Double Microporous Layer Research Articles

Effect of Hydrophilic Layer in Double Microporous Layer Coated Gas Diffusion Layer on Performance of a Polymer Electrolyte Fuel Cell

Abstract Water flooding under high current and humidity conditions is a main barrier to enhancing the performance of polymer electrolyte fuel cells (PEFCs). This study evaluated a double microporous layer (MPL) coated gas diffusion layer (GDL) consisting of a thin hydrophilic layer coated on a hydrophobic MPL coated GDL. An accurate measurement of the contact angle was introduced to assess the wettability of the MPL. In addition, the water breakthrough pressure and water vapor permeance values were measured to evaluate the water transport ability of the MPL. The oxygen transport resistance was measured using the limiting current density in polarization curves. Appropriate hydrophilic MPL containing 5% Nafion, 25% TiO2, and carbon black in the double MPL enhanced the ability of the GDL to discharge water at the catalyst layer, effectively reducing water flooding. The total oxygen transport resistance obtained with the double MPL was reduced by about 20% compared to that obtained with a hydrophobic MPL. Moreover, the pressure-independent and pressure-dependent resistances were separated from the total oxygen transport resistance measured under various back pressure conditions. The double MPL exhibited a substantially reduced pressure-independent resistance at the interface between the MPL and the catalyst layer.

Performance of polymer electrolyte fuel cells with gradient pore microporous layers at moderate/high humidity

In this paper, carbon black and acetylene black are used as conductive materials of microporous layer (MPL) in GDL, and four MPLs with different materials and structures are prepared by spray method. Respectively, GDL prepared using carbon black, acetylene black, blend of carbon black and acetylene black, double-microporous layer structure are used. In double MPLs, MPL near carbon paper side is acetylene black, and MPL near catalyst layer side is carbon black. The polarization curve, power density, electrochemical impedance spectroscopy, water permeability, pore size distribution and water contact angle of the four samples are tested. It indicated that GDL with double MPL structure has maximum current and power density. When humidity is 60%, limiting current density increased by 41%, and power density increased by 30% (Relative to GDL without gradient pore size). When humidity is 100%, limiting current density increased by 41.3%, power density increased by 50% (Relative to GDL without gradient pore size).

Carbon nanotube-based double-layer microporous cathode for micro-direct methanol fuel cell

The micro-direct methanol fuel cell (μDMFC) has the advantages of high energy density, high conversion efficiency, and simple structure, which brought vast application prospects in portable devices. However, some shortcomings still exist, such as low catalyst utilization and power density. This paper proposes a new cathode electrode structure for the μDMFC. The structure consists of a multi-walled carbon nanotube layer and a cathode double microporous layer (CD-MPL) prepared from carbon powder. The outer microporous layer (OMPL) is composed of multi-walled carbon nanotubes (MWCNTs), Nafion solution, and carbon powder, and the inner microporous layer (IMPL) is composed of carbon powder and polytetrafluoroethylene (PTFE). The experimental results show that the maximum power density of the μDMFC with a CD-MPL (CD-μDMFC) is 42.8 mW/cm2, which is 31.6% higher than that of the μDMFC with a cathode single microporous layer (CS-μDMFC). The pore size distribution of the OMPL of the CNT is measured by the mercury intrusion method. It can be seen that the distribution of pore size is wider and there are more pores with larger pore sizes, which are more conducive to the utilization of catalysts. The discharge experiment of the cell shows that the CD-μDMFC shows high discharge performance and fuel utilization at different concentrations. The double microporous layer (MPL) structure increases the porosity and pore range, broadens the three-phase interface for the reaction, and allows the catalyst to have more attachment sites. The existence of MWCNTs improves the conductivity and mass transfer capacity of the cathode.

