Metal Foam Flow Field Research Articles

Comparison and optimization of electrochemical and thermal performances of SOFC with different configurations of a metal foam flow field

The effects of different configurations of a metal foam flow field on current density and temperature gradient of a single channel solid oxide fuel cell (SOFC) are investigated, and the overall performance of the optimum configuration is optimized. First, model A (conventional channel-rib flow field) is compared with three different configurations (i.e., model B with metal foam flow field only at anode, model C with that only at cathode, and model D at both). Although model C achieves the highest current density, its temperature is also fairly high. Although model B achieves the lowest temperature gradient, its current density is also fairly low. Model D performs well in both current density and temperature gradient. Then, the effect of electrode thickness and metal foam thickness on the performance of model D is investigated. The Ohmic polarization of model D remains almost constant with different electrode thicknesses, and its concentration polarization decreases as the electrode thickness decreases, which is totally different from the channel-rib flow field. Moreover, a thinner cathode causes lower activation overpotential, whereas a thinner anode causes higher activation overpotential. In general, a thick anode, a thin cathode, and thin metal foam can maximize the current density of model D, while a thick electrode and metal foam can always reduce the temperature gradient. Finally, the Taguchi method and gray relational analysis are used to optimize the current density and temperature gradient of model D. The current density of an optimized model is 3.27% higher than that of the original model with a temperature gradient of 9.05 K/cm.

Experimental study on the performance of proton exchange membrane fuel cell with foam/channel composite flow fields

Metal foam flow field (MF-FF) has shown great potential in enhancing the proton exchange membrane fuel cell (PEMFC) performance, while the deficiency of lacking mainstream directions still merits improvement. In this work, we proposed a foam/channel composite flow field (FCC-FF), which combines the advantages of enhanced transport of the MF-FF and clear mainstream direction of the parallel serpentine flow field (PS-FF). The polarization curves, high-frequency resistance, low-frequency resistance, cathode pressure drop, and voltage stability of different flow fields were compared. Results show that, the maximum power density of the FCC-FF can be greatly increased compared to the MF-FF and the PS-FF. By introducing guide ribs into the corners of the flow field, the PEMFC performance could be further improved due to enhanced mass transfer, provided that the guide ribs do not bring in the negative effect of the under-rib weak flows. FCC-FF with an intermediate number of guide ribs, through balancing the in-plane and through-plane transport, show optimal performance of both power density and voltage stability at the expense of a moderately increased pressure drop, which is merited for practical applications. The present results are insightful for the development of the next-generation PEMFC towards higher power density.

Ni/Graphene Coating for Enhanced Corrosion Resistance of Metal Foam Flow Field in Simulated PEMFC Cathode Environment.

Metal foam flow field suffers serious corrosion issues in proton exchange membrane fuel cells due to its large surface area. Ni and Ni/graphene coatings are prepared under constant and gradient current modes, respectively, to improve the corrosion resistance. The effect of the electrodeposition current mode and the deposition mechanism is studied. Compared with Ni coating, Ni/graphene coating brings low corrosion current density and high coating resistance, effectively enhancing the stability of Ni foam in an acidic environment. Different from Ni coating with a single layer, Ni/graphene deposits have core-shell structure, with graphene coated on the surface of Ni nanoparticles. It is shown that graphene deposits cover the Ni particles during the electrodeposition, which protects nickel particles from agglomeration and forms an inert film on the surface of the porous structure. After an 8 h constant potential test, no significant pitting is observed on the surface of Ni/graphene coating, showing excellent anticorrosion performance. As to the effect of the deposition current mode, it is shown that more composite particles deposit on the upper layer under the gradient current mode, which brings denser protective film and fewer surface defects on the surface. Ni/graphene coating electrodeposited under a gradient current mode between 0 and 10 mA·cm-2 exhibits the lowest corrosion current densities. The values at 50 and 80 °C are only 62.9 and 26.0% of those of uncoated Ni foam, respectively.

