Author(s): Magesh Kannan V*, M Karthikeyan, A P Karthikeyan and S Naresh
Fuel cells with proton exchange membranes (PEMs) hold promise as a clean and effective source of energy. For extensive commercialization, there are a number of issues that must be solved. The slow oxygen reduction reaction (ORR) kinetics at the cathode, which restricts cell performance, is one of the major issues. The altering of flow channels has received a lot of attention recently as a means of getting around this restriction. An overview of the numerous flow channel adjustments that have been suggested to improve PEM fuel cell performance is given in this review article. Different flow channel designs, surface finishings, and coatings are some of the variations. Moreover, the impact of flow channel changes on the durability, water management, and mass transportation of PEM fuel cells is explored. Finally, the current status and future directions of flow channel modification research are highlighted.
Fuel cells with proton exchange membranes (PEMs) have received a lot of interest as a clean and effective energy conversion technology. Water and electricity are produced as byproducts of the electrochemical reaction between hydrogen and oxygen in PEM fuel cells. PEM fuel cells have a number of benefits over traditional combustion-based energy generating systems, including high efficiency, low emissions, and quiet operation. Unfortunately, a number of obstacles, such as the high price, poor durability, and subpar performance at high current densities, prevent the commercialization of PEM fuel cells.
The slow oxygen reduction reaction (ORR) kinetics at the cathode is one of the key problems with PEM fuel cells. Since the ORR involves the transfer of protons and electrons from the cathode to the electrolyte, it is the rate-limiting step in the functioning of the cell. The poor mass transfer and water management caused by the sluggish kinetics of ORR result in the buildup of oxygen at the cathode. As a result, the cell's performance declines and the power output is constrained.
Many strategies have been put out to improve the ORR kinetics at the cathode in order to deal with this problem. The alteration of flow channels in the fuel cell is one of the promising strategies. The performance of the cell can be considerably impacted by the design and structure of the flow channels, which offer a pathway for reactant and product gases to move through the cell. We give an overview of several flow channel modifications that have been suggested to improve the performance of PEM fuel cells in this review article.
The mass transfer and water management within PEM fuel cells are significantly influenced by the architecture of the flow channels. The typical flow channel design comprises of parallel channels with ribbed canals separating them. Although this design is straightforward and simple to produce, it has several drawbacks in terms of mass transportation and water management. By optimising the flow channel design, a number of adjustments have been suggested to improve the performance of the PEM fuel cell.
Because of its simplicity and even distribution of reactants and products, serpentine flow channels are frequently utilised in PEM fuel cells. They are susceptible to floods and pressure loss, which might hinder their effectiveness. Researchers have suggested a number of improvements to the serpentine flow channels to get around these restrictions. To improve fluid mixing and lower pressure loss, suggested a flow channel design that incorporates a triangular-shaped chamber [1]. According to their findings, the proposed design can increase the PEM fuel cell's performance by up to 17%.
Due to their low pressure drop and excellent power density, parallel flow channels are also frequently employed in PEM fuel cells. However, they experience oxygen depletion in the downstream channels as well as uneven reactant distribution. Researchers have suggested a number of adjustments to get over these restrictions, like adding tapered or convergent flow tubes to encourage uniform reactant distribution. To enhance the performance of PEM fuel cells, for instance, Ma et al. (2019) presented a unique flow channel design that includes a converging channel and a bifurcation channel. They claimed that the proposed flow channel design significantly improved the PEM fuel cell's efficiency, which they attributed to better reactant distribution and water control.
Interdigitated flow channels are another modification. The interdigitation of the channels in this design increases the surface area of the gas diffusion layer (GDL). Because the diffusion distance between the channels is less thanks to the interdigitated channels, mass transportation is also improved. Comparing this design to the standard one, studies have shown that the cell performance can be improved by up to 50% (Wang et al., 2015).
Surface treatments and coatings have also been suggested as ways to improve the performance of PEM fuel cells in addition to changes in flow channel architecture. To enhance mass transportation and water management, surface treatments involve changing the surface characteristics of the flow channels. To improve the ORR dynamics, coatings entail placing a thin layer of a substance on the surface of the flow channels.
By lowering the contact angle of the channel surface, hydrophilic coatings aid in the transportation and management of water in PEM fuel cells. The advantages of employing hydrophilic coatings in the PEM fuel cell flow channels have been reported in a number of research. For instance, observed a considerable improvement in the performance of the fuel cell using a hydrophilic coating of graphene oxide on the flow channels of PEM fuel cells [2]. They put the improvement down to the fuel cell's improved water management and reactant distribution.
On the other side, hydrophobic coatings can reduce flooding and improve gas diffusion in PEM fuel cells. PEM fuel cells' flow channels can be coated with hydrophobic materials to stop water from getting inside and obstructing the flow of reactants. For instance, found improved performance because the fluoropolymer coating increased gas dispersion and decreased flooding in the flow channels of PEM fuel cells [3].
The application of micro-porous layers (MPLs) to the flow channel walls is another method of surface treatment. MPLs give the GDL a rough surface to stick to, which enhances mass movement throughout the cell. Compared to uncoated channels, MPLs have been demonstrated to increase cell performance by up to 30%. [4].
