Hydrophobic Gas Diffusion Layer Research Articles

Solar to hydrogen conversion by a 25 cm2-photoelectrochemical cell with upscaled components

An innovative tandem photoelectrochemical cell with a scaled-up active area from 0.25 to 25 cm2 based on low-cost and non-critical raw materials was employed to produce green hydrogen by water splitting. It uses a photoanode/membrane/photocathode tandem cell configuration in which a hematite-based photoanode is layered on a fluorine-doped tin oxide glass for the oxygen evolution reaction, CuO is deposited on a hydrophobic gas diffusion layer as the photocathode for the hydrogen evolution reaction and an anion exchange membrane is used as the electrolyte and gas separator. The solid membrane's low hydrogen and oxygen crossover guarantees the operational stability of the tandem photoelectrochemical cell and the efficient separation of water-splitting products. Significant efforts have been focused on scaling up the cell. It has allowed obtaining, for the first time, a 25 cm2 unit cell prototype. Appropriate design approaches have been considered to optimise water/gas management, current collection, gas-tightness and clamping. The adopted architecture allowed for the reduction of the bias-potential from −1.23 V, generally employed to investigate PEC cells, up to −0.6/-0.4 V 20 h-durability tests demonstrated good resistance to corrosion, showing a constant photocurrent. Efficiency at −0.6 V was about 0.2%. Selective hydrogen production was demonstrated by mass spectrometric analysis.

Patterned hydrophobic gas diffusion layers for enhanced water management in polymer electrolyte fuel cells

Flooding of the cathode due to water accumulation is one of the biggest limiting factors in the performance of polymer electrolyte fuel cells (PEFCs). This study therefore attempts to solve this issue by fabricating gas diffusion layers (GDLs) with differently patterned hydrophobic regions. The GDLs in three different patterns (triangular, diamond, and inverted-triangular) were prepared by brushing a Polytetrafluoroethylene (PTFE) solution onto commercial carbon papers through a mask and tested in PEFCs. The patterned GDLs results in superior performance in all cases compared to a uniformly PTFE-treated GDL. Notably, the oxygen transport resistance is significantly reduced, indicating that the water accumulation in the cathode is avoided. This is attributed to the patterned hydrophobicity gradient providing distinct pathways for water and oxygen. The GDL with triangular patterning displays the highest peak power density, due to the fact that the untreated less hydrophobic region is in direct contact with the cathode outlet in this case, facilitating the removal of excess liquid water. Overall, the study confirms that the GDLs with patterned hydrophobicity could be used to enhance the performance of commercial PEFC systems by facilitating water management, potentially leading to improved efficiency and durability.

Triphase photocatalytic water-gas-shift reaction for hydrogen production with enhanced interfacial diffusion at gas–liquid–solid interfaces

Supporting Rh/TiO2 on hydrophobic gas diffusion layers enhanced the photocatalytic WGS for H2 production. Triphase interfaces play a crucial role in interfacial CO mass transfer, especially at low CO concentrations.

Effect of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layers on PEFC Performance