(Digital Presentation) Effect of the Hydrophilic Layer in Double Microporous Layer Coated Gas Diffusion Layer on PEFC Performance

The polymer electrolyte fuel cells (PEFCs) are commonly used in the vehicle industry, but the relatively higher costs of power generation limit the potential for further application. The PEFCs output power can be mainly undermined by the water management of the membrane electrode assembly (MEA). If the water content balance in the MEA is broken by fast water expelling, the dehydrated membrane significantly raises the proton transport resistance, which results in severe ohmic resistance loss. Oppositely, the slow water removal pace makes the production water stay at the catalyst layer (CL) surface, and the reactants are prohibited from accessing the reaction area and causing high reactants concentration overpotential during the high current density range. To elongate the limiting current density and raise the output power, beneficial water management should keep the MEA from dehydration by using the water generated from electrochemical reactions and can expel additional water from the CL and gas diffusion layer (GDL) interface. To implement the favorable water balance in the cell, the GDL with the microporous layer (MPL) is necessary.Traditional MPL mainly contains carbon black and hydrophobic binder Polytetrafluoroethylene (PTFE), which can guarantee water-unoccupied pathways for gas transport. The produced water can be expelled by the relatively large pores, and the water transportability is mainly controlled by the pore size and hydrophobicity. When the pore size is excessively narrow, the easily gathered water creates flooding between the CL and GDL. Large pores can solve this issue but bring the water stored in the MPL. Thus, a double MPL is developed to achieve better water management when it cannot forwardly enlarge the pore sizes under low and high humidity conditions. A commercially available hydrophobic MPL coated GDL (SGL 22BB) is the standard sample in this study. As for double MPL coated GDL, the hydrophilic layer is coated on the hydrophobic MPL coated GDL. One candidate composition uses Nafion as the hydrophilic binder, TiO2 as the hydrophilicity improvement particles, and the rest of the part is carbon black; the other way applies only Polyvinyl alcohol (PVA) as the hydrophilic binder and mixes with carbon black. Both types of hydrophilic slurry are directly coated on the 22BB, and the maximum pore diameter slightly changed from 45um (SGL 22BB) to a smaller size. These very thin hydrophilic layers modify the surface properties, which can help reduce the surface contact angle and make water easier to be introduced into the hydrophobic MPL.According to the tests, the performance of the double MPL containing PVA binder becomes worse than the Nafion-TiO2 double MPL, even than standard hydrophobic MPL. Due to the strong hydrophilicity of the PVA binder, even though a tiny amount of it is added to the top layer, water accumulation still occurs in the MPL, so the PVA binder is not suitable for the MPL property modification. The double MPL, which applied a Nafion-TiO2 hydrophilic layer, achieves lower oxygen transport resistance under high humidity conditions than the standard hydrophobic MPL. Besides, the appropriate composition of the hydrophilic contents is determined. With the increase of the TiO2 and Nafion content, the significantly enhanced hydrophilicity leads to more water absorption. However, it blocks the gas pathways, showing terrible reactants transport and high concentration over-potential. When the hydrophilic content becomes overly low, it is not enough to afford the water expelling, and water still occupies the MPL and CL interface. The thickness of the top hydrophilic MPL is another critical design parameter. A too thick hydrophilic layer can hold more water and cause a high risk of hampering reactants supply. The moderate thickness of the hydrophilic layer should be less than 5μm, which guarantees the function of the water transport and keeps away from severe water absorption.

(Digital Presentation) Effect of the Hydrophilic Layer in Double Microporous Layer Coated Gas Diffusion Layer on PEFC Performance

Water management is always one of the main problems of polymer electrolyte fuel cells performance enhancement because it dramatically influences oxygen transport resistance. Typically, the MPL coated GDL with strong hydrophobicity effectively prevents flooding between the catalyst layer and the MPL. To further improve PEFC performance, directly coating an extra hydrophilic MPL on the hydrophobic MPL coated GDL as double MPL can further promote performance. The double MPL using Nafion binder cannot provide enough hydrophilicity to lower the oxygen transport resistance. Combining utilization of the Nafion and TiO2 is efficacious in decreasing the breakthrough pressure and contact angle and ameliorating water drainage from the MEA so that the gas transport ability can be improved. Besides, the appropriate thickness of the double MPL was investigated to better design the double MPL coated GDL.