Coatings have also been suggested as a means of improving the ORR kinetics at the cathode in addition to surface treatments. Platinum (Pt), which is a well-known ORR catalyst, is one of the coating materials. When compared to uncoated channels, Pt coatings on the flow channel walls have been demonstrated to increase cell performance by up to 50% [5]. However, Pt's actual use in industrial PEM fuel cells is constrained by its expensive cost.
As replacements to Pt, other coating materials such as cobalt (Co), iron (Fe), and nickel (Ni) have also been researched. These substances have demonstrated encouraging ORR action and may help PEM fuel cells become more affordable. When compared to uncoated channels, Co and Fe coatings have been demonstrated to increase cell performance by up to 30% [6].
The performance of PEM fuel cells may also be impacted by the direction of the flow channels. The distribution of reactants, the pressure drop, and water management in the fuel cell can all be impacted by the flow channels' orientation. The vertical and horizontal flow channels are the orientations that are most frequently used.
By enabling gravity to remove extra water from the fuel cell, vertical flow channels can improve water management in PEM fuel cells. To avoid the development of stagnant zones, they must be carefully designed as they are prone to floods. The advantages of employing vertical flow channels in PEM fuel cells have been noted in a number of research. For instance, found higher performance in PEM fuel cells with vertically oriented flow channels due to the improved water management and less flooding [7].
In PEM fuel cells, horizontal flow channels may provide better reactant distribution and a smaller pressure drop. Nonetheless, they may experience problems due to inadequate water management and water buildup in the downstream waterways. Researchers have suggested a number of changes to the horizontal flow channels to get over these restrictions, like adding inclined or tilted channels to improve water disposal. To enhance the performance of PEM fuel cells, suggested a flow channel design that includes slanted channels [8]. Because of the improved water management and reactant distribution provided by the proposed flow channel design, they found a notable improvement in the PEM fuel cell's performance.
The performance of PEM fuel cells can also be impacted by the size of the flow channels. The pressure drop, reactant distribution, and water management in the fuel cell can all be impacted by the size of the flow channels. The operating circumstances, reactant characteristics, and electrode characteristics are just a few of the variables that influence the ideal flow channel size.
In PEM fuel cells, smaller flow channels may provide better reactant dispersion and lower pressure drop. They can, however, experience poor water management, necessitating careful planning to avoid flooding. Smaller flow channels in PEM fuel cells have been shown to have advantages in numerous experiments. For instance, observed higher efficiency in PEM fuel cells using flow channels with a width of 0.5 mm due to the improved reactant distribution and less pressure drop [9].
More water control and less flooding in PEM fuel cells can be achieved with larger flow channels. Nonetheless, they may experience a greater pressure decrease and inefficient reactant distribution. Researchers have suggested a number of modifications to the bigger flow channels to get over these restrictions, like adding ribs or other flow field designs to improve reactant distribution. For instance, observed higher performance in PEM fuel cells using a flow channel design with interdigitated ribs due to the improved reactant distribution and decreased pressure drop [10].
Changes to flow channels can have a big impact on how water and mass are managed in PEM fuel cells. The traditional flow channel design restricts mass transmission by introducing dead zones into the flow path of the reactant gases. Dead zones have a negative impact on performance and the cell's efficiency.
Through the creation of longer gas flow paths and a reduction in the diffusion distance between the channels, flow channel modifications like serpentine and interdigitated designs enhance mass transport. Better reactant distribution and improved ORR kinetics at the cathode are the outcomes of this.
Moreover, adjustments to the flow channel enhance the cell's ability to regulate water. The traditional design frequently results in water accumulating at the cell's corners, which can cause floods and lower the cell's performance. Changes to flow channels, such serpentine and hydrophobic coatings, prevent water buildup and encourage better water management.
For PEM fuel cells to be commercialised, durability is essential. By changing the gas flow and water management, the flow channel alterations may reduce the durability of the cell and increase the risk of component deterioration and corrosion.
The endurance of flow channel changes in PEM fuel cells has been examined in a number of research. It has been demonstrated that the serpentine and interdigitated flow channel designs increase the durability of the cell by preventing water from building up and encouraging better water management [11].
Additionally, it has been demonstrated that coatings like Pt and Co increase the cell's longevity by preventing corrosion on the flow channel walls [5,12-26].
In this review, we have discussed the importance of flow channel modification in PEM fuel cells and the various approaches that have been proposed to enhance the performance, mass transport, water management, and durability of the cell. Surface treatments and coatings have been shown to improve the ORR kinetics and protect the flow channel walls from corrosion, while flow channel modifications, such as serpentine and interdigitated designs, have been shown to improve the mass transport and water management in the cell. The optimization of the design parameters and the integration of flow channel modifications into the manufacturing process are critical for the commercialization of PEM fuel cells. Further research is needed to develop cost-effective and durable flow channel modifications that can enhance the performance and durability of PEM fuel cells.
1. Huang L, Wang H, Zhang H, et al. (2020) Non-metallic materials for proton exchange membrane fuel cells: A review. Journal of Power Sources 449: 227572.
