Membrane Electrode Assembly Preparation Research Articles

Probing the Efficiency of PPMG-Based Composite Electrolytes for Applications of Proton Exchange Membrane Fuel Cell

PPMG-based composite electrolytes were fabricated via the solution method using the polyvinyl alcohol and polyvinylpyrrolidone blend reinforced with various contents of sulfonated inorganic filler. Sulfuric acid was employed as the sulfonating agent to functionalize the external surface of the inorganic filler, i.e., graphene oxide. The proton conductivities of the newly prepared proton exchange membranes (PEMs) were increased by increasing the temperature and content of sulfonated graphene oxide (SGO), i.e., ranging from 0.025 S/cm to 0.060 S/cm. The induction of the optimum level of SGO is determined to be an excellent route to enhance ionic conductivity. The single-cell performance test was conducted by sandwiching the newly prepared PEMs between an anode (0.2 mg/cm2 Pt/Ru) and a cathode (0.2 mg/cm2 Pt) to prepare membrane electrode assemblies, followed by hot pressing under a pressure of approximately 100 kg/cm2 at 60 °C for 5–10 min. The highest power densities achieved with PPMG PEMs were 14.9 and 35.60 mW/cm2 at 25 °C and 70 °C, respectively, at ambient pressure with 100% relative humidity. Results showed that the newly prepared PEMs exhibit good electrochemical performance. The results indicated that the prepared composite membrane with 6 wt% filler can be used as an alternative membrane for applications of high-performance proton exchange membrane fuel cell.

An asymmetric membrane electrode assembly for high-performance proton exchange membrane fuel cells

The membrane electrode assembly (MEA) is a critical part of proton exchange membrane fuel cells (PEMFCs) and has a significant impact on their performance. A novel preparation method of MEA is proposed in this work to inhibit the swelling and deformation of the proton exchange membrane (PEM) during MEA preparation and improve the interface between the PEM and cathode catalyst layer (CL). Using this novel fabrication method, an asymmetric MEA is prepared, where the anode and cathode parts are fabricated separately and then integrated by a hot-pressing process. The cathode part is prepared by covering the gas diffusion electrode (GDE) onto a layer of a perfluorosulfonic acid dispersion to form a membrane-coated electrode according to a wet-contact interface design, thereby ensuring a tight and concave-convex PEM/CL interface on the cathode. The anode part is prepared by spraying the CL onto a commercial PEM with a substrate to form a CL-coated PEM. An MEA was also prepared according to the traditional catalyst-coated membrane (CCM) method for comparison. The asymmetric MEA based on the new manufacturing process performs better than the traditional CCM-type MEA under the same PEM thickness prerequisite. The peak power densities of the asymmetric MEA are verified to be 18% (H2/air) and 31% (H2/O2) higher than conventional CCM-type MEA. In addition, the asymmetric MEA shows less cell performance degradation after 3000 dry/wet test cycles than the CCM-type MEA.

Preparation of Membrane Electrode Assemblies Using Waste Tire Derived Carbon Supported Platinum Catalyst

Since the world’s population and energy demand are constantly growing and energy is largely based on the use of non-renewable energy sources, it would be necessary to find an alternative, more environmentally friendly energy carrier [1]. One of the most important alternative energy carriers is hydrogen, which is used in the operation of the polymer electrolyte membrane fuel cell (PEMFC), where chemical energy is converted into electrical energy, and only heat and pure water are released during operation [2]. As the demand for means of transport is also increasing in the world, more and more old tires are generated every year (5 billion are predicted for 2030 ) [3]. Waste tires do not decompose and generally end up in landfills, which is not a sustainable solution. Therefore, opportunities are being sought for the recycling of waste tires in various fields. In this work, a Pt catalyst material is synthesized using carbon made from waste tires as a support material [4].The aim of this work was to investigate the activity of oxygen reduction reaction (ORR) of synthesized platinum catalysts. The Pt deposition was performed by two different methods. Synthesized catalyst materials (S1 and S2) and commercial catalyst (K) for comparison were characterized physically to obtain information on Pt weight percent and Pt crystallite size, material elemental composition, specific surface area, and porosity. Catalysts were characterized electrochemically using rotating disk electrode and cyclic voltammetry methods to determine their ORR kinetics. Measurements of PEMFC performance in air showed that catalyst materials with smaller Pt crystallite size and higher ECA values also had higher ORR activity. In addition, it was found that the power density depends significantly on the carbon used in the synthesis of the Pt catalyst and the method of preparation of the membrane electrode assembly (MEA). Based on the PEMFC measurements of the optimized MEAs, the power density increased in the order S1 < S2 < K.