Hydrophilic and Hydrophobic Microporous Layer Coated Gas Diffusion Layer for Enhancing PEFC Performance

The gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). An MPL coated GDL designed to prevent dehydration of the membrane electrode assembly (MEA) under low humidity conditions is generally inferior at reducing flooding under high humidity conditions. Thus, it is important to develop an MPL coated GDL to enhance the PEFC performance under both low and high humidity conditions. To overcome the defects of pure hydrophobic MPL, several plans are raised to develop a composite MPL coated GDL which possesses both hydrophobic and hydrophilic structures in the same MPL to enhance PEFC performance under both low and high humidity conditions. One method is a hydrophilic and hydrophobic double MPL coated GDL. The hydrophobic MPL with 20mass% hydrophobic polytetrafluoroethylene (PTFE) and 80mass% carbon black is coated on the carbon paper substrate as the first layer, then the hydrophilic MPL with 20mass% titanium dioxide (TiO2) and 80 mass% carbon black is coated as a relatively thin second layer. The contact angle of the hydrophobic MPL is 134°, while that of the hydrophilic MPL is 82°. A thin hydrophilic layer is effective at conserving membrane humidity under low humidity, while a hydrophobic intermediate MPL between the hydrophilic layer and the carbon paper substrate prevents the removal of water from the hydrophilic layer. This results in a significant enhancement of PEFC performance under low humidity conditions. The oxygen transport resistance is measured using the limiting current density of polarization curves to evaluate the ability of the GDL to prevent flooding under high humidity conditions. This value obtained with a pure hydrophobic MPL coated GDL is 80 sm-1, while the double MPL coated GDL is 70 sm-1. In the case of the double MPL coated GDL, excess water can be expelled from the catalyst layer, thereby enhancing PEFC performance under high humidity conditions. Except for the double MPL coated GDL, directly changing the part of the hydrophobic carbon black to hydrophilic carbon black is another method. This MPL consists of 16mass% hydrophilic carbon black with 64mass% hydrophobic carbon black and 20mass% PTFE. The prepared MPL is expected to keep the hydrophilic and hydrophobic structures in the same layer. However, the contact angle of the composite MPL coated GDL is 131°. The cell performance obtained with the composite MPL is lower than that with the hydrophobic MPL. The reason is the carbon blacks with different properties in composite MPL coated GDL are completely bonding together and cannot generate hydrophobic and hydrophilic pores separately. As a result, under high humidity conditions, most pore structures of composite MPL are occupied by liquid water, and oxygen transportation is deteriorated, which results in low performance under high humidity conditions. Another designed plan is mixing hydrophilic carbon nanotubes (CNTs) with a hydrophobic MPL. The MPL that contains 4mass% CNTs, 76mass% carbon black, and 20mass% PTFE is coated on the carbon paper. Since it is difficult for the hydrophilic CNTs and PTFE to fully bond together, the hydrophobic pores and hydrophilic pores can be generated separately. In the case of a hydrophobic MPL, decreasing the mean flow pore diameter is effective at preventing membrane dehydration, which enhances cell performance under low humidity conditions. However, when the pore diameter decreases to 2 μm, the water breakthrough pressure significantly increases. This increases the oxygen transport resistance under high humidity conditions. In the case of an MPL with hydrophilic CNTs, the ability to retain membrane humidity is improved, which enhances cell performance under low humidity conditions. It is possible to decrease the pore diameter to 2 μm without raising the water breakthrough pressure. This decreases the oxygen transport resistance to 62 sm-1 under high humidity conditions. Both decreasing the pore diameter and using hydrophilic CNTs in the MPL allow much higher cell performance under both low and high humidity conditions compared to that obtained with a hydrophobic MPL coated GDL.

Hydrophilic and Hydrophobic Microporous Layer Coated Gas Diffusion Layer for Enhancing PEFC Performance

The hydrophobic microporous layer (MPL) coated on the gas diffusion layers (GDLs) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). An MPL coated GDL designed to prevent dehydration of the membrane electrode assembly (MEA) under low humidity conditions is generally inferior at reducing flooding under high humidity conditions. Thus, developing an MPL coated GDL to enhance the PEFC performance under low and high humidity conditions is crucial. One method to overcome the defects of pure hydrophobic MPL is to make double and triple MPLs, in which a thin hydrophilic layer coated on the hydrophobic MPL. Another method is a hydrophobic MPL containing hydrophilic carbon nanotubes (CNTs). Both methods effectively conserve membrane humidity and reduce flooding under high humidity conditions.

