Water Management In Proton Exchange Membrane Fuel Cell Research Articles

Optimization strategies and diagnostic techniques for water management in proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) are efficient and zero emission energy conversion technology with promising application prospects towards carbon neutrality. The PEMFC's performance is largely affected by the poor water management, which is a substantial concern for long term durability. Herein, we overview the water management problems in PEMFCs, such as flooding and dehydration of membrane electrode assembly and analyze the causes and their impacts on the device performance. Major problems such as flooding impedes the gas transport and electrode reactions, while dehydration increases the membrane resistance and hinders proton transport. We have thoroughly overviewed several electrochemical and physicochemical diagnostic techniques for water management in PEMFCs. Additionally, material development and optimization approaches for the flow field structural design are explored in order to improve mass transport and wetting characteristics for optimized water management. Therefore, it is anticipated that this review will provide insights into the effective operation of PEMFCs as well as practical guidance for resolving water management issues in PEMFCs and associated technologies, like PEM water and CO2 electrolyzers.

Pressure and Impedance Based in Situ Diagnostic Methods for Water Management in Proton Exchange Membrane Fuel Cells Applications

Recent advancements in proton exchange membrane fuel cells (PEMFCs) have led to significant developments in low-carbon transport technology, enabling the generation of clean, efficient electricity with minimal noise and toxic emissions for heavy-duty applications. However, effective water management remains a critical challenge in PEMFCs due to the intricate phase changes and liquid-gas transport processes within key components, which significantly impact cell performance and longevity in industrial applications. Given the rapid dynamics of water activities and material responses within cells, in situ diagnostic techniques for water management in PEMFCs are essential for optimizing cell performance and extending the lifespan of fuel cell stack and system.Water, electrochemically produced on the cathode side, can cause potential flooding in key components including the catalyst layer (CL) and gas diffusion layers (GDLs), impeding air/oxygen supply to the cathode side. To characterize the performance loss induced by water flooding, Electrochemical Impedance Spectroscopy (EIS) is commonly employed as a fuel cell diagnostic tool. EIS records the contributions of different polarization processes to the global impedance with individual time constants during operation. However, the interpretation of complex EIS spectra can be very challenging, as polarization processes may overlap in frequency and be difficult to identify. To address this issue, Distribution of Relaxation Times (DRT) analysis is implemented as a powerful tool that allows for a clear separation and quantification of the polarization processes showing as peaks in a frequency domain [1]. Thus, we utilize EIS-based DRT analysis as an in-situ diagnostic tool to detect cathode flooding during cell operation. To validate this approach, we have conducted tests on a 300 cm2 low temperature PEMFC, varying one operation parameter at a time and evaluating its effects on cathode flooding by studying the frequency and height evolution of DRT peaks.Nevertheless, water flooding is not confined to the cathode side, as water can also permeate through the proton exchange membrane (PEM) and reach the anode side, resulting in potential fuel starvation on the cathode's counterpart and subsequent degradation of carbon-based materials. To address the sensitivity limitation of the EIS-based DRT method in detecting anode flooding, we employ an in-house developed pressure drop indicator (PDI) tool, as a non-invasive and real-time approach for diagnosing water flooding in the anode. The PDI tool assesses the pressure drop across anode channels, which is a function of the liquid water contents in bipolar plates considering the pressure reduction mainly caused by the frictional drag [2]. The effectiveness of the PDI tool is validated through cell testing at different water flooding levels by varying relative humidity and pressure conditions. This technique offers timely and sensitive detection of anode water flooding in PEMFCs, which is crucial for alarming irreversible material degradation in the electrode and facilitating appropriate follow-up actions.To conclude, we have developed and employed in situ PDI and EIS-based DRT methods within our water management framework for diagnosing water flooding in both the anode and cathode of PEMFCs in industrial applications. The combination of these techniques offers real-time and accurate assessments on water management conditions, which is crucial for optimizing overall performance and longevity of PEMFC stacks and systems.[1] Heinzmann, M., Weber, A., Ivers-Tiffée, E. (2018). Advanced impedance study of polymer electrolyte membrane single cells by means of distribution of relaxation times. Journal of Power Sources, 402, 24-33.[2] Barbir, F., Gorgun, H., & Wang, X. (2005). Relationship between pressure drop and cell resistance as a diagnostic tool for PEM fuel cells. Journal of Power Sources, 141(1), 96-101. Figure 1