(Invited) Lowering the Noble Metal Requirement for PEM Water Electrolysis: Membrane Electrode Assembly and Porous Transport Layer Design Considerations

The Net Zero Emission scenario proposed by the International Energy Agency projects a required electrolytic generation of hydrogen equivalent to 3600 GW by 2050 [1], averaging to an annual installation of ~130 GW/a between 2023 and 2050. If this were to be provided by proton exchange membrane based water electrolyzers (PEM-WEs) based on platinum catalysts for the hydrogen evolution reaction (HER) and iridium catalysts for the oxygen evolution reaction (OER), the current PEM-WE noble metal requirements of ~0.7 gIr/kW and ~0.3 gPt/kW [1] would have to be drastically reduced in view of the noble metal supply constraints. As argued previously, for PEM-WEs to be sustainable on such a large scale would require to achieve platinum and iridium loadings of ~0.05 mg/cm2 electrode [2,3]. While the former can be easily achieved due to the fast HER kinetics on Pt, the latter requires either ultra-thin OER catalyst layers or improved OER catalysts with a substantially reduced iridium packing density (in units of gIr/cm3 electrode) [2], like the recently developed catalyst with a hydrous iridium oxide shell supported on a titanium oxide core (IrOx/TiO2) [4,5].In this contribution, we will discuss the effect of the design of membrane electrode assemblies (MEAs) and of the adjacent porous transport layers on PEM-WE performance. In general, the preparation of MEAs with low platinum loading cathodes is straightforward, due to the availability of carbon supported platinum catalysts (Pt/C) with a low Pt packing density. For the optimization of the ionomer content in the cathode electrode, however, its effect on the high current density performance and on the hydrogen permeation rate from cathode to anode have to be considered [6,7].With regards to the anode electrode, we will further discuss the MEA design challenges when targeting ultra-low iridium loadings. In the case of the ultra-thin catalyst layers that result when using conventional OER catalysts, additional contact resistances between the anode catalyst layer and the titanium based porous transport layer (Ti-PTL) are observed [2]. As will be shown, these can be largely mitigated by the use of a titanium based microporous layer (MPL) coated on the Ti-PTL, highlighting the importance of the interface between the PTL and the anode catalyst layer. In case of using the above described IrOx/TiO2 catalysts with low iridium packing density, their typically lower electrical conductivity also results in apparent contact resistances within and across the anode catalyst layer [4], which poses an additional constraint on the allowable range of the catalyst/ionomer ratio in the anode electrode. The interplay between the anode catalyst type, the anode ionomer content, and the type of interface between the anode electrode and the PTL (i.e., with and without MPL) will be discussed.

Ag-Cu Nanoparticles as Cathodic Catalysts for an Anion Exchange Membrane Fuel Cell

In this work, the synthesis of bimetallic Ag and Cu particles on carbon vulcan (AgCu/C) is reported, synthesized by a simple galvanic displacement method using citrate tribasic hydrate as a co-reducing agent and a commercial material based on Cu/C as a template. The materials were characterized by several physicochemical techniques, including TGA, ICP-OES, XRD, SEM, and BET. The catalysts were evaluated as cathodic catalysts for the oxygen reduction reaction (ORR) and were used for the preparation of membrane electrode assemblies for evaluation in an Anion Exchange Membrane Fuel Cell (AEMFC). The results were compared with the commercial Ag/C and Cu/C catalysts; the bimetallic catalyst obtained a higher power density, which was attributed to a synergistic effect between Ag and Cu particles.

