Performance Of Membrane Electrode Assembly Research Articles

Effect of Solvent Ratio (Ethylene Glycol/Water) in the Synthesis of Pt/C Cathode Catalysts on PEM Fuel Cell Performance

Abstract The ethylene glycol (EG)/water mixture composition of an alkaline one-step polyol synthesis for Pt/C catalysts was systematically investigated and optimized for a low ethylene glycol content with regards to resulting Pt particle size and electrochemical performance of membrane electrode assemblies tested as proton exchange membrane (PEM) fuel cell cathode catalysts. Beginning test fuel cell data show a possible reduction of the required EG amount per gram of synthesized catalyst by up to 98% without significantly compromising the initial electrochemical performance. Taking catalyst durability into account, a Pt/C catalyst synthesized with 40 vol% H2O and 32 mM Pt precursor concentration showed a decent initial electrochemical performance (716 mV at 1 A cm-2) as well as an accelerated stress test-derived stability similar to an internal reference catalyst, obtained with 100 vol% EG. In summary, our study shows that optimizing the amount of water and platinum precursor in the synthesis process can lead to catalysts with excellent performance for PEM fuel cells while contributing significantly to cost reduction by using less EG during synthesis.

Highly Hydrophilic Zirconia Composite Anion Exchange Membrane for Water Electrolysis and Fuel Cells.

To prepare anion exchange membranes with high water electrolysis and single fuel cell performance, an inorganic-organic composite (IOC) strategy with click cross-linked membranes coated with different contents of hydrophilic polar nanozirconia is proposed to fabricate composite membranes (CM) PBP-SH-Zrx. The performance test results showed that the CM PBP-SH-Zr4 not only has good through-plane ionic conductivity (167.7 mS cm-1, 80 °C), but also exhibits satisfactory dimensional stability (SR 16.5%, WU 206.4%, 80 °C), especially demonstrating excellent alkaline stability with only 16% degradation (2 M NaOH for 2200 h). In water electrolysis, the "microgap" between the membrane and catalyst layer (solid-solid interface) is alleviated, and the membrane electrode assembly (MEA) interfacial compatibility (liquid-solid-solid interface) is enhanced. The CM PBP-SH-Zr4 showed the lowest charge transfer resistance (Rct, 0.037 Ω cm2) and a high current density of 2.5 A cm-2 at 2.2 V, while the voltage drop was 0.361 mV h-1 after 360 h of endurance (six start-stop cycles) at 60 °C and 500 mA cm-2, proving a good water electrolysis durability. Moreover, an acceptable peak power density of 0.464 W cm-2 at 80 °C is achieved in a H2/O2 fuel cell with a PBP-SH-Zr4-AEM. Therefore, the IOC strategy can enhance the membrane's comprehensive performance and interface compatibility of MEA and may promote the development of anion exchange membranes (AEMs) for water electrolysis and fuel cells.

100 W-class green hydrogen production from ammonia at a dual-layer electrode containing a Pt-Ir catalyst for an alkaline electrolytic process

Ammonia allows storage and transport of hydrogen over long distances and is an attractive potential hydrogen carrier. Electrochemical decomposition has recently been used for the conversion of ammonia to hydrogen and is regarded as a future technology for production of CO2-free pure hydrogen. Herein, a heterostructural Pt-Ir dual-layer electrode is developed and shown to achieve successful long-term operation in an ammonia electrolyzer with an anion exchange membrane (AEM). This electrolyzer consisted of eight membrane electrode assemblies (MEAs) with a total geometric area of 200 cm2 on the anode side, which resulted in a hydrogen production rate of 25 L h−1. We observed the degradation in MEA performance attributed to changes in the anode catalyst layer during hydrogen production via ammonia electrolysis. Furthermore, we demonstrated the relationship between the ammonia oxidation reaction (AOR) and the oxygen evolution reaction (OER).

