Cathode Channel Research Articles

Numerical Investigation on Two-Phase Flow Pressure Drop in Cathode Channels of Proton Exchange Membrane Fuel Cells

As liquid water is produced by electrochemical reactions in a proton exchange membrane (PEM) fuel cell, liquid–gas two-phase flow forms within the porous structure of the electrodes and gas channels (GCs), resulting in complex gas pressure drop within GCs. This study investigates the two-phase flow pressure drop in a GC connected with a fibrous gas diffusion layer (GDL) using volume of fluid simulations. Fibrous GDLs are stochastically reconstructed to give a rather realistic liquid water breakthrough, and the effect of GDL straight and curved carbon fibers is studied. The results show that droplet breakthrough position and breakthrough size are dependent on the carbon fiber shape, resulting in further distinct pressure drop in GCs. It is also found that the two-phase flow pressure drop has no close correlation with the water content within the GC but a strong relationship with the liquid flow types. Specifically, the cross-section liquid area variation along the gas flow direction is found to be proportional to the pressure drop variation. This study aims to provide the information required for an accurate two-phase flow pressure drop prediction model.

A comprehensive modeling, analysis, and optimization of two phase, non–isobaric, and non–isothermal PEM fuel cell

This study models a non-isobaric, non-isothermal two-phase flow in a Polymer Electrolyte Membrane Fuel Cell (PEM-FC), focusing on conservation equations for mass, energy, and momentum across its components. Verification involves comparing PEM-FC performance and temperature distribution with experimental and literature data, showing consistent agreements. Results indicate that increasing cathode channel pressure enhances membrane moisture and reduces power loss. Higher oxygen partial pressure improves PEM-FC performance, whereas increased anode channel pressure heightens ohmic losses and lowers output voltage. Temperature distribution reveals highest temperatures near the cathode catalyst layer due to electrochemical reactions. Adjusting pressures in cathode and anode channels affects these temperatures accordingly. PEM-FC power density is optimized using various algorithms, with simulated annealing proving most effective. Optimal values for gas diffusion layer thickness, electrode porosity, and inlet humidity are determined. Under constant current density, power density increases by 6 % compared to baseline conditions, demonstrating effective parameter optimization for enhancing PEM-FC performance.

Dynamic modeling of polymer electrolyte membrane fuel cells under real-world automotive driving cycle with experimental validation on segmented single cell

A 1+1D transient non-isothermal and multiphase polymer electrolyte membrane fuel cell model is developed. The model is validated on experimental data gathered on a segmented single cell and representative of a real-world automotive driving cycle, derived from the stack protocol defined in the ID-FAST H2020 project. During Low-Power operation, cell voltage response is mainly controlled by platinum oxide and water dynamics: the low hydration significantly affects cathode inlet performance. Throughout High-Power operation, instead, voltage transients are ascribable to local mass-transport related phenomena: in particular, liquid water accumulation along the channel strongly decreases the efficiency of cathode outlet region. Finally, the effect of relative humidity at cathode channel inlet is investigated: an increase in the humidification of the air inlet stream from 30% to 50% leads to a better proton conductivity and, therefore, to a significant enhancement of the performance of cathode inlet regions, which also means a slight improvement in the average stack efficiency from 62.2% to 62.8%. Lowering RH of the air-inlet stream from 30% to 15%, a worsening of proton conductivity is observed, which exacerbates performance heterogeneities and leads to a reduction of the average stack efficiency from 62.2% to 61.5%, consistently with experimental results.

Improving polymer electrolyte membrane fuel cell performance and preventing flooding by exciting gas flow

Effective water management is necessary to prevent the performance degradation of polymer electrolyte membrane fuel cells (PEMFCs). In this study, acoustic pressure waves (AWs) are superimposed on an oxygen gas flow passing through a cathode to evaluate its potential to mitigate the flooding issue in flow channels. The goal is to expedite droplet removal by exciting droplets at frequencies close to their natural frequency. In-situ experiments are conducted to investigate the influence of AWs on two-phase flows in the cathode channel and the corresponding PEMFC performance. When AWs are applied, the frequency of water discharge from the cathode channel increases, and reduces the internal accumulated water, resulting in the pressure drop decreases. The internal flooding is also decreased, resulting in the reduction of the high frequency resistance attributed to decreased contact resistance. The external excitation improves the PEMFC performance owing to the effective and frequent water discharge induced by the increase in the local inertial force related to the droplet oscillation. The water management method propose in this study is considered to be an efficient method not only for PEMFC systems but also for other systems requiring water management.