Double-Layer ePTFE-Reinforced Membrane Electrode Assemblies Prepared by a Reverse Membrane Deposition Process for High-Performance and Durable Proton Exchange Membrane Fuel Cells

To promote further commercialization of proton exchange membrane (PEM) fuel cells, developing a novel preparation method for high-performance and durable membrane electrode assemblies (MEAs) is imperative. In this study, we adopt the reverse membrane deposition process and expanded polytetrafluoroethylene (ePTFE) reinforcing technology to optimize the interface combination and durability of MEAs simultaneously for the preparation of novel MEAs with double-layer ePTFE reinforcement skeletons (DR-MEA). With the wet-contact between the liquid ionomer solution and porous catalyst layers (CLs), a tight 3D PEM/CL interface is formed in the DR-MEA. Based on this enhanced PEM/CL interface combination, the DR-MEA exhibits a significantly increased electrochemical surface area, reduced interfacial resistance, and improved power performance compared with a conventional MEA (C-MEA) based on a catalyst-coated membrane method. Furthermore, with the reinforcement of double-layer ePTFE skeletons and the support of rigid electrodes for the membranes, the DR-MEA demonstrates less mechanical degradation than the C-MEA after wet/dry cycle test, reflected in lower increase in hydrogen crossover current, interfacial resistance, and charge-transfer resistance and reduced power performance attenuation. With less mechanical degradation, the DR-MEA therefore shows less chemical degradation than the C-MEA after an open-circuit voltage durability test.

An ePTFE-reinforced membrane electrode assembly based on a wet-contact interface design strategy for high-performance proton exchange membrane fuel cells

The interfacial bonding between a proton exchange membrane (PEM) and catalyst layers (CLs) is a critical factor that dominates the power performance and durability of the membrane electrode assembly (MEA) in a proton exchange membrane fuel cell and therefore must be designed with considerable attention. On this basis, we present a novel MEA preparation approach by combining a wet-contact interface design strategy and expanded polytetrafluoroethylene (ePTFE) reinforcing technology to optimize the PEM/CL interfacial combination and durability of MEAs simultaneously. With a tight and robust three-dimensional PEM/CL interface, the MEAs based on the wet-contact process exhibit significantly reduced interfacial resistance and charge-transfer resistance and improved electrochemical surface area, resulting in superior power performance compared with conventional MEAs. Simultaneously, intercalating ePTFE reinforcement skeletons into the PFSA membrane obviously reduces the hydrogen crossover of the novel MEAs. Furthermore, due to the tighter PEM/CL interfacial bonding and the support of the rigid electrodes, the novel ePTFE-reinforced MEA shows less mechanical degradation than a conventional MEA based on the catalyst coated membrane method (with a Gore membrane) after a wet/dry cycle test. This is reflected by the lower increase in hydrogen crossover current, interfacial resistance, and charge-transfer resistance, as well as less power performance attenuation.

Preparation of Membrane Electrode Assemblies Using Waste Tire Derived Carbon Supported Platinum Catalyst

Carbon supported Pt catalyst materials were synthesized from waste tire derived carbon by two different methods (microwave and refluxing). Catalysts and carbons were physically (XRD, N2 sorption analysis, TGA) and electrochemically characterized (RDE, CV, PEMFC single cell measurements). The RDE measurements were performed in 0.1 M HClO4 solution. For PEMFC single cell measurements, membrane-electrode assembly systems (MEAs) were prepared from catalyst materials by using different methods of coating the cathode layer and additional treatments. Catalysts were sprayed onto the membrane or GDL. In addition, MEAs were prepared where the catalyst was pipetted into GDL in several drops. Some of the MEAs were additionally treated with extra layer of Nafion and hot-pressed. The highest power density (0.42 W cm−2) was achieved with the MEA where the Pt catalyst synthesized via refluxing method was coated on the GDL with multiple drops and additional treatments were applied.

Effect of Different Hot-Pressing Pressure and Temperature on the Performance of Titanium Mesh-Based MEA for DMFC.

