of the PEMFC with the new flow field increased by an average of 1.35% compared to the PEMFC with Parallel flow field and Single Channel Serpentine flow field, and the pressure drop was reduced by 47.67% and 90.06% respectively compared to the PEMFC with the Single Channel Serpentine flow field and Double Channel Serpentine flow field. Meanwhile, the distribution of current density characteristics in a PEMFC with the new flow field was investigated and optimization of its structure size is analyzed. The reason for its non-uniform distribution of current density was revealed in this study, and an improvement scheme was proposed to improve the uniformity of current density, and the results of structural optimization research will have a certain guiding effect on practical applications.

The Effects of Anode Serpentine Flow Field Structure and Humidity on Performance of PEMFCs

Hydrogen is one of the promising energy sources as its clean and effective properties. Proton exchange membrane fuel cell (PEMFC) utilizes hydrogen and oxygen to produce electrical energy through electrochemical reactions [1]. PEMFC shows many advantages as high conversion efficiency [2] and no poisonous emission [3], low working temperature [4], high power density [5], so that it can be applied in widely field. However, the water management is a critical issue which has great impact on the performance of PEMFC. The power density will greatly drop when the PEMFC suffer flooding problem [6]. The water transportation can be concluded as three ways, which is including proton drag, concentration diffusion, permeation by pressure deviation. Thus, flooding phenomenon can be found both in cathode side and anode side. Many researches have reported the flooding which occur in cathode side while the case located in anode side have less analysis.The bipolar plates play an important role in transporting gas and water. In addition, the flow field of the bipolar plates can greatly affect the distribution of two-phases flow, and it will further change the performance of the PEMFC [7]. The serpentine flow field is one of the typical flow fields as it can Facilitate the reactant convection and the mass transfer within the cell [8]. The serpentine flow field has a unique structure with the U-turn corner and the corner can cause local current density increases at the channel corner due to the blocking effect on the reaction fluid. At present, there are many researches on the optimal size of single serpentine flow field, while few researches investigate the impact of serpentine corners location. But this point undoubtedly needs to be further studied as it is an effective way to optimize the flow field design. In this paper, we explored the anode metal plate flow field characteristics with single serpentine and double serpentine influence toward the PEMFC performance under various humidification conditions. The drawing which presented the performance with two types serpentine flow field under different relative humidity (RH) was exhibited as Fig.1. It can be concluded that the highest power density achieved with the double serpentine flow field under the RH as 30%. What’s more, both these cells with two flow field structures show a trend as performance improve when the RH raise to 30% and then decrease as the gas humidity increase further. Moreover, the performance of single serpentine case drops greatly when RH raise to 70% while double serpentine flow field shows better performance under the high RH (RH70%), and get the lower pressure drop (Fig.2). The double serpentine flow field which located in anode side possess higher water removal capability than the single serpentine flow field so that it can prevent a sharp performance fall under the high gas humidity condition.[1] P. Ribeirinha, M. Abdollahzadeh, A. Pereira, F. Relvas, M. Boaventura, A. Mendes. Applied Energy, 2018, 215:659-669.[2] Y. Li, Y. Feng, X.D. Sun. ACS sustainable chemistry & engineering, 2018;6:12827-34.[3] S. Caux, W. Hankache, M. Fadel, D. Hissel. Energy Conversion and Management, 2010;51:320–8.[4] A. Raj, T. Shamim. Energy Conversion and Management, 2014;86:443–52.[5] H. Park. Energy Conversion and Management, 2015, 103:623-638.[6] Z. Shi, W. Xia. Journal of Power Sources, 2008, 185(2):985-992.[7] H. Kahraman, M.F. Orhan. Energy Conversion and Management, 2017;133:363–84[8] F.B Weng, A. Su, G.B. Jung. Journal of Power Sources, 2005, 145(2):546-554. Figure 1

A convection-enhanced flow field for aqueous redox flow batteries

In this work, we propose and fabricate a convection-enhanced flow field for aqueous redox flow batteries. Similar to the conventional single serpentine flow field, the new flow field here has an inlet and outlet, but the repatterned flow path induces higher pressure differences between adjacent flow channels over the entire electrode surface, thereby enhancing the under-rib convection between adjacent flow channels. The application of the new flow field to a vanadium redox flow battery enables substantial performance improvements. At 1.67 mL min−1 cm−2, which is a typical flow rate for a kilowatt-class VRFB stack, the energy efficiency, and electrolyte utilization reach 75.3% and 49.6% at a current density of 250 mA cm−2, increasing by 10.0% and 33.3% as opposed to the use of the conventional serpentine flow field, respectively. Three-dimensional numerical modelling shows that the improved performance is ascribed to the more uniform in-plane distribution of reactants and current with the new flow field. Another important finding of this work is that there is a critical flow rate above which energy efficiency tends to stabilize for a given current density.

