The effects of ionomer content on PEM water electrolyser membrane electrode assembly performance

In this study, the effects of Nafion^® ionomer content in membrane electrode assemblies (MEAs) of polymer electrolyte membrane (PEM) water electrolyser were discussed. The MEAs were prepared with a catalyst coated membrane (CCM) method. The catalysts inks with Nafion ionomer could form uniform coatings deposited on the membrane surfaces. SEM and area EDX mapping demonstrated that anode catalyst coating was uniformly distributed, with a microporous structure. The contents of Nafion ionomer were optimized to 25% for the anode and 20% for cathode. A current density of 1 A cm⁻² was achieved at terminal voltage 1.586 V at 80 °C in a PEMWE single cell, with Nafion 117, Pt/C as cathode, and Ru_0.7Ir_0.3O₂ as anode.     

Ultra-low Pt loading for proton exchange membrane fuel cells by catalyst coating technique with ultrasonic spray coating machine

This paper reports use of an ultrasonic spray for producing ultra-low Pt load membrane electrode assemblies (MEAs) with the catalyst coated membrane (CCM) fabrication technique. Anode Pt loading optimization and rough cathode Pt loading were investigated in the first stage of this research. Accurate cathode Pt coating with catalyst ink using the ultrasonic spray method was investigated in the second stage. It was found that 0.272 mg_Pt/cm² showed the best observed performance for a 33 wt% Nafion CCM when it was ultrasonically spray coated with SGL 24BC, a Sigracet manufactured gas diffusion layer (GDL). Two different loadings (0.232 and 0.155 mg_Pt/cm²) exposed to 600 mA/cm² showed cathode power mass densities of 1.69 and 2.36 W/mg_Pt, respectively. This paper presents impressive cathode mass power density and high fuel cell performance using air as the oxidant and operated at ambient pressure.     

Effect of platinum amount in carbon supported platinum catalyst on performance of polymer electrolyte membrane fuel cell

The performance of polymer electrolyte membrane fuel cells fabricated with different catalyst loadings (20, 40 and 60 wt.% on a carbon support) was examined. The membrane electrode assembly (MEA) of the catalyst coated membrane (CCM) type was fabricated without a hot-pressing process using a spray coating method with a Pt loading of 0.2 mg cm⁻². The surface was examined using scanning electron microscopy. The catalysts with different loadings were characterized by X-ray diffraction and cyclic voltammetry. The single cell performance with the fabricated MEAs was evaluated and electrochemical impedance spectroscopy was used to characterize the fuel cell. The best performance of 742 mA cm⁻² at a cell voltage of 0.6 V was obtained using 40 wt.% Pt/C in both the anode and cathode.     

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.     

Effects of hot pressing conditions on the performance of Nafion membranes coated by ink-jet printing of Pt/MWCNTs electrocatalyst for PEMFCs

In our previous work, a hydrothermal method was employed to prepare Pt/MWCNTs nanocomposites with 20 wt.% Pt, a low mean Pt nanoparticles size (2.8 nm) and a specific surface area of 99 m² g⁻¹. In this work, the membrane electrode assemblies (MEAs) with hydrothermally synthesized Pt/MWCNTs nanocatalysts were fabricated by catalyst-coated membrane (CCM) method. For this purpose, a commercial HP inkjet printer was used to deposit Pt/MWCNTs ink (as catalyst ink) directly on to the substrate (Nafion membrane or decal substrate) with a loading of 0.2 mg cm⁻² Pt for both the anode and cathode. The effects of hot-pressing conditions on the performance of MEAs were investigated through Taguchi design of experiments method using temperature (100 and 130 °C), pressure (800 and 1000 psi) and time (3 and 5 min) as effective experimental parameters. The compression ratios of MEAs were determined by testing the thicknesses before and after hot-pressing process. The performance of MEAs was characterized by the polarization curves and cyclic voltammetry (CV) and the surface morphologies of the electrodes were observed by scanning electron microscopy (SEM). The results showed that the most appropriate hot-pressing conditions were 800 psi, 100 °C, and 3 min. Electrochemical analysis and physical property examination revealed that the MEA fabricated by CCM method has a better performance compared to the one prepared by conventional decal transfer (DT) method.     

Effect of loading and distributions of Nafion ionomer in the catalyst layer for PEMFCs

The electrode with various contents of Nafion ionomer for inside and/or on the surface in the catalyst layer, respectively, was designed for proton exchange membrane fuel cell (PEMFC) electrode to investigate the effect of Nafion ionomer distribution in the catalyst layer on cell performance and improve electrode performance. The effect of Nafion ionomer on the electrode of each design was judged by a cyclic voltammetry measurement and the cell performance obtained through a single cell test using H₂/O₂ gases. Electrodes with different ionomer distributions for inside and on the surface in the catalyst layer, respectively, were examined. It is found that the electrode where the Nafion ionomer is impregnated on the surface of catalyst layer shows better cell performance than that where the Nafion ionomer is incorporated in the inside of catalyst layer. The best cell performance among the catalyst layers tested in this study was obtained for the electrode with 0.5 mg cm⁻² of Nafion ionomer inside the catalyst layer and 1.0 mg cm⁻² of Nafion ionomer on the surface of the catalyst layer together.     