Superhydrophobic Stainless Steel Bipolar Plates with Fractal Structure for Fuel Cells by Nanosecond Laser Ablation

Bipolar plate (BP) is one of the crucial components in proton exchange membrane fuel cells (PEMFCs). In extreme cold weather, massive vapor condensation happens right at vehicle start‐ups, which likely causes “water flooding” and thus shortens the lifespan of PEMFCs. Herein, a superhydrophobic stainless steel bipolar plate (SH‐SS BP) that is fabricated by nanosecond laser ablation is reported. Through a repeated low‐energy processing strategy, fractal surface microstructure is fabricated, which has not been reported for SS BP. By grafting stearic acid (SA) monolayer, a robust SH‐SS BP is obtained with a contact angle of 151.74°. The fractal microstructure greatly enhances the contact area between SH‐SS BP and membrane electrode assembly (MEA), which improves interfacial contact resistance (ICR: 9.816 mΩ cm2 at 1.5 MPa). The SH‐SS BP shows significantly enhanced anticorrosion performance (= A cm−2) by effectively reducing penetration of corrosive. The ability of improving water management in PEMFC under extreme cold condition is further demonstrated in a simulated PEMFC. This study opens new opportunity to reinforce metallic BPs by a simple, low‐cost, and robust route, which is valuable in improving comprehensive weather fastness of PEMFC.

Water droplet detachment characteristics on surfaces of gas diffusion layers in PEMFCs

Water management is one of the key issues affecting the performance and stability of proton exchange membrane fuel cells (PEMFCs). Water detachment on the gas diffusion layer (GDL) surface is critically important to water management in PEMFCs. In this study, water droplet detachment characteristics under various GDL surface contact angles and channel heights are investigated, by using a customized transparent model cell for direct ex-situ water visualization. The droplet height, chord, height/chord ratio, and contact angle hysteresis at the instant of droplet detachment are quantitatively analyzed. The droplet detachment is easier for higher gas Reynolds number (Reg). The height and chord of the droplet both decrease with Reg for both GDLs with and without PTFE but their decrement rates become smaller in higher Reg regions for all the channel heights investigated. Compared with droplets on the untreated GDL, the droplet height/chord ratio on the PTFE-treated GDL with larger static contact angle is increased by 36.7%, 64.1% and 76.0% and the contact angle hysteresis is reduced by 17.1%, 16.3% and 12.6% for the channel height H of 1 mm, 2 mm and 3 mm, respectively, which indicates that the PTFE-treated GDL improves water detachment. It shows that the water detachment is improved by reducing the channel height due to the smaller contact angle hysteresis at the instant of droplet detachment.

Effect of Pore Shape and Spacing on Water Droplet Dynamics in Flow Channels of Proton Exchange Membrane Fuel Cells

Effective water management increases the performance of proton exchange membrane fuel cells (PEMFCs). The liquid droplet movement mechanism in the cathode channel, the gas-liquid two-phase flow pattern, and the resulting pressure drop are important to water management in PEMFCs. This work employed computational fluid dynamics (CFD) with a volume of fluid (VOF) to simulate the effects of two operating parameters on the liquid water flow in the cathode flow channel: Gas diffusion layer (GDL) pore shape for water emergence, and distance between GDL pores. From seven pore shapes considered in this work, the longer the windward side of the micropore is, the larger the droplet can grow, and the duration of droplet growth movement will be longer. In the cases of two micropores for water introduction, a critical pore distance is noted for whether two droplets coalesce. When the micropore distance was shorter than this critical value, different droplets coalesce after the droplets grew to a certain extent. These results indicate that the pore shape and the distance between pores should be accounted for in future simulations of PEMFC droplet dynamics and that these parameters need to be optimized when designing novel GDL structures.

