Fuel Cell Membrane Electrode Assemblies Research Articles

CO tolerance of nano-architectured Pt–Mo anode electrocatalysts for PEM fuel cells

PEM fuel cell membrane electrode assemblies with Nafion electrolytes and commercial Pt-based cathodes were tested with Pt0.8Mo0.2 alloy and MoOx@Pt core–shell anode electrocatalysts for CO tolerance and short-term stability to corroborate earlier thin-film RDE results. Polarization curves at 70 °C for the Pt0.8Mo0.2 alloy in H2 with 25–1000 ppm CO showed a significant increase in CO tolerance based on peak power densities in comparison to PtRu electrocatalysts. MoOx@Pt core–shell electrocatalysts, which showed extremely high activity for H2 in 1000 ppm CO during RDE studies, performed relatively poorly in comparison to the Pt0.8Mo0.2 and PtRu alloys for the same total catalyst loading on a per area basis in MEA testing. The discrepancy is attributed to residual stabilizer from the core–shell synthesis impacting catalyst-ionomer interfaces. Nonetheless, the MoOx@Pt electrochemical performance is superior on a per-gram-of-precious-metal basis to the Pt0.8Mo0.2 electrocatalyst for CO concentrations below 100 ppm. Due to cross-membrane Mo migration, the stability of the Mo-containing anode electrocatalysts remains a challenge for developing stable enhanced CO tolerance for low-temperature PEM fuel cells.

Pulse electrodeposition of platinum catalyst using different pulse current waveforms

The effects of waveform and other associated parameters on the pulse current electrodeposition of platinum electrocatalysts for use in polymer electrolyte membrane fuel cells were investigated. Using microsecond pulses with ramp-down waveforms yielded well dispersed, high surface area nanoparticles of 2–3nm diameter, which, when incorporated into fuel cell membrane-electrode assemblies (MEAs), resulted in fuel cell performance comparable with commercial MEAs that employed ten times as much platinum loading.

Magneli phase Ti n O2n − 1 as corrosion-resistant PEM fuel cell catalyst support

Magneli phase titanium suboxide, Ti n O2n − 1, with Brunauer–Emmett–Teller surface area up to 25 m2 g−1 was prepared using the heat treatment of titanium oxide (rutile) mixed with polyvinyl alcohol in ratios from 1:3 to 3:1. XRD patterns showed Ti4O7 as the major phase formed during the heat treatment process. The Ti n O2n − 1 showed excellent electrochemical stability in the potential range of −0.25 to 2.75 V vs. standard hydrogen electrode. The Ti n O2n − 1 was employed as a polymer electrolyte membrane fuel cell catalyst support to prepare 20 wt% platinum (Pt)/Ti n O2n − 1 catalyst. A fuel cell membrane electrode assembly was fabricated using the 20 wt% Pt/Ti n O2n − 1 catalyst, and its performance was evaluated using H2/O2 at 80 °C. A current density of 0.125 A cm−2 at 0.6 V was obtained at 80 °C.

Scalable Fabrication of Multifunctional Freestanding Carbon Nanotube/Polymer Composite Thin Films for Energy Conversion

Translating the unique properties of individual single-walled carbon nanotubes (SWNTs) to the macroscale while simultaneously incorporating additional functionalities into composites has been stymied by inadequate assembly methods. Here we describe a technique for developing multifunctional SWNT/polymer composite thin films that provides a fundamental engineering basis to bridge the gap between their nano- and macroscale properties. Selected polymers are infiltrated into a Mayer rod coated conductive SWNT network to fabricate solar cell transparent conductive electrodes (TCEs), fuel cell membrane electrode assemblies (MEAs), and lithium ion battery electrodes. Our TCEs have an outstanding optoelectronic figure of merit σ(dc)/σ(ac) of 19.4 and roughness of 3.8 nm yet are also mechanically robust enough to withstand delamination, a step toward scratch resistance necessary for flexible electronics. Our MEAs show platinum utilization as high as 1550 mW/mg(Pt), demonstrating our technique's ability to integrate ionic conductivity of the polymer with electrical conductivity of the SWNTs at the Pt surface. Our battery anodes, which show reversible capacity of ∼850 mAh/g after 15 cycles, demonstrate the integration of electrode and separator to simplify device architecture and decrease overall weight. Each of these applications demonstrates our technique's ability to maintain the conductivity of SWNT networks and their dispersion within a polymer matrix while concurrently optimizing key complementary properties of the composite. Here, we lay the foundation for the assembly of nanotubes and nanostructured components (rods, wires, particles, etc.) into macroscopic multifunctional materials using a low-cost and scalable solution-based processing technique.