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.     

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.     

Optimum compositions of membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell

We investigated the effects of the compositions of catalyst layers and diffusion layers on performances of the membrane electrode assemblies (MEAs) for direct dimethyl ether fuel cell. The performances of the MEAs with different thicknesses of Nafion membranes were compared in this work. The optimal compositions in the anode are: 20 wt% Nafion content and 3.6 mg cm⁻² Pt loading in the catalyst layer, and 30 wt% PTFE content and 1 mg cm⁻² carbon black loading in the diffusion layer. In the cathode, MEA with 20 wt% Nafion content in the catalyst layer and 30 wt% PTFE content in the diffusion layer presented the optimal performance. The MEA with Nafion 115 membrane displayed the highest maximum power density of 46 mW cm⁻² among the three MEAs with different Nafion membranes. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Platinum-plated nanoporous gold: An efficient,low Pt loading electrocatalyst for PEM fuel cells

Platinum-plated nanoporous gold leaf (Pt-NPGL) is made by coating a conformal, atomically thin skin of platinum over the high surface area pores of a thin membrane of nanoporous gold. Because Pt loading in Pt-NPGL can be controlled down to 0.01 mg cm⁻² using only simple benchtop chemistry, the material holds promise as a low Pt loading, carbon-free electrocatalyst. Here, we report successful use of Pt-NPGL as a catalyst in proton exchange membrane (PEM) fuel cells. Stable and high performance Pt-NPGL/Nafion membrane electrode assemblies (MEAs) were made using a stamping technique. The performance of Pt-NPGL MEAs is comparable to conventional carbon-supported nanoparticles-based MEAs with much higher loading, generating an output power density of up to 4.5 kW g⁻¹ Pt in our non-optimized test configuration. Correlations between the performance of Pt-NPGL MEAs, the electrochemically accessible surface area, and material microstructure are discussed. Our success in using Pt-NPGL as a fuel cell catalyst suggests that creating precious metals skins over nanoporous metal supports is a viable strategy for designing new catalysts for PEM fuel cells. This promising approach allows tailoring catalytic activity by engineering precious metal/substrate interactions, employs materials with dual functionality acting both as current collector and catalyst, and may avoid the sintering problems plaguing conventional nanoparticle-based catalysts.     

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.     

Durability improvement at high current density by graphene networks on PEM fuel cell

This study presents a novel structure of catalyst layers of membrane electrode assemblies (MEAs) by adding graphene to platinum on carbon black (Pt/C) to improve the durability at high current density operation (3 A cm⁻²). Graphene displays outstanding low electrical resistance and has the advantage of high electron mobility. It is also used in lithium ion batteries to improve electrical performance such as high rate charge/discharge capability and cycle-life stability. In this study, three MEAs are compared, and graphene is used as an excellent conductive additive in catalyst layers for better electrons transport at high current density operation. The MEA coated Pt/C mixed with 0.1 wt% graphene shows best durability for 0.3 V h⁻¹ which is almost 3.7 times better than that of without graphene additive (1.1 V h⁻¹). The graphene additive effectively extends the durability of the MEA. Furthermore, the MEAs are analyzed by AC impedance. The impedance arc of the MEA coated with Pt/C only is getting worse, but those two coated with graphene show similar and smaller impedance arcs after high current density operation for 80 h.     

Optimization of Nafion content in Nafion–polyaniline nano-composite modified cathodes for PEMFC application

In this research several Nafion–Polyaniline nano-composite modified cathodes have been fabricated and evaluated in oxygen reduction reaction (ORR) in order to use in proton exchange membrane fuel cell (PEMFC). Modified cathodes made by the wide range of Nafion content (from 0 to 1.6 mg cm⁻²) and investigated in the acidic solution by different electrochemical techniques at 25 °C. The results indicate the activity of the modified electrodes is increased by employing of Nafion–Polyaniline nano-composite in the reaction layer, but there is an optimum value for Nafion content in the catalyst layer. The modified electrode impregnated by 0.4 mg cm⁻² of Nafion shows the highest activity. Analysis of the surface morphology of the Nafion–polyaniline modified electrodes by scanning electron microscopy and electrochemical data reveal that the existence of polyaniline (PANI) nanofibers in the catalyst layer before adding Nafion solution, improves the homogeneity distribution of the ionomer in catalyst layer, change the morphology of electrode and increase the performance of gas diffusion electrodes (GDEs) in oxygen reduction reaction.     

