Self-humidifying membrane electrode assembly prepared by adding microcrystalline cellulose in anode catalyst layer as preserve moisture

A novel self-humidifying membrane electrode assemblies (MEAs) with the addition of microcrystalline cellulose (MCC) as a hygroscopic agent into anode catalyst layer was prepared to improve the performance of proton exchange membrane fuel cell (PEMFC) under low humidity conditions. The MEAs were characterized by SEM, contact angles and water uptake measurements. The MEAs with addition of MCC exhibit excellent self-humidifying single cell performance, the cell temperature for self-humidification running is up to 60 °C. As an optimized MEA with 4 wt.％ MCC in its anode catalyst layer, its current density at 0.6 V could be up to 760 mA cm⁻² under 20% of relative humidity, and remains at 680 mA cm⁻² after 22 h long time continuous testing, the attenuation of the current density is only 10%. While the current density of the blank MEA without addition of MCC degraded sharply from 300 mA cm⁻² to 110 mA cm⁻², the attenuation of the current density is high up to 70% within 2 h.     

Enhanced low-humidity performance of proton exchange membrane fuel cell by incorporating phosphoric acid-loaded covalent organic framework in anode catalyst layer

Developing self-humidifying membrane electrode assembly (MEA) is of great significance for the practical use of proton exchange membrane fuel cell (PEMFC). In this work, a phosphoric acid (PA)-loaded Schiff base networks (SNW)-type covalent organic framework (COF) is proposed as the anode catalyst layer (CL) additive to enhance the PEMFC performance under low humidity conditions. The unique polymer structure and immobilized PA endow the proposed COF network with not only excellent water retention capacity but also proton transfer ability, thus leading to the superior low humidity performance of the PEMFC. The optimization of the additive content, the effect of relative humidity (RH) and PEMFC operating temperature are investigated by means of electrochemical characterization and single cell test. At a normal operation temperature of 60 °C and 38% RH, the MEA with optimized COF content (10 wt%) showes the maximum power density of 582 mW cm^?2, which is almost 7 times higher than that of the routine MEA (85 mW cm^?2). Furthermore, a preliminary durability test demonstrates the potential of the proposed PEMFC for practice operation under low humidity environment.     

High performance membrane electrode assembly with ultra-low platinum loading prepared by a novel multi catalyst layer technique

An ultra-low platinum loading membrane electrode assembly (MEA) with a novel double catalyst layer (DCL) structure was prepared by using two layers of platinum catalysts with different loadings. The inner layer consisted of a high loading platinum catalyst and high Nafion content for keeping good platinum utilization efficiency and the outer layer contained a low loading platinum catalyst with low Nafion content for obtaining a proper thickness thereby enhancing mass transfer in the catalyst layers. Polarization characteristics of MEAs with novel DCL, conventional DCL and single catalyst layer (SCL) were evaluated in a H₂–air single cell system. The results show that the performance of the novel DCL MEA is improved substantially, particularly at high current densities. Although the platinum loadings of the anode and cathode are as low as 0.04 and 0.12 mg cm⁻² respectively, the current density of the novel DCL MEA still reached 0.73 A cm⁻² at a working voltage of 0.65 V, comparable to that of the SCL MEA. In addition, the maximum power density of the novel DCL MEA reached 0.66 W cm⁻² at 1.3 A cm⁻² and 0.51 V, 11.9% higher than that of the SCL MEA, indicative of improved mass transfer for the novel MEA. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests revealed that the novel DCL MEA possesses an efficient electrochemical active layer and good platinum utilization efficiency.     

A novel self-humidifying membrane electrode assembly with water transfer region for proton exchange membrane fuel cells

A novel self-humidifying membrane electrode assembly (MEA) with the active electrode region surrounded by a unactive “water transfer region (WTR)” was proposed to achieve effective water management and high performance for proton exchange membrane fuel cells (PEMFCs). By this configuration, excess water in the cathode was transferred to anode through Nafion membrane to humidify hydrogen. Polarization curves and power curves of conventional and the self-humidifying MEAs were compared. The self-humidifying MEA showed power density of 85 mW cm⁻² at 0.5 V, which is two times higher than that of a conventional MEA with cathode open. The effects of anode hydrogen flow rates on the performance of the self-humidifying MEA were investigated and its best performance was obtained at a flow rate of 40 ml min⁻¹. Its performance was the best when the environmental temperature was 40 °C. The performance of the self-humidifying MEA was slightly affected by environmental humidity. The area of WTR was optimized, and feasible area ratio of the self-humidifying MEA was 28%.     