Extended Kalman filter for quantifying hydrogen leaks in PEM fuel cells by estimating oxygen concentration

Hydrogen transfer leaks are one of the most important life-limiting faults in polymer electrolyte membrane fuel cells (PEMFCs). Hydrogen transfer leaks result in a reduction in the amount of oxygen available in the cathode (air) channel, with large leaks resulting in oxygen starvation and hydrogen emission. This paper aims to develop an adaptive extended Kalman filter (EKF) to estimate the unknown oxygen concentration, which is then used to infer hydrogen leaks. To this end, the paper first develops the lumped model of the fuel cell from a pseudo-2D model of a fuel cell. Next, a (non-adaptive) EKF is developed to estimate the fuel cell states under both normal and oxygen-starved conditions. The adaptive EKF is then implemented by adding the unknown hydrogen leak to the list of estimated states. Finally, the paper demonstrates the efficacy of the proposed adaptive EKF by using it to accurately estimate unknown hydrogen leaks in a high-fidelity virtual fuel cell under excessively noisy conditions.

Performance of proton exchange membrane fuel cell system by considering the effects of the gas diffusion layer thickness, catalyst layer thickness, and operating temperature of the cell

BackgroundIn this research, the effect of anode and cathode channel cross-sectional shape on the performance of PEM fuel cell was investigated and the appropriate length and dimensions of the channel were determined. Finally, for the determined geometric conditions, the cell performance at different voltages was investigated. MethodsThe purpose of this study was to investigate the structural characteristics of the fuel cell on its performance. The results show that the pressure and temperature in the catalyst layer (CL) of the cathode side are greater than the anode, and the temperature in the central regions of the catalyst layer is higher than the lateral regions. Also, the channel with a length of 100 mm is optimal in terms of producing the maximum current density and the amount of pressure drop is much lower than the channel with a length of 150 mm, which reduces the power consumption of the cell. Significant findingsIn general, a higher electric current is produced by increasing the thickness of the gas diffusion layer (GDL) and the catalyst layer. At a voltage of 0.8 V, with increasing thickness from 0.25 mm to 0.5 mm, the current density increases above 6 %. The percentage increase in current density at 60 °C–80 °C for 0.85 V and 0.75 V voltages is 42.1 % and 9.28 %, respectively.

Electrochemical impedance spectroscopy analysis and thermal mapping of different cross-sectional cathode channels in open-cathode polymer electrolyte membrane fuel cell stack

The Electrochemical impedance spectroscopy (EIS) of three novel cathode channels designs square, boot, and triangular for open cathode polymer electrolyte cathode fuel cell stacks are analyzed. Fundamental mechanisms such as oxygen reduction reaction, proton conductivity, bulk resistance of stack, capacitance and structure features of the porous carbon electrode etc. are investigated with the help of Nyquist/Bode plots and Randles circuit. Operational parameters including airflow rate, current, H2 gas condition (humidified and dry), and stack temperature are studied focused on understanding the trend of high and low frequency resistance. The minimum resistance and temperature mapping for cross-section designs at different operating conditions is utilized for parametric optimization. Overall, it is recommended to operate the stacks at minimum resistance obtained just before the peak power density and its corresponding temperature ∼40 °C. Finally, a data-driven hybrid model integrating EIS and artificial intelligence is presented with root mean square error of ∼0.98.

Operando X-ray radiography of liquid water distribution in 100 mm polymer electrolyte fuel cell channels

Preventing the accumulation of water in the gas diffusion layer (GDL) proves effective in enhancing the performance of polymer electrolyte fuel cells (PEFCs). To understand the water transport phenomena in GDLs and channels of PEFCs, cell hardware for operando synchrotron X-ray radiography was developed with a 100 mm channel length, facilitating the separate quantification of liquid water in the cathode and anode GDLs. The presence of liquid water in the cathode and anode GDLs was confirmed during operation with a supply of dry gas in a counter-flow configuration. Furthermore, the amount of liquid water in the cathode and anode GDLs increased toward the cathode inlet, while the amount of water in the cathode and anode channel regions increased toward each outlet. The liquid water distribution in the GDLs along the channel direction can be attributed to water transport from cathode to anode (back-diffusion), decreasing toward the anode outlet. Therefore, conducting radiography experiments aligned parallel to the GDLs and perpendicular to the channel could provide valuable insights for a more comprehensive understanding of water transport in cells.