In order to widen the market application of the polymer electrolyte fuel cell (PEFC), the output power of the PEFC system must be increased. One of the barriers is the cell voltage loss under high current density conditions. This is mainly caused by the deteriorated reactant mass transport, which is blocked by the water flooding at the catalyst layer (CL), microporous layer (MPL), and gas diffusion layer (GDL). Modifying the MPL coated on the GDL is an accessible way to provide better water management for PEFCs to elongate the operating range of the cell, so a novel MPL-coated GDL should be developed to realize the goal. Previously, we evaluated double MPL-coated GDLs, which coated a thin hydrophilic layer on the hydrophobic MPL-coated GDL in the through-plane direction. The extra hydrophilic layer was influential in promoting the introduction of water into the small pores of the hydrophobic MPL, enhancing the ability to reduce flooding, and the oxygen transport resistance under high humidity conditions can be declined.The present study evaluates a novel composite MPL that the hydrophobic and hydrophilic pores are randomly allocated in the same layer. Excess water is expelled from the hydrophilic pores while maintaining gas transport by the hydrophobic pores. To determine the appropriate hydrophobic and hydrophilic compositions, we first evaluated the most commonly used hydrophobic polytetrafluoroethylene (PTFE) binder, and the contact angle of PTFE-MPL was 136°. Polyvinyl alcohol (PVA) was chosen as the hydrophilic binder, and the contact angle of PVA-MPL was 105°. The slurry containing PTFE, PVA, carbon black, and distilled water was mixed using a mixer and then spread on the carbon paper substrate by a bar coating machine. The temperature was heated at 350°C to sinter the MPL on the substrate. However, the sintering temperature of PVA should be lower than 150°C, so the PVA in the composite MPL was burned and led to a similar contact angle as the PTFE-MPL. Meanwhile, the performance enhancement could not be obtained compared with a PTFE-MPL-coated GDL. Oppositely, when decreasing the sintering temperature to 150C°, the PTFE-PVA composite MPL demonstrated strong hydrophilicity with a small contact angle value, and the performance was exacerbated than the PTFE-MPL. Therefore, to coordinate the lower sintering temperature of PVA, polyvinylidene difluoride (PVDF) was selected as the hydrophobic binder. The contact angle of PVDF-MPL was 143°. After the PVA was preserved, the unexpectedly strong hydrophilicity was exhibited in PVDF-PVA composite MPL, aggravating the liquid water accumulation in the MPL and without performance improvement. Finally, the Nafion ionomer with relatively weak hydrophobicity was used for the composite MPL. As a hydrophilicity complement, titanium dioxide (TiO2) particles were added to the slurry to control hydrophilicity. The contact angle of Nafion/TiO2-MPL was 113°. Similarly, the Nafion/TiO2-PVDF composite MPL indicated a contact angle of 114°, and the water permeability test proved that separate hydrophobic and hydrophilic pores were generated.The oxygen transport resistances were measured based on the limiting current density values of polarization curves to evaluate the ability of the MPL-coated GDL to reduce flooding under high humidity conditions. The active area of the MEA was 1.0 cm2, and the cell temperature was kept at 35°C. Pure hydrogen and diluted oxygen (2 vol% O2 and 98 vol% N2) gases were supplied at the anode and cathode, respectively, and the flow rates were set at 1000 cm3 min-1. The relative humidity of gases supplied to the anode and cathode was 200%RH, and the gas backpressure was set at zero. The oxygen transport resistance of the Nafion/TiO2-PVDF composite MPL-coated GDL was lower than that obtained with a commercial SGL-22BB GDL. Thus, an appropriate composite MPL-coated GDL effectively enhanced PEFC performance under high humidity conditions.

Design Principles for Hydroxide Exchange Membrane Water Electrolyzers

Green hydrogen, produced by via water splitting using renewable electricity, will play a crucial role as a renewable energy carrier and in decarbonizing hard-to-decarbonize sectors in the future.1 Hydroxide-exchange-membrane water electrolyzers (HEMWE) have the potential to be more cost effective compared to the incumbent technology, proton-exchange-membrane water electrolyzers (PEMWE), through the use of cheaper catalysts and cell component materials.2 However, HEMWE are at much earlier stage of development compared to PEMWE and, in part, generally operate at lower efficiencies due to a lack of established guiding design and operating principles. Herein, we study how membrane electrode assembly (MEA) component design and cell operating conditions influence the performance of HEMWE. A custom design three-electrode MEA is used to breakdown the overpotential contributions from the anode and cathode, showing that anode OER still dominates the kinetic loss while cathode mass transport limitations is more severe compared to anode. A significant improvement in cell performance is observed for more porous anode porous transport electrode (PTE) compared to dense ones, due to a higher anode catalyst utilization. On the cathode, the use of a hydrophobic gas diffusion layer (GDL) improves performance at high current densities by facilitating the removal of hydrogen gas. The impact of feed configurations including electrolyte fed to both sides, anode fed only, and cathode fed only, on HEMWE performance is thoroughly investigated. In various electrolytes including KOH, KHCO3, K2CO3 and DI water, HEMWEs perform the best with anode fed only, signifying that back diffusion of water through the membrane is sufficient to supply enough reactant to the cathode. These learned principles were used to assemble a completely PGM-free HEMWE that reached 1.6 A cm-2 at 2 V in 1 M KOH, and exhibited stable performance in 0.1 M KOH at 1.5 A cm-2 for over 500 h.AcknowledgementsThis work was funded under the HydroGEN Consortium by the Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.References B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018).K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual review of chemical and biomolecular engineering, 10, 219 (2019).