The hot-pressing process of the membrane electrode assembly (MEA) is one of the research hotspots in the field of the fuel cell. To obtain suitable titanium mesh-based MEA hot pressing process parameters, titanium mesh was used as electrode substrate material. The anode and cathode of MEA were prepared by the drip-coated method, and the titanium mesh-based MEA was prepared under different hot-pressing pressure and temperature, respectively. The performance of titanium mesh-based MEA was studied by morphological observation, elemental analysis, thickness measurement, single cell test and numerical fitting analysis. The results demonstrated that: with increasing hot-pressing pressure from 0 MPa to 10 MPa, the forming thickness of titanium mesh-based MEA is getting thin gradually, and the peak power density of titanium mesh-based MEA first increased and then gradually decreased; with increasing hot-pressing temperature from 115 °C to 155 °C, the peak power density of titanium mesh-based MEA enhanced at the beginning and then also gradually decreased. Under the premise of a hot-pressing time of 180 s and the optimal operating temperature of DMFC of 60 °C, the appropriate hot-pressing process conditions of titanium mesh-based MEA are a hot-pressing pressure of 5 MPa and a hot-pressing temperature of 135 °C. The results can provide a technological reference for the preparation of titanium mesh MEA for DMFC.

Rational Design of Photoelectrodes for the Fully Integrated Polymer Electrode Membrane–Photoelectrochemical Water-Splitting System: A Case Study of Bismuth Vanadate

Photoelectrochemical (PEC) reactors based on polymer electrolyte membrane (PEM) electrolyzers are an attractive alternative to improve scalability compared to conventional monolithic devices. To introduce narrow band gap photoabsorbers such as BiVO4 in PEM-PEC system requires cost-effective and scalable deposition techniques beyond those previously demonstrated on monolithic FTO-coated glass substrates, followed by the preparation of membrane electrode assemblies. Herein, we address the significant challenges in coating narrow band gap metal-oxides on porous substrates as suitable photoelectrodes for the PEM-PEC configuration. In particular, we demonstrate the deposition and integration of W-doped BiVO4 on porous conductive substrates by a simple, cost-effective, and scalable deposition based on the SILAR (successive ionic layer adsorption and reaction) technique. The resultant W-doped BiVO4 photoanode exhibits a photocurrent density of 2.1 mA·cm–2, @1.23V vs RHE, the highest reported so far for the BiVO4 on any porous substrates. Furthermore, we integrated the BiVO4 on the PEM-PEC reactor to demonstrate the solar hydrogen production from ambient air with humidity as the only water source, retaining 1.55 mA·cm–2, @1.23V vs RHE. The concept provides insights into the features necessary for the successful development of materials suitable for the PEM-PEC tandem configuration reactors and the gas-phase operation of the reactor, which is a promising approach for low-cost, large-scale solar hydrogen production.

Effects of cathode gas diffusion layer type and membrane electrode assembly preparation on the performance of immobilized glucose oxidase‐based enzyme fuel cell

AbstractDifferent cathode configurations with carbon paper (CP) and carbon cloth (CC) gas diffusion layer (GDL) are combined with Nafion® 115 for GOx enzyme fuel cells. Catalyst‐coated Nafion membrane (without a GDL) has resulted with highest impedance and lowest polarization response. Hot pressing of cathode gas diffusion electrode (GDE) onto the Nafion or physical placement onto the alternative chitosan membrane has reduced interface resistance 10 times compared with no‐GDL case. The best performance for the Nafion membrane is 2.1 mA cm−2 current density with hot‐pressed CC‐GDE. Smallest high‐frequency electrolyte (0.55 ohm) and charge transfer resistances (0.15 ohm) were measured with physically placed CC‐GDE on the alternative chitosan membrane resulting in maximum short current density of 3 mA cm−2 with a 4‐cm2 single enzyme fuel cell.

A Novel Impregnation-Reduction Method Combined with Galvanic Replacement for Fabricating Low Cost MEA with High Performance for PEM Fuel Cells