Effect of manifold size on PEMFC performance with metal foam flow field

Metal foam flow fields are considered as an alternative to conventional channel/rib flow field in polymer electrolyte membrane fuel cell (PEMFC) because of the advantages of three-dimensional pore structure. In this study, the effect of metal foam flow field with different manifold size on PEMFC performance was investigated, with a 25 cm2 unit cell. Polarization curve and electrochemical impedance spectroscopy results were analyzed to investigate the effects of gas stoichiometry and relative humidity on performance. The mass transfer loss was decreased with reduced manifold size. However, mass transfer loss was increased due to difficulty of water discharge in small manifold case. The metal foam flow field offer advantages in water discharge and mass transfer loss. At 100% relative humidity, performance was improved with increased air stoichiometry for different manifold size. At 25% relative humidity, performance was a little improved with increased air stoichiometry for small manifold case. Regardless of relative humidity, fuel cell performance with metal foam flow field was most improved in case of smallest manifold size based on air stoichiometry due to the high pressure drop.

Water transport in PEMFC with metal foam flow fields: Visualization based on AI image recognition

Water transport is an essential process in proton exchange membrane fuel cells (PEMFC). For the novel metal foam flow fields, water transport is difficult to be visualized and still remains inadequately understood. In this work, for the first time, the two-phase flows in the metal foam flow fields of a transparent PEMFC was visualized by using an artificial intelligence (AI) image recognition method. In order to distinguish water from the metal foam ligaments, a scoring system was developed, which effectively solved the problem of inconsistent reflectance of liquid water between the ligament and the gas diffusion layer. According to the state of liquid water, the scoring system categorized the local images into three labels of waterless state, wet state, and slug state for AI image recognition network training. The trained AI image recognition model was then used to visualize the liquid water state in the metal foam flow fields under different operating conditions of relative humidity (RH), temperature, and inlet flow rate. Results show that, since the porous structure of the metal foam provides flexible transport paths, the PEMFC can operate effectively in a wide range of wet states. Even a 25% difference in the wet-state percentage between different operating conditions yields an almost consistent voltage. The increased slugs in the flow fields are the primary reason for the performance degradation of the PEMFC. At a high current density of 2 A/cm2, the voltage is as low as 0.03 V when the slug state occupies 35% of the flow fields (100% RH, 60 °C, 1.0 SLPM cathode inlet flow rate), and as high as 0.56 V when the slug state is absent in the flow fields (100% RH, 60 °C, 2.0 SLPM cathode inlet flow rate). The present work provides a novel approach for the studies of water transport in PEMFC.

Water management and mass transport of a fractal metal foam flow-field based polymer electrolyte fuel cell using operando neutron imaging

Metal foam flow-fields (MFFs) exhibit immense potential for enhancing the performance of polymer electrolyte fuel cells (PEFCs) owing to their advantageous pore connectivity and abundant gas pathways. Nevertheless, challenges remain with the conventional MFF concerning reactant homogeneity and water management. To address these concerns, this study incorporates a fractal manifold into the MFF design. By employing operando neutron imaging, device-level testing, and electrochemical impedance spectroscopy (EIS), a comprehensive understanding of mass transfer and water management characteristics across the fractal manifold MFF is obtained. This novel design delivers better cell performance and lower mass transport resistance compared to the conventional MFF under all experimental conditions investigated. Notably, neutron imaging reveals that the fractal manifold MFF consistently exhibits a reduced liquid water content and more uniformly distributed liquid water compared to the conventional MFF. These superior characteristics of the design contribute to a substantial ∼15% increase in maximum power density compared to the conventional MFF-based PEFC. The results indicate the potential for further performance improvement by optimizing manifold parameters.