Performance improvement and numerical study on cathode channel for air-cooled open-cathode proton exchange membrane fuel cells

Bipolar plates perform multiple functions for the proton exchange membrane fuel cell (PEMFC). This study focuses on optimizing cathode channels to leverage a local loss mechanism to enhance gas transfer and diffusion efficiency. Through the investigation of 3D simulations, this research delves into the effects of curvature of cathode channels on both reactant transfer and diffusion. The results illustrated that compared with straight channels, the cell performance improves as the bending angle ( θ ) of 2.5° and 5° at different current densities. Specifically, at a bending angle of 5°, a 5.5% higher current density than the channel of 0° is obtained. This suggests that moderate curvature can effectively promote efficient mass transport and diffusion, ultimately contributing to enhanced cell performance. Furthermore, the analysis of local mass transfer and diffusion around the bends of channels underscores the importance of the balance between these factors. While bending angles within the range of 2.5° to 5° offer optimal performance gains, excessive curvature, such as a 10° angle, may lead to diminished cell performance. By identifying the optimal bending angle range and elucidating the underlying mechanisms driving performance improvements, this study provides insights into the design and optimization of cathode flow fields in AO-PEMFC.

Communication—Oscillating Oxygen Concentration Transport through PEM Fuel Cell Gas Diffusion Layer: Variation of the Phase Angle

Recently, it was shown that performance of the cathode catalyst layer in PEM fuel cell dramatically improves if the oxygen concentration (OC) at the catalyst/ gas diffusion layer (GDL) interface oscillates in–phase with the overpotential. However, OC oscillations could only be organized in the cathode channel. Does transport through the GDL affect the phase angle of OC oscillations? Below, it is shown that at low frequencies below 1 Hz, the GDL does not change this phase angle. At high frequencies, the phase angle after transport through the GDL is −3π/4 regardless of the GDL parameters.

Understanding water dynamics in operating fuel cells by operando neutron tomography: investigation of different flow field designs

Water management plays a key role in ensuring optimum polymer electrolyte fuel cell (PEFC) performance, and flow field design can influence the ability of a cell to balance maintaining hydration, whilst avoiding flooding and cell failure. This work deepens the understanding of water evolution in different PEFC flow channel designs, namely single serpentine (SS), double serpentine (DS) and parallel, using our novel high-speed neutron computed tomography method. We developed our previously-reported method by introducing continuous cell rotation, enabling 18 s per tomogram during 1 h holds at 300, 400 and 500 mA cm−2. The volume of water evolved in the cathode, membrane electrode assembly and anode was quantified, and key mechanisms for water droplet formation in the different flow channel designs were elucidated. The parallel flow field design had the poorest water management, with 47% of the cathode flow channel becoming filled after 1 h at 400 mA cm−2. This significant flooding blocked reactant sites and contributed to unstable cell performance and, ultimately, cell failure at higher current densities. The SS cell displayed the best water management, with only 11% of the cathode channel filled with water after 1 h at 500 mA cm−2, compared with 28% of the DS cathode channel. 3D visualisation and analysis of droplet behaviour elucidated how water ‘slugs’ in the SS were removed in the gas stream, whereas three of the four parallel cathode flow channels became entirely filled with water plugs, blocking gas flow and exacerbating cell flooding. The new insights gained here are expected to extend to novel flow field designs and image-based models, with the use of operando neutron CT demonstrated as a powerful technique for both visualising and quantifying water management in operating PEFCs, as well as deepening the knowledge of droplet behaviour in different flow field types.

Performance evaluation of cathode channels with different cross-sections for open-cathode polymer electrolyte membrane fuel cell stack

This study proposes six different cross-sectional cathode flow field designs such as square, trapezoid, dome, boot, pentagon, and triangular constructing four cells open cathode polymer electrolyte membrane fuel cell stack with various parameters optimization and suitability for system level development. Parameters, including pressure drop, oxygen concentration, airflow rate, blower power, stack temperature, cooling rates, net power output, and stability are investigated with focus on understanding the trend, interconnected dependencies among the parameters, which collectively influence the overall performance of the cross-section designs. Overall, studies show that, boot cross-section design possessing the optimum pressure drop of 23.9 Pa, shows better performance compared to other cross-section designs due to better oxygen gas distribution, water retention/removal, heat removal/retention, and net power output. Conversely, for galvanostatic analysis done at a higher current value of 35 A, dome and square cross-section designs show highest and stable potential, along with balanced stack temperature.

