Optimizing Proton Exchange Membrane Fuel Cell Performance Through Flow Field Design Analysis

Fuel cells are an emerging energy technology that offers an alternative to traditional combustion-based power generation systems. They generate electricity through an electrochemical process that converts the chemical energy stored in fuels, such as hydrogen and methane, into electricity, with water and heat as byproducts.

Applications for fuel cells today range from stationary power generation to transportation. Despite their advantages, fuel cells face several challenges that limit their widespread adoption. One of the main challenges is the cost of fuel cell systems, which remains relatively high compared to traditional power generation systems. Additionally, fuel cells require high-purity fuels and specific operating conditions, which can be difficult and expensive to achieve. Another challenge is the lack of infrastructure for storing and distributing hydrogen, which limits the use of fuel cells in transportation applications [1, 2].

Fuel cells are an emerging energy technology that offers several advantages over conventional power generation systems. They generate electricity through an electrochemical process that converts the chemical energy stored in fuels such as hydrogen and methane into electricity [3]. Fuel cells are highly efficient and produce fewer greenhouse gas emissions than traditional power plants, making them an attractive option for addressing [4]. The fundamental design of the proton exchange membrane (PEM) fuel cell involves placing two electrodes on either side of an electrolyte. Hydrogen and oxygen cross over each electrode, producing electricity, heat, and water through a chemical reaction. The fuel cell supplies hydrogen fuel to its anode (negative terminal). The fuel cell's cathode (positive terminal) receives oxygen. A chemical process divides hydrogen into an electron and a proton. Each route to the cathode is unique. When used effectively, electrons can create energy for a load without going through the electrolyte. The proton travels through the electrolyte before rejoining the electron at the cathode. The electron, proton, and oxygen combine to make water, which is a harmless byproduct. Figure 1 depicts this procedure [5].

In general, fuel cells are defined primarily by the kind of electrolyte used and the difference in start time, which ranges from one second for PEM fuel cells to 10 minutes for solid oxide fuel cells.

Fuel cells can be classified into different types based on their electrolyte, operating temperature, and fuel source [6, 7]. The main types of fuel cells are PEM fuel cells (PEMFCs), solid oxide fuel cells (SOFCs), alkaline fuel cells (AFCs), direct methanol fuel cells (DMFCs), and phosphoric acid fuel cells (PAFCs) [8-10]. PEMFCs are the most commonly used fuel cells, operating at relatively low temperatures and using hydrogen as the fuel source. SOFCs operate at high temperatures and can use a variety of fuels, including hydrogen, natural gas, and biogas. AFCs use potassium hydroxide as an electrolyte and operate at relatively high temperatures. Portable applications like mobile phones and laptops use DMFCs, which use methanol as their fuel source. PAFCs use phosphoric acid as the electrolyte and operate at relatively high temperatures [11]. Table 1 provides a detailed description and explanation of each type of fuel cell [12, 13]. Fuel cells offer several advantages over conventional power generation systems, including high efficiency, low emissions, and low noise. A range of applications, from small portable devices to large power plants, can utilize their high scalability.

Fuel cells can provide reliable and secure power, particularly in remote areas where grid access is limited or nonexistent. Due to their high efficiency, low emissions, and versatility, fuel cells have a wide range of potential applications. Vehicle manufacturers are developing fuel cells for use in cars, buses, and even airplanes. Hydrogen fuel cell vehicles can potentially reduce greenhouse gas emissions and dependence on fossil fuels. Buildings, data centers, and other applications that require reliable and uninterrupted power can utilize fuel cells as stationary power generators.

In many cases, fuel cells can provide heat and electricity, making them more efficient than traditional combustion-based generators. Fuel cells can also power portable devices like laptops, smartphones, and other electronics. Compared to batteries, fuel cells offer longer runtimes and faster recharge times, making them attractive for a range of applications [14, 15]. A crucial determinant impacting the efficiency of PEM fuel cells is the configuration and fortification of the gas flow pathways within the cell. Effective gas transfer is indispensable for attaining optimal electrochemical reactions and ensuring uniform dispersal of reactants across the membrane's surface. A careful study of the existing literature shows that there is a big knowledge gap and not many systematic studies that look into how to improve gas flow channels in PEM fuel cells. This is mostly because doing experiments is too expensive. Consequently, many researchers have turned to exploring alternative avenues, with COMSOL Multiphysics emerging as a pivotal tool that has broadened the scope for enhancing gas flow channels. Recognizing the pivotal role of these channels in overall cell performance, researchers have embarked on innovative approaches aimed at augmenting mass transport, minimizing pressure differentials, and refining water management within the cell. Table 2 provides an overview of the key researchers involved in advancing PEM fuel cell technology and their respective design endeavors.