Investigation of the catalyst ink compositions for a uniform microporous catalyst layer preparation via electrospray deposition technique and MEA assembling conditions in PEMFC specific

High utilization of catalyst and preserving evenly distributed pores for Proton Exchange Membrane Fuel Cell (PEMFC) electrodes were optimized using an in-house designed electrospray system. In order to hold the porous electrode structure prepared through the electrospray technique by varying ink compositions. Using optimized electrodes and commercially available Nafion-212 membrane, a series of membrane-electrode assemblies (MEAs) were fabricated by varying the hot-pressing parameters of pressure, temperature, and time for evaluating the performance at 60 °C to 80 °C with varying relative humidity. The MEAs were hot-pressed at 8 MPa for 390 s at a temperature of 150 °C generating a maximum peak power density of 903 mW cm−2 and current density of 1040 mA cm−2 at 0.6 V and calculated electrochemical surface area (ECSA) is 23.96 m2/gPt. In contrast, the MEAs hot-pressed for the same length of time at the same temperature but with a lower pressure of 2.67 MPa generated higher peak power density of 1130 mW cm−2, higher current density of 1320 mA cm−2 at 0.6 V, despite having a lower ECSA of 19.18 m2/gPt. Overall, results in this study present that low hot-pressing pressure and a high pressing temperature enable a negative effect on the porous structure of electrospray electrodes for producing the high achievement of MEA performance.

Advances in Reinforced Polymer Electrolyte Membrane Designs for Improved Direct Coated Electrodes

In recent years, hydrogen fuel cells have become a key clean technology for the decarbonization of the transport sector. Significant investments are directed towards scaling the hydrogen infrastructure and the production of fuel cell vehicles to meet cost and climate targets set by governments across the globe. To achieve the required scale at cost, manufacturers of fuel cell components such as membrane electrode assembly (MEA) need to adopt high throughput processes while maintaining quality and performance of MEAs to meet heavy duty vehicle requirements.Roll to roll direct coating (DC) process using slot die coating technique is proposed to deliver the lowest cost/highest throughput method for production of MEAs. Electrode ink containing catalyst, ionomer and solvents are applied directly on the membrane before drying to remove the solvents from the coating. The direct contact of solvents with PEM ionomer can create challenges resulting from ionomer swelling and shrinking to produce poor electrode quality and MEA performance.This talk will discuss different design approaches to produce direct coated MEAs and present a novel approach in membrane design to address DC challenges to meet performance and quality targets that would enable the use of DC for scaling the fuel cell production.Applying Gore’s knowledge in expanded poly-tetra-flour-ethylene (ePTFE) reinforcement properties and fuel cells research we developed a membrane that would reinforce the polymer electrolyte and electrode layers simultaneously while minimizing the impact of solvents used in DC processes. This results in improved MEA quality and performance compared to a traditional reinforced membrane design and enables the use of DC for high throughput/low-cost MEA manufacturing. Figure 1

Comparison of MEA Degradation through FCV Actual Driving Test and Load-Cycle Durability Test