Alcohol Crossover Behavior in Direct Alcohol Fuel Cells (DAFCs) System

AbstractThe alcohols (methanol, ethanol, and 1‐propanol) crossover behavior of through fuel cell membrane electrode assembly (MEA) in direct alcohol fuel cell (DAFC) system was studied. We divided five different factors which affect alcohol crossover behavior through MEA to analyze alcohol crossover behavior. Those are membrane effect, physical blocking effect of anode, alcohol oxidation effect of anode electrocatalysts, physical blocking effect of cathode, and alcohol oxidation effect of cathode. Among these five factors, the four factors caused by two different electrodes (anode and cathode) were evaluated by fabricating various types of MEA. In the case of alcohols through membrane without any electrode was increased when the cell temperature was raised from room temperature to 100 °C, but it was decreased above the cell temperature of 100 °C. Among the electrode effects on alcohol crossover rate, physical blocking effect of electrodes played dominant role below 100 °C. However alcohol oxidation effects of electrodes was predominant above the 100 °C.

Ortho-Dichlorobenzene as a pore modifier for PEMFC catalyst electrodes and dense Nafion membranes with one porous surface

ortho-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membranes and proton exchange membrane fuel cell (PEMFC) catalyst layers. When ODB containing Nafion dispersions are cast into a film, evaporation leads to dense membranes with one highly porous surface layer occupying 20–30% of the overall thickness. Dense Nafion membranes with a porous top layer are interesting for use in membrane humidifiers, for increasing the electrode–membrane interface areas in electrochemical devices like fuel cells or electrolysers, and other applications. Fuel cell membrane electrode assemblies were obtained by spray coating commercial Nafion 212 membranes with ODB containing catalyst inks. ODB does not poison the catalyst, and 54–120% higher potentials in comparison to the 217 mV obtained with an ODB free ink were achieved at 1.5 stoic air flow, 100% rh and a current density of 1 A cm−2. This shows that the porous catalyst electrode structure is changed, resulting in a reduced contribution of mass transport limited overpotentials. Furthermore, MEAs prepared with ODB in the catalyst ink are less sensitive towards changes in the air flow rate and the cathode relative humidity (between 50% rh and 100% rh: 217–292 mV at 1 A cm−2 without ODB and 439–478 mV with ODB).

Thermal curing of PBI membranes for high temperature PEM fuel cells

Phosphoric acid doped polybenzimidazole (PBI) has emerged as one of the most promising electrolyte materials for proton exchange membrane (PEM) fuel cells operating under anhydrous conditions at temperatures of up to 200 °C. The limited long-term durability of the membrane electrode assemblies (MEAs) is currently hampering the commercial viability of the technology. In the present study, thermoset PBI membranes were prepared by curing the membranes under inert atmosphere at temperatures of up to 350 °C prior to the acid doping. The systematic membrane characterizations with respect to solubility, phosphoric acid doping, radical-oxidative resistance and mechanical strength indicated that the PBI membranes were irreversibly cured by the thermal treatment. After curing, the PBI membranes demonstrated features that are fundamental characteristics of a thermoset resin including complete insolubility, high resistance to swelling and improved mechanical toughness. Additionally, the thermal treatment was found to increase the degree of crystallinity of the membranes. The improved physicochemical characteristics of the membranes after curing were further illustrated by a dramatically improved long-term durability of the corresponding fuel cell MEAs. During continuous operation for 1800 h at 160 °C and 600 mA cm−2, the average cell voltage decay rate of the MEA based on the cured membrane was 43 μV h−1. This should be compared with an average cell voltage decay rate of 308 μV h−1 which was recorded for the MEA based on its non-cured counterpart.

Integrated micro fuel cell with on-demand hydrogen production and passive control MEMS

An ever increasing demand for packaging more energy on-board to meet the needs of power hungry microsystems is driving the miniaturization of power generators. We report a fully integrated Power MEMS, in the 10-μL size, designed to deliver high energy and power densities. On-board hydrogen production and an efficient control scheme that facilitates integration with a fuel cell membrane electrode assembly are key elements for micro energy conversion. A millimeter-scale reactor produces hydrogen by hydrolysis of CaH2 and LiAlH4, to yield energy densities of the order of 200 Whr/L. A passive microfluidic control scheme, incorporating surface tension to pump water in a microchannel for hydrolysis and microvalve control using hydrogen backpressure, facilitates delivery and regulation and eliminates bulky auxiliaries that consume parasitic power. We tested the ability of this control scheme to improve uniformity of power delivery during long periods of lower demand, with fast switching to mass transport regime on the order of seconds, and realized peak power density of up to 391.85 W/L. Prototypes have been tested for duty periods from 2–48 h, with multiple switching of power demand in order to establish performance across multiple regimes. Critical to the realization of the integrated power MEMS, and its energy and power density, are effects of water transport and byproduct hydrate swelling on hydrogen production in the microreactor. While CaH2 showed superior hydrogen release kinetics that enhances power density, LiAlH4 provided greater energy density due to reduced byproduct expansion that permitted increased hydrogen production.