Self-humidification of a PEM fuel cell using a novel Pt/SiO2/C anode catalyst

In this work, a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) operating under no external humidification has been successfully fabricated by using a composite Pt/SiO₂/C catalyst at the anode. In the composite catalyst, amorphous silica, which originated from the hydrolysis of tetraethyl orthosilicate (TEOS), was immobilized on the surface of carbon powder to enhance the stability of silica and provide a well-humidified surrounding for proton transport in the catalyst layer. The characteristics of silica in the composite catalyst were investigated by XRD, SEM and XPS analysis. The single cell tests showed that the performance of the novel MEA was comparable to MEAs prepared using a standard commercial Pt/C catalyst with 100% external humidification, when both were operated on hydrogen and air. However, in the absence of humidification, the MEA using Pt/SiO₂/C catalyst at the anode continued to show excellent performance, while the performance of the MEA containing only the Pt/C catalyst rapidly decayed. Long-term testing for 80 h further confirmed the high performance of the non-humidified MEA prepared with the composite catalyst. Based on the experimental data, a possible self-humidifying mechanism was proposed.     

Study on the membrane electrode assembly fabrication with carbon supported cobalt triethylenetetramine as cathode catalyst for proton exchange membrane fuel cell

An improved fabrication technique for conventional hot-pressed membrane electrode assemblies (MEAs) with carbon supported cobalt triethylenetetramine (CoTETA/C) as the cathode catalyst is investigated. The V-I results of PEM single cell tests show that addition of glycol to the cathode catalyst ink leads to significantly higher electrochemical performance and power density than the single cell prepared by the traditional method. SEM analysis shows that the MEAs prepared by the conventional hot-pressed method have cracks between the cathode catalyst layer and Nafion membrane, and the contact problem between cathode catalyst layer and Nafion membrane is greatly suppressed by addition of glycol to the cathode catalyst ink. Current density-voltage curve and impedance studies illuminate that the MEAs prepared by adding glycol to the cathode catalyst ink have a higher electrochemical surface area, lower cell ohmic resistance, and lower charge transfer resistance. The effects of CoTETA/C loading, Nafion content, and Pt loading are also studied. By optimizing the preparation parameters of the MEA, the as-fabricated cell with a Pt loading of 0.15 mg cm⁻² delivers a maximum power density of 181.1 mW cm⁻², and a power density of 126.2 mW cm⁻² at a voltage of 0.4 V.     

Investigation of membrane electrode assembly (MEA) hot-pressing parameters for proton exchange membrane fuel cell

The hot-pressing conditions for fabricating the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC) was investigated by using a 2ⁿ full factorial design. Time, temperature and pressure were key parameters that were varied from 500 to 1500 psi, 1 to 5 min and 100 to 160 °C, respectively. The results from the full factorial analysis indicated that the order of significance of the main MEA fabricating effects was temperature, pressure, time–temperature interaction and pressure–time–temperature interaction. By examining the cell performance curves, the lower fabrication conditions of temperature and pressure were suitable for MEA preparation. The conductive layer between the membrane and the catalyst layer became thin at high pressure and high temperature, as seen from scanning electron microscopy (SEM) images. In the ranges of condition studied, the most suitable hot-pressing condition for MEA fabrication was at 100 °C, 1000 psi and 2 min. This condition provided the highest maximum power density from the MEA and the best contact at the interfaces between the gas diffusion layer, the active layer and the electrolyte membrane. The experimental results were verified by testing with a commercial MEA in the same operating condition and with the same equipment. The performance of the fabricated MEA was better than that of the commercial one.     