Introduction In research and development of high-durability polymer electrolyte fuel cells (PEFCs) for fuel cell vehicles (FCVs), accelerated stress tests (ASTs) are employed to evaluate durability of materials with a short time [1-3]. In order to validate an AST, it is necessary to confirm that the degradation mechanisms in the AST and in actual FCV operation are consistent, and to elucidate quantitative correspondence of their degradation rates. In this study, we analyzed degradation of a membrane electrode assembly (MEA) after FCV real-world driving and compared the degradation factor with that of a load-cycle durability test in a laboratory. Experiments MEA samples were extracted from an FC stack of a Toyota MIRAI 2014 model which was operated in real-world driving of 200,000 km, about 6000 h. MEA performance and electrochemical properties of them were investigated using a small differential cell with a straight flow field. As a comparison, another MEA at beginning of life (BOL) was subjected to a load-cycle durability test following a protocol encouraged by New Energy and Industrial Technology Development Organization (NEDO), Japan. Cell temperature and relative humidity were controlled at 80°C and 100%, respectively. A square-wave potential cycle shown in Figure 1 was adopted. MEA performance was investigated after cycles of 500, 1000, 3000, 10,000, and 30,000. Structures of catalyst layers and catalyst particles were analyzed for the MEAs after driving test and 30,000 cycles of the load-cycle test using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS). Results and discussion The performance of the MEA after 200,000 km driving is close to that of the MEA after 30,000 cycles of the load-cycle test as shown in Figure 2. The performance degradation is mainly attributed to degradation of the catalyst layer, and properties of a gas diffusion layer and a proton exchange membrane are unchanged from those of the BOL sample. Degradation mechanisms of the catalyst layers in the driving test and the load cycle test are well corresponding. First, mass activities of PtCo catalyst decay to about a half of the BOL value mainly due to the decrease in electrochemically effective surface areas (ECSAs) as represented in Figure 3. Decrease rates of the ECSAs are consistent with the increase in average particle sizes of the catalyst. The catalyst size distributions of the two samples are also comparable. Then, oxygen transport resistance in the catalyst layers is increased. The resistance of the samples after the driving test and 30,000 cycles of the load-cycle test are twice as large as the BOL value. As shown in Figure 4, the transport resistance obviously exhibits inverse proportion to the catalyst surface area. This relationship represents that the primary factor of the resistance is one at vicinity of catalyst particles including ionomer permeation [4], and increase in it is attributed to decrease in the catalyst surface area. A performance simulation based on a simple 1-dimensioal MEA model supports that the decrease in the ECSA causes most of the MEA performance degradation through the deterioration in the catalyst activity and the oxygen transport resistance. Conclusions The MEA performance degradation after the 200,000 km real-world driving with the system of MIRAI 2014 model is primarily caused by catalyst metal coarsening and is well simulated by NEDO load-cycle durability test of 30,000 cycles. This result has validated the test protocol and should contribute to a target-setting of durability of future MEAs.

Characterization of Catalyst Layer Using Gas Diffusion Electrode Half-Cell System for High Temperature Polymer Electrolyte Membrane Fuel Cell

High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is being developed for the heavy-duty vehicle which requires high power density and operation under extreme conditions. Conventional HT-PEMFC using phosphoric acid (PA) immersed PBI membranes and polytetrafluoroethylene (PTFE) binder faced issues such as unstable durability and low performance of membrane electrode assembly (MEA) due to PA leakage and uneven distribution within the catalyst layer.In recent years, ion-pair membranes and ionomers for high temperatures have been developed, which can reduce PA leakage in MEA and improve ionic conduction within the catalyst layer. Incorporation of a new material into the MEA requires further research to enhance electrode design, catalyst utilization, and performance for the appropriate ionomer, as this material exhibits different characteristics from the conventional PTFE binder.In this study, various gas diffusion electrode (GDE) was fabricated with the new ionomer, and GDE half-cell setups were introduced for rapid and efficient characterization of performance in the oxygen reduction reaction. This system serves as an intermediate step between rotating disk electrodes and single cells, providing a powerful tool for quickly screening and evaluating GDEs using small amounts of catalyst. Recent publications from Wilkinson [1] and Gasteiger [2] groups reviewed this new system, proposed new measurement protocols, and suggested improvements. Accordingly, GDE half-cell setups are designed to simulate HT-PEMFC operating conditions at 150 ℃ temperature with 85 wt.% PA electrolyte.Electrochemical characteristics were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) following the protocols in previous papers with GDE half-cell. Resistance values obtained through EIS were further differentiated by peaks and frequency-based responses through the distribution of relaxation times transformation. Performance comparison between GDEs was carried out by measuring the voltage at 0.2 A/cm² and peak power density at 150 ℃, simulating a single cell-like environment. GDEs were fabricated with variables such as Pt loading, thickness, and porosity. And their physical properties were confirmed through mercury intrusion porosimetry and scanning electron microscopy. Ultimately, the study elucidated the correlation between the electrochemical data and physical properties.

