Development Of Membrane Electrode Assemblies Research Articles

Development of Membrane Electrode Assembly with Double-Catalytic Layer for Micro Direct Methanol Fuel Cell

This paper presents a membrane electrode assembly (MEA) with a double-catalytic layered structure to improve the performance of the micro direct methanol fuel cell. The inner and outer parts of the double-catalytic layer comprise an unsupported and carbon-supported catalyst, respectively. A two-dimensional two-phase model of mass transport and electrochemical reaction is established and simulated to analyze the superiority of the double-catalytic layered structure. Simulation results show that this structure has a more uniform current density distribution and less over-potential across the catalyst layer. Methanol crossover is also reduced. Experimental results confirm that the MEA with the double-catalytic layered structure exhibits better performance than the traditional MEA. The adoption of a gas diffusion electrode as the outer catalytic layer and a catalyst-coated membrane as the inner layer of the double-catalytic layered structure can further improve the performance of the MEA. Both simulation and experimental results show the existence of an optimum number of metal loadings of the inner and outer parts of the double-catalytic layer.

Modeling water phenomena in the cathode side of polymer electrolyte fuel cells

Water exerts a crucial influence on the performance of a polymer electrolyte fuel cell as both “catalyst activating agent” and “oxygen blocker”. Therefore, fine-tuning the water distribution is imperative for high performance. In this work, we present a water balance model to calculate the distribution of liquid water in cathode catalyst layer and diffusion media. The model incorporates the influence of the local liquid water saturation on the effective transport properties. Liquid water saturation is both a composition variable determining the effective properties and a variable that depends on the solution of the transport equations that use the effective properties. The model reveals the formation of a thin water layer in the diffusion medium adjacent to the catalyst layer at high current density. This interfacial water layer strongly impedes oxygen transport and reduces the oxygen concentration in the catalyst layer, which causes a drastic increase in the voltage loss at high current density that drastically reduces the cell performance. We elucidate the origin of the water layer, present parametric studies of this effect, and propose mitigation strategies. The fundamental understanding gained will aid the development of membrane electrode assemblies with tailored pore network properties to achieve vital improvements in performance.

Development of Polymer Electrolyte Fuel Cell (PEFC) Cathodes with High Oxygen Permeability Ionomer (HOPI) for High Performance and Durability

The electrolyte-catalyst interface in the cathodes of polymer electrolyte fuel cells (PEFCs) has a significant impact on the utilization, performance, and durability of fuel cell systems. The ionomer plays a critical role in providing a facile proton conduction pathway from the membrane to the Pt-based catalyst and creating an acidic local environment for the oxygen reduction reaction with high specific activity. However, the commonly used perfluorosulfonic acid (PFSAs) ionomers also negatively impact performance by hindering oxygen transport and partial poisoning of the catalyst by the anionic acid groups. There is a growing consensus that the densification of the PFSA ionomers at the Pt-alloy catalyst greatly increases the local oxygen transport resistance relative to permeation through bulk PFSA films. To address this issue, new high oxygen permeability ionomers (HOPIs) that resist the densification are being developed. This presentation will present our development of membrane electrode assemblies (MEAs) with HOPI in the cathode. The results include a model-based analysis, ink and coating optimization, and experimental fuel cell and transport characterization. The results highlight the significant increase in voltage efficiency and maximum power density when fabricating cathodes with HOPI as well as the significant positive impact on performance durability.This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.

Oxygen Reduction Reaction Activity and Durability of Pt-Ni Catalysts Synthesized By a Continuous Flow Reactor

In recent years, polymer electrolyte membrane fuel cell (PEMFC) technology has attracted much attention and enabled the successful commercialization of fuel cell electric vehicles (FCEVs). However, the continuation of FCEV deployment still faces various hurdles, of which one major challenge is related to the high cost of platinum-based catalysts.[1] Substantial efforts have been dedicated for improving catalyst structure and composition to enhance their performance and thus lower the loadings for cost reduction. For example, shape-controlled catalysts such as octahedral PtNi and PtCo alloy nanoparticles showed much higher activity for oxygen reduction reaction (ORR) than the conventional Pt/C catalyst. [2-5] However, those advanced catalysts were typically prepared by batch synthesis with quantities often as little as a few milligrams, making it difficult for validation and further development of membrane electrode assembly (MEA) for commercial application. Attempt in increasing the catalyst amount by multiple batches can be time-consuming and sometimes challenging to maintain the consistency.We recently designed a flow reactor (FR) to explore the continuous synthesis of Pt alloy nanoparticles (Fig. 1.) under elevated temperature and pressure (up to 350 °C and 1000 psi). It has several advantages including fast heat-exchange, fast mixing, uniform concentration and uniform temperature as compared to batch synthesis. These features made it possible to accurately control the reaction parameters to produce monodisperse Pt alloy catalysts up to 10 grams per day with high reproducibility. In this study, systematic investigation was conducted on the FR synthetic conditions for highly active catalyst. We were able to control the size and composition of resulting PtNi nanoparticles to achieve much higher ORR activity than commercial catalysts by optimizing synthesis conditions. As shown in Fig. 2 and Fig. 3, octahedral PtNi alloy catalysts synthesized by the FR showed much higher mass activity and specific activity compared to commercial benchmark. Attempts were also made to use machine learning tools to assist experimental design and data analysis for process optimization. It is expected that the combination of the latest development of data science and the inherent features of such flow reactors can substantially accelerate future FC catalyst R&D. Figure 1

