The dependence of performance degradation of membrane electrode assembly on platinum loading in polymer electrolyte membrane fuel cell

The durability of membrane electrode assemblies (MEAs) with varying amounts of Pt loading on the cathode of polymer electrolyte membrane fuel cells was investigated using load cycling as an accelerated degradation test (ADT). The single-cell performance of the MEA as determined by the ADT declined by approximately 34, 48, and 78%, when cathode Pt loading in the MEA was reduced to 0.3, 0.2, and 0.1 mg cm⁻², respectively. The increase in MEA performance declined at higher cathode Pt loading conditions, and the degradation rate of MEA performance was also diminished. To characterize the electrochemical and structural properties of the MEAs, cyclic voltammograms, electrochemical impedance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy were utilized before and after ADT.     

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.     

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.     

Nanosphere-structured composites consisting of Cs-substituted phosphotungstates and antimony doped tin oxides as catalyst supports for proton exchange membrane liquid water electrolysis

Proton exchange membrane liquid water electrolyser operated blow 80 °C suffers from insufficient catalyst activity and durability due to the slow oxygen evolution kinetics and poor stability. Aiming at enhancing oxygen electrode kinetics and stability, composite materials consisting of antimony doped tin oxide and Cs-substituted phosphotungstate were synthesized as the support of iridium oxide and possessed functionality of mixed electronic and protonic conductivity. At 80 °C under dry ambient atmosphere, the materials showed an overall conductivity of 0.33 S cm⁻¹. The supported IrO₂ catalysts were characterized in sulfuric acid electrolyte, showing significant enhancement of the oxygen evolution reaction (OER) activity. Electrolyser tests of the catalysts were conducted at 80 °C with a Nafion membrane. At an IrO₂ loading of 0.75 mg cm⁻² and a Pt loading of 0.2 mg cm⁻², the cell performance of a current density of 2 A cm⁻² at 1.66 V was achieved. The cell showed good durability at 35 °C under a current density of 300 mA cm⁻² in a period of 464 h.     

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.     

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.     

Effects of platinum loading on the performance of proton exchange membrane fuel cells with high ionomer content in catalyst layers

The effect of Pt loading on the performance of proton exchange membrane fuel cells with atmospheric air feed was evaluated at various relative humidities. The membrane electrode assemblies (MEAs) were fabricated by decal methods with high Nafion ionomer content (30 and 40 wt.%). When the Pt loading was decreased, the performance of the MEAs with an ionomer content of 30 wt.% gradually decreased, mainly due to the insufficient active Pt surfaces with low proton conductivity. With a higher ionomer content of 40 wt.%, the activation overpotential was not significantly increased by the decrease in Pt loading, and the concentration overpotential could be largely reduced by decreasing the Pt loading to 0.25 mg/cm². When the Pt loading was further decreased to 0.15 mg/cm², even though the flooding became more severe, the cell performance at 0.6 V and intermediate relative humidity of 55% was about 71.6%, compared to the MEA with a high Pt loading of 0.35 mg/cm² (ionomer content: 30 wt.%). The cell performance could be further enhanced by decreasing the ionomer content in the anode to enhance the water back diffusion.     

New highly proton-conducting membrane based on sulfonated poly(arylene ether sulfone)s containing fluorophenyl pendant groups,for low-temperature polymer electrolyte membrane fuel cells

A novel series of sulfonated poly(arylene ether sulfone)s (SPAESs) containing fluorophenyl pendant groups are successfully developed and their membranes are evaluated in low-temperature proton exchange membrane fuel cells. The SPAESs are synthesized from 4,4′-dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), and (4-fluorophenyl)hydroquinone by nucleophilic aromatic substitution polycondensation. The structure and properties of SPAESs membranes are characterized using ¹H-NMR, EA, FT-IR, TG, and DSC, along with the proton conductivity, water uptake, ion exchange capacity and chemical stability. A maximum proton conductivity of 0.35 S cm⁻¹ at 90 °C is achieved for SPAES membrane with 50% SDCDPS. These SPAES membranes display high dimensional stability and oxidative durability, due to the introduction of fluorophenyl pendant groups on the polymer backbone. The fuel cell performances of the MEAs with SPAES reaches an initial power density of 120.6 mW cm⁻² at 30 °C, and greatly increases to 224.3 mW cm⁻² at 80 °C using H₂ and O₂ gases.     