Operation of PEMFC Anodes in Dead-Ended Vs. Flow-through Modes

Low system complexity and high hydrogen utilization are important attributes for effective proton exchange membrane fuel cells (PEMFCs). Operating a PEMFC with a dead-ended anode (DEA) mode configuration is a simple and effective way to solve these two challenges1, 2. In comparison with the hydrogen flow-through and recirculation mode, in DEA mode the hydrogen supplied to the anode compartment is controlled by pressure regulation instead of a mass flow controller, where a pressure regulator is installed at the anode inlet and a normally closed solenoid valve blocks the outlet. Over time, accumulated water and nitrogen diffused from the cathode are removed by forced gas convection through intermittent opening of the solenoid valve.The anode and cathode gas diffusion media (GDM) play a role in PEMFC water management and have a significant impact on PEMFC performance. We compare an asymmetric GDM pairing with Freudenberg GDM (H24C3 at anode, H23C2 at cathode) to a symmetric GDM pairing frequently used in the open literature containing SGL 29BC at both the anode and cathode, to highlight the impact of the GDM water management on fuel cell operation in flow-through mode and DEA mode. We have previously shown in open-cathode fuel cells that an asymmetric GDM pairing featuring higher porosity in the anode GDM than the cathode significantly improves hydration and power production3, 4.The results at 25% relative humidity (RH) are shown in Figure 1. Consistent with our prior results5, in regular flow-through mode, Figure 1A shows the PEMFC with an asymmetric Freudenberg GDM pairing has significantly higher current densities vs. the PEMFC with symmetric SGL 29BC GDM at an operating cell voltage ≤ 0.60 V. The advantage of using asymmetric GDM observed in flow-through mode is maintained when the PEMFCs are operated in DEA mode (i.e. open symbols). There is only a marginal decrease in cell voltages during operation in DEA mode compared to flow-through mode probably due to the use of dry hydrogen on the anode side during testing in DEA mode.Figure 1B shows that the cell voltage decay is significantly different for a PEMFC containing the symmetric SGL 29BC GDM compared one with asymmetric Freudenberg GDM when tested in DEA mode configuration. The time between purge events is much greater for the asymmetric Freudenberg GDM pairing. The anode is purged with 99.999% H2 when the cell voltage drops by 100 mV. The PEMFC tested with the asymmetric Freudenberg GDM pairing dwells longer at steady-state prior to voltage decay, and its periods of voltage decay are more gradual. The PEMFC containing the symmetric SGL 29BC pairing has a mean purge interval of about 2min 33s and a total of fourteen purge events are necessary over 80 minutes operation, compared to a mean purge interval of about 18min 29s and a total of four purge events are necessary for the PEMFC containing the asymmetric Freudenberg pairing.A longer purge duration is desirable in a fuel cell system because it increases H2 utilization and reduces valve wear. The results show that the asymmetric GDM pairing improves water management in PEMFCs and improves both power density and system level performance.Acknowledgements:The authors are grateful to the Office of Naval Research for support of this research. References I.-S. Han, J. Jeong and H. K. Shin, Int. J. Hydrogen Energy, 38, 11996 (2013).K. Nikiforow, H. Karimäki, T. M. Keränen and J. Ihonen, J. Power Sources, 238, 336 (2013).R. W. Atkinson, M. W. Hazard, J. A. Rodgers, R. O. Stroman and B. D. Gould, J. Electrochem. Soc., 166, F926 (2019).R. W. Atkinson, J. A. Rodgers, M. W. Hazard, R. O. Stroman and B. D. Gould, J. Electrochem. Soc., 165, F1002 (2018).R. W. Atkinson, Y. Garsany, B. D. Gould, K. E. Swider-Lyons and I. V. Zenyuk, ACS Appl. Energy Mater., 1, 191 (2018) Figure 1. (A) Comparison of I-V polarization curves measured for a PEMFC containing a typical symmetric SGL 29BC GDM pairing on the anode and cathode side and a PEMFC containing an asymmetric Freudenberg GDM pairing . Polarization curves are measured in DEA mode and flow-through mode at 25 % RHinlet cathode. In all cases the cell temperature is 65 °C, in H2|air, with air supplied to the cathode a stoichiometric ratio of 2 at atmospheric pressure. During DEA mode, dry H2 is supplied to the anode at 2 psi. (B) Time evolution of the cell voltage obtained at a current density of 1200 mA cm-2 for an H2 inlet pressure of 2 psi and 25 % RHinlet cathode. Figure 1