Multiphase flow dynamics in metal foam proton exchange membrane fuel cell

Porous metal foam holds substantial promise as a material for bipolar plates in high-performance proton exchange membrane fuel cells (PEMFC) due to its exceptional properties in reactant redistribution. However, the intricate structure of metal foam flow field (MFF) presents challenges for mass transfer and water management. In this study, a three-dimensional two-phase flow model for metal foam is developed to analyze and capture flow patterns. MFFs are reconstructed based on detailed structural analysis and various pore sizes are discussed. Employing the Volume of Fluid (VOF) method, we delve into multiphase flow dynamics, specifically focusing on the removal of liquid droplets within the MFF. It reveals the MFF with moderate pore sizes exhibit a trade-off performance, striking a balance between optimal mass transfer and minimal parasitic loss. The porous structure's pivotal role is highlighted, contributing significantly to both through-plane and in-plane mass transfer and convection. Furthermore, we classify three flow patterns of liquid droplet, with the “split-up” pattern emerging as the most effective for water management and mass transfer. This study illuminates water behavior in porous metal foam bipolar plates, introduces a systematic methodology for assessing mass transfer and water management capabilities in MFFs for PEMFC.

Effect of startup modes on cold start performance of PEM fuel cells with different cathode flow fields

Proton Exchange Membrane Fuel Cell (PEMFC) is widely recognized for its cleanliness and high efficiency, but is still facing challenges in cold environments. At low temperatures, the formation of ice and repeated freezing/thawing cycles may cause cell performance reduction and irreversible degradation. The cathode flow field of PEMFCs has a significant effect on the performance. In contrast to the conventional “channel-ridge” flow field, the metal foam has the advantages of excellent pre-distribution of gases and water drainage, which make it a promising candidate for the cold start. This paper examines the cold start of PEMFCs with metal foam flow field (MFFF) and serpentine flow field (SFF), and the influence of constant current mode, constant voltage mode, and ramping current mode is investigated experimentally through performance test and electrochemical characterization. The results show that lowering the voltage and increasing the current can enhance the cold-start performance of fuel cells. The MFFF fuel cell has superior cold start performance compared to the SFF fuel cell under the constant voltage mode of 0.3 V. Furthermore, the variable current mode is developed by considering the distinct properties of heat and water production during various phases, and the results indicate that increasing the current density at the unsaturated stage leads to an elevated rate of heat production and a reduced rate of water production, which can improve the cold start of PEMFCs.

Porous metal foam flow field and heat evaluation in PEMFC: A review

Abstract A proton-exchange membrane fuel cell (PEMFC) generates electricity, heat, and water from oxygen and fuel. Hydrogen is recommended as a fuel because it is a renewable fuel when manufactured, for example, by water electrolysis using renewable energy power. Porous metal has excellent characteristics such as controlled permeability, low density, and high porosity. Corrosion is now the most major hurdle to the use of porous metal in PEMFCs, and owing to the porous metal’s complicated internal structure, additional challenges must be addressed in the coating preparation process. As a result, this article figures out how to successfully handle the porous metal corrosion problem in a PEMFC setting, which increases the porous metal utilization in the fuel cell industry. This article also examined the flow field in PEMFC and important characteristics. The influence of flow field in the fuel cell was also investigated.

Liquid water discharge capability enhancement of hierarchical pore structure in metal foam flow field of proton exchange membrane fuel cell

AbstractMetal foam flow field shows great potential for next‐generation proton exchange membrane (PEM) fuel cell of high power density due to its well‐connected pore structure, high thermal and electrical conductivity. However, the complicated pore structure makes it a challenge for water management. To tackle this issue, a novel design of metal foam flow field with hierarchical pore structure was proposed. Based on lattice Boltzmann method (LBM), the structure‐performance relationship between hierarchical pore structure and water discharge capability of flow field was explored by using breakthrough time. Furthermore, an optimal hierarchical pore structure for metal foam flow field that shows superior water discharge capability was obtained. Compared with metal foam with uniform coarse pore structure, breakthrough time can be reduced roughly by 17.6% in the one with optimal hierarchical pore structures. This finding provides a theoretical foundation and technical guidance for developing metal foam flow field.