Design and Simulation of Air-Breathing Micro Direct Methanol Fuel Cells with Different Anode Flow Fields.

The design of the anode flow field is critical for yielding better performance of micro direct methanol fuel cells (µDMFCs). In this work, the effect of different flow fields on cell performance was investigated by the simulation method. Compared with grid, parallel and double-serpentine flow fields, a single-serpentine flow field can better improve the mass transfer efficiency of methanol and the emission efficiency of the carbon dioxide by-product. The opening ratio and channel length also have important effects on the cell performance. The cells were manufactured using silicon-based micro-electro-mechanical system (MEMS) technologies and tested to verify the simulation results. The experimental results show that the single-serpentine flow field represents a higher peak power density (16.83 mWcm−2) than other flow fields. Moreover, the results show that an open ratio of 47.3% and a channel length of 63.5 mm are the optimal parameters for the single-serpentine flow field.

Numerical study on the impact of interface contact resistance on the performance of a PEMFC with serpentine flow field

The performance of a proton exchange membrane fuel cell (PEMFC) strongly relies on the flow-field design. In this study, a three-dimensional, multiphase, and non-isothermal PEMFC model with single serpentine flow field has been developed to investigate the effect of interface contact resistance (ICR) between the bipolar plate (BP) and gas diffusion layer (GDL) on the flow field dimension. In the cases of 25 different combinations of channel and rib width, polarization curves and power density curves of the PEMFC without ICR and with ICR of 7.418 mΩ.cm2 as well as 21 mΩ.2 are investigated. The results show that ICR has little effect on channel pressure drop but on liquid water accumulation. The value of ICR affects both the ohmic loss stage and concentration loss stage of the polarization curves. The power density of the PEMFC without ICR at the operating voltage 0.5V decreases as the rib width increases, while that with ICR increases as the rib width increases. Furthermore, the influence of invalid active area in BPs caused by flow field configuration on the cell performance should not be neglected when the ICR value is lower than 10 mΩ.2.

Study effects of bio-inspired flow filed design on Polymer Electrolyte Membrane fuel cell performance

The performance of the Polymer Electrolyte Membrane (PEM) fuel cells is affected by the flow fields design and dimensions because this fields distribute gases to reactive sites, remove reaction products efficiently, and supply a path for electrons of electrical circuit. The present work is an experimental investigation conducted to study effects of using the bio-inspired flow fields configurations on performance of PEM fuel cells. The fuel cell used in the experiments is of PROTIUM- 150 type which has 6 cells, its rated power 150 W (10 A @ 15 V) and its voltage range from 15 V to 23 V. Two new flow fields (i.e. leaf veins, tree shape) inspired from biological system are proposed with active area of 9.84 cm2. Graphite metal is used to produce bipolar plates contain these flow fields. The performance of the proposed fuel cells is recorded in power and polarization curves, comparing them with that of fuel cell with single-serpentine flow field. The results demonstrate that there is improvement in performance of PEM fuel cell as leaf veins flow field design is used. It is superiors the single – serpentine design by 5.12% and tree shape design by 3.75%.

Effective splitting of serpentine flow field for applications in large-scale flow batteries

Industrial flow battery stacks require large area cells for which flow fields are essential to ensure uniform distribution of the electrolyte. Serpentine flow fields have proven to be ideal from a flow distribution point of view but suffer from high pressure drop. In the present work, a new flip-flop directional split serpentine flow field is proposed to reduce pressure drop by splitting the flow field into segments and improving electrochemical performance by quick evacuation of reaction products. Comparative experimental studies with a single serpentine and two other split serpentine flow fields confirm the effectiveness of the new flow field. An improvement of around 12% in discharge energy and 3% in round-trip efficiency has been observed with flip-flop at current densities of 90 mA cm−2 and 120 mA cm−2 over a single serpentine flow field for a cell active area of 900 cm2. Calibrated computational fluid dynamics simulations confirm that the proposed flow field ensures good distribution and quick evacuation of product species. Scalability of the new flow field to large cell size has been demonstrated by obtaining good performance data on a cell of 2200 cm2 active area, which is among the largest reported in the literature.