Effects of thickness and hydrophobicity of double microporous layer on the performance in proton exchange membrane fuel cells

AbstractIn this paper, a multi‐layer gas diffusion layer (GDL) is designed. The GDL consists of a single carbon paper backing layer and dual microporous layers (MPLs). Moreover, the effects of thickness and hydrophobicity of double MPL on the performance of proton exchange membrane fuel cells are investigated. From the test results of the water contact angle, conductivity, pore size distribution, and the polarization curve, it is found that the thickness adjustment increases the number of 0.5 to 7 μm and 20 to 100 μm pores in GDL, which is more conducive to water discharge. Therefore, the thickness adjustment is more favorable to the cell performance under high humidity. While the gradient hydrophobic design makes the MPL of the modified intermediate layer have a certain water‐retaining capacity to humidify the reaction gas, which has better effect under low humidity. At last, the results show that the optimized GDL meets a limit power density of 1.772 W/cm2 under 60% humidification and 1.600 W/cm2 under 100% humidification.

Improving cell performance and alleviating performance degradation by constructing a novel structure of membrane electrode assembly (MEA) of DMFCs

The conventional electrodes of direct methanol fuel cells (DMFCs) usually encounter a problem that the catalysts sink into the diffusion layer after a period of operation, causing a lowered catalyst utilization and degraded cell performance. Aiming to alleviate this problem, in this work a novel anode electrode structure is proposed, in which a microporous layer containing Nafion polymer is added between the catalyst layer and the microporous layer with PTFE. The presence of the Nafion-contained layer can expand the three-phase interface region of the electrochemical reactions and improve the utilization of the catalyst. The single cell test showed that the peak power densities of the novel membrane electrode assembly (MEA) fed with 0.5 M and 2 M methanol solutions reached 38.35 mW cm−2 and 101.82 mW cm−2, which increased by 100.42% and 15.27% compared with those of conventional single microporous layer. Electrochemical impedance spectroscopy (EIS) measurements indicated the charge transfer resistance of the conventional MEA structure was increased by 303.78%, while the new one was decreased by 47.91% after continuously operating for 48 h. The anode electrochemical active surface area (ECSA) values of the novel MEA and the conventional MEA were 52.6 m2 g-1 and 44.3 m2 g-1. These experimental results showed that the performance of the double microporous layer MEA was higher than that of the conventional MEA. This new microporous layer structure is promising to be used in fuel cells to improve cell performance and alleviate performance degradation after long-term operating.

Impact of Porosity Gradients within Catalyst Layer and MPL of a PEM Fuel Cell on the Water Management and Performance: A Neutron Radiography Investigation

The influence of porosity modifications of either microporous layer (MPL) or the catalyst layer of a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) on the performance of the cell has been investigated in many studies. However, we have been focusing in our study on the interactive impact of this morphological modification of both cathode MPL and catalyst layer in the water distribution and transport inside the cell and consequently also on the performance of the cell. In this study, three types of cathode MPLs with different porosity distributions and three type of membrane electrode assemblies (MEA) with different porosity of the catalyst layer are manufactured. Five one-cell fuel cells are investigated using combinations of those in-house made layers. To modify the porosity of the cathode MPL polymer particle in two sizes of 30 µm and 1.5 µm from company Chemisnow® are introduced into the carbon slurry, which are then evaporated out of the MPL during the sintering process. For the catalyst layers, 0.5 µm Polystyrene particles are mixed in the electrode slurry with variable weight fractions and then washed out of the dried MEA. A more detailed description of the production procedure of these layers will be demonstrated in the presentation. Performance of fuel cells using these five combination of cathode MPL and electrode are measured using a Fuel Cell with 25 cm² active area and 3 serpentine channel flow fields. Neutron Radiography is used to investigate the water distribution dynamics and water content of the fuel cell. For this purpose, a specially designed single cell with 8 cm² active area and 3 serpentine channel flow fields is used. The measurements are obtained at two different humidity values on both cathode and anode inlet gases of RH=70% and RH=120% and different current densities. With an exposure time of 10 s, images with 12.4 µm pixel size are achieved. The quantitative analysis of the water thickness in the cathode GDL and cathode electrode of 5 cells at RH=120% for an increasing current density is shown at an exemplary radiogram for water distribution inside the cell with our reference cathode MPL and electrode (without porosity modification). Also the Current (ICell) and Voltage (VCell) evolution of the same cell is shown in figure 1. All cells have reached a water content plateau even before reaching the highest current density of 1A/cm². The cell with a porous catalyst layer and a double layer cathode MPL shows the highest water content on the cathode side of the cell, whereas the cell with a highly porous catalyst layer and a porous MPL shows the lowest water content of all cells, comparable to the water thickness observed for the cell without modified layers. Further results of both water content and performance dependent on porosity changes will be provided in the presentation. Figure 1