Influence of Contact Pressure and Flow Rate on the Performance of Anion Exchange Membrane Electrolysis

Hydrogen production by electrolysis is a key aspect of a climate-neutral economy. However, there are still weak points in the established low-temperature technologies such as high material costs in case of PEM electrolysis and poor dynamic operations in case of alkaline electrolysis. The emerging electrolysis technology, the anion exchange membrane (AEM) electrolysis, addresses these weaknesses and combines their advantages. Due to the solid polymer electrolyte and the alkaline environment, AEM water electrolysis is featured by a compact zero-gap cell design and inexpensive materials like non-noble metal catalysts. Hence, it offers the potential to a cost-effective and efficient electrolysis technology.To enable the breakthrough of this technology, we contribute by conducting performance evaluations of membrane electrode assemblies (MEAs) under application-oriented conditions. One focus is on non-noble metal MEAs with an active area of 25 cm2 operated with pure water and low concentrated potassium hydroxide solution.To ensure comparability of different MEAs, it is crucial to compare them at their performance optimum. This is achieved by determining the optimal set-up parameters like contact pressure and operation parameters like flow rate for each MEA type. Otherwise, deviation from the optimal operating point by up to 50 % may occur.The influence of the parameters contact pressure and flow rate on the MEA performance is discussed in this presentation. To investigate their impact, we analysed the MEAs in an electrolyser test station using polarisation curves, electrochemical impedance spectroscopy and load tests at constant current and constant voltage.Some of the results presented are obtained within the project “REVAL – reversible anion exchange membrane electrolysis” (funding code 03ZZ0732D) funded by the German Federal Ministry of Education and Research (BMBF).

Dynamics Management of Intermediate Water Storage in an Air-Breathing Single-Cell Membrane Electrode Assembly.

In air-breathing proton exchange membrane fuel cells (Air PEM FCs), a high rate of water evaporation from the cathode might influence the resistance of the membrane electrode assembly (MEA), which is highly dependent on the water content of the Nafion membrane. We propose a dead-end hydrogen anode as a means of intermediate storage of water/humidity for self-humidification of the membrane. Such an inflatable bag integrated with a single lightweight MEA FC has the potential in blimp applications for anode self-humidification. A dynamic numerical water balance model, validated by experimental measurements, is derived to predict the effect of MEA configuration, and the membrane's hydration state and water transfer rate at the anode on MEA resistance and performance. The experimental setup included humidity measurements, and polarization and electrochemical impedance spectroscopy tests to quantify the effect of membrane hydration on its resistance in a lightweight MEA (12 g) integrated with an inflatable dead-end hydrogen storage bag. Varying current densities (5, 10, and 15 mA/cm2) and cathode humidity levels (20, 50, and 80%) were examined and compared with the numerical results. The validated model predicts that the hydration state of the membrane and water transfer rate at the anode can be increased by using a thin membrane and thicker gas diffusion layer.

Understanding Charge, Mass, and Heat Transfer in Fuel Cells for Transport Applications – Insights from the Camelot Project