Reinforced short-side-chain Aquivion® membrane for proton exchange membrane water electrolysis

A reinforced short-side-chain per?uorosulfonic acid (PFSA) Aquivion® membrane with equivalent weight (EW) of 980 g/eq and 50 μm thickness produced by Solvay Specialty Polymers was investigated for operation in polymer electrolyte membrane (PEM) water electrolysis. The membrane produced by a dispersion casting process was reinforced by introducing polytetrafluoroethylene (PTFE) fibres in order to enhance mechanical and dimensional stability properties while keeping high conductivity and decreased ohmic drop for operation at high current density. A conventional extruded PFSA Aquivion® membrane with similar EW and thickness was investigated for comparison under similar operating conditions. Membrane-electrode assemblies (MEAs) made of reinforced membranes were tested in a single cell and compared to extruded membranes bared MEAs. All MEAs consisted of home-made unsupported IrRuOx anode and carbon-supported Pt (40%) cathode electrocatalysts. Electrochemical tests showed better water splitting performance for the reinforced Aquivion® based membrane-electrode assembly as compared to the benchmark based MEA. At 90 °C, a current density of 5 Acm^?2 was recorded at 1.8 V (～80% voltage efficiency vs. Higher Heating Value (HHV) with the reinforced Aquivion® membrane. The cell voltage for the reinforced membrane-based cell was about 50 mV lower than the extruded one during a 3500 h durability test. Moreover, lower recoverable losses were observed for the reinforced membrane based MEA during steady-state durability tests and no membrane thinning appeared after prolonged operation.     

Diagnosis of membrane electrode assembly degradation with drive cycle test technique

One of important factors determining the lifetime of proton exchange membrane fuel cells (PEMFCs) is degradation and failure of membrane electrode assembly (MEA). The lack of effective mitigation methods is largely due to the currently limited understanding of the degradation mechanisms for fuel cell MEAs. This study adopted the accelerating degradation technique to analyze durability of MEA using drive cycle test protocol developed by Chinese NERC Fuel Cell & Hydrogen Technology to assess the long-term durability of fuel cells for vehicular application. During 900 h durability test of the MEA, the polarization curve, cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were performed as diagnostics during and on completion the test. The experimental results show that the performance degradation rate of the cell is about 70 μV h⁻¹ at the operating current density of 500 mA cm⁻², failure of the proton exchange membrane is the decisive factor leading to the failure of the MEA. And the damage of the micro-structural of catalytic layer, crucial for electrochemical reaction, is the decisive factor for the performance degradation.     

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.     

A completely slot die coated membrane electrode assembly

This work shows how to manufacture completely coated membrane electrode assemblies (CC-MEAs) for PEM water electrolysis by only using a slot die. Platinum, Nafion^®, and IrO₂ dispersions are successively coated to the respective dried layer. For comparison reasons, MEAs with the same Iridium loading of 2.1 mg cm⁻² and Platinum loading of 0.4 mg cm⁻², assembled with a commercial membrane of the same 20 μm thickness, were produced via decal method. Differences in polarization curves are attributed to the lower high frequency resistance of CC-MEAs determined by impedance spectroscopy. The easy-to-scale CC-MEA method presented here offers the advantages of direct membrane deposition (DMD) without the challenge of homogenously coating a porous transport layer (PTL). Therefore, it allows a free choice of different PTLs – regardless if in sintered form or as expanded metal. The comparability between the produced CC-MEAs and published DMD results is shown by means of cross-sectional and electrochemical measurements.     

Feasibility of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells based in phosphoric acid-doped membrane

Factors as the Pt/C ratio of the catalyst, the binder content of the electrode and the catalyst deposition method were studied within the scope of ultra-low Pt loading electrodes for high temperature proton exchange membrane fuel cells (HT-PEMFCs). The Pt/C ratio of the catalyst allowed to tune the thickness of the catalytic layer and so to minimize the detrimental effect of the phosphoric acid flooding. A membrane electrode assembly (MEA) with 0.05 mg_Ptcm⁻² at anode and 0.1 mg_Ptcm⁻² at cathode (0.150 mg_Ptcm⁻² in total) attained a peak power density of 346 mW cm⁻². It was proven that including a binder in the catalytic layer of ultra-low Pt loading electrodes lowers its performance. Electrospraying-based MEAs with ultra-low Pt loaded electrodes (0.1 mg_Ptcm⁻²) rendered the best (peak power density of 400 mW cm⁻²) compared to conventional methods (spraying or ultrasonic spraying) but with the penalty of a low catalyst deposition rate.     