The fuel cells have outstanding advantages in the new energy application, but the membrane electrode assembly (MEA) of fuel cells is difficult to produce at low-cost and large-scale, which restricts their applications. To simplify the preparation of MEA, for the first time, we successfully develop a novel impregnation-reduction method combined with galvanic replacement to grow Ag/Pt bimetallic nanocatalyst onto a Nafion membrane (Nafion-Ag/Pt membrane), and the deposited Ag/Pt catalyst is very stable, which can be directly used as a novel ultra-thin catalyst layer in MEA. This novel method possesses mild conditions, simple procedure, good repeatability and practicability in a large-scale production. Moreover, a very low Pt loading amount of Nafion-Ag/Pt membrane can be achieved by regulating experimental conditions, which brings excellent Pt utilization. Therefore, the MEA made from Nafion-Ag/Pt membrane exhibits a Pt mass specific power (1.519 W mgPt −1) that is 12.3 times higher than that of a conventional MEA. These results demonstrate that this novel impregnation-reduction method can reduce the cost of fuel cells by reducing the difficulty of MEA preparation and the Pt loading amount of MEA and simultaneously enhancing its performance, which shows great potential in fuel cell application.

Performance optimization of ultra-low platinum loading membrane electrode assembly prepared by electrostatic spraying

To improve the utilization of platinum and reduce the manufacturing cost of proton exchange membrane fuel cell (PEMFC), the electrostatic spraying was used to prepare the cathode catalyst layer of membrane electrode assembly (MEA) with platinum loading varying from 0.1 to 0.01 mg cm−2. The performance of fuel cell was tested and analyzed by electrochemical impedance and polarization curve. Our results show that the platinum carbon (Pt/C) particles deposited by electrostatic spraying were well dispersed and the microporous structure of catalyst layer (CL) were relatively uniform. Replacing the CCS type MEA (catalyst coated on gas diffusion layer substrate) with the CCM type MEA (catalyst coated on proton exchange membrane) can reduce its electrochemical impedance and improve the power density of fuel cell. Compared to the Pt/C catalyst with a platinum mass fraction of 60%, a lower platinum-carbon ratio catalyst is more conducive to the uniform dispersion of catalyst particles and efficient utilization of platinum in the preparation of MEA with ultra-low platinum loading. However, their difference in peak power density decreases with the increase of platinum loading. Besides, increasing the back pressure can improve the performance of fuel cell, when the back pressure increased to 0.15 Mpa and the feeding gases were set as H2/O2, the peak power density of 0.56 W cm−2 was obtained by the MEA with cathode platinum loading of 0.01 mg cm−2, which is corresponding to the cathode platinum utilization of 56 kW·gPt−1cathode.

MEA Preparation for Direct Formate/Formic Acid Fuel Cell-Comparison of Palladium Black and Palladium Supported on Activated Carbon Performance on Power Generation in Passive Fuel Cell.

Membrane electrode assemblies (MEAs) with palladium catalysts were successfully prepared by using a home-made manual pressing system with Nafion glue application that contributed to a decrease of additional energy consumption. The catalyst coated membranes were prepared with supported palladium on activated carbon (PdC) and unsupported palladium black (PdB) for comparison. The performance of passive, air breathing, functioning under ambient conditions and with low concentration (1 M) formate/formic acid fuel cell was evaluated. Based on polarization curves, the best result was obtained with carbon supported catalyst and HCOOK fuel, achieving 21.01 mW/mgPd. Still, constant current discharge with PdC showed an energy generation efficiency of 14% with HCOOH over 3% with HCOOK caused by lower potassium ion conductivity and its permeability through the proton exchange membrane. The faradic efficiency of conversion in the cell is equal to the overall energy efficiency and makes the cell self-sufficient.

Impact of Surface Functionalization on the Intrinsic Properties of the Resulting Fe–N–C Catalysts for Fuel Cell Applications

Herein, Fe–N–C catalysts are prepared from surface functionalized carbon nanotubes (CNTs) in combination with iron acetate and phenanthroline. An improved performance and structural composition is obtained by surface functionalization of the CNTs with indazole or pyridine. Catalyst composition and morphology are characterized by transmission electron microscopy, N2 sorption, photoelectron spectroscopy, and 57Fe transmission Mössbauer spectroscopy. However, activity and selectivity toward oxygen reduction reaction are determined from rotating ring disc electrode (RRDE) experiments. The durability and stability are evaluated by accelerated stress tests (0.0–1.2 V) and differential electrochemical mass spectroscopy (DEMS), respectively. It is shown that surface functionalization with indazole enables the direct attachment of FeN4 centers to CNTs so that no impurity species are detected and a high activity is achieved, that can be attributed to an improved turnover frequency and higher mass‐based site density. Even more striking is the excellent durability and stability of the realized catalyst. While these trends are well pronounced in RRDE and DEMS, challenges in the preparation of membrane electrode assemblies make the trend not as obvious in fuel cells (FCs).