Janus few layered graphene with asymmetric wettability as anti-flooding cathode supports in proton exchange membrane fuel cells

Water balance in cathode catalyst layer (CCL) is crucial for proton exchange membrane fuel cells (PEMFCs). Herein, we report a novel strategy to develop a Janus few layered graphene particles (FLGP) with asymmetric wettability by varying the carbon precursors in the chemical vapor deposition (CVD) process. Using the Janus FLGP supported Pt with asymmetric wettability as the cathode of a PEMFC, a peak power density of 632 mW cm−2 was achieved, which was about two-folds of the hydrophobic FLGP and three-folds of hydrophilic FLGP based cathode, respectively. The enhanced performance could be ascribed to the well-constructed three-phase boundary in an anti-flooding cathode, leading to enlarged electrochemical active surface area and facilitated mass transfer. This work may provide new clues for improving water management in PEMFCs.

Effect of Ni content on the electrical and corrosion properties of CrNiN coating in simulated proton exchange membrane fuel cell

In this paper, CrNiN coatings with various Ni content are deposited on 304ss bipolar plates by closed field unbalanced magnetron sputter ion plating from CrNi alloy targets. Simulative working environment of proton exchange membrane fuel cell (PEMFC) is applied to test the electrical and corrosion properties of uncoated 304ss and CrNiN-coated samples. The influence of Ni content on microstructure, phase structure, contact angle with water and electrochemical performance is investigated. Results show that all the coated samples significantly enhanced the corrosion resistance of the 304ss, and the CrN-coated 304ss sample without Ni has the best corrosion resistance of 153.8 and −141.9 mV in the simulated anodic and cathodic environments, respectively. Electrochemical impedance spectroscopy (EIS) studies reveal that the resistance of CrN coating is higher than that of other coated samples and 304ss in the cathodic environment. Furthermore, Interfacial contact resistance (ICR) studies revealed that CrN coating has a superior ICR of 11 mΩ cm2 at a compaction force of 160 N cm−2. In addition, the contact angle of the CrNiN coatings with water is approximately 114°, which is beneficial for water management in PEMFC. Analysis result indicates that the enhanced performance of the coated 304ss bipolar plates is related to the high film density determined by closed field unbalanced magnetron sputter ion plating, and the synergistic function of the CrNiN layered structure.

Effects of metal buffer layer for amorphous carbon film of 304 stainless steel bipolar plate

Amorphous carbon (a-C) films comprising different buffer layers were prepared by direct current magnetron sputtering on a 304 stainless steel (SS) substrate surface. Microstructures and performances of a-C films with buffer layers comprising Ti, Cr and W were investigated and evaluated as bipolar plate for proton exchange membrane fuel cell (PEMFC). All prepared a-C films are graphite-like carbon, and predeposition of the buffer layer promote the graphitization of the a-C film. The a-C film comprising a Cr buffer layer has highest percentage of sp2 hybridization contents, which directly improved the current conductivity with a resistivity of 2.73×10−6Ωm and an interfacial contact resistance of 16.65mΩcm2. Furthermore, dynamic polarization under a simulated PEMFC working environment shows that the corrosion resistance greatly improved. The corrosion current density of an a-C film with a Cr buffer layer stabilizes at a negative value after potentiostatic tests for 4h. The hydrophobic property is improved as well, which is beneficial to water management in PEMFC and for anticorrosion of the bipolar plate itself. Thus, the metal buffer layers make the a-C film more suitable for surface modification of a 304 SS bipolar plate, especially the a-C film with a Cr buffer layer.

