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.     

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.     

Durability study of proton exchange membrane fuel cells under dynamic testing conditions with cyclic current profile

This work addresses issues of long-term durability of hydrogen–air proton exchange membrane fuel cells (PEMFCs) under cyclic current loading conditions, simulating the real road driving conditions for automotives. The same type of membrane–electrode assembly (MEA) was also aged under constant current mode as a control and the results were compared with those of the cyclically aged MEA. Both MEAs were characterized for cell polarizations, impedance spectra, Tafel plots, hydrogen crossover rates as well as electrochemical active surface areas at intervals of 100 h of aging. It was demonstrated that hydrogen crossover increased dramatically after 500 h of current cycling due to pinhole formation and was the most dominant degradation source. The fuel cell approached the end of its useful lifetime after 1000 h of operation. On the other hand, the hydrogen crossover rate remained approximately constant for the MEA under constant current operation. Mass transport limitations were identified as the major source of decreased performance during the constant current operation. This decrease in performance was partially reversible when cathode flooding was resolved by setting the cell at lower current densities. At the end, a phenomenological durability model was established successfully to describe the aging processes and cell performance at different time nodes.     

Life prediction of membrane electrode assembly through load and potential cycling accelerated degradation testing in polymer electrolyte membrane fuel cells

Accelerated degradation tests (ADTs) are commonly used to assess the durability of membrane electrode assembly (MEA) components consisting of polymer electrolyte membrane fuel cells (PEMFC) under harsh stress conditions, estimating their lifetime in actual use condition and uncovering their vital degradation mechanisms. ADTs apply mechanically, chemically, or thermally combined stressors to efficiently investigate the durability of MEAs. However, combined stressors for ADTs might cause biased lifetime prediction because major deterioration mechanisms of MEA components are mixed with each other. This work proposes a method to accurately predict the lifetime of MEA through empirical modeling of its performance degradation through ADTs under potential cycle (carbon corrosion) and load cycle tests (electrocatalysts). To simulate operation modes of fuel cell electric vehicles, MEAs are tested under continuous on-off cycle testing (24 h operating and 1 h break) for 5000 h. Degradation patterns of MEAs are first modeled by the empirical model. The relationship between ADTs (potential and load cycle) and continuous on-off condition is then closely examined to accurately predict MEA lifetime under actual operation environments. The proposed idea has a potential to resolve critical durability issues of MEAs by identifying intermingling effects from other constituents.     

Degradation analysis of the core components of metal plate proton exchange membrane fuel cell stack under dynamic load cycles

The durability of metal plate proton exchange membrane fuel cell (PEMFC) stack is still an important factor that hinders its large-scale commercial application. In this paper, we have conducted a 1000 h durability test on a 1 kW metal plate PEMFC stack, and explored the degradation of the core components. After 1000 h of dynamic load cycles, the voltage decay percentage of the stack under the current densities of 1000 mA cm^?2 is 5.67%. By analyzing the scanning electron microscopy (SEM) images, the surfaces of the metal plates are contaminated locally by organic matter precipitated from the membrane electrode assembly (MEA). The SEM images of the catalyst coated membrane (CCM) cross section indicate that the MEA has undergone severe degradation, including the agglomeration of the catalyst layer, and the thinning and perforation of the PEM. These are the main factors that cause the rapid increase in hydrogen crossover flow rate and performance decay of the PEMFC stack.     

Degradation of a polymer exchange membrane fuel cell stack with Nafion membranes of different thicknesses: Part I. In situ diagnosis

The durability of polymer exchange membrane (PEM) fuel cells, under a wide range of operational conditions, has been attracting intensive attention, as durability is one of the largest barriers for commercialization of this promising technology. In the present work, membrane electrode assembly (MEA) degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, was carried out for 1000 h under idle conditions. By means of several on-line electrochemical measurements, the performance of the individual cells was analyzed at different times during the degradation process. The results indicate that the cells with thinner membranes have a lower open circuit voltage (OCV) due to the higher fuel crossover. Before degradation, the thickness of the membranes correlates with performance of the cell. However, with the advancement of degradation, the performance of cells with thinner membranes degraded much faster than those with thicker membranes, especially after 800 h of operation. The fast performance degradation for thinner membranes is evident by a dramatic increase in hydrogen crossover indicating membrane thinning or pinhole formation.     

Highly efficient,cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst

In order to obtain a fuel cell with both enhanced power generation performance and cell reversal resistance, the composite catalyst consisting of the self-made PtNi/C octahedral and the oxygen evolution reaction (OER) catalyst IrO₂ and RuO₂ is mixed and applied in the anode, and the only octahedral catalyst is employed as the cathode to prepare the membrane electrode assembly (MEA). The electrochemical activity of the composite catalyst decreases slightly, but its performance retention after the accelerated durability test (ADT) is higher. In the single cell test, the MEA fabricated using the composite catalyst maintains good single cell power generation performance. Compared with the control fabricated with Pt/C (JM), the cell voltage at 1 A cm⁻² and the maximum power density are increased by 23 mV and 119 mW cm⁻², respectively. Especially, its durability under continuous cell reversal condition is also improved significantly, and the holding time is prolonged by 1 h. This work realizes the transformation of the octahedral catalyst from the laboratory research to the actual application, and solves the difficulties in fuel cell application, and promotes its commercialization.     