Experimental investigation of time-dependent electrical load effects through multipoints in-situ measurement of temperature and relative humidity of PEMFC bipolar plate under transient operation

In this study, multiple micro-relative humidity and temperature (RH/T) sensors were installed in the anode and cathode channels of a proton exchange membrane fuel cell (PEMFC) bipolar plate to simultaneously observe and analyze the variation in RH/T behaviors during transient operation. In order to simulate the acceleration and deceleration process, the electrical load was ramped from 10 to 40 A and then back to 10 A, with time intervals of 0, 2, and 5 s. The data corresponding to different acceleration/deceleration time intervals were compared and analyzed to assess the time-dependent effects of load changes. The analyzed data provide visual information, including the transient voltage response, transient behavior of temperature and water distribution, and evolution of RH/T within PEMFC. The results indicate that the acceleration and deceleration interval times significantly influence the temperature and water distribution within PEMFC during transient operation. Shorter acceleration times lead to more rapid changes in temperature and humidity within the PEMFC active area, resulting in higher transient temperature and water concentration. This finding explains why the output voltage decreases more when the load changes with a short time interval. This research enhances our understanding of transient temperature and water behavior, providing a foundation for further research and development of effective operational strategies and vehicle PEMFC designs.

Mathematical Modelling and Simulations of Active Direct Methanol Fuel Cell

A one dimensional isothermal model is proposed by modelling the kinetics of methanol transport at anode flow channel (AFC), membrane and cathode catalyst layer of direct methanol fuel cell (DMFC). Analytical model is proposed to predict methanol cross-over rate through the electrolyte membrane and cell performance. The model presented in this paper considered methanol diffusion and electrochemical oxidation at the anode and cathode channels. The analytical solution of the proposed model was simulated in a MATLAB environment to obtain the polarization curve and leakage current. The effect of methanol concentration on cell voltage and leakage current is studied. The methanol cross-over has the significant impact on cell performance. The presented model predicts higher leakage current with the increase of methanol feed concentration. The cell performance was predicted at 70°C and various methanol feed concentration. The proposed model was validated with the experimental polarization curve of active DMFC.

Exploring the sustainability of serpentine flow-field fuel cell, straight channel PEM fuel cells hight temperature through numerical analysis

This study focuses on investigating the performance dynamics of high-temperature Proton Exchange Membrane fuel cells, with an emphasis on critical design parameters. Utilizing a comprehensive mathematical model, the research explores concentration profiles, current density profiles, and polarization curves within a three-dimensional, isothermal, steady-state PEM fuel cell.The model incorporates the intricate processes of gas transport in anode and cathode channels, diffusion in catalyst layers, and the transport of water and hydronium ions in both the polymer electrolyte and catalyst layers. Additionally, it accounts for electrical current transport in the solid phase. Simulations conducted with Comsol Multiphysics 6.1 demonstrate a robust alignment between model results and experimental polarization data obtained at 180 °C. Optimal conditions for performance are outlined, specifying an inlet hydrogen gas velocity of 0.12 m/s and an inlet air velocity of 1.2 m/s, with consideration for a proton conductivity of 9.825 S/m.In a parallel investigation, numerical analysis assesses the sustainability of Serpentine Flow-Field PEM fuel cells, using critical parameters. The model applied in this research considers gas, water, and electrical current transport across various layers of the fuel cell, with a crucial focus on optimizing the membrane electrode assembly's design. The finite element method and ANSYS Fluent are employed for model solution.This study contributes significantly to the understanding of HT-PEM fuel cell dynamics, providing insights into the interdependencies of design parameters and their impact on system performance. The study emphasizes the pivotal roles of air and hydrogen inlet velocities in shaping fuel cell performance, elucidating the intricate dynamics dictating reactant distributions within diverse cell components.