Development of Membrane Electrode Assemblies for State-of-the-Art Anion Exchange and Proton Exchange Membrane Electrolysis

Proton exchange membrane (PEM) electrolysis and anion exchange membrane (AEM) electrolysis are both able to directly produce high purity hydrogen from electricity and water. Key benefits of electrolysis using polymer membrane separators include a quick response rate, enabling load following, and ability to operate with high differential pressure. Operation under differential pressure allows for simultaneous electrolysis and electrochemical compression, simplifying overall system design. The development and stack integration of new, high performance electrolysis materials must include consideration of operating range and durability under differential pressure to maintain the technologic benefits. PEM electrolyzers are commercially available on the megawatt scale and produce hydrogen fuel that is increasingly cost competitive with fossil fuel in select parts of the world. Better utilization of low cost electricity from renewable energy (wind and solar) is one route to additional hydrogen cost reductions, for which a wide current operating range is beneficial. Thinner membranes, more active catalysts, and better electrode design enable high currents at acceptable cell efficiencies. Performance and durability data will be presented on state-of-the-art PEM electrolyzer materials operating under differential pressure. AEM electrolyzers are not currently commercially available, but promise membrane, catalyst, and balance of stack cost reductions. To begin to compete with PEM technology, performance and durability need to be improved. This work focuses on membrane stability under differential cell pressure and material integration into high performance AEM electrolyzers.

Development of PEFC Membrane Electrode Assemblies for Iron-Doped Metal Organic Framework Catalysts

Polymer electrolyte fuel cells (PEFCs) have been identified as one of the most promising technologies for future electric vehicles by using clean H2 with much improved energy conversion efficiency, long range, and rapid refueling. However, due to the large amount of platinum group metal (PGM) catalyst used in their electrodes, their prohibitively high cost hinders broad commercialization of PEFCs for transportation. Therefore, there is a critical need to develop low cost, high-performance PGM-free cathode catalysts that have the potential to dramatically transform the economics of PEFC commercialization by reducing catalyst costs by one to two orders of magnitude. However, before PGM-free cathodes become viable, several technical challenges associated with PGM-free cathodes must be addressed, including insufficient activity and stability of the catalysts, and serious water flooding and large transport losses in the electrodes. Overcoming those barriers and ultimately meeting the challenging automotive PEFC performance targets requires comprehensive research and development effort on new PGM-free cathodes. In this work, we use a newly developed approach to synthesize PGM-free catalysts for Fe-doped metal-organic framework (MOF) precursors that yield atomically-dispersed FeN4-type active sites. These catalysts exhibit high activity and improved stability at typical fuel cell operating voltages. This presentation will focus on the development of membrane electrode assemblies with cathodes prepared from this catalyst. Specific areas that will be covered are water management in thick PGM-free cathodes, ionomer integration, and cathode fabrication. The implementation of these new materials and electrode designs is supported by a suite of advanced experimental and simulation tools that identify performance and durability bottlenecks, devise solutions, and establish rational material design and future synthesis targets. This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under Award Number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract Number DE-EE0008076.

Tomography Aided Development of Membrane Electrode Assemblies for PEM Water Electrolysis

In polymer electrolyte membrane water electrolysis (PEMWE) the anode is crucial for the overall performance. State-of-the-art anodes comprise Ir, IrOx or IrRuOx, typically bound by an ionomer and can be TiOx supported [1]. Besides the material also the microstructure of the anode has an impact on the electrolyzer’s performance as it determines catalyst accessibility and species transport [2]. Optimizing the microstructure therefore offers a potential to increase cell efficiency. In our approach we use tomographic methods in order to establish a microstructure-performance relation for PEMWE anodes (see microstructure of a FuelCellsEtc PEMWE anode in Fig.1). We then apply our findings from the reconstructed anodes in order to develop improved membrane electrode assemblies (MEAs) for PEMWEs with novel manufacturing and design approaches. The experimental data will then be used as input for our theoretical models.