High‐Performance Nanofiber Fuel Cell Electrodes

A nanofiber electrode is fabricated by electrospinning an ink composed of Pt/C catalyst particles in a solution of Nafion and poly(acrylic acid). Exceptionally high power densities and platinum mass activity are achieved when using the mat as cathode in H2/air and H2/O2 fuel cell membrane–electrode assemblies. The nanofiber cathode also exhibits outstanding stability in accelerated durability tests.

연료전지(燃料電池) 막전극접합체(膜電極接合體)의 막분리(膜分離) 및 백금(白金) 회수(回收)에 관(關)한 연구(硏究)

본 논문에서는 초음파나 교반 없이 전해질막과 확산층을 분리하기위한 새로운 방법에 대해 연구하였다. 증류수, 부탄올, 계면활성제를 이용하여 연료전지 막전극접합체의 전해질막과 확산층을 침지법으로 촉매입자의 분산 없이 분리하였다. 또한 분리된 확산층의 촉매와 연료전지 Pt/C 촉매를 왕수에서 <TEX>$80{\sim}85^{\circ}C$</TEX>로 가열하여 촉매입자를 녹여 침전제를 첨가하였다. 이후 소성하여 백긍 금속을 회수하였고 이는 새로운 연료전지용 전극촉매를 만드는데 사용될 것이다. Present paper reports a new method to separate the electrolyte membranes and carbon paper without using ultrasonic waves and stirring. In this method, these were separated from fuel cell membrane-electrode assembly(MEA) using the distilled water, butanol and surfactant by dipping method without the dispersion of catalyst particles. Separated carbon paper catalysts and fuel cell Pt/C catalysts were heated in aqua regia at <TEX>$80{\sim}85^{\circ}C$</TEX> and added to precipitant. After calcination, Pt metal was recovered which might be used in fabricating new fuel cells.

Extraordinary Oxygen Reduction Activity of Pt3Ni7

Nanostructured thin film catalysts (NSTF) with widely varying compositions of PtxMy and PtxMyNz (M, N = Ni, Co, Zr, Hf, Fe, Mn) have been evaluated for 0 ≤ x, y, z < 1. The catalysts’ activity for oxygen reduction (ORR) was measured in 50 cm2 fuel cell membrane electrode assemblies. Pt1-xNix was found to be unique in showing an extraordinarily sharp peak in ORR activity as a function of the as-made composition around x = 0.69 ± 0.02 determined gravimetrically. This composition gave a corresponding fcc lattice parameter of 3.71 Angstroms and a grain size of 7.5 nm. Both surface area and specific activity increases contribute to the increased mass activity of the resultant dealloyed films. The ORR mass activity of the Pt3Ni7 is 60% higher than for the NSTF standard Pt68Co29Mn3 alloy. Rotating disk electrode measurements of a Pt1-xNix series on NSTF coated glassy carbon disks show a similar large and sharp peak in activity. In contrast, PtCo shows a diminished but still sharply peaked mass activity in 50 cm2 tests near x = 0.62 by electron microprobe over the 0 < x < 0.7 range examined.

High Performance plasma sputtered PdPt fuel cell electrodes with ultra low loading

A PdPt (10 wt% Pt) catalyst is used to replace platinum at the cathode of a proton exchange membrane fuel cell membrane electrode assembly (PEMFC MEA) whereas pure palladium is used as the anode catalyst. The catalysts are deposited on commercial carbon woven web and carbon paper GDLs by plasma sputtering. The relations between the depth density profiles, the electrode support and the fuel cell performances are discussed. It is shown that the catalyst gradient is an important parameter which can be controlled by the catalyst depth density profile and/or the choice of electrode support. An optimised electrode structure has been obtained, which allows limiting the platinum requirement. Under suitable conditions of a working PEMFC (80 °C and 3 bar absolute pressure), very high catalysts utilization is obtained at both electrodes, leading to 250 kW g Pt −1 and 12.5 kW g Pd −1 with a monocell fitted with a PdPt (10:1 weight ratio) cathode and a pure Pd anode.