Investigation on cold start of polymer electrolyte membrane fuel cells stacks with diverse cathode flow fields

The shape of gas flow field determines the distribution of reactive gas and the drainage performance so it has a significant impact on cold start performance. This work designs three novel cathode flow fields of stacks through variable cross-section design to improve drainage, which are the single variable section serpentine flow field, the variable section interdigitate flow field and the variable section parallel flow field. The cold start characteristics and internal behavior of diverse novel stack flow fields are investigated by segmented cell technology. The results show that stack with the single variable section serpentine flow field realizes the fastest cold start when the temperature is below −5 °C. However, the variable section interdigitate flow field displays the shortest cold start time when the temperature is above −5 °C. The evolution of the current density distribution of the single cell in different position of the same stack is inconsistent during cold start. The key regions with strong electrochemical performance of different stack flow fields are found. The performance degradation of the stack with the single variable section serpentine flow field is the lowest when start fails. This work can supply experimental support for the selection of flow fields for cold start.

WaterDistribution in the Flow Field of the BipolarPlate on the CathodeSide of the PEM FuelCell

The presence of water in the flow field greatly affects the performance of PEM fuel cell. One of the problems is caused by the water imbalance in the PEM fuel cell. If the water content is too high it causes flooding in the PEM fuel cell stack. As a result, the distribution flow of raw materials (hydrogen and oxygen) flowing into the stack is blocked. Conversely, if it is too dry it will cause the membrane to crack. Both cases resulted in a decrease in the performance of the PEM fuel cell system. The method used for water management in the flow field of a bipolar plate flow Computating Fluids Dynamics (CFD) software. The results showed that the highest water content occurred in the spiral flow field at a flow rate of 4 x 10-8 kg/s with a water content of 0.75 g/g. The lowest water content occurs in the multiple channel serpentine flow field at a flow rate of 4 x 10-8 kg/s with the water content of 0.47 g/g. In this condition the performance of PEM fuel cell is relatively stable in the single channel serpentine flow field with a flow rate of 4 x 10-8 kg/s and a depth of 0.3 mm because the formation of water is insignificant compared to using other flow fields.

X-ray Imaging of Water Distribution in Cathode Electrode of PEFC and Control of Liquid Water Transport by Electrode Perforation

Water flooding in cathode electrodes is a critical issue for achieving high efficiency and high durability of polymer electrolyte fuel cells (PEFCs). To alleviate flooding, it’s necessary to design the optimum electrode/channel structure for positively removing liquid water from catalyst layers (CLs) and gas diffusion layers (GDLs) toward flow channels. In the previous works, Gerteisen et al. [1] presented a concept of perforated GDL structure to secure water passages through the porous electrode. Turhan et al. [2] revealed that the hydrophilization of cathode channel wall effectively enhances the liquid suction from the under-land locations into gas channels. Nishida et al. [3] have proposed the novel electrode/channel structure combining the electrode perforation and channel hydrophilization, and have investigated its effect on the improvements of water discharge and cell performance. In this study, the liquid water distribution in the cathode electrode of an operating PEFC was directly visualized using X-ray imaging, and the effects of introduction of penetration groove on the water transport inside the GDL were examined. Furthermore, the impact of combinational structure with electrode perforation and channel hydrophilization on the performance characteristics of the cell was demonstrated during the constant-current operation test.Figs. 1(a) and 1(b) show the outline assembly drawing of the small-sized visualization cell for X-ray radiography, and the measurement region in the cross-sectional view. The membrane electrode assembly (MEA) is sandwiched between two carbon separators with a single-serpentine flow field (number of channels: 7, channel width: 1.0 mm, depth: 1.0 mm, length: 88.5 mm). The effective electrode area is 2.88cm2. The X-ray beam is emitted to the cathode GDL in the in-plane direction, and the through-plane water distributions in the GDL are observed under the 4th channel and under the land between the 3rd and 4th channel. As shown in Fig. 1(b), the penetration groove (width: 100 or 200 µm, length: 11 mm) installed into the porous media by using a thin-edged blade is positioned along the sidewall of the 4th channel. Liquid water accumulated in the CL is firstly discharged into the largely opened groove. Subsequently, water droplets gathered in the groove grow up gradually and come into contact with the channel sidewall. When the droplets are attached to the hydrophilized sidewall, they are spread out on the wall surface and liquid films are moved upward. This water suction through the penetration groove and along the hydrophilic channel wall effectively reduces water flooding near the cathode CL.Fig. 2 presents the through-plane distributions of water saturation in the cathode GDL under the channel and land. Fig. 2(a) denotes the result for the non-modified GDL/channel structure (non-perforated GDL and non-hydrophilized channel); Figs. 2(b) and 2(c) denote for the customized structures with penetration grooves (width: 100 and 200 µm) and channel hydrophilization. The current density is increased stepwise from 0.17 to 1.39 A/cm2 for 40 min. All visualization images are obtained after 40 min of operation. In the case with the penetration groove, the water saturation in the GDL is clearly decreased around the groove because liquid water accumulated in the porous media is discharged into the large groove. Furthermore, the reduction of water saturation under the channel due to the electrode perforation is more remarkable as compared to that under the land. The region of water saturation reduction in the GDL is enlarged with increasing the groove width from 100 to 200 µm.