A polymer electrolyte fuel cell life test: 3 years of continuous operation

Implementation of polymer electrolyte fuel cells (PEMFCs) for stationary power applications requires the demonstration of reliable fuel cell stack life. One of the most critical components in the stack and that most likely to ultimately dictate stack life is the membrane electrode assembly (MEA). This publication reports the results of a 26,300 h single cell life test operated with a commercial MEA at conditions relevant to stationary fuel cell applications. In this experiment, the ultimate MEA life was dictated by failure of the membrane. In addition, the performance degradation rate of the cell was determined to be between 4 and 6 μV h⁻¹, at the operating current density of 800 mA cm⁻². AC impedance analysis and DC electrochemical tests (cyclic voltammetry and polarization curves) were performed as diagnostics during and on completion the test, to understand materials changes occurring during the test. Post mortem analyses of the fuel cell components were also performed.     

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.     

Demonstration of a 20 W class high-temperature polymer electrolyte fuel cell stack with novel fabrication of a membrane electrode assembly

Acid-doped polybenzimidazole (PBI) membrane and polytetrafluoroethylene (PTFE)-based electrodes are used for the membrane electrode assembly (MEA) in high-temperature polymer electrolyte fuel cells (HTPEFCs). To find the optimum PTFE content for the catalyst layer, the PTFE ratio in the electrodes is varied from 25 to 50 wt%. To improve the performance of the electrodes, PBI is added to the catalyst layer. With a weight ratio of PTFE to Pt/C of 45:55 (45 wt% PTFE in the catalyst layer), the fuel cell shows good performance at 150 °C under non-humidified conditions. When 5 wt% PBI is added to the electrodes, performance is further improved (250 mA cm⁻² at 0.6 V). Our 20 W class HTPEFC stack is fabricated with a novel MEA. This MEA consists of 8 layers (1 phosphoric acid-doped PBI membrane, 2 electrodes, 1 sub-gasket, 2 gas-diffusion media, 2 gas-sealing gaskets). The sub-gasket mitigates the destruction of a highly acid-doped PBI membrane and provides long-term durability to the fuel cell stack. The stack operates for 1200 h without noticeable cell degradation.     

Degradation studies of proton exchange membrane water electrolysis cells with low platinum group metals – Catalyst coating achieved by atomic layer deposition

Activity and durability of a polymer electrolyte membrane (PEM) water electrolysis single cell, assembled with porous transport electrodes (PTEs) with a low catalyst loading were investigated for 500 h. A current density of 160 mA/cm² and a high mass activity of 1368 A/g_Ir were achieved while operating at 60 °C with 1 mol/L sulfuric acid. The degradation of the cell was characterized using different electrochemical and physicochemical methods before, during and after operation of the electrolysis cell and a mean degradation rate for the cell of 67 μV/h was determined at 15 mA/cm². To the best of our knowledge this is the first time that long-term performance of a PEM water electrolysis cell assembled with PTEs coated by ALD is investigated.     

Effect of the fabrication condition of membrane electrode assemblies with carbon-supported ordered PtCo electrocatalyst on the durability of polymer electrolyte membrane fuel cells

Electrode structure improvement is one of the most promising paths for improving the durability of polymer electrolyte membrane fuel cells (PEMFCs). As strategies to prevent structural deformation and enhance the durability of membrane electrode assemblies (MEAs) with structurally ordered PtCo/C-based cathodes, we evaluated the effect of hot pressing and reinforcing the electrode's structure by increasing the ionomer content. Even though the initial performances of the hot-pressed MEA (HP) and the MEA with extra cathode ionomer (EI) were lower than that of the conventional MEA (CE) by 13.6% and 19.1%, respectively, CE degraded much more significantly than HP and EI after an accelerated degradation test. Therefore, HP and EI could deliver significantly higher single cell performances than CE (22.7% and 43.7%, respectively). The improvements in the durability of HP and EI could be correlated with the structural stability which could be evaluated by structure and electrochemical analysis including electrochemical impedance spectroscopy.     

Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis

High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electrochemical and physical characterization of the MEAs was performed by I–V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm⁻², it still reached a high performance of 1.633 V at 2 A cm⁻² and 80 °C, with IrO₂ as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm⁻² showed that the MEA has good stability: the cell voltage maintained at ∼1.60 V without distinct degradation after 122 h operation at 80 °C and atmospheric pressure.     