PREPARATION OF MEMBRANE ELECTRODE ASSEMBLY FOR HIGH PERFORMANCE OF FORMIC ACID FUEL CELL

This study is focused on development of membrane electrode assembly (MEA) for direct formic acid fuel cell (DFAFC). The effects of the backing layer, the loading of the gas diffusion layer (GDL), the carbon structures and the electrolyte membrane types, and fuel concentrations on the DFAFC’s performance are investigated. Two types of backing layer are used in either a carbon paper (CP) or carbon cloth (CC) form, and three different types of carbon structures, carbon black (CB), carbon nanofiber (CNF) and carbon nanotube (CNT), are studied. A single cell DFAFC is tested to obtain the performance of the MEA, including the open circuit potential (OCP), current density, and power density. From the results, carbon paper indicates a much better performance than carbon cloth and gas diffusion layer (GDL) with 1 mg cm loading shows a uniform surface morphology under scanning electron microscopy (SEM) and records a higher power density than 2.5 mg cm. Moreover, it is found that the power density increases with increase of the formic acid concentration up to an optimum concentration. However, the optimum fuel concentrations are different for each type of carbon structure. The highest power density is obtained using a combination of CNT and electrolyte membrane of Nafion 117 at 18.36 mW cm using 10 M fuel concentration.

Development of membrane electrode assembly for high temperature proton exchange membrane fuel cell by catalyst coating membrane method

Membrane electrode assembly (MEA), which contains cathode and anode catalytic layer, gas diffusion layers (GDL) and electrolyte membrane, is the key unit of a PEMFC. An attempt to develop MEA for ABPBI membrane based high temperature (HT) PEMFC is conducted in this work by catalyst coating membrane (CCM) method. The structure and performance of the MEA are examined by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and I–V curve. Effects of the CCM preparation method, Pt loading and binder type are investigated for the optimization of the single cell performance. Under 160 °C and atmospheric pressure, the peak power density of the MEA, with Pt loading of 0.5 mg cm−2 and 0.3 mg cm−2 for the cathode and the anode, can reach 277 mW cm−2, while a current density of 620 A cm−2 is delivered at the working voltage of 0.4 V. The MEA prepared by CCM method shows good stability operating in a short term durability test: the cell voltage maintained at ∼0.45 V without obvious drop when operated at a constant current density of 300 mA cm−2 and 160 °C under ambient pressure for 140 h.

Chronoamperometric study of membrane electrode assembly operation in continuous flow photoelectrochemical water splitting

Water splitting was performed in a photoelectrochemical cell (PEC) with water oxidation and hydrogen formation reactions in two separate compartments. A photoanode consisting of carbon paper loaded with TiO2 and a cathode made of Pt dispersed on carbon black spread also on carbon paper were fixed on both sides of a Nafion® membrane and electrically coupled via an external circuit. Anode and cathode compartments with serpentine flow field were operated either in the liquid or vapour phase. Electrical current was monitored with chronoamperometry and D2 formation from deuterated water using mass spectrometry. Mapping the photocurrent under a variety of reaction conditions enabled identification of the limiting factors related to proton and photocarrier transport and reaction product evacuation. This comprehensive research approach to the operation of a PEC will assist future optimisation of cell design and development of membrane electrode assemblies.

Membrane electrode assemblies for high-temperature polymer electrolyte fuel cells based on poly(2,5-benzimidazole) membranes with phosphoric acid impregnation via the catalyst layers

Abstract A novel strategy for introducing phosphoric acid as the electrolyte into high-temperature polymer electrolyte fuel cells by using acid impregnated catalyst layers instead of pre-doped membranes is presented in this paper. This experimental approach is used for the development of membrane electrode assemblies based on poly (2,5-benzimidazole) (ABPBI) as the membrane polymer. The acid uptake of free-standing ABPBI used for this work amounts to ABPBI × 3.1 H 3 PO 4 which has a specific conductivity of ∼80 mS cm −1 at 140 °C. Rather thick catalyst layers (20% Pt/C, 1 mg Pt cm −2 , 40% PTFE as binder, d = 100–150 μm) are prepared on gas diffusion layers with a dense hydrophobic microlayer. After impregnation of the catalyst layers with phosphoric acid and assembling them with a mechanically robust undoped ABPBI membrane a fast redistribution of the electrolyte occurs during cell start-up. Power densities of about 250 mW cm −2 are achieved at 160 °C and ambient pressure with hydrogen and air as reactants. Details of membrane properties, preparation and optimization of gas diffusion electrodes and fuel cell characterization are discussed. We consider our novel approach to be especially suitable for an easy and reproducible fabrication of MEAs with large active areas.