Proton Exchange Membrane Fuel Cells (PEMFCs) are a promising solution for zero-emission vehicle propulsion owing to their high energy density, low operating temperature, and high efficiency. The overall aim of the CAMELOT project is to improve the power density of fuel cells by understanding the limitations on the performance of state-of-the-art (SoA) and beyond SoA PEMFC membrane electrode assemblies (MEAs). To achieve this, the CAMELOT project has diagnosed the fundamental transport properties that limit performance of these MEAs and materials. Not only has the CAMELOT project produced MEAs with features that have the potential to enable disruptive performance increases but have further developed leading open-source models to enable accurate simulations validated through experimental work. In-depth parametrisation of fuel cell components through extensive ex-situ and in-situ characterisation has been performed to provide input to the modelling activities. The two major modelling advances achieved by the CAMELOT project are i) the improvement of water uptake and transport models, especially concerning ultra-thin PEMs, and ii) extending a leading open-source model (FAST-FC) to enable accurate simulation of beyond SoA fuel cell performance and voltage loss breakdown. CAMELOT has developed a series of beyond-SoA fuel cell components to ensure that the modelling inputs are representative of SoA component properties. A series of membranes with varying thicknesses were prepared and a range of ex-situ experiments were carried out to gather water uptake and permeability properties for the water transport models. Additional in-situ electrochemical characterisation was carried out on a series of catalyst coated membranes (CCMs) to extract important properties of the catalyst and membrane components as inputs to improve the physics-based fuel cell performance model.Significant results from the project to be highlighted in this presentation include the development of a water transport model with improved description of water uptake and transport in thin ionomeric layers, the development of a predictive modelling framework from which we can identify the most important material parameters to tune to reach our MEA performance targets of 2.7 A/cm2 at >0.67 V with total catalyst loadings <0.08 mgPt/cm2, the development of ultrathin (< 10 µm) proton exchange membranes and ultra-low loading cathode catalyst loadings (0.08 mgPt/cm2), the development of catalyst coated membranes (CCMs) with in-plane catalyst and ionomer gradients, and extensive in-situ fuel cell characterization of the SoA CAMELOT CCMs/MEAs.The CAMELOT project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under grant agreement No 875155. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.

Catalyst Layer Structure Properties and Electrode Performance with the Addition of Polyethylene Glycol

Reducing the platinum loading in Proton Exchange Membrane Fuel Cells to mitigation costs is of topical interest. Lowering the Pt content beyond critical thresholds has a direct impact on the kinetic conversion efficiency of O2, and result in local oxygen transport resistance in the catalyst layer at high current densities. Improvements in the Pt use efficiency can be achieved by affecting the catalyst layer structure properties with improved Pt dispersion and increased ionomer interface1-3.In this study, we are investigating how the structure properties of the catalyst layer are affected by the addition of polyethylene glycol (PEG) during the ink step. PEG has a high boiling point (>200°C) and is known to have pore forming properties4. It has also been reported to extend the reach of the ionomer and its resulting protonic connectivity. Increasing the porosity in the catalyst layer can increase the triple phase boundaries and reduce interfacial resistances 5.Membrane electrode assemblies (MEAs) have been made with inks containing increasing wt.% PEG. The resulting inks were coated onto membranes to form catalyst layers containing 0.2 mgPt/cm2. The addition of PEG affected the binding of the ionomer and the catalyst, which will likely affect the packing of the agglomerates in the resulting catalyst layer structure. The catalyst layer thickness, surface area and porosity were determined. The coated substrates were assembled into single cells for electrochemical evaluation. The resulting MEAs showed that the inclusion of PEG reduced the kinetic losses at low current density due to improved electronic connectivity between the catalyst and the ionomer. Overall, the performance increased by ≈30mV at 1A/cm2.However, PEG content higher than 3% resulted in a significant decrease in performance in the high current density region. This is due to a higher packing density and therefore higher mass transport resistance with higher PEG content.The inclusion of PEG into the catalyst ink reduced the amount of flammable organic content and improved the MEA performance especially at low current density. Catalyst layer deposition was smoother with reduced cracking. Ultimately, the ambitions for low loading MEAs can be achieved by optimising the structure performance properties in the catalyst layer. PEG is considered a viable candidate for performance enhancement for low loading MEAs, yet a number of practical obstacles were experienced and require some optimization.