A Super Uniform Hydrophobic Gas Diffusion Layer for a Proton Exchange Membrane Fuel Cell.

The design and optimization of the gas diffusion layer (GDL) play a crucial role in the improvement of proton exchange membrane fuel cell performance. Hydrophobic treatment of a GDL is an important method for facilitating mass transfer, while conventional Teflon treatment is not uniform and leads to an increase in ohmic and heat resistance. Herein, a homogeneous molecular hydrophobic GDL was prepared by liquid phase synthesis, and a two-dimensional non-isothermal model was developed to investigate the transfer mechanism. The peak power density of cells with the GDL described above was improved by 46% compared to that of the conventional GDL. The ohmic and mass transport resistance decreased by 15% and 52%, respectively, under a current density of 1 A cm-2 using the uniform hydrophobic GDL. The simulation results proved that the uniform hydrophobic GDL eliminates the hydrophilic dots, which prevents the formation of water pools and reduces the resistance to gas flow. The water saturation of the conventional GDL reaches 0.19 at a current density of 1 A cm-2, and the saturation of a modified GDL under the same conditions is only 0.13. A dimensionless parameter, Tf, is proposed to characterize the resistance of oxygen diffusion. In conclusion, molecular-level uniform hydrophobic treatment can effectively reduce the ohmic and mass transfer resistance of a GDL and effectively improve the performance of fuel cells.

Biomass derived S, N self-doped catalytic Janus cathode for flow-through metal-free electrochemical advanced oxidation process: Better removal efficiency and lower energy consumption under neutral conditions

Facing low treatment efficiency, narrow adaptive pH and high energy consumption in electro-Fenton (EF), we proposed a novel flow-through metal-free electrochemical advanced oxidation processes (EAOPs) using biomass derived S, N self-doped catalytic Janus cathode named SNJC. The SNJC was composed of a hydrophobic gas diffusion layer in the middle and hydrophilic catalytic membrane at both ends, while the catalytic membrane of S, N self-doped biomass carbon named SN-BC was derived from waste ginkgo leaves without additional supporting templates or activation processes. The conversion of graphite N, pyridinic N and thiophene S in SN-BC played a significant role in efficient oxygen reduction reaction (ORR) for H2O2 generation and in-situ active species generation. The efficient enrichment and rapid degradation of pollutants in catalytic membrane achieved almost complete removal of tetracycline within 120 min with a low energy consumption of 16.8 kWh/kg TOC. This flow-through system exhibited superior catalytic performance in wide pH ranges (3–11) due to the collective effect of radicals (•OH and O2•−) and non-radical (1O2). This work provides a new insight towards the design of S, N self-doped Janus electrode and activation mechanism of in-situ generation and metal-free catalysis of H2O2 in flow-through EAOPs.

Hydrophobicity graded gas diffusion electrode with enhanced CO intermediate coverage for high-performance electroreduction of CO2 to ethylene

Electroreduction using a gas diffusion electrode (GDE) provides an efficient method for high rate conversion of CO2 to value-added chemicals. However, long term production with high yields remains challenging due to rapid electrolyte flooding through the hydrophobic gas diffusion layer (GDL). Here, we report a universal strategy to convert a commercial GDL into a hydrophobicity graded GDL (HGGDL) that resists electrolyte flooding. The CO2 electroreduction performance of a family of tandem catalysts consisting of a nickel-single-atom catalyst and Cu nanoparticles immobilized on GDLs and HGGDLs is compared with respect to ethylene production. In situ Raman studies reveal that the HGGDL increases the CO intermediate coverage as a result of the higher differential pressure across the electrodes. Lower carbonate formation also is observed. Enhanced ethylene production efficiency and an order of magnitude improvement in long term stability is achieved in a membrane electrode assembly electrolyzer.