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 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.     

Facile electrochemical preparation of nonprecious Co-Cu alloy catalysts for hydrogen production in proton exchange membrane water electrolysis

To realize nonprecious-metal catalysts with practical applicability for the hydrogen evolution reaction (HER), improved corrosion resistance and catalytic activity are required. In this study, composition-controlled Co-Cu alloys were fabricated by electrodeposition for use as HER catalysts in proton exchange membrane water electrolyzers (PEMWEs). As the Cu content in the alloy increased, the morphology changed from needle-shaped particles to small round particles. Furthermore, a phase transition from a hexagonal close-packed structure to a face-centered cubic structure occurs because the latter structure is stabilized by adding Cu to Co. The optimum catalyst composition for the HER was found to be Co₅₉Cu₄₁, which had an overpotential of 342 mV at −10 mA cm⁻². This catalyst exhibited excellent durability, showing a potential reduction of approximately 100 mV over 12 hours under a constant current density. This superior performance was attributed to the increase in the electrochemical surface area resulting from the addition of Cu, as confirmed by electrochemical double layer capacitance measurements, in addition to a counterbalance between the hydrogen adsorption energies of Co and Cu. Finally, the application of the Co-Cu alloy catalyst as a cathode catalyst in a PEMWE resulted in excellent performance of 1.2 A cm⁻² at 2.0 V_cell.     

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.     

Improving cell performance for anion exchange membrane fuel cells with FeNC cathode by optimizing ionomer content

To improve the performance of anion exchange membrane fuel cells (AEMFCs) with platinum-group-metal (PGM)-free cathode, significant efforts are still needed. Herein, we prepare high oxygen reduction reaction activity FeNC catalyst and integrate such catalyst into AEMFCs with different ionomer/catalyst (I/C) ratios from 0.1 to 1.0. We show that suitable quaternary ammonia poly (methyl-piperidine-co-p-terphenyl) (QAPPT) ionomer content can provide better catalyst layers (CLs) microstructure, in which the transfer efficiency of electron and charge can be improved so as to decrease the active polarization. High ohmic resistance is caused by either low or excess ionomer which leads to inconsecutive ionic network of CLs or high coverage of non-electronic conductor. In addition, mass-transfer polarization is also brought out by excess QAPPT ionomer which fills up the gas–liquid transport pores inside FeNC/QAPPT aggregates. With the I/C ratio of 0.7, AEMFC with FeNC cathode exhibits the best cell performance achieving a peak power density of 660 mW cm^?2 at 1500 mA cm^?2 under H₂/air (CO₂-free). To verify the feasibility of FeNC cathode in realistic applications, an AEMFC stack with 29 cells of 270 cm² MEAs was assembled with a power output of 508 W under H₂/air.     

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.     

A novel catalyst coated membrane embedded with Cs-substituted phosphotungstates for proton exchange membrane water electrolysis

Catalyst coated membrane (CCM) is the core component of proton exchange membrane (PEM) water electrolysis and the main place for electrochemical reaction and mass transfer. Its properties directly affect the performance of PEM water electrolysis. Aiming at decreasing the polarization loss and the ohmic loss, a novel CCM embedded with Cs_1.5HPA in the skeleton of the Nafion^® ionomer and the Nafion^® membrane was prepared and possessed functionality of improved protonic conductivity. Meanwhile, the Cs_1.5HPA-Nafion ionomer content in the catalyst layers was further optimized. The SEM, EDS and pore volume distribution measurement showed that the Cs_1.5HPA embedded in the CCM without agglomeration and the micropore and mesopore were well distributed in the catalyst layer. Furthermore, CCMs were tested in a PEM water electrolyser at 80 °C, beneficial effects on both the Tafel slope and the iR loss were obtained due to the improved protonic conductivity as well as the appropriate pore structure and increased specific pore volume. The performance of the electrolyser cell was obviously improved with the novel CCM. The highest cell performance of 1.59 V at 2 A cm⁻² was achieved at 80 °C. At 35 °C and 300 mA cm⁻², the cell showed good durability within the test period of up to 570 h.