Improvement of PEMFC performance with Nafion/inorganic nanocomposite membrane electrode assembly prepared by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium silicon dioxide (TiSiO₄) composite membranes were manufactured with a novel ultrasonic-spray technique and tested in proton exchange membrane fuel cell (PEMFC). Nafion/TiO₂ and Nafion/SiO₂ nanocomposite membranes were also fabricated by the same technique and their characteristics and performances in PEMFC were compared with Nafion/TiSiO₄ mixed oxide membrane. The composite membranes have been characterized by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, water uptake, and proton conductivity. The composite membranes gained good thermal resistance with insertion of inorganic oxides. Uniform and homogeneous distribution of inorganic oxides enhanced crystalline character of these membranes. Gas diffusion electrodes (GDE) were fabricated by Ultrasonic Coating Technique. Catalyst loading was 0.4 mg Pt/cm² for both anode and cathode sides. Fuel cell performances of Nafion/TiSiO₄ composite membrane were better than that of other membranes. The power density obtained at 0.5 V at 75 °C was 0.456 W cm⁻², 0.547 W cm⁻², 0.477 W cm⁻² and 0.803 W cm⁻² for Nafion, Nafion/TiO₂, Nafion/SiO₂, and Nafion/TiSiO₄ composite membranes, respectively.     

Optimization of catalyst ink composition for the preparation of a membrane electrode assembly in a proton exchange membrane fuel cell using the decal transfer

For low interfacial resistance and feasibility of forming catalyst layer (CL), decal transfer (DT) is considered as one of the most effective methods for preparing a membrane electrode assembly. However, optimization of the catalyst ink composition is necessary, because of the complexity of the CL. Here, 1-propanol is adsorbed onto the CL coated onto the decal, as a swelling agent, for complete transfer of the CL onto Nafion membrane. Using this methodology, flat and complete DT is achieved at the hot-pressing conditions of 60 °C and 5 MPa. For optimization, the solvent-to-carbon ratio (SCR) and Nafion-to-carbon ratio (NCR) are controlled to achieve improved cell performance. In this study, by considering the morphology of CL and the cell performance when CL is annealed at temperatures sufficiently below the boiling point of the solvent, optimized SCR and NCR values of approximately 12.0 and 0.65, respectively, are obtained. In addition, microstructure, thickness and various electrochemical properties of the CLs are examined in detail.     

Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm^?2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.     

A Nafion-based self-humidifying membrane with ordered dispersed Pt layer

A double-layer Nafion-based membrane consisting of a pure Nafion layer and an ordered dispersed Pt particles layer was investigated. The Pt particles were dispersed under the anode graphite ribs, which provide the sites for the recombination of the permeating _H2${\mathrm{H}}_2$ and _O2${\mathrm{O}}_2$ into water. The electrochemical performances of the ordered Pt particles dispersed membrane in proton exchange membrane fuel cell (PEMFC) were studied and compared with those of the common Pt particles dispersed membrane and the pure Nafion membrane. The results indicate that the ordered Pt dispersed membrane reduces the amount of Pt dosage than the common Pt dispersed membrane and improves the performance of PEMFC operated under dry conditions than the pure Nafion membrane as well.     

Performance of membrane electrode assemblies using PdPt alloy as anode catalysts in polymer electrolyte membrane fuel cell

Pd-based nanoparticles, such as 40 wt.% carbon-supported Pd₅₀Pt₅₀, Pd₇₅Pt₂₅, Pd₉₀Pt₁₀ and Pd₉₅Pt₅, for anode electrocatalyst on polymer electrolyte membrane fuel cells (PEMFCs) were synthesized by the borohydride reduction method. PdPt metal particles with a narrow size distribution were dispersed uniformly on a carbon support. The membrane electrode assembly (MEA) with Pd₉₅Pt₅/C as the anode catalyst exhibited comparable single-cell performance to that of commercial Pt/C at 0.7 V. Although the Pt loading of the anode with Pd₉₅Pt₅/C was as low as 0.02 mg cm⁻², the specific power (power to mass of Pt in the MEA) of Pd₉₅Pt₅/C was higher than that of Pt/C at 0.7 V. Furthermore, the single-cell performance with Pd₅₀Pt₅₀/C and Pd₇₅Pt₂₅/C as the anode catalyst at 0.4 V was approximately 95% that of the MEA with the Pt/C catalyst. This indicated that a Pd-based catalyst that has an extremely small amount of Pt (only 5 or 50 at.%) can be replaced as an anode electrocatalyst in PEMFC.     