Direct electrochemical CO2 conversion using oxygen-mixed gas on a Cu network cathode and tailored anode.

Electrochemical CO2 reduction (eCO2R) by direct introduction of 60% air-containing CO2 mixed gas was demonstrated using a porous Cu network cathode formed on a hydrophobic gas diffusion layer (Cu/P-GDL). Cu/P-GDL exhibited eCO2R using the mixed gas with a remarkable faradaic efficiency of 85% for the production of C2+ chemicals, whereas a Cu cathode constructed on a conventional carbon gas diffusion layer (Cu/C-GDL) produced neither eCO2R products nor H2. Furthermore, the electrolyzer with Cu/P-GDL and optimized anode configuration achieved a partial current density of 132 mA cm-2 for C2+ chemicals even in the presence of 12% O2. Demonstration of eCO2R with impure CO2 gas would greatly expand its future applications.

Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO2

AbstractTo mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO2, we report a hydrophobicity‐graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel‐single‐atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm−2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.

Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO2.

To mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO2 , we report a hydrophobicity-graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel-single-atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm-2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.

Study on droplet motion behavior on a rough gas diffusion layer surface of a PEM fuel cell

Understanding the dynamic characteristics of the droplets on the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC) is important to improve fuel cell performance. This paper studies the dynamic characteristics of water droplet detachment from a simplified rough GDL surface by volume of fluid (VOF) method. The rough GDL surface was restructured by designing grooves with cubic pillars on the GDL surface. Results indicate that the gas velocity, space distance, and wettability of the cubic pillars remarkably affect the water droplet detachment. On a high hydrophilic, water droplet exhibits a shorter detachment time regardless of spatial distance and gas velocity. Whereas on a moderate hydrophilic GDL, a large space distance benefits the droplet detachment. However, in both situations referred to above, droplets tend to deviate and adhere to the corner between the channel wall and the GDL surface. On a high hydrophobic GDL, a large space distance and a high gas velocity favor droplet detachment, moreover, droplet shows Cassie mode and can be easily drained out. These findings can guide the optimal design of GDL for water management of high-performance fuel cells.

Modeling of Two Phase Flow in a Hydrophobic Porous Medium Interacting with a Hydrophilic Structure

Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor.

Simulation of Mass and Heat Transfer in an Evaporatively Cooled PEM Fuel Cell

Evaporative cooling is a promising concept to improve proton exchange membrane fuel cells. While the particular concept based on gas diffusion layers (GDLs) modified with hydrophilic lines (HPILs) has recently been demonstrated, there is a lack in the understanding of the mass and heat transport processes. We have developed a 3-D, non-isothermal, macro-homogeneous numerical model focusing on one interface between a HPIL and an anode gas flow channel (AGFC). In the base case model, water evaporates within a thin film adjacent to the interfaces of the HPIL with the AGFC and with the hydrophobic anode GDL. The largest part of the generated water vapor leaves the cell via the AGFC. The transport to the cathode side is shown to be partly limited by the ab-/desorption into/from the membrane. The cooling due to the latent heat has a strong effect on the local evaporation rate. An increase of the mass transfer coefficient for evaporation leads to a transport limited regime inside the MEA while the transport via the AGFC is limited by evaporation kinetics.