Inkjet printing of carbon supported platinum 3-D catalyst layers for use in fuel cells

We present a method of using inkjet printing (IJP) to deposit catalyst materials onto gas diffusion layers (GDLs) that are made into membrane electrode assemblies (MEAs) for polymer electrolyte fuel cell (PEMFC). Existing ink deposition methods such as spray painting or screen printing are not well suited for ultra low (<0.5 mg Pt cm⁻²) loadings. The IJP method can be used to deposit smaller volumes of water based catalyst ink solutions with picoliter precision provided the solution properties are compatible with the cartridge design. By optimizing the dispersion of the ink solution we have shown that this technique can be successfully used with catalysts supported on different carbon black (i.e. XC-72R, Monarch 700, Black Pearls 2000, etc.). Our ink jet printed MEAs with catalyst loadings of 0.020 mg Pt cm⁻² have shown Pt utilizations in excess of 16,000 mW mg⁻¹ Pt which is higher than our traditional screen printed MEAs (800 mW mg⁻¹ Pt). As a further demonstration of IJP versatility, we present results of a graded distribution of Pt/C catalyst structure using standard Johnson Matthey (JM) catalyst. Compared to a continuous catalyst layer of JM Pt/C (20% Pt), the graded catalyst structure showed enhanced performance.     

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.     

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.     

The development of PTFE/Nafion/TEOS membranes for application in moderate and high temperature proton exchange membrane fuel cells

PTFE/Nafion (PN) and PTFE/Nafion/TEOS (PNS) membranes were fabricated for the application of moderate and high temperature proton exchange membrane fuel cells (PEMFCs), respectively. Membrane electrode assemblies (MEAs) were fabricated by PTFE/Nafion (and PTFE/Nafion/TEOS) membranes with commercially available low and high temperature gas diffusion electrodes (GDEs). The effects of relative humidity, operation temperature, and back pressure on the performance and durability test of the as-prepared MEAs were investigated. Incorporating TEOS into a PNS membrane and adding another layer of carbon onto a GDE would result in low membrane conductivity and low fuel cell performance respectively. However, in this work it is shown that HT-PNS MEAs demonstrate a higher performance than LT-PN MEAs in severe conditions - high temperature (118 °C) and low humidity (25% RH). The TEOS and additional carbon layer function as water retaining agents which are especially important for high temperature and low humidity conditions. The HT-PNS MEA showed good stability in a 50 h fuel cell test at high temperature, moderate relative humidity (50% RH) and back pressure of 14.7 psi.     

The influence of the membrane thickness on the performance and durability of PEFC during dynamic aging

The influence of the membrane thickness on the performance and durability of 25 cm² membrane electrode assembly (MEA) toward dynamic aging test was investigated. The tested MEAs consist of chemically stabilized membranes (AQUIVION™) with thicknesses of 30 and 50 μm, electrocatalyst – 46 %Pt/C (Tanaka) with Pt loadings of 0.25 (anode), 0.45 mg cm⁻² (cathode) and gas diffusion layers 25 BC (SGL Group). The applied dynamic aging procedure is repetitive current cycling between 0.12 A cm⁻² for 40 s and 0.6 A cm⁻² for 20 s. The testing conditions were 80 °C, fully saturated hydrogen and air, total pressure of 2.5 atm abs. The aging procedure was regularly interrupted for evaluating the MEAs' “health” via electrochemical methods and mass spectrometry. The carbon support degradation as a function of the electrode potential, current cycling and supplied gas was studied. The effects of the Pt particles agglomeration and Pt physical loss in the active layer of the cathode on the MEAs performance degradation were individually assessed. The effect of the membrane thicknesses on the performance and durability of the PEFC was established. The reasons and stages of MEAs performance degradation were analyzed.     

Preparation and characterization of partial-cocrystallized catalyst-coated membrane for solid polymer electrolyte water electrolysis

A novel catalyst-coated membrane (CCM) for solid polymer electrolyte water electrolysis was fabricated by together crystallizing partial-crystallized Nafion membrane and catalyst layers. The properties and performance of the partial-cocrystallized CCM (PCCCM) were evaluated and analyzed by destructive soaking test, scanning electron microscope, mercury intrusion and single cell test. The results revealed that the optimum annealing temperature and time for fabricating partial-crystallized Nafion membrane and PCCCM was 100 °C for 4 h and 120 °C for 4 h, respectively. The PCCCM not only possessed much stronger cohesion between membrane and catalyst layers, but also had higher porosity than conventional CCM. The electrolysis voltage of the SPE water electrolyser with the new CCM was as low as 1.748 V at 2000 mA cm⁻² under 80 °C and atmospheric pressure. Moreover, there was no obvious increase of electrolysis voltage during stability test conducted under 2000 mA cm⁻² for about 180 h.