Carbon Monoxide-Resistant Anode Catalysts for Single-Cell Direct Carbon Monoxide Fuel Cells: Binary, Ternary, And Quaternary Platinum Alloys as Anode Electrocatalysts

The objective of this paper is to present the results of experimentations on the custom-made anode electrocatalysts for direct carbon monoxide fuel cells (DCMFCs) inspired by catalysts commonly used for direct alcohol fuel cells. Seven different catalysts were fabricated and tested. The uniform and consistent manufacturing process and the test procedure allowed a meaningful comparison of the developed fuel cells. The results indicated that homemade Pt-Ru membrane-electrode assembly (MEA) could not compete with the Pt-Sn MEA. While the performance of the MEAs with Pt-Ru-Ni, Pt-Ru-Sn-Ni, and Pt-Ru-Sn-Co was not satisfactory, the Pt-Ru-Sn-Co-W MEA achieved the best performance among all MEAs with Nafion® 117 membrane. The last MEA was made of the Pt-Sn anode catalyst and Nafion® 212 membrane and outperformed all other MEAs by a wide margin. The experiments demonstrated that the performance of the best-developed MEA was three times better than the performance of the commercial Pt-Ru MEA. This means the performance of DCMFCs can be significantly improved by developing a suitable anode electrocatalyst, using a thinner membrane, and operating at optimum conditions. These results are not only applicable for DCMFCs but also are very useful for other proton exchange membrane fuel cells (PEMFCs) operating with CO-containing fuels.

Mechanism study of the improved catalytic activity of PEMFC catalyst layer by short-side-chain ionomer: Focusing on the ionomer/Pt interface

In the field of proton exchange membrane fuel cells (PEMFCs), short-side-chain (SSC) ionomers are widely considered to enhance the catalytic activity of the catalyst layer, but the mechanism of enhancement is controversial. In this work, the density functional theory (DFT) calculations and practical membrane electrode assemblies (MEAs) experiments were performed to explore the mechanism of the improved catalytic activity by SSC ionomers. The interactions between Pt representative crystal planes and low-molecular-weight model anions/PFSA fragments were investigated by DFT calculations, which revealed and divided the effects of sulfonic groups, ether groups, and side-chain structures on the adsorption energy and adsorption state. The calculations showed that the ether group of the short side chain has difficulty in interacting with the Pt surface, while the ether group around the midpoint of the long side chain could still interact with the platinum. Therefore, the ionomers having longer side chains more strongly block ORR. In practical catalyst layers, the SSC ionomer significantly improved the MEA performance especially at high voltages, and increased the rated power density by up to 56.3% compared with conventional Nafion®. This work provides a reference for developing desirable ionomers to enhance the catalytic activity of PEMFC catalyst layers.

Degradation mechanism analysis of substrate and microporous layer of gas diffusion layer in proton exchange membrane fuel cell

Robust electrochemical corrosion of gas diffusion layers (GDL) in proton exchange membrane fuel cell (PEMFC) could cause significant decline of cell performance. However, the detailed mechanism still remains elusive. Herein, the structural characteristics of GDL after electrochemical accelerated stress test (AST) and sequent impacts on the mass-transfer performance of membrane electrode assemblies were explored. With the electrochemical corrosion duration increasing, polytetrafluoroethylene (PTFE) peeling and carbon fibers exposure were observed on substrate layer surface, while corrosion pores were detected on microporous layer (MPL). Both substrate layer and MPL experienced significant increase in surface roughness, which was reflected in the surface and bulk resistance. Surface contact angle and water permeability threshold tests showed that surface and internal hydrophobicity of GDL degraded comprehensively. More significant carbon corrosion in MPL and PTFE loss in substrate layer were revealed by X-ray photoelectron spectroscopy and thermogravimetric analysis. Collectively, worse power density and severe ohmic and mass-transfer polarization after AST were confirmed and the oxygen mass-transfer performance was analyzed in single-cell tests. This work clearly explains the distinctive degradation mechanisms of the substrate layer and MPL and provides guidance for the design and application of GDL.