Two-phase flow in porous metal foam flow fields of PEM fuel cells

Porous metal foam (PMF) flow field is a potential option for proton exchange membrane fuel cells (PEMFCs) due to its excellent capabilities in gas distribution and water drainage. However, the gas-liquid two-phase flow in the PMF flow field on the pore scale is still unclear. In this study, we investigate the gas-liquid two-phase flow in the PMF flow field. Film, plug, and ligament flows are found in the hydrophilic PMF flow field, while slug and droplet flows are found in the hydrophobic PMF flow field. The results suggest that optimizing the pore size, increasing the metal foam surface hydrophobicity, and optimizing the operating condition are helpful for the water management of the PMF flow field. The frequency analysis of the pressure drop also shows that the dominant frequency can be used as an indicator to analyze the transition between different flow patterns.

Mass transfer and water management in proton exchange membrane fuel cells with a composite foam-rib flow field

Mass transfer capability of reactants and hydrothermal management is important for the performance and durability of proton exchange membrane fuel cells. In the conventional rib flow field, the oxygen transport is affected by the accumulation of under-rib liquid water which causes excessive concentration loss and limits cell performance. To improve the cell performance, a composite foam-rib flow field structure is proposed by combining the metal foam flow field and the conventional rib flow field. The proposed design is simulated by using a three-dimensional homogeneous non-isothermal numerical model. The results show that the composite foam-rib flow field, by improving the oxygen transfer and water removal capabilities under the ribs, can improve the oxygen concentration and current density without increasing the pumping power, thus improving the cell performance under different conditions. The key parameters of the composite foam-rib flow field are optimized. With the optimal metal foam filling ratio of 0.75 and porosity of 0.85, the peak power density and the limiting current density for the composite foam-rib flow field are higher than the conventional rib flow field by 5.20% and 22.68%.

Water Management Capacity of Metal Foam Flow Field for PEMFC under Flooding Situation.

Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam flow field is experimentally investigated by polarization curve tests and electrochemical impedance spectroscopy measurements. Additionally, the dynamic behavior of water at the cathode and anode under various flooding situations is examined. It is found that obvious flooding phenomena are observed after water addition both into the anode and cathode, which are alleviated during a constant-potential test at 0.6 V. Greater abilities of anti-flooding and mass transfer and higher current densities are found as the same amount of water is added at the anode. No diffusion loop is depicted in the impedance plots although a 58.3% flow volume is occupied by water. The maximum current density of 1.0 A cm-2 and the lowest Rct around 17 mΩ cm2 are obtained at the optimum state after 40 and 50 min of operation as 2.0 and 2.5 g of water are added, respectively. The porous metal pores store a certain amount of water to humidify the membrane and achieve an internal "self-humidification" function.

Three-dimensional performance simulation of PEMFC of metal foam flow plate reconstructed with improved full morphology

Recently, Proton Exchange Membrane Fuel Cell (PEMFC) with metal foam flow field has attracted extensive attention from scholars. In the present work, the full morphological reconstruction method of metal foam is improved and is successfully applied to a three-dimensional simulation of a metal foam PEMFC. The numerical predictions of metal foam PEMFC before and after reconstruction improvement are compared. The numerical results of the traditional channel flow field and two metal foam flow fields with pore sizes (40PPI and 100PPI) are compared. It is found that the application of metal foam can greatly improve the performance of PEMFC at higher current densities, and the smaller pore size (100PPI) of the metal foam makes the performance better. In addition, the numerical results of the oxygen concentration, ohmic loss, intra-membrane ionic current density and pressure drop of the cathode component are elaborated to explain the phenomenon.