Failure of PEM water electrolysis cells: Case study involving anode dissolution and membrane thinning

Polymer electrolyte membrane (PEM) water electrolysis is an efficient and environmental friendly method that can be used for the production of molecular hydrogen of electrolytic grade using zero-carbon power sources such as renewable and nuclear. However, market applications are asking for cost reduction and performances improvement. This can be achieved by increasing operating current density and lifetime of operation. Concerning performance, safety, reliability and durability issues, the membrane-electrode assembly (MEA) is the weakest cell component. Most performance losses and most accidents occurring during PEM water electrolysis are usually due to the MEA. The purpose of this communication is to report on some specific degradation mechanisms that have been identified as a potential source of performance loss and membrane failure. An accelerated degradation test has been performed on a MEA by applying galvanostatic pulses. Platinum has been used as electrocatalyst at both anode and cathode in order to accelerate degradation rate by maintaining higher cell voltage and higher anodic potential that otherwise would have occurred if conventional Ir/IrO_x catalysts had been used. Experimental evidence of degradation mechanisms have been obtained by post-mortem analysis of the MEA using microscopy and chemical analysis. Details of these degradation processes are presented and discussed.     

Performance and stability characteristics of MEAs with carbon-supported Pt and Pt1Ni1 nanoparticles as cathode catalysts in PEM fuel cell

Polarization curves of membrane electrode assemblies (MEAs) containing carbon-supported platinum (Pt/C) and platinum-nickel alloy (Pt₁Ni₁/C) as cathode catalysts were obtained for durability test as a function of time over 1100 h at constant current. Charge transfer resistance was measured using electrochemical impedance spectroscopy and postmortem analysis such as X-ray diffraction and high-resolution transmission electron microscopy was conducted in order to elucidate the degradation factors of each MEA. Our results demonstrate that the reduced performance of MEAs containing Pt₁Ni₁/C as a cathode catalyst was due to decreased oxygen reduction reaction caused by the corrosion of Ni, whereas that of MEAs containing Pt/C was because of reduced electrochemical surface area induced by increased Pt particle size.     

Investigation of the recoverable degradation of PEM fuel cell operated under drive cycle and different humidities

Recoverable degradation of a proton exchange membrane fuel cell (PEMFC) under different relative humidities (RHs) after a whole night rest was investigated. A single cell was operated under drive cycle to simulate the working conditions of fuel cell vehicle. It was found that the cell performance decreased after 5 h operation and recovered mostly after one night rest at higher humidities, i.e. 100%, 75% and 50% RH for both cathode and anode sides; while continuous decrease took place at lower humidity, 35%RH. Polarization curve, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted before and after every 5 h drive cycle for investigating the mechanism of the recoverable degradation. It was found that water content, current density and thermal management might be the main contributions to the performance degradation, by impacting the membrane conductivity, internal resistance, electrode kinetics, and catalyst utilization. A good understanding of voltage recovery phenomenon after several hours rest and its effect on durability will be helpful in improving the reliability and durability of PEMFC.     

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.     

Understanding the performance degradation of anion-exchange membrane direct ethanol fuel cells

It has recently been demonstrated that anion-exchange membrane direct ethanol fuel cells (AEM DEFCs) can yield a high power density. The operating stability and durability of this type of fuel cell is, however, a concern. In this work, we report the durability test of an AEM DEFC that is composed of a Pd/C anode, an A201 membrane, and a Fe-Co cathode and show that the major voltage loss occurs in the initial discharge stage, but the loss becomes smaller and more stable with the discharge time. It is also found that the irreversible degradation rate of the fuel cell is around 0.02 mV h⁻¹, which is similar to the degradation rate of conventional acid direct methanol fuel cells (DMFCs). The experimental results also reveal that the performance loss of the AEM DEFC is mainly attributed to the anode degradation, while the performance of the cathode and the membrane remains relatively stable. The TEM results indicate that the particle size of the anode catalyst increases from 2.3 to 3.5 nm after the long-term discharge, which reduces the electrochemical active surface area and hence causes a decrease in the anode performance.     

Investigation of sintered stainless steel fiber felt as gas diffusion layer in proton exchange membrane fuel cells

The feasibility of using sintered stainless steel fiber felt (SSSFF) as gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) is evaluated in this study. The SSSFF is coated with an amorphous carbon (a-C) film by closed field unbalanced magnetron sputter ion plating (CFUBMSIP) to enhance the corrosion resistance and reduce the contact resistance. The characteristics of treated SSSFF, including microscopic morphology, mechanical properties, electrical conductivity, electrochemical behavior and wettablity characterization, are systematically investigated and summarized according to the requirements of GDL in PEMFC. A membrane electrode assembly (MEA) with a-C coated SSSFF-15 GDL is fabricated and assembled with a-C coated stainless steel bipolar plates in a single cell. The initial peak power density of the single cell is 877.8 mW cm⁻² at a current density of 2324.9 mA cm⁻². Lifetime test of the single cell over 200 h indicates that the a-C coating protects the SSSFF-15 GDL from corrosion and decreases the performance degradation from 30.6% to 6.3%. The results show that the SSSFF GDL, enjoying higher compressive modulus and ductility, is a promising solution to improve fluid permeability of GDL under compression and PEMFC durability.     

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.