Highly sensitive chemoresistor based on Ag/TiO2/FTO sandwich structure for evaluation of component concentration in mixed ambient

The performance of membrane electrode assemblies (MEAs) in direct methanol fuel cells (DMFCs) can be greatly affected by ethanol as an impurity in methanol fuels. It is thus necessary to explore an effective method for accurately detecting the ethanol concentration in a mixed atmosphere of methanol and ethanol. Herein, we developed a chemoresistor based on Ag/TiO2/FTO sandwich structure and achieved accurate prediction for the concentration of each component in methanol-ethanol mixed atmosphere. First principles calculations were first performed to reveal the gas adsorption characteristics of TiO2 sensitive layer in different resistive state. It was indicated that methanol and ethanol molecules could be clearly distinguished by TiO2-based device in the high resistive state. In the gas-sensing test, the response value of Ag/TiO2/FTO chemoresistor in the high resistive state to 1 ppm methanol was 2.55, 14.8, 13.19, 15.04 and 17.34 times higher than that of the same concentration of ethanol, acetone, isopropanol, acetic acid and methyl formate, respectively. Meanwhile, when the device was in direct current mode after the response, an ultra-fast recovery characteristic (0.7 s) was observed due to the resistive switching function. Finally, the prediction of the component gas concentration in the methanol-ethanol mixed atmosphere was achieved by combining the optimized neural network algorithm. The present work brings new inspiration for future research on gas sensors.

High-performance and durable membrane electrode assemblies based on CeO2 and ePTFE double-reinforcement strategy for proton exchange membrane fuel cells operating at elevated temperatures

The membrane electrode assemblies (MEAs) play a decisive role in operating conditions and lifetime of fuel cell. In this study, MEAs that could work stably at elevated temperatures were prepared. With this method, a short-side chain perfluorosulfonic acid ionomer coating with CeO2 nanoparticles and two layers of expanded polytetrafluoroethylene reinforcement, to be used as a proton exchange membrane, was directly deposited between the cathode and anode gas diffusion electrodes, forming a double-reinforced integrated MEA. The effects of CeO2 doping amount on performance and other electrochemical properties of MEAs were systematically studied. Under the coupling effect of the water-retention and non-proton-conducting properties of CeO2, the 0.5 wt% CeO2-doped MEA (MEA-S0.5) had optimal performance above 100 °C and under low relative humidity (RH) conditions. At 120 °C and 30% RH, MEA-S0.5 exhibited peak power density of 0.460 W cm−2 (H2/air operation, 100 kPa), which was about 1.28 times that of MEA without CeO2 doping (MEA-S0). Furthermore, CeO2 effectively enhanced the durability of the MEA. Compared with MEA-S0, MEA-S0.5 did not exhibit significant degradation in output power, H2 crossover, or proton conductivity in the 100-h open-circuit voltage-holding test. This work paves the way for developing high-performance, durable MEAs that are suitable for elevated temperatures.

Insight into Defect Engineering of Atomically Dispersed Iron Electrocatalysts for High-Performance Proton Exchange Membrane Fuel Cell.

Atomically dispersed and nitrogen coordinated iron catalysts (Fe-NCs) demonstrate potential as alternatives to platinum-group metal (PGM) catalysts in oxygen reduction reaction (ORR). However, in the context of practical proton exchange membrane fuel cell (PEMFC) applications, the membrane electrode assembly (MEA) performances of Fe-NCs remain unsatisfactory. Herein, improved MEA performance is achieved by tuning the local environment of the Fe-NC catalysts through defect engineering. Zeolitic imidazolate framework (ZIF)-derived nitrogen-doped carbon with additional CO2 activation is employed to construct atomically dispersed iron sites with a controlled defect number. The Fe-NC species with the optimal number of defect sites exhibit excellent ORR performance with a high half-wave potential of 0.83V in 0.5M H2 SO4 . Variation in the number of defects allows for fine-tuning of the reaction intermediate binding energies by changing the contribution of the Fe d-orbitals, thereby optimizing the ORR activity. The MEA based on a defect-engineered Fe-NC catalyst is found to exhibit a remarkable peak power density of 1.1W cm-2 in an H2 /O2 fuel cell, and 0.67W cm-2 in an H2 /air fuel cell, rendering it one of the most active atomically dispersed catalyst materials at the MEA level. This article is protected by copyright. All rights reserved.