Thermal management improvement of air-cooled proton exchange membrane fuel cell by using metal foam flow field

The key factor that limits the output performance and commercial applications of air-cooled proton exchange membrane fuel cell (PEMFC) is how to maintain the balance between heat dissipation and water retention. In order to tackle this issue, new cathode flow field with metal foam is experimentally investigated due to superior heat dissipation and water retention capability of metal foam. Experimental results demonstrated that when the height of metal foam is 1 mm and the width of metal foam increases from 1 mm (case 2) to 5 mm (case 6), the temperature of air-cooled PEMFC decreases by 8.4 ℃ under current of 15 A due to the synergic enhancement of heat dissipation and electrochemical performance, indicating the thermal management improvement of air-cooled PEMFC. As the metal foam height increases, however, the thermal management performance of air-cooled PEMFC first increases and then decreases. Therefore, case 6 is considered to be the optimal sample under the constraints of the thermal management performance and compactness of air-cooled PEMFC. By comparing with conventional parallel flow fields with the widths of 1 mm, 3 mm and 5 mm (case 1, case 3 and case 5), the net output performance of case 6 increases by 3.4 %, 8.8 % and 55.1 % and the compression work of case 6 decreases by 69.7 %, 38.3 % and 64.4 % under the same temperature (50 ℃) and current (15 A), which means higher practical application potential and lower parasitic power requirement.

Flow field plate of polymer electrolyte membrane fuel cells: A review

Recently, pursuing a strategic alternative to traditional fossil fuels has become an important method to meet the increasing energy demands and environmental improvement needs. Polymer electrolyte membrane fuel cells (PEMFCs) can directly convert the chemical energy of fuels into electricity without contamination and the restriction of the Carnot cycle effect. The flow field plate (FFP) is a critical part of a PEMFC that provides mechanical support, conductive medium, the channel of reaction gases, and water and thermal management. However, the complicated mechanisms of the FFP are not very clearly understood since the materials and structures are associated closely with cost, performance, and lifetime. In this paper, different materials and structures are analyzed and their characteristics are summarized. Meanwhile, an opinion was proposed that the porous metal foam flow field will be the most promising development direction in the future, mainly focusing on surface treatment, pattern, and manifold design.

Numerical investigation of design and operating parameter effects on permeability-differentiated alkaline fuel cell with metal foam flow field

• Effect of design and operating parameters are investigated and optimized numerically. • Temperature and pressure have different effect in different current density regions. • Anode metal foam thickness has significant effect while cathode is negligible. • Lower anode and higher cathode permeability lead to better performance. • Permeability-differentiated layout of metal foam flow fields is originally proposed. Metal foam (MF) material is recognized as an attractive flow field for the alkaline anion exchange membrane fuel cell (AAEMFC). In this paper, the effect of design parameters (MF thickness and permeability) and operating parameters (operating temperature and back pressure) are investigated and optimized through the numerical study. The maximum temperature of the AAEMFC with MF flow field is lower and temperature distribution is more uniform compared to that of AAEMFC with serpentine flow field. In general, the higher operating temperature decreases the cell performance slightly in the low current density region but enhances the cell performance obviously in the medium and high current density regions. The higher back pressure promotes the cell performance in the low current density region but decreases the cell performance in the high current density region. The anode MF thickness has the significant effect on the cell performance, and the thinner anode MF thickness benefits the cell performance. However, the effect of cathode MF thickness is relatively negligible. The lower permeability of the anode MF and higher permeability of cathode MF lead to the better performance. The permeability-differentiated layout of MFs in anode and cathode sides is proposed for the first time, and it is proven to improve the cell performance effectively due to the enhanced hydraulic permeation and membrane hydration. Electrochemical kinetics, thermal and water transport characteristics (including pressure drop, liquid water transport, membrane water distribution and ohmic loss) are analyzed in detail to explain the cell performance improvement.