Fuel cell technology is one of the most promising approaches to energy generation. However, there are some obstacles to using this technology as a replacement for fossil fuels. The effect of the design of the flow field (paths of flow gases) on the performance of PEM fuel cells is one of the most significant obstacles. However, numerous researchers in this discipline have theorized about this issue. In contrast, this study will experimentally investigate the effect of flow field design on the efficacy of PEM fuel cells.

References	Method	Parameters /Type	Boundary Conditions	Figures
Isanaka et al. [16]	HT	Schematic of flow field plate (parallel Z-type) -The dimensions of the flow field plate Ap = 5×5 cm2 Wc = 1-2 mm Hc = 1 mm	Operating temperature = 80℃ -Pressure inlet = 2 atm	t1.png
Dehsara et al. [17]	EX	The bipolar plates of PEM fuel cells are fabricated by (A) Graphite, (B) Stainless Steel (SS316), (C) Aluminum, and (D) Titanium. (Parallel Z-type and serpentine) The dimensions of the field flow plate Ap = 5×5 cm2 Wc = 1 mm Hc = 1 Wr = 1 m	operating temperature = 80℃ -Cathode inlet flow rate  = 5.83×10-6 [m3/s] -Anode inlet flow rate = 5×10-6 [m3/s] -Pressure inlet = 2 atm	t2.png
Maharudrayya et al. [13]	TH	Schematic diagram of flow field plates (A- U-type, B- 2U-type with and without modification, CZ-type, D- 3Z-type). The dimensions of the field flow plate Wh = 4 mm, Hh = 1.5 mm Wc = 2 mm, Hc = 0.72 mm Wr = 2 mm	The mass flow rate of Air = 2.2×10−5 kg/s	t3.png
Wang [18]	TH	-Schematic of flow field plates: (A)-single serpentine, (B)- Multiple serpentine, (C)-Straight parallel and (D)- Interdigitated. -The dimensions of the flow field plate Wh = 4 mm, Hh = 1.5 mm Wc = 2 mm, Hc = 0.72 mm Wr = 2 mm	Re = 0-1000	t4.png
Edupuganti and Daglen [19]	TH	Schematic of the flow field plates (A-Single serpentine with Wc = 0.5,1 and 1.5) and (B-Parallel Z-type with Wc = 0.5, 1 and 1.5) -The dimensions of the flow field plate Plate width = 24 mm Wc = 0.5-2 mm, Hc = 1 mm N = 10, Hc = 1 mm, length of channel Lc = 10 mm.	Velocity of air = 0.1 m/s	t5.png
Pal et al. [20]	TH	The flow field channels (A) Uniform pin type, (B) Zigzag pin type, and (C) single serpentine. -The dimensions of the flow field plate Ap = 50×50 mm2 Wc = 2 mm, Hc = 2 mm Wr = 2 mm	Pressure = 1 bar Temperature = 325 K	t6.png
Her et al. [21]	EX	The dimensions of the flow field plate Ap = 5 cm2 Hp = 0.25 mm, Wc = 0.3 mm Hc = 0.2 mm, Wr = 0.6, 0.3 and 0.15 mm	The hydrogen flow rate = 20 and 30 cm3/s -The airflow rate = 100 and 150 ccm/s, - Pressure = 97 kPa, Temperature = 25℃	t7.png
Ahmed and Sung [22]	TH	cross-sectional view of different geometrical configurations analyzed: A) Rectangular; B) Trapezoidal; C) Parallelogram. -The dimensions of the flow field plate Case (a): Wc = 0.8 mm, Hc = 1 mm and Wr = 0.4 mm Case (b): Wc = 0.9 mm, Hc =1 mm and Wr  = 0.35 mm Case (c): Wc = 0.8 mm, Hc = 1 mm and Wr = 0.4 mm	Anode and cathode pressure = 1atm -Cell temperature = 70℃ -Anode temperature = 80℃ -Cathode temperature = 70℃	r22.png
Ramesh and Duttagupta [23]	TH	The schematic PEM fuel cell model The dimensions of the field flow plate Wc = 0.5, 1, 1.5, and 2 mm Wr = 0.2, 0.7, 1, and 1.2 mm	Anode inlet flow velocity of hydrogen = 0.2 m/s -Cathode inlet flow velocity of oxygen = 0.5 m/s	r23.png
Shen and Tu [24]	TH	Height of main channel 1.0 x 10-3 m, length of main channel 1.0 x 10-3 m, Number of flow channel 50, Thickness of catalyst layer 1.0 x 10-5 m.	Output voltage increasing to 4.4% at 1.6 A cm-2 and up to 10% at 2 A cm-2	t10.png
Yang et al. [11]	TH	Channel width/depth [mm]: 1 / 1, BP length/width/height [mm]: 100 / 2 / 1.5, Block width [mm]: 2.0, GDL thickness [mm]: 0.3, CL thickness [mm]: 0.0129, PEM thickness [mm]: 0.108	Inlet Pressure: 101,325 Pa, Inlet Temperature: 343.14 K, Ratios: Anode: 1.5 and 3.0, Cathode: 2.0 and 3.0	t11.png
Sugii and Okamoto, [25]	EX	Schematic of flow field such as: A-Single serpentine and B- Parallel Z-type. The dimensions of the field flow plate Wc = 1 mm, Hc = 0.5 mm	Averaged velocity = 0.4 and 2.0 m/sec, which corresponded to Reynolds number = 26 and 130, respectively	t12.png
Almaliki et al. [26]	TH	Z-shaped flow field with 19 designs (Z, S, U, W, spherical.	Anode in flow = 0.27 m/s, Cathode in flow = 0.5 m/s H2 molar mass = 0.002 kg/mol,	t13.png