Microporous layer-coated gas diffusion layer to reduce oxygen transport resistance in a polymer electrolyte fuel cell under high humidity conditions

A hydrophilic and hydrophobic microporous layer (MPL)-coated gas diffusion layer (GDL) is developed to enhance the performance of polymer electrolyte fuel cells (PEFCs) under high humidity conditions. The oxygen transport resistance is determined from the limiting current density value of polarization curves as a means of evaluating the ability of the GDL to prevent flooding. A double MPL coated GDL, in which a thin hydrophilic layer is coated on the hydrophobic MPL, is effective at expelling excess water from the catalyst layer, thus reducing the oxygen transport resistance. The PEFC performance is highly dependent on the hydrophobic MPL in the double MPL. Appropriate enhancement of the hydrophobicity, obtained when incorporating 20 mass% polytetrafluoroethylene (PTFE) in the MPL, is essential for reducing the oxygen transport resistance. A triple MPL-coated GDL, in which the PTFE content in the hydrophobic MPL in contact with the hydrophilic layer is 20 mass% and that in contact with the carbon paper substrate is 10 mass%, exhibits much lower oxygen transport resistance than a conventional hydrophobic MPL-coated GDL.

Influence of Hydrophilic and Hydrophobic Triple MPL Coated GDL on the Oxygen Transport Resistance in a PEFC under High Humidity Conditions

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the performance of polymer electrolyte fuel cells (PEFCs). In the present study, a hydrophilic and hydrophobic triple MPL coated GDL, in which a thin hydrophilic layer was coated on the hydrophobic double MPL, was developed to achieve further enhancement of the PEFC performance under high humidity conditions. The oxygen transport resistance was determined from the limiting current density values of polarization curves to evaluate the ability of the GDL to prevent flooding. A triple MPL coated GDL, in which the polytetrafluoroethylene (PTFE) content in the hydrophobic MPL in contact with the hydrophilic layer is 20 mass% and that in the MPL in contact with the carbon paper substrate is 10 mass%, exhibits much lower oxygen transport resistance than a conventional hydrophobic MPL coated GDL.

Influence of Hydrophilic and Hydrophobic Triple MPL Coated GDL on the Oxygen Transport Resistance in a PEFC under High Humidity Conditions

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management characteristics of polymer electrolyte fuel cells (PEFCs). However, the appropriate design parameters for the MPL coated GDL are different under low and high humidity conditions [1]. An MPL coated GDL designed to prevent dehydration of the membrane electrode assembly (MEA) under low humidity conditions is generally inferior at reducing flooding under high humidity conditions. It is highly desirable to have a PEFC that can be operated under a wide range of conditions varying from low (or no) to high humidity. The authors have reported that a hydrophilic and hydrophobic double MPL coated GDLs was more effective at enhancing the PEFC performance under low humidity conditions than a hydrophobic MPL coated GDL [2,3]. This design involves the application of a thin hydrophilic layer on top of a hydrophobic MPL. The hydrophilic layer works to conserve the water content of the MEA, while the hydrophobic MPL between the hydrophilic layer and the carbon paper substrate prevents removal of water from the hydrophilic layer. This results in a significant enhancement of the ability to prevent dehydration of the MEA. In the present study, a hydrophilic and hydrophobic triple MPL coated GDL was developed to achieve further enhancement of the PEFC performance under high humidity conditions at a low temperature of 35°C. The active area of the MEA (GORE PRIMEA5580) was 1cm2. The relative humidity (RH) of the gas supplied to the anode and cathode was varied between 50 and 200%. The oxygen transport resistance [4] was measured using the limiting current density of polarization curves to evaluate the ability of the GDL to prevent flooding under high humidity conditions. Single (hydrophobic), double and triple MPL coated GDLs were used at the cathode. The hydrophobic MPL coated GDL consisted of a carbon paper substrate (SGL24BA) coated with an MPL of 20 mass% PTFE (polytetrafluoroethylene) and carbon black. For both the double MPL and the triple MPL coated GDLs, a hydrophilic layer of 25 mass% titanium dioxide, 5 mass% silicone, and carbon black was coated on the hydrophobic MPL coated GDL. The PTFE content in the hydrophobic intermediate MPL of the double MPL coated GDL was varied between 10 and 40 mass%. For the triple MPL coated GDL, the PTFE content in the hydrophobic MPL in contact with the hydrophilic layer was set to 20 mass% and that in contact with the substrate was set to 10 mass%. The contact angle for the hydrophilic MPL was 82°, while those for the hydrophobic MPLs were greater than 120°. When the PTFE content in the hydrophobic MPL was increased from 10 to 40 mass%, the hydrophobicity was enhanced, thereby increasing the contact angle. When the RH of the supplied gases increases from 50 to 100%, the oxygen transport resistance significantly increases due to flooding. However, the oxygen transport resistance becomes almost constant under high humidity conditions varying from 100 to 200 %RH. A double MPL coated GDL is effective to expel excess water from the catalyst layer [2], which results in lower oxygen transport resistance under high humidity conditions, compared with that for the hydrophobic MPL coated GDL. The performance is strongly dependent on the hydrophobic intermediate MPL in the double MPL. Increasing the PTFE content from 10 to 20 mass% represents an effective means of reducing flooding, thereby lowering the oxygen transport resistance. However, when the PTFE content becomes too high, such as 40 mass%, the discharge of excess water at the catalyst layer is inhibited, which increases the oxygen transport resistance. For the triple MPL coated GDL, the hydrophobic gradient promotes water transport from the hydrophobic MPL containing 20 mass% PFTE to the hydrophobic MPL containing 10 mass% PTFE, which causes a relatively large amount of water to be stored in the latter MPL in contact with the substrate, which is effective at expelling excess water from the catalyst layer, while maintaining the oxygen flow pathways inside the MPL from the substrate to the catalyst layer. This results in a significantly lower oxygen transport resistance than that obtained when employing the double MPL coated GDL.