Effective removal and transport of water in a PEM fuel cell flow channel having a hydrophilic plate

Effective removal and transport of water in the flow channel of a proton exchange membrane (PEM) fuel cell (PEMFC) is significantly important to the critical water management in PEMFCs. In this study, the process of water removal and transport is investigated numerically by using the volume-of-fluid method for a flow channel having a hydrophilic plate in the middle of the channel. The results show that the liquid water droplet on the membrane-electrode assembly (MEA) surface can be removed effectively, and the removal process is facilitated significantly by the hydrophilic plate which should have a surface contact angle larger than the bottom channel surface but less than the MEA surface. Once the liquid water contacts the plate, it is detached from the MEA surface, and transported to the channel surface along the plate surface; whereas without the plate the water droplet is transported along the MEA surface under the same flow condition. The pressure drop associated with the flow in the channel can be reduced substantially by the presence of the plate due to a characteristic change in the water removal and transport process, when compared to the pressure drop in a conventional flow channel or a channel with a needle shown in literature. The wettability, the length and the height of the plate all can have an impact on the water transport and dynamics as well as the associated pressure drop in the flow channel. A parametric study is carried out to determine the optimal values for the surface contact angle, the length and height of the plate.

Effect of wettability on water removal from the gas diffusion layer surface in a novel proton exchange membrane fuel cell flow channel

Effective water removal from the proton exchange membrane fuel cell (PEMFC) surface exposed to the flow channel is critical to the operation and water management in PEMFCs. In this study, the water removal process is investigated numerically for a novel flow channel formed by inserting a hydrophilic needle in the conventional PEMFC flow channel, and the effect of the surface wettability of the membrane electrode assembly (MEA) and the inserted needle on the water removal process is studied. The results show that the liquid water can be more effectively removed from the MEA surface for larger MEA surface contact angles and smaller needle surface contact angles. The pressure drop for the flow in the channel is also examined and it is seen to be indicative of the liquid water flow and transport in the flow channel, suggesting that pressure drop is a useful parameter for the investigation of water transport and dynamics in the flow channel.

Gas diffusion layer with PTFE gradients for effective water management in PEM fuel cells

Experimental procedures to establish in-plane and through plane polytetrafluroethylene (PTFE) gradient in Gas Diffusion Layer (GDL) used in proton exchange membrane fuel cells (PEMFC) are presented in this work. In-plane PTFE gradients were obtained by exploiting capillary wicking of PTFE suspension. The through plane PTFE gradients were obtained by changing the drying temperature employed in PTFE loading procedure. The samples were characterized for fluorine distribution using energy dispersive spectrum (EDS) to gauge the PTFE distribution and change in hydrophobicity after PTFE treatment. The results indicate that manipulation of PTFE gradients are expected to result in effective water management in PEMFC.

Model predictive control of water management in PEMFC

Water management is critical for Proton Exchange Membrane Fuel Cells (PEMFC). An appropriate humidity condition not only can improve the performances and efficiency of the fuel cell, but can also prevent irreversible degradation of internal composition such as the catalyst or the membrane. In this paper we built the model of water management systems which consist of stack voltage model, water balance equation in anode and cathode, and water transport process in membrane. Based on this model, model predictive control mechanism was proposed by utilizing Recurrent Neural Network (RNN) optimization. The models and model predictive controller have been implemented in the MATLAB and SIMULINK environment. Simulation results showed that this approach can avoid fluctuation of water concentration in cathode and can extend the lifetime of PEM fuel cell stack.

Effects of Temperature Difference on Water Management in PEMFCs

A quantitative investigation has been carried out to examine the effect of through-plane temperature gradients on water transport across the membrane-electrode assembly (MEA) of a Proton Exchange Membrane (PEM) fuel cell. The presence of a temperature gradient across the cell was found to cause a significant amount of water to transport through the MEA in the direction towards the colder side; the water transport rate increased with temperature and temperature gradient. This study reveals the importance of thermo-osmosis in PEM fuel cells (PEMFCs) and the need to consider the through-plane temperature profile in water management design and operation in PEMFCs.