Improvement of polymer electrolyte fuel cell performance by gas diffusion layer with relatively hydrophilic surface

To improve the performance of polymer electrolyte fuel cells under high current density operation, the flooding problem in gas diffusion layers (GDLs) should be solved. In this study, a novel GDL with a relatively hydrophilic surface, consisting of hydrophilic and hydrophobic pores, which yielded a wettability distribution in the thickness direction, was proposed to achieve smooth water transport. First, we fabricated GDLs with surfaces partially hydrophilized by Nafion, and we demonstrated that the cell performance improved with this treatment. Cell performance tests suggest that a GDL with optimized surface treatment could reduce the water accumulation compared with the hydrophobic GDL used in this study; it could also improve cell performance owing to low mass transport losses. To verify the surface treatment-induced improvement in the oxygen diffusivity of the GDL, the water transport in the GDL was simulated using a lattice Boltzmann method. The results showed that the water accumulation in the GDL with surface treatment was small because the water flow was limited to the thin relatively hydrophilic region. Consequently, the oxygen diffusivity was higher than that of the hydrophobic GDL. Therefore, the flooding problem can be suppressed by the surface treatment, which yields a relatively hydrophilic surface.

Highly Durable Gas Diffusion Electrodes Made from Non-Aqueous Catalyst Inks

In a PEM fuel cell, catalyst ink formulation and mixing processes are closely related to catalyst layer coating quality and the subsequent fuel cell performance and durability. Catalyst inks based on non-aqueous solvents such as glycerol and ethylene glycol (EG) have shown significant durability advantages over 1-propanol/water-based inks when using decal coating.1,2 Complex solvent-catalyst-ionomer interactions were used to direct the ink properties for coating requirements and optimize them for maximum fuel cell performance, matching the performance of 1-propanol/water-based CLs, while retaining improved durability. Ink rheology and catalyst particle size were used to monitor ink properties, which were later correlated to electrode morphology and structure. These methods were also used to monitor the ink quality and consistency from batch to batch, and from small lab scale to subsequent scale-up. The transition from coating EG-based catalyst ink on decals to coating on gas diffusion layers (GDLs), followed by a roll-to-roll (R2R) fabrication process are crucial for scale up and commercialization. However, coating EG-based catalyst inks on hydrophobic GDLs presented an initial challenge due to EG’s high boiling point and viscosity. Air plasma treatment was successfully used to allow coating of EG-based ink on hydrophobic GDLs. To establish the correlation between ink properties and MEA performance, gas diffusion electrodes made of 1-propanol/water and EG-based inks were tested for fuel cell performance and durability and compared to previously obtained results with decals. The performance and durability of EG-GDEs was better than that of the 1-propanol/water GDEs. The EG-GDE fabrication process was transferred from Giner to NREL for small scale ‘in-operando’ R2R trials. Multiple drying temperatures were evaluated, and the optimal drying temperature was identified. Finally, the electrode performance and durability of R2R fabricated GDEs was tested, and correlated to catalyst microstructures.This work provides a comprehensive understanding of interactions between Pt, carbon, ionomer, GDL and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up. Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-SC0012049. References K-S. Lee, T. Rockward, A. Labouriau, N. Mack, Y. S. Kim, C. Johnston, 2009, Impact of Solvent on Ionomer Structure and Fuel Cell Durability. ECS Transactions. 25. 10.1149/1.3210717.C. Lei, F. Yang, N. Macauley, M. Spinetta, G. Purdy, J. Jankovic, D. Cullen, K. More, H. Xu, JES, 2021 168 044517.

Optimization of Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines menisci morphology and percolation behavior of water through the porous fiber matrix of the Gas Diffusion Layer (GDL), and the transport characteristics of droplets according to the energy landscape of the medium. The hydrophobic GDL, which shows promise for improved water management, can be classified as non-wetting (NW, i.e. Nafion coated), and mixed-non-wetting (MNW, i.e. PTFE coated). The mixed-non-wetting behavior is caused by the hydrophobic coating which allows parts of the meniscus contact line to deform freely in contact with the fibers, while other parts of the meniscus remain pinned due to coating defects. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume, setting it apart from both NW and wetting GDL. The main difference between the two non-wetting media, NW and MNW, is evidenced by the breakthrough pressure which is significantly lower for the former, as shown by existing experimental data. This fact seems to indicate that the main transport mechanism for NW media is by droplet gliding along the fibers, made possible by low adhesion forces. “Clamshell” droplets are energetically favored at high contact angles, optimal design would require small volume droplets yielding low adhesion forces for this morphology. On the other hand, if MNW conditions are present, optimal design should aim for a small droplet volume and high breakthrough pressure as shown in present simulations. The numerical model employed herein captures the meniscus evolution and the corresponding breakthrough pressure for MNW and wetting media, and various degree of pinning. The model predicts up to 50% higher breakthrough pressure when 20% of the meniscus perimeter is pinned, for the MNW medium when compared to the wetting (non-coated) counterpart, results being supported by recent experimental studies.