Investigation of non-uniform temperature distribution in air-cooled proton exchange membrane fuel cells with multizone temperature measurement

ABSTRACT Open-cathode air-cooled proton exchange membrane fuel cell stack relies on air fans both for fuel supply and stack cooling. Inappropriate stack thermal management and non-uniform temperature distribution can lead to compromised stack performance, reduced lifespan, and even thermal runaway. Thus, temperature distribution measurement, investigation and analysis are essential for air-cooled PEMFC’s optimized operation and performance. This study uses a multi-zone temperature measurement approach to investigate the impact of air supply method, airflow, and output current on stack temperature distributions. The experimental results reveal that the highest stack temperature occurs at the cathode channel outlet, while the lowest temperature is near the hydrogen inlet. At a 75A load, the maximum temperature difference between the inlet and outlet is 17°C. Increasing fan speed from 4500 to 8800 r/min reduces temperature non-uniformity in cell 10, the most uneven among the 19 cells, by 11.2%. Comparing blowing and suction air supply modes, blowing enhances stack output performance by 2.1%, with smaller temperature differences. Specifically, cell 10 experiences a 7.5°C lower difference at 4500 r/min and a 3.6°C lower difference at 8800 r/min airflow. Under blowing air supply, temperature non-uniformity decreases by 36.95% at 4500 r/min and 29.2% at 8800 r/min.

Investigation of the Distribution of the Mass Transport and Reaction Rates in a Fuel Cell By the Integrated Fuel Cell System Simulator Including the Dynamics of Air, H2, and Cooling Systems

:A model to estimate the distribution of the current density, pressure, flowrate, temperature, and gas composition in the through-plane and along-channel (1+1D) directions of a fuel cell (FC) was developed. The developed model was integrated to the FC system model of the 2nd-Generation MIRAI, state-of-the-art fuel cell electric vehicle (FCEV), and the controllers of the system components. The impacts of the dynamic operating conditions of the FC system components on the 1+1D distribution in a fuel cell were investigated with the developed model. Modeling method: The modeling method of the distribution in a fuel cell is depicted in Fig. 1. In this study, the distribution in the through-plane and along-channel (1+1D) directions is considered and the distribution in the across-channel direction (2D) is assumed to be uniform to ensure acceptable computational time. The anode and cathode channels are divided into 20 nodes in the along-the-channel direction, respectively. The mass, momentum, and energy balance between the adjacent nodes of the channels were expressed by the similar methods as the model developed in the authors’ past research [1]. The models of the mass transport and reactions in the through-plane direction of MEA developed in the authors’ past research [2] were connected to each node of the cathode and anode channels. The in-house numerical solvers which calculate the distribution of current density, flowrate, total pressure, partial pressure of each gas component, and temperature in 1+1D direction were implemented. This model was integrated to the FC system models of the 2nd-Generation MIRAI [1], state-of-the-art fuel cell electric vehicle (FCEV) [3], and controllers for H2, air, and cooling systems developed in the authors’ past research [4] as shown in Fig. 2 to investigate the interactions among the dynamics behaviors of the system components, controller specification, and distribution in a fuel cell. Results and discussion: The impacts of operating conditions of the fuel cell system components on the distribution in a fuel cell were investigated as shown in Table 1. In case 2 in Table 1, rotational speed of the hydrogen pump (HP) is increased and other variables changed accordingly. The dynamic target power shown in Fig. 3 was given to the system model as the input and simulation was done for 700 s. Figs. 4(a)–4(e) show the simulation results at 480 s. In case1, current density was lower due to the high cell resistance in the region of the nodes 1–12 as shown in Figs. 4(a) and 4(b). In this region, the PEM was intensively dried and the H2O activity in PEM was below 0.2 as shown in Fig. 4(c) due to the no-humidifier configuration in air system. The H2O flowrate in through-plane and along-channel direction at the anode channel became almost 0 as shown in Figs. 4(d) and 4(e), suggesting that H2O cannot be delivered on both the cathode and anode sides on this region. In case 2, where the gas flowrate of anode inlet was increased by accelerating hydrogen circulation pump, the current density was higher and the resistance was lower in the region of the nodes 4-12 as shown in Figs. 4(a) and 4(b). The H2O activity at PEM in this region excesses 0.2 following the increased H2O flowrate in along-channel direction at the anode channel as shown in Figs. 4(c)ｰ4(e). The mechanism of the interactions between the system operating condition and the distribution in a fuel cell was depicted in Fig. 5. The increase in HP rotational speed enlarged the humidity difference between anode and cathode, thus, the through-plane H2O transported from the cathode to the anode side around the cathode outlet region. It also enlarged the H2O transport in along-channel direction from the anode inlet to outlet by increasing the volumetric flowrate in the anode channel. Despite of the improvement of the distribution, HP power consumption increased from 125.9 W to 806.5 W following the acceleration of HP speed from 3009 rpm to 7200 rpm as shown in Table 1. It was demonstrated that the complicated relationships among the distribution of reaction and mass transport, the specifications of the system components, and controllers can be investigated with the proposed model. References : [1] S. Hasegawa, et al., ECS Trans., 109(15), 15–70 (2022).[2] S. Hasegawa, et al., ECS Trans., 104(8), 3–26 (2021).[3] T. Takahashi and Y. Kakeno, EVTEC 2021 Proceeding, No. B1.1 (2021).[4] S. Hasegawa, et al., Comput. Aided Chem. Eng, 49, 1123–1128 (2022). Figure 1