Triple microporous layer coated gas diffusion layer for performance enhancement of polymer electrolyte fuel cells under both low and high humidity conditions

Enhancement of the performance of polymer electrolyte fuel cells (PEFCs) requires an appropriate water balance between the conservation of membrane humidity and the discharge of excess water produced in the cell. In the present study, a novel triple microporous layer (MPL) coated gas diffusion layer (GDL), in which a hydrophilic layer was coated on a hydrophobic double MPL, was developed to enhance the PEFC performance under both low and high humidity. The thin hydrophilic layer in the triple MPL is effective at conserving the humidity of the membrane electrode assembly (MEA) under low humidity, while the hydrophobic double MPL between the hydrophilic layer and the carbon paper substrate prevents removal of water from the hydrophilic layer. This results in a significant enhancement of the ability of the GDL to prevent dehydration of the MEA. The triple MPL coated GDL, where the polytetrafluoroethylene (PTFE) content in the hydrophobic MPL in contact with the hydrophilic layer is set to 30 mass% and that in contact with the substrate is set to 10 mass%, is effective at expelling excess water from the catalyst layer, which results in much higher PEFC performance under high humidity than that for a conventional hydrophobic MPL coated GDL.

Influence of Triple MPL Coated GDL on the PEFC Performance under Low and High Humidity

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a novel triple MPL coated GDL, in which the hydrophilic layer was coated on the hydrophobic double MPL, was developed to achieve further enhancement of the PEFC performance under both low and high humidity. Under low humidity, a hydrophilic layer is effective to conserve the humidity of the MEA, while a hydrophobic double MPL prevents the removal of water from the hydrophilic layer. The triple MPL coated GDL, in which the polytetrafluoroethylene (PTFE) content in the hydrophobic MPL in contact with the hydrophilic layer is 30 mass% and that in contact with the carbon paper substrate is 10 mass%, is effective to expel excess water at the catalyst layer, which results in a much higher performance under high humidity.

Development of a porosity-graded micro porous layer using thermal expandable graphite for proton exchange membrane fuel cells

In this study, a porosity-graded micro porous layer (MPL) was prepared using the double coating method to enhance the water removal ability of the gas diffusion layer (GDL). In the double MPL, the porosity of each layer was controlled using thermal expandable graphite (TEG), which could produce pores in MPL through thermal expansibility. The porosity of the inner layer of the porosity-graded MPL was smaller than the outer layer, so the gradient direction in porosity was from the MPL/catalyst layer interface to the gas diffusion backing layer (GDBL)/MPL interface. In addition, the pore forming ability of TEG and the water removal ability of porosity-graded MPL were characterized. The performance of the porosity-graded MPL was evaluated and compared to the single layer conventional MPL. The porosity-gradient structure in MPL increased the water permeability of GDL and the performance of the single cell in the high current density region. Since the porosity-graded MPL increased the water removal ability of GDL, concentration loss due to water flooding in the high current density region was decreased. These results demonstrate that porosity-graded MPL was beneficial to PEMFC, which has to operate in the high current density region.