Relationship between number of turns of serpentine structure with metal foam flow field and polymer electrolyte membrane fuel cell performance

Metal foam flow field is applied on a polymer electrolyte membrane fuel cell (PEMFC) to improve its performance by enhancing mass transfer property. Generally, the metal foam is employed without any structure in the channel location, which results in the mainstream of reactants not flowing to the corner of the reaction area and instead of flowing straight from inlet to outlet. This causes an uneven reaction rate throughout the reaction area. To resolve the problem, the serpentine structure was devised on a metal foam flow field at the cathode to guide the reactant flow path to the corner of the reaction area. The number of turns of the serpentine structure was controlled as variables. With the increase in the number of turns, the reactant concentration at reaction sited increased, improving the PEMFC performance. At 0.5 V, PEMFC with metal foam and 2 turns serpentine structure shows 4.7% improved performance. However, due to the increased length of flow from the structure, the pressure drop that induced high parasitic loss became higher. As a result, the net power of PEMFC with serpentine structure considering parasitic loss improved 1.7% comparing to PEMFC with bulk metal foam.

Oxygen transport in proton exchange membrane fuel cells with metal foam flow fields

Metal foam flow fields have shown great potential in improving the performance of proton exchange membrane (PEM) fuel cells, while their effect on the oxygen transport process remains inadequately understood. In this study, oxygen transport in metal foam flow fields (under zero-humidity operating conditions) is simulated by using a three-dimensional multi-species lattice Boltzmann model. Comparison is done between the metal foam flow field and the conventional channel-rib flow field, and parametric studies are conducted on the metal foam porosity, pore density, and compression ratio. Results show that the metal foam flow field enhances mass transfer of oxygen to the catalyst layer and improves the oxygen distribution homogeneity. Within the range of parameters considered, decrease in the metal foam porosity yields nonmonotonic variation of the mass transfer rate of oxygen to the catalyst layer, which increases at high inlet velocities (higher than 2 m/s) but decreases at low inlet velocities (less than 2 m/s). The increase in metal foam pore density and compression ratio leads to enhanced mass transfer of oxygen, which becomes increasingly prominent at high inlet velocity. The results of this study could be insightful for the implementation of metal foam flow fields in PEM fuel cells. • Oxygen transport in PEM ofuel cells is studied by using lattice Boltzmann method. • Metal foam flow field has stronger oxygen transport than channel-rib flow field. • Increasing metal foam pore density/compression ratio facilitates oxygen transport. • Reducing porosity suppresses/enhances oxygen transport at low/high inlet velocity.

Water management and structure optimization study of nickel metal foam as flow distributors in proton exchange membrane fuel cell

In order to tackle the water flooding issue in proton exchange membrane fuel cell (PEMFC), the effects of structure parameters of nickel metal foam on water management and the performance of PEMFC were experimentally investigated. Experimental results indicated that when compression ratio of nickel metal foam on cathode is beyond 0.69, the voltage of PEMFC is completely stable in a 3-hour constant current density test. Furthermore, the performance of PEMFC enhances with the rise of compression ratio on cathode. However, there is an optimal compression ratio of nickel metal foam on anode, namely 0.38. Regarding PPI (pores per inch) of nickel metal foam, it has been found that there is an optimal PPI on cathode, namely 75, due to the synergic effect between the distribution of reactant gas and water management in nickel metal foam flow fields with different PPIs. In contrast with cathode, a higher PPI of nickel metal foam results in better performance on anode. Compared with the case that uncompressed nickel metal foam with 110 PPI for anode and cathode, the maximum power density and energy conversion efficiency of the optimized metal foam fuel cell, namely 110 PPI and compression ratio of 0.38 for anode and 75 PPI and compression ratio of 0.75 for cathode, increase by 9.8% and 4.6%, respectively. In order to further intensify the performance of PEMFC, the effect of assembly force was considered. Since nickel metal foam could protect the MEA, a higher assembly force can be tolerated to obtain better performance.