Water Transport and Salt Precipitation in Anion-Exchange Membrane Electrolyzers

The hydrophilic nature of hydrocarbon ionomers and membranes presents a major challenge in anion-exchange membrane (AEM) electrolysis, despite improved stability from reinforcements and modified polymer chemistry. Durability and performance are still highly influenced by the operation mode and water management within the membrane-electrode-assembly (MEA).Dry cathode operation in AEM water electrolysis, where only the anode is supplied with liquid electrolyte (KOH), offers increased hydrogen purity but poses challenges for non-fluorinated anion-exchange polymers that are sensitive to water content. In-situ neutron imaging with high resolution (~6 µm effective resolution) revealed that adjusting the anion-exchange capacity of the cathode binder ionomer can retain membrane humidification (Fig. 1)1.In the electrochemical reduction of CO2 using AEM, water management and salt precipitation are significant challenges. High-resolution neutron imaging of a zero-gap CO2 electrolyzer operating at 200 mA cm-² and 2.8 V showed salt precipitates penetrating the cathode gas diffusion layer, leading to blocked CO2 gas transport and a decay in Faraday efficiency. Salt accumulation was higher under the cathode channel of the flow field than the land2.Both studies demonstrate the substantial impact of water management and salt precipitation on the operation of AEM-based electrolyzers and how neutron imaging can assist in addressing these challenges. References (1) Koch, S.; Disch, J.; Kilian, S. K.; Han, Y.; Metzler, L.; Tengattini, A.; Helfen, L.; Schulz, M.; Breitwieser, M.; Vierrath, S. Water management in anion-exchange membrane water electrolyzers under dry cathode operation. RSC Adv 2022, 12, 20778–20784.(2) Disch, J.; Bohn, L.; Koch, S.; Schulz, M.; Han, Y.; Tengattini, A.; Helfen, L.; Breitwieser, M.; Vierrath, S.; High-resolution neutron imaging of salt precipitation and water transport in zero-gap CO2 electrolysis. Nat Commun 2022, 13, 6099. Figure 1

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.

Numerical investigation on the performance enhancement of PEMFC with gradient sinusoidal-wave fins in cathode channel

As the cathode channel structure plays significant effects on the performance of the proton exchange membrane fuel cell (PEMFC), in this work, a 3D multi-phase model of PEMFC is established and effects of cathode channel structure (conventional channel, normal sinusoidal-wave fins and gradient sinusoidal-wave fins) on the performance of PEMFC are numerically investigated. Results indicate that the PEMFC with gradient sinusoidal-wave fins in cathode channel can achieve higher power density and more uniform membrane current density. This is due to that the gas velocity in cathode channel with gradient sinusoidal-wave fins is significantly increased, leading to better oxygen transport and liquid water removal. Furthermore, effects of the geometrical parameters of gradient sinusoidal-wave fins on the electricity generation performance, membrane current density, and mass fraction of oxygen and liquid water of PEMFC are analyzed and discussed. It is found that the optimum waveform depth growth rate and wavelength of the gradient sinusoidal-wave fins is 0.035 and 2.5 mm, respectively. At 0.5 V, the maximum power density of the PEMFC with gradient sinusoidal-wave fins is 5.3% higher than that of the PEMFC with conventional channel.