Performance of an ultra-low platinum loading membrane electrode assembly prepared by a novel catalyst-sprayed membrane technique

Membrane electrode assemblies (MEAs) with ultra-low platinum loadings are attracting significant attention as one method of reducing the quantity of precious metal in polymer electrolyte membrane fuel cells (PEMFCs) and thereby decreasing their cost, one of the key obstacles to the commercialization of PEMFCs. In the present work, high-performance MEAs with ultra-low platinum loadings are developed using a novel catalyst-sprayed membrane technique. The platinum loadings of the anode and cathode are lowered to 0.04 and 0.12 mg cm⁻², respectively, but still yield a high performance of 0.7 A cm⁻² at 0.7 V. The influence of Nafion content, cell temperature, and back pressures of the reactant gases are investigated. The optimal Nafion content in the catalyst layer is ca. 25 wt.%. This is significantly lower than for low platinum loading MEAs prepared by other methods, indicating ample interfacial contact between the catalyst layer and membrane in our prepared MEAs. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) measurements reveal that our prepared MEA has very thin anode and cathode catalyst layers that come in close contact with the membrane, resulting in a MEA with low resistance and reduced mass transport limitations.     

Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer

Gas diffusion electrodes (GDEs) prepared with various polymer binders in their catalyst layers (CLs) were investigated to optimize the performance of phosphoric acid doped polybenzimidazole (PBI)-based high temperature proton exchange membrane fuel cells (HT-PEMFCs). The properties of these binders in the CLs were evaluated by structure characterization, electrochemical analysis, single cell polarization and durability test. The results showed that polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as CL binders than conventional PBI or Nafion binder. At ambient pressure and 160 °C, the maximum power density can reach ∼ 0.61 W cm⁻² (PTFE GDE), and the current density at 0.6 V is up to ca. 0.52 A cm⁻² (PVDF GDE), with H₂/air and a platinum loading of 0.5 mg cm⁻² on these electrodes. Also, both GDEs showed good stability for fuel cell operation in a short term durability test.     

The effect of materials on proton exchange membrane fuel cell electrode performance

This paper describes the optimisation in the fabrication materials and techniques used in proton exchange membrane fuel cell (PEMFC) electrodes. The effect on the performance of membrane electrode assemblies (MEAs) from the solvents used in producing catalyst inks is reported. Comparison in MEA performances between various gas diffusion layers (GDLs) and the importance of microporous layers (MPLs) in gas diffusion electrodes (GDEs) are also shown. It was found that the best performances were achieved for GDEs using tetrahydrofuran (THF) as the solvent in the catalyst ink formulation and Sigracet 10BC as the GDL. The results also showed that our in-house painted GDEs were comparable to commercial ones (using Johnson Matthey HiSpec™ and E-TEK catalysts).     

Self-humidifying nanocomposite membranes based on sulfonated poly(ether ether ketone) and heteropolyacid supported Pt catalyst for fuel cells

In the present study, the self-humidifying nanocomposite membranes based on sPEEK and Cs_2.5H_0.5PW₁₂O₄₀ supported Pt catalyst (Pt-Cs_2.5H_0.5PW₁₂O₄₀ catalyst or Pt-Cs_2.5) and their performance in proton exchange membrane fuel cells with dry reactants has been investigated. The XRD, FTIR, SEM-EDXA and TEM analysis were conducted to characterize the catalyst and membrane structure. The ion exchange capacity (IEC), water uptake and proton conductivity measurements indicated that the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes have higher water absorption, acid and proton-conductive properties compared to the plain sPEEK membrane and Nafion-117 membrane due to the highly hygroscopic and acidy properties of Pt-Cs_2.5 catalyst. The single cells employing the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes exhibited higher cell OCV values and cell performances than those of plain sPEEK membrane and Nafion-117 membrane under dry or wet conditions. Furthermore, the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes showed good water stability in aqueous medium. After investigation of several membranes such as sPEEK and sPEEK/Pt-Cs_2.5 membranes, the self-humidifying nanocomposite membrane with sulfonation degree of 65.12% for its sPEEK and 15 wt.% of catalyst with 1.25 wt.% Pt within catalyst was found to be the best proton exchange membrane for fuel cell applications. This self-humidifying nanocomposite membrane has a higher single cell performance than the Nafion-117 which was frequently used as a proton exchange membrane for fuel cell applications.     