The objective of this paper is to develop a novel fuel cell design aimed at enhancing performance. Specifically, the study focuses on optimizing the distribution of reacting gases within the fuel cell, aiming to achieve even distribution across electrodes. This optimization serves two main purposes: firstly, to increase power density by maximizing power generation per unit electrode area, thereby facilitating the development of smaller, lighter, and more efficient fuel cell systems. Secondly, it enhances durability by mitigating localized electrode degradation caused by uneven gas distribution, thus prolonging the lifespan of the fuel cell.

3.1 Validation of the models

Validation was conducted by comparing the results obtained with those reported by Dhahad et al. [28] performed by a previous researcher. The comparison revealed that our findings closely aligned with those of the earlier study. Figure 2 shows the comparison of the numerical results for present work by COMSOL Multiphysics 6.1 and experimental results [28] of the baseline design single serpentine Z flow field, i.e., the operation voltage, V_cell versus the current density of fuel cells, I (A/m²).

The comparison indicates that the simulation results are in favorable agreement with experimental data. At high current densities, the experimental results of Dhahad et al. [28] have low value compared to the simulation results of the present work due to some differences in physical parameters, like reactants inlet boundary conditions, relative humidity of gases, coefficient stoichiometric of anode, and cathode.

The numerical results illustrate the behavior of the flow field in terms of pressure loss distributions, species concentration distributions, and current density distribution over the electrolyte surface. Pressure distribution is thought to be a key component of the PEM fuel cell's performance. The pressure distribution through the various flow field designs on the cathode and anode side at 0.4 V, respectively, is depicted in Figure 3. The results show that the pressure falls throughout the flow field since it is highest at the start of the flow field and lowest with 0 Pa at the outlet with a reference pressure is 101,325 Pa. The parallel Z flow field design exhibits low-pressure drop-in comparison to other flow field designs, as can also be seen from the findings of Model B1, Model C1, Model C2, Model D1, Model D2, Model E1, and Model E2. Gases are compelled to pass through the serpentine, connecting the intake and outlet, which is the cause of this.