Effect of Nafion loading and the novel flow field designs on innovative anode electrocatalyst for improved Direct Methanol Fuel cells performance

Efficiency of a Direct methanol fuel cells (DMFCs) not just merely depends on the catalyst, but also on the flow channels, physical/electrochemical kinetics, Membrane Electrode Assembly (MEA) preparation and other operating parameters. This article is focused on the influence of novel flow field design and the effect of Nafion loading during MEA preparation on the performance of DMFC. A novel Pt/NiTiO3 was used as the anode electrocatalyst in the DMFC. The results show a 27.8% & 5.1% increment in cell performance due to changes in Nafion loading and flow field designs, respectively. A Nafion loading of 0.5 mg/cm2 and the sinuous flow field gave the highest performance. Thus, Pt-NiTiO3/C performed to be an encouraging anode catalyst with the new sinuous flow field.

Development of Mesoporous Carbon Fibers for PEFC Catalyst Supports

Introduction PEFCs have been known as an energy technology with high efficiency and low carbon emission. Among the components of PEFCs, the electrocatalyst layer is an important component to determine PEFC performance and mainly made by noble metal particles dispersed on carbon supports. In order to increase the efficiency and durability of electrocatalysts, our group has been focusing on developing novel carbon supports, and we have previously demonstrated the improvement of durability by utilizing mesoporous carbon (MC) with 6-8 nm pore size [1]. Even though the nanostructure of electrocatalysts has been successfully controlled, further control of the microstructure of electrocatalyst layers is required to improve efficiency of PEFC. In this study, we are trying to control the microstructure though making our MC into fibers with an electrospinning technique. Experimental MC fibers (MCFs) were synthesized by electrospinning the solution containing the resol-formaldehyde type resin polymer and Pluronic F127, after adding polyvinyl alcohol (PVA) as a polymer additive. Then, Pluronic F127 was removed by heat treatments to generate mesopores. MCFs were characterized by N2 sorption in order to analyze their mesoporosity. To make comparison on mechanical strength and conductivity among Vulcan® carbon black, MC, and MCF, FIB-SEM observation and electro-impedance measurements were performed, respectively, after spray printing carbon dispersions on the substrate. Electrochemical analyses were performed by both half-cell measurements in the solution and full-cell measurements with membrane-electrode assemblies (MEAs), after successful Pt deposition into mesopores of MCF. Results and discussion The morphology of MCF is shown in Figure 1, and both the fiber structure and mesopores were confirmed. The N2 adsorption measurement indicated the pore size of MCF is around 4-6 nm, which is slightly smaller than the pore size of MC. Regarding to the mechanical strength, MCF showed smaller change in the thickness after compression in comparison to the regular MC and Vulcan® carbon black. This probably comes from higher elasticity provided by the fiber structure. Moreover, according to the conductivity measurements, MCF showed higher conductivity than MC and Vulcan® carbon black. The higher conductivity is probably due to the fact that the fiber-fiber contact provides a better conductive path than the particle-particle contact. From electrochemical analyses through half-cell measurements, Pt deposited MCF catalyst (Pt/MCF) showed similar ECSA and ORR activity to Pt deposited MC catalyst (Pt/MC). However, based on better mechanical strength and conductivity of MCF, advantages on full-cell measurements with MEAs are expected. Details of preparation and evaluation of MEAs will be discussed.

APPLICATION OF SULFONATED POLYSTYRENE IN POLYMER ELECTROLYTE FUEL CELL

APPLICATION OF SULFONATED POLYSTYRENE IN POLYMER ELECTROLYTE FUEL CELL. Sulfonated polystyrene (SPS) is polyelectrolyte solid that widely used in many aplications. In this works SPS is applied for some parts of polymer electrolyte fuel cell membrane due sulfonate group available in the structure. The investigation involve the application for membrane with addition of small molecules, i.e. benzimidazole and evaluating its microstructure and performance. Application of SPS solution as binding agent in MEA will also be presented. The results show that when using SPS as fuel cell membrane, the additon of small molecules such as benzimidazole would modify its microstrusture as well as improve its ion conductivity. Meanwhile, some improvement still required for application of SPS solution as binding agent for preparation of Membrane Electrode Assembly or MEA.