Optimization of Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines menisci morphology and percolation behavior of water through the porous fiber matrix of the Gas Diffusion Layer (GDL), and the transport characteristics of droplets according to the energy landscape of the medium. The hydrophobic GDL, which shows promise for improved water management, can be classified as non-wetting (NW), and mixed-non-wetting (MNW, i.e. PTFE coated). The mixed-non-wetting behavior is caused by the hydrophobic coating which allows parts of the meniscus contact line to deform freely in contact with the fibers, while other parts of the meniscus remain pinned due to coating defects. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume, setting it apart from both NW and wetting GDL. The main transport mechanism for NW media is by droplet gliding along the fibers, made possible by low adhesion forces. “Clamshell” droplets are energetically favored at high contact angles, optimal design would require small volume droplets yielding low adhesion forces for this morphology. On the other hand, if MNW conditions are present, optimal design should aim for a small droplet volume and high breakthrough pressure as shown in present simulations. The numerical model employed herein captures the meniscus evolution and the corresponding breakthrough pressure for MNW and wetting media, and various degree of pinning. The model predicts up to 50% higher breakthrough pressure when 20% of the meniscus perimeter is pinned, for the MNW medium when compared to the wetting (non-coated) counterpart, results being supported by recent experimental studies.

Theoretical and experimental study on the preparation of hydrophobic GDL materials by ultrasonic dispersion

Gas diffusion layer (GDL), as an important transmission component of gas, electricity and liquid, is usually composed of carbon paper, which needs hydrophobic treatment before it is applied in fuel cell. In the paper, ultrasonic dispersion technique is added to the traditional method of preparing hydrophobic carbon paper, and the effect of ultrasonic dispersion on the PTFE load in hydrophobic carbon paper is studied. The theoretical study shows that the ultrasonic dispersion increases the movement of the liquid, thus improving the diffusion performance of the liquid molecules. The experimental results show that compared with the hydrophobic performance of the original carbon paper, the hydrophobic carbon paper prepared by ultrasonic method improves the hydrophobic performance by 13.24%. However, there is no obvious relationship between the PTFE content of the carbon paper treated by ultrasonic dispersion and the hydrophobicity of the carbon paper surface. In addition, ultrasonic dispersion also has a great influence on the gas permeability of hydrophobic treated carbon paper, but the effect on the surface conductivity of carbon paper is not obvious. The results can provide a guidance for the preparation of hydrophobic carbon paper for fuel cells.

Droplet dynamic characteristics on PEM fuel cell cathode gas diffusion layer with gradient pore size distribution

Understanding of droplet dynamic characteristics on gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cell is of great importance for cell performance improvement. This study comprehensively investigated droplet dynamic characteristics on fuel cell cathode GDL with gradient pore size distribution (GPSD). The influence of different pore sizes, GPSD and wettabilities of GDL on droplet dynamic characteristics is numerically evaluated by using the volume of fluid (VOF) method through the analysis of the interaction among the forces over droplet. Results indicate that droplet has a relatively short detachment time and a smaller detachment radius on superhydrophobic and superhydrophilic GDLs compared with on a moderately hydrophobic GDL regardless of pore size. Moreover, large pores can facilitate droplet detachment, but increase droplet detachment radius and pressure drop. Compared with uniform (U)PSD, for transverse (T)-GPSDs with a small pore distance at a relatively low airflow velocity or a large pore distance at a high airflow velocity, or for the longitudinal (L)-GPSD with a large pore in the upstream and a small pore in the downstream at a large pore distance, the droplet detachment time decreases by 34.3% and 25.2% with a reduction of pressure drop, respectively.