Physics-Based Model to Represent Membrane-Electrode Assemblies of Solid-Oxide Fuel Cells Based on Gadolinium-Doped Ceria

This paper reports a physics-based model that predicts membrane-electrode assembly (MEA) performance of solid-oxide fuel cells (SOFCs) with Ce0.9Gd0.1O2−δ (GDC10) electrolyte membranes. The paper derives self-consistent thermodynamic and transport properties for GDC1o mobile charged defects (oxide vacancies and reduced-ceria small polarons) by fitting published measurements of oxygen non-stoichiometry and conductivity over ranges of temperature and O2 partial pressures. The button-cell model is applied to evaluate how mixed ionic-electronic conductivity influences the performance of an SOFC MEA with a GDC10 electrolyte sandwiched between a porous, composite Ni-GDC10 anode and a porous, composite cathode of Sm0.5Sr0.5CoO3−δ (i.e., SSC) and GDC10. SSC properties are also derived by fitting published conductivity and oxygen non-stoichiometry measurements. Mixed conductivity of GDC10 and competing charge transfer reactions at both electrodes reduce open circuit voltages due to leakage current and buildup of defect concentrations at electrode-electrolyte interfaces. To fit polarization data, the button-cell model includes heterogeneous reaction rates for defect incorporation on the GDC10 surface along with Butler–Volmer expressions derived for competing charge transfer reaction rates from rigorous analyses assuming rate-limiting, elementary charge transfer reactions for each electrode. The calibrated MEA model can support rigorous SOFC modeling with GDC10 electrolytes over the range of conditions within a fully operating cell.

Comparison of MEA Degradation through FCV Actual Driving Test and Load-Cycle Durability Test

The degradation of a membrane electrode assembly (MEA) after an actual driving test was analyzed, and its mechanism was compared with that of a load-cycle durability test in a laboratory. MEA samples were extracted from an FC stack of a Toyota MIRAI 2014th model which had been operated in actual driving of 200,000 km for approximately 6000 h. The degradation distribution across the MEA plane was found to be insignificant. The electrolyte membrane did not show significant degradation affecting its properties following the durability tests. The MEA performance degradation is primarily attributed to the deterioration of the catalyst activity and oxygen transport properties in the catalyst layer, which is mainly caused by catalyst coarsening. The degradation was well simulated by the NEDO load-cycle durability test of 30,000 cycles. The evaluation results are applicable to validation of AST protocols and model-simulation of MEA degradation.

Optimizing Catalyst Layer Structure with Carbon Nanofiber Additive for Better Performance of Proton Exchange Membrane Fuel Cell

Increasing the power density of proton exchange membrane fuel cell (PEMFC) is essential for its commercialization. Cathode catalyst layer (CCL) carbon additive is an effective method that can improve membrane electrode assembly (MEA) performance under high current density. In this work, carbon nanofiber (CNF) is used as CCL additive and its mechanism is studied. The influence of CNF on the CCL structure is studied by scanning electron microscope (SEM), nitrogen adsorption method and contact angle experiment. Meanwhile, the mechanism is examined by using polarization decomposition and impedance analysis combined with the result in characterization experiments. The results show that: (1) the MEA used in this work has the best performance when adding 1 wt%. The voltage rises 74 mV (15.42%) at 2 A cm−2; (2) CNF varies the MEA performance mainly through changing the hydrophobicity of CCL, influencing the mass transport resistance and the concentration polarization. The mass transport resistance decreases 57.18% at 2 A cm−2; (3) activation polarization values have a negative linear correlation with the peak volume values of the primary pores at around 4 nm in diameter. This study provided a detailed understanding of the mechanism of CNF additive in CCL and will be helpful for improving PEMFC performance.