Micro fluidic structure selection of metal mesh combinations in proton exchange membrane fuel cells for air supply enhancement

One of the most significant factors affecting the performance of a proton exchange membrane fuel cell is the flow path for the passage of air and water, which is responsible for oxygen dispersion. A three-dimensional fine mesh, with optimized flow paths, exhibits the best performance in commercialized fuel cell electric vehicles, but the manufacturing cost is significantly high. To achieve high performance at a lower cost, the possibility of using a combination of commercially available screen meshes was investigated. The overlapped screen meshes should provide improved mass transport similar to a 3-D fine mesh. By using an optimized combination of screen meshes (200 and 100 mesh) and gasket thickness (150 μm thinner than the mesh flow field), an improvement in oxygen mass transport was achieved. The suggested combination shows a lower oxygen gain (0.030 V) than a single mesh (0.050 V) and a conventional single serpentine flow field (0.150 V).

Performance Comparison of PEM Fuel Cell with Enhanced Cross-Flow Split Serpentine and Single Serpentine Flow Field Designs

The present study is aimed at demonstrating the efficacy of enhanced cross-flow split serpentine flow field (ECSSFF) over the single serpentine flow field (SSFF) for a polymer electrolyte membrane fuel cell of 55 cm2 active area using three-dimensional, multiphase, full-scale CFD simulations. For the present study, pure air and hydrogen are used as reactants on cathode and anode side, respectively. The effect of rib width-to-channel width ratio on the cell performance for the two flow field designs is studied. The power output of the three-channeled ECSSFF is studied and compared with the performance of SSFF at different operating temperatures and pressures. The performance displayed by ECSSFF design is on par with that of SSFF design with almost 30 times lesser pressure drop. ECSSFF has exhibited superior performance in terms of offering high currents and low pressure drops compared to SSFF.

Evaluation criterion of different flow field patterns in a proton exchange membrane fuel cell

Flow field plays an important role in the design and application of proton exchange membrane fuel cell (PEMFC). The superiority of flow field is commonly evaluated by comparing the performance improvement of PEMFC. However, it’s necessary to decrease the flow resistance to reduce the parasitic power and to obtain more uniform water and gas distributions during operation. As a consequence, the combined effect of performance and resistance should be considered during the optimal design of flow channel in PEMFC. A new criterion of efficiency evaluation criterion (EEC) using Sherwood number and Euler number has been proposed to evaluate the relationship between the mass transfer and the pressure drop in this study. The performances of PEMFCs with parallel, single-serpentine, and pressured parallel flow fields are investigated in detail. The results show that PEMFC with single-serpentine flow field has a better performance under normal atmospheric pressure, while the pressure drop in cathode is much larger than that in the parallel flow field. The pressured parallel flow field presents better performance and uniform gas distribution and it is thus proposed as the flow channel in the application of PEMFC.