2.png

Figure 2. Comparison of the numerical results for present work and experimental results of Dhahad et al. [28]

Figure 3. The distribution of pressure drops across flow field designs Model (A1, B1, C1, D1, E1, A2, B2, C2, D2, E2) on the anode side at 0.4 V

Serpentine is beneficial for managing water. However, because of the significant pressure loss, it also results in power losses. The Parallel Z flow field's maximum pressure loss values for Models A1, B1, C1, D2, and E1 are 180, 25, 40, 20, 12, and 10 Pa, respectively, and for Models A2, B2, D2, and E2 are 100, 18, 20, 12 and 7 Pa, respectively. The performance of double and triple serpentines is inferior to single serpentines, although an increase in the number of channels, particularly serpentine flow fields, reduces pressure losses. Due to a single serpentine flow channel, high pressure and high power are provided. The pressure generally fell as the fluids moved from the entrance to the outlet in the pressure distribution scenes of the flow fields for all flow field designs.

Figures 4 and 5 show the Bar chart for the Cathode and Anode side, respectively, and show that the lowest pressure obtained is model D2 with 90 pa for the cathode side and model E2 with 7 pa for the anode side. The distribution of oxygen concentration plays a crucial role in the performance of PEM fuel cells, with restrictions in oxygen transport significantly impacting their efficiency. It is essential to comprehend how oxygen transport operates in the cathode channel, gas diffusion layer (GDL), and catalyst layer. The Schemes (Model E1 and Model E2) flow field design offers a low-pressure difference; however, its drawback is poor water management inside the cell. This is due to two main factors: the first is friction, which causes a pressure loss along the header, and the second is inertial forces, which represent the momentum of working fluid going into the channel's inlet header. These forces tend to bring the gases toward the closed end and produce a pressure rise, leading to the maximum pressure at the lateral channel (higher flow velocity). The gases pass over different parallelly divided ways, resulting in dropping the length of the paths; consequently, the gases flow in smaller paths than in a serpentine design. This behavior concurrently reduces the pressure drop and the velocity of reactant gases along the channels.

Additionally, because of many parallel paths, the velocity of reactant gases from the inlet to the outlet is not identical; it varies from channel to channel. Reactants spread heterogeneously above the active surface area as a result. At high current density regions (low voltage), the electrochemical reaction is swift and consumes much oxygen. Therefore, the quantity of oxygen is not adequate for the reactions, leading to a reduction of the reactant gases at the zones with low gas flow, which will reduce the performance of the fuel cell significantly. From simulation results, it can be seen that high-pressure losses on the cathode side compared with those on the anode side. This can be related to the form of water caused by an electrochemical reaction on the cathode side. So, it needs to have high power to overcome the accumulation of water. This power needs to be high.

4.png

Figure 4. Pressure drop in the cathode side of ten simulated models

The simulation prediction of pressure on both sides, anode, and cathode, it can be seen that the serpentine Model A1 is the worst part of the high-pressure drop. This can be related to providing high power and accomplished power. Oxygen distribution was examined in both the Cathode and Anode sides across ten different flow field designs, revealing a progressive decrease in oxygen concentration from the entrance to the output due to consumption at the catalyst layer. Additionally, the GDL exhibited higher oxygen content under the channel area compared to the land area, highlighting a typical feature of its distribution. Water concentration, a byproduct of the electrochemical reaction within the PEM fuel cell, poses challenges as its accumulation obstructs pores in the GDL and catalyst layers, impairing cell function.

5.png

Figure 5. Pressure drop in the anode side of the ten simulated models

Methods to mitigate water buildup include evaporation, water-vapor diffusion, capillary transport through the GDL into the flow channels, and water back-diffusion through the membrane to the anode. Analysis indicated that Model B2 exhibited similar water intake levels at 5 mole/m³ but lower outflow levels at 0.016 mole/m³, attributed to water used for electrolyte moistening. These findings are detailed in Table 5.

Activation losses arise due to the sluggish kinetics of the electrode surface reactions, leading to a notably nonlinear voltage drop. Fuel crossover and internal currents, resulting from fuel wastage across the electrolyte and electron conduction within it, can be disregarded for PEM applications. Ohmic losses denote resistive effects occurring as electrons traverse the electrodes and interconnections alongside ion flow within the electrolyte. Mass transport or concentration losses predominantly emanate from changes in reactant concentrations occurring at the electrode surface. The current density was extracted after completing the range for the models (Model A1, Model A2, Model B1, Model B2, Model C1, Model C2, Model D1, Model D2, Model E1, Model E2) in Figures 6 and 7 show the comparison between each model that was designed at W_h = 1 and 2 mm, respectively and it turns out that the maximum current density design obtained is Model A2.