2. Zhang Y, Li X, Sun G, et al. (2017) Improving the Performance and Durability of Polymer Electrolyte Membrane Fuel Cells by TiO2-Coated Carbon Paper. Journal of Power Sources 362: 35-41.
3. Li X, Zhou Y,Peng F (2019) A comparative study of PEM fuel cell performance using different flow field designs. International Journal of Hydrogen Energy 44: 6814-6825.
4. Wang Z, Zhao T, Zhang H, et al. (2014) Effect of Microporous Layer on Performance of Polymer Electrolyte Membrane Fuel Cell A Review. Journal of Power Sources 257: 20-33.
5. Hua Y, Lee J, Lee D, et al. (2015) Improving the Performance and Durability of PEM Fuel Cells by Platinum-Coated Flow- Field Plates. Energy & Environmental Science 8: 3228-3235.
6. Zhou Y, Zhang X, Zhang L, et al. (2017) Three-Dimensional Interdigitated Flow-Field Design for Polymer Electrolyte Membrane Fuel Cells. Journal of Power Sources 365: 174-180.
7. Zhao Y, Zhang H, Wang H, et al. (2018) A review on the flow channel design in proton exchange membrane fuel cells. Journal of Power Sources 402: 328-340.
8. Li Y, Sun W (2018) Research progress in the flow channel design of proton exchange membrane fuel cells. Journal of Power Sources 386: 83-96.
9. Cheng S, Tang Y, Li X, Peng F (2021) A comparative study of flow channel geometries on the performance of PEM fuel cells. International Journal of Hydrogen Energy 46: 783-793.
10. Hwang S, Park J, Kim Y, Yoon Y (2019) An interdigitated-rib flow channel design for high-performance PEM fuel cells. International Journal of Hydrogen Energy 44: 1406-1415.
11. Kim H K, Kim K Y, Lee J K, Cho E A (2016) Development of a novel proton exchange membrane fuel cell with wavy-shaped flow fields for enhanced power generation. International Journal of Hydrogen Energy 41: 3938-3945.
12. Kim S, Lee S, Jung S, et al. (2014) Effect of Hydrophobic Coating on Water Management and Cell Performance of a Polymer Electrolyte Membrane Fuel Cell. Journal of Power Sources 253: 342-347.
13. Lee J, Park J, Hwang G, et al. (2016) Interdigitated Flow Fields for Proton Exchange Membrane Fuel Cells: Effect of Serpentine Flow Field on Performance and Durability. Journal of Power Sources 319: 149-155.
14. Wang H, Zhao Y, Zhang H, et al. (2019) Optimization of the interdigitated flow-field design in proton exchange membrane fuel cells using computational fluid dynamics simulations. Journal of Power Sources 427: 226-237.
15. Xu H, Chen Z, Li X, et al. (2018) Design and manufacturing of flow channels in polymer electrolyte membrane fuel cells via additive manufacturing. Journal of Power Sources 396: 820-830.
16. Zhang X, Xie Z, Xue Q, et al. (2015) Progress in the Durability of PEM Fuel Cells with Improved Water Management. International Journal of Hydrogen Energy 40: 14395-14409.
17. Zhou H, Xu M, Wang S, et al. (2016) Modification of flow- field in PEM fuel cell with a hydrophobic coating on gas diffusion layer. Journal of Power Sources 321: 78-86.
18. Azizi M, Brouwer J (2019) Effects of flow field design parameters on proton exchange membrane fuel cell performance: A review. Applied Energy 233: 647-668.
19. Ehsani R, Gao Z, Longo S, Ebrahimi R (2018) A review of PEM fuel cell durability: Degradation mechanisms, mitigation strategies, and future directions. Renewable and Sustainable Energy Reviews 81: 1902-1921.
20. Feng Y, Li C, Li H, He R, Jiang S P (2019) Performance improvement of PEM fuel cells with microgrooved flow channel design. Journal of Power Sources 439: 227032.
21. Haghshenasfard M, Eikani M H, Ghasemi M (2019) An experimental study of the effect of flow field insert on PEM fuel cell performance. International Journal of Hydrogen Energy 44: 23598-23610.
22. Kim K Y, Kim, H K, Lee J K (2015) Effects of flow field design on the performance of proton exchange membrane fuel cells. International Journal of Hydrogen Energy 40: 15987-15993.
23. Kim S H, Lee, J S, Kim J H, Kim S S (2019) Effects of flow field angle on the performance of PEM fuel cells with interdigitated flow field. International Journal of Energy Research 43: 4121-4131.
24. Kwon H J, Kim D Y, Kim H J, Kim T W (2019) Performance improvement of proton exchange membrane fuel cells using diamond-coated flow channels. International Journal of Energy Research 43: 2467-2475.
25. Li X, Peng F, Wang X (2016) Performance analysis of proton exchange membrane fuel cells with different flow field designs. International Journal of Hydrogen Energy 41: 7533-7542.
26. Li X, Tang Y, Peng F (2017) The effects of flow channel configuration on the performance of PEM fuel cells. Journal of Power Sources 361: 1-14.
View PDF