Electrodeposition preparation of highly dispersed Pt/HxWO3 composite catalysts for PEMFCs

Platinum/hydrogen tungsten bronze (Pt/HxWO3) composite catalysts were prepared by electrodeposition on the carbon cloth with varying HxWO3 content. To obtain highly dispersed catalyst layer, the carbon cloth was modified by introducing a hydrophilic–hydrophobic double microporous layer. The catalytic activity of prepared catalysts was investigated by single cell polarization test and in situ cyclic voltammetry (CV). The application of double microporous layer facilitates electrodeposition process, which benefits the dispersion of catalysts. HxWO3 used as auxiliary catalyst enhances the catalytic activity of Pt for hydrogen oxidation. Pt/HxWO3 hydrophilic electrode with composite catalyst loading of 0.35mgcm−2 exhibits the higher current density of 340mAcm−2 at 0.4V and electrochemical active surface area (EASA) of 89.40m2g−1 than traditional Pt/C does at room temperature.

Influence of Hydrohilic and Hydrophobic Double MPL Coated GDL on PEFC Performance

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a novel hydrophilic and hydrophobic double MPL coated GDL was developed to further enhance the PEFC performance under both low and high humidity conditions. Under low humidity conditions, a thin hydrophilic layer using titanium dioxide coated on the hydrophobic MPL is effective to conserve the humidity of the MEA, while a hydrophobic intermediate MPL between the hydrophilic layer and the GDL substrate prevents the removal of water in the hydrophilic layer. Under high humidity conditions, a double MPL coated GDL is also effective to reduce flooding on the cathode catalyst layer, which results in a higher PEFC performance compared with that for a conventional hydrophobic MPL coated GDL.

Novel hydrophilic and hydrophobic double microporous layer coated gas diffusion layer to enhance performance of polymer electrolyte fuel cells under both low and high humidity

A novel hydrophilic and hydrophobic double microporous layer (MPL) coated gas diffusion layers (GDL) was developed to enhance the performance of polymer electrolyte fuel cells (PEFCs) under both low and high humidity. A thin hydrophilic layer using titanium dioxide (TiO2) coated on the hydrophobic MPL is effective at conserving the humidity of the membrane electrode assembly (MEA) under low humidity, while a hydrophobic intermediate MPL between the hydrophilic layer and the carbon paper substrate prevents the removal of water from the hydrophilic layer. This results in a significant enhancement of PEFC performance under low humidity over that for a conventional hydrophobic MPL coated GDL.The double MPL coated GDL is also effective at increasing the discharge of excess water from the catalyst layer, which reduces flooding and achieves further enhancement of the PEFC performance under high humidity, compared with that for a conventional hydrophobic MPL coated GDL. The appropriate pore diameter and hydrophobicity, and decrease in the thickness of the hydrophobic intermediate MPL in the double MPL, are essential to enhance the PEFC performance.

Hydrophilic and hydrophobic double microporous layer coated gas diffusion layer for enhancing performance of polymer electrolyte fuel cells under no-humidification at the cathode

Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a new hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of PEFC performance under no-humidification at the cathode. The hydrophobic MPL, which consists of carbon black and polytetrafluoroethylene (PTFE), was coated on the carbon paper substrate. The hydrophilic layer, which consists of carbon black and polyvinyl alcohol (PVA), was also coated on the hydrophobic MPL. The hydrophilic layer is effective for conserving humidity at the catalyst layer, while the hydrophobic intermediate layer between the hydrophilic layer and the substrate prevents the removal of water in the hydrophilic layer via dry air in the substrate. Both decrease in the hydrophilic layer thickness to 5 μm and appropriate enhancement of hydrophilicity by increasing the PVA content to 5 mass% are effective for enhancing PEFC performance. Reducing the maximum pore diameter of hydrophobic intermediate layer to 20 μm is also effective for enhancing PEFC performance. However, when the pore diameter of the hydrophobic layer becomes too small, concentration overpotential tends to increase, thereby lowering PEFC performance.