A family of platinum group metal-free catalysts for oxygen reduction in alkaline media

In this work a series of platinum group metal-free catalysts based on iron, cobalt, copper, nickel, silver and their bimetallic combinations are synthesized and their behavior for oxygen reduction in alkaline media is tested. A phthalocyanine-like ligand supported on carbon black serves as the nitrogen source and carbon support, respectively, for the catalysts. The as-prepared materials are thermally activated by pyrolysis at temperatures ranging from 600 °C to 1000 °C. Oxygen reduction reaction (ORR) activity and stability in 0.1 M KOH are tested by rotating ring disk electrode (RRDE) experiments. Several of the catalysts show ORR activities in the RRDE experiment that are superior to Pt, with Co, Co/Fe and Ag/Co being the best. All catalysts show remarkable stability, even when they are tested under air for 5000 RRDE cycles. RRDE experiments are also used to study the effect of catalyst loading and to determine reaction order. A thorough study of the catalyst performance in a single cell fuel cell test is conducted; exploring different methods to prepare the electrodes and the effects of catalyst loading, the catalyst-to-binder ratio and the removal of excess metal on the cell performance. Different methods of preparation of membrane electrode assemblies are also studied.

Evaluation of Poly(phenylene oxide)-Based Anion Exchange Membranes in Fuel Cells

Anion exchange membrane fuel cells (AEMFC) or hydroxide exchange membrane fuel cells (HEMFC) are emerging as possible alternatives to proton exchange membrane fuels cells [1]. The alkaline environment in these fuel cells make possible the use of platinum free catalysts since the oxygen reduction is more easily catalysed. In addition, the higher pH is less corrosive towards the stainless steel bipolar plates. Thereby, AEMFC has potential to be produced at a lower cost. However, further research is still needed to improve cell components and to commercialize the technology. The polymeric material is a very important part in AEMFC, and new polymers are continuously being developed to improve the fuel cells [1-3]. The polymer electrolyte membranes have to be impermeable to gases and need to have a high hydroxide conductivity. If used as ionomers in the electrodes, high hydroxide conductivity, low swelling and a good interaction with the catalyst powder are desirable. During operation water is produced at the anode and consumed at the cathode meaning that the water will affect the polymer performance and, so electrochemical out-put. Further, the water balance across the cell is dependent on the membrane properties [4]. Thus, for better understanding of these materials, they have to be evaluated in a real fuel cell set-up. In this study the performance of novel poly(phenylene oxide) (PPO)-based polymer electrolytes with quaternary amines is evaluated. These materials have been synthesized to avoid hydroxide degradation of the backbone by attaching the quaternary amine at the end of a longer side-chain. Distancing it from the polymer backbone results in steric hindering of hydroxide attack. The chain structures compared in this study are shown in figure 1. Their polymer backbone remains the same, but the side-chains altered to have varying length or a different quaternary amine group. These materials have previously shown very promising properties in ex-situ tests at 80 °C. Among these, high conductivity for fully humidified membranes, over 100 mS cm-1, and high stability up to 200 h in 1 M NaOH with very low loss of ion-exchange capacity were measured [3]. Figure 1 -The polymeric backbone investigated is shown in a), and the three side chains that replaces the R in the backbone are shown in b), c) and d). Membrane electrode assemblies (MEAs) are prepared using the PPO-based membranes and in house made electrodes using Tokuyama AS-4 ionomer and Pt/C catalyst prepared on the gas diffusion layer. The ion-exchange of the membranes synthesized in bromide form was performed in carbon dioxide free environment prior to MEA preparation. The investigation focuses on electrochemical measurements of the cell, including in-cell gas crossover, cell resistance and fuel cell performance. Among other methods polarization curves, cyclic voltammograms and impedance spectra are used for cell characterization. In addition the water production and flux across the MEA is measured using humidity sensors.