Optimal catalyst layer structure of polymer electrolyte membrane fuel cell

In a membrane electrode assembly (MEA) of polymer electrolyte membrane fuel cells, the structure and morphology of catalyst layers are important to reduce electrochemical resistance and thus obtain high single cell performance. In this study, the catalyst layers fabricated by two catalyst coating methods, spraying method and screen printing method, were characterized by the microscopic images of catalyst layer surface, pore distributions, and electrochemical performances to study the effective MEA fabrication process. For this purpose, a micro-porous layer (MPL) was applied to two different coating methods intending to increase single cell performances by enhancing mass transport. Here, the morphology and structure of catalyst layers were controlled by different catalyst coating methods without varying the ionomer ratio. In particular, MEA fabricated by a screen printing method in a catalyst coated substrate showed uniformly dispersed pores for maximum mass transport. This catalyst layer on micro porous layer resulted in lower ohmic resistance of 0.087 Ω cm² and low mass transport resistance because of enhanced adhesion between catalyst layers and a membrane and improved mass transport of fuel and vapors. Consequently, higher electrochemical performance of current density of 1000 mA cm^-2 at 0.6 V and 1600 mAcm⁻² under 0.5 V came from these low electrochemical resistances comparing the catalyst layer fabricated by a spraying method on membranes because adhesion between catalyst layers and a membrane was much enhanced by screen printing method.     

Development of a tubular microbial fuel cell (MFC) employing a membrane electrode assembly cathode

Tubular microbial fuel cells (MFC) with air cathode might be amenable to scale-up but with increasing volume a mechanically robust, cost-effective cathode structure is required. Membrane electrode assemblies (MEA) are investigated in a tubular MFC using cost-effective cation (CEM) or anion (AEM) exchange membrane. The MEA fabrication mechanically combines a cathode electrode with the membrane between a perforated cylindrical polypropylene shell and tube. Hydrogel application between membrane and cathode increases cathode potential by ∼100 mV over a 0–5.5 mA range in a CEM-MEA. Consequently, 6.1 W m⁻³ based on reactor liquid volume (200 cm³) are generated compared with 5 W m⁻³ without hydrogel. Cathode potential is also improved in AEM-MEA using hydrogel. Electrochemical Impedance Spectroscopy (EIS) to compare MEA's performance suggests reduced impedance and enhanced membrane–cathode contact area when using hydrogel. The maximum coulombic efficiency observed with CEM-MEA is 71% and 63% with AEM-MEA. Water loss through the membrane varies with external load resistance, indicating that total charge transfer in the MFC is related to electro-osmotic drag of water through the membrane. The MEA developed here has been shown to be mechanically robust, operating for more than six month at this scale without problem.     

High performance membrane electrode assemblies by optimization of coating process and catalyst layer structure in direct methanol fuel cells

High performance membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs) are developed by changing the coating process, optimizing the structure of the catalyst layer, adding a pore forming agent to the cathode catalyst layer, and adjusting the hot-pressing conditions, such as pressure and temperature. The effects of these MEA fabrication methods on the DMFC performance are examined using a range of physicochemical and electrochemical analysis tools, such as FE-SEM, electrochemical impedance spectroscopy (EIS), polarization curves, and differential scanning calorimetry (DSC) of the membrane. EIS and polarization curve analysis show that an increase in the thickness and porosity of the cathode catalyst layer plays a key role in improving the cell performance with reduced cathode reaction resistance, whereas the MEA preparation methods have no significant effects on the anode impedance. In addition, the addition of magnesium sulfate as a pore former reduces the cathode reaction transfer resistance by approximately 30 wt%, resulting in improved cell performance.