Performance test and degradation analysis of direct methanol fuel cell membrane electrode assembly during freeze/thaw cycles

Performance and degradation of direct methanol fuel cell (DMFC) membrane electrode assembly (MEA) are analyzed after repeated freeze/thaw cycles. Three different MEAs stored at −20°C for 8h with the anode side full of methanol solution are selected to test the effects of low temperatures on performance. After the cell heated to 60°C within 30min, they are inspected to determine the degradation mechanism. The resistance R obtained by the polarization curve is essential for identifying the main component affecting cell performance. The electrochemical impedance spectroscopy (EIS) technique is used to characterize the DMFC after freeze/thaw cycles. Thus, deterioration is assessed by measuring the high-frequency resistance (HFR) and the charge-transfer resistance (CTR). The electrochemical surface area (ECA) is employed to investigate not only the actual chemical degradation but also membrane status since sudden loss of ECA on the cathode side can result from a broken membrane. Moreover, a strategy is designed to simulate actual conditions that may prevent the membrane from being broken. A DMFC stack without any heating or heat-insulation devices shall avoid to be stored at subzero temperatures since the membrane will be useless due to frozen of methanol solution.

Extraordinary Oxygen Reduction Activity of Pt3Ni7

Nanostructured thin film catalysts (NSTF) with widely varying compositions of PtxMyNz (M, N = Ni, Co, Zr, Hf, Fe, Mn) have been evaluated for 0 < x,y,z < 1. The catalysts' activity for oxygen reduction (ORR) was measured in 50 cm2 fuel cell membrane electrode assemblies. PtxNiy was found to be unique in showing an extraordinarily sharp peak in ORR activity as a function of the as-made composition around x=3, y=7. This composition gave a corresponding fcc lattice parameter of 3.71 Angstroms and a grain size of 7.5 nm. Both surface area and specific activity increases contribute to the increased mass activity. The ORR mass activity of the Pt3Ni7 is 60% higher than for the NSTF standard Pt68Co29Mn3 alloy.

A novel non-platinum group electrocatalyst for PEM fuel cell application

Precious-metal catalysts (predominantly Pt or Pt-based alloys supported on carbon) have traditionally been used to catalyze the electrode reactions in polymer electrolyte membrane (PEM) fuel cells. However as PEM fuel systems begin to approach commercial reality, there is an impending need to replace Pt with a lower cost alternative. The present study investigates the performance of a carbon-supported tantalum oxide material as a potential oxygen reduction reaction (ORR) catalyst for use on the cathode side of the PEM fuel cell membrane electrode assembly. Although bulk tantalum oxide tends to exhibit poor electrochemical performance due to limited electrical conductivity, it displays a high oxygen reduction potential; one that is comparable to Pt. Analysis of the Pourbaix electrochemical equilibrium database also indicates that tantalum oxide (Ta 2O 5) is chemically stable under the pH and applied potential conditions to which the cathode catalyst is typically exposed during stack operation. Nanoscale tantalum oxide catalysts were fabricated using two approaches, by reactive oxidation sputtering and by direct chemical synthesis, each carried out on a carbon support material. Nanoscale tantalum oxide particles measuring approximately 6 nm in size that were sputtered onto carbon paper exhibited a mass-specific current density as high as one-third that of Pt when measured at 0.6 V vs. NHE. However, because of the two-dimensional nature of this particle-on-paper structure, which limits the overall length of the triple-phase boundary junctions where the oxide, carbon paper, and aqueous electrolyte meet, the corresponding area-specific current density was quite low. The second synthesis approach yielded a more extended, three-dimensional structure via chemical deposition of nanoscale tantalum oxide particles on carbon powder. These catalysts exhibited a high ORR onset potential, comparable to that of Pt, and displayed a significant improvement in the area-specific current density. Overall, the highest mass-specific current density of the carbon-powder supported catalyst was ˜9% of that of Pt.

Performance of Hydrogen Fuel Cell MEAs Based on Perfluorinated Nanocomposite Membranes Modified by Polyaniline

This work summarizes the results obtained from the modification of perfluorinated sulfocationic MF-4SC membranes by in situ polymerization of aniline. The transport properties of polyaniline/MF-4SC composite membranes after different times of polymerization have been analyzed. It is observed that after 3 h of aniline polymerization, composite membranes exhibit higher protonic conductivity compared to the pristine sample. The performance of fuel cells containing membrane electrode assemblies (MEAs) from MF-4SC and polyaniline/MF-4SC has also been studied. The kinetic parameters governing the voltage dependence on current density have been estimated and the results have been fitted to a previously established one-dimensional isothermal model by Springer et al. [ J. Electrochem. Soc. 138 , 2334 (1991)] . Good agreement between experimental data and model has been found for low density currents. Some insights about the membrane proton conductivity mechanism are given.

Influence of carbon support microstructure on the polarization behavior of a polymer electrolyte membrane fuel cell membrane electrode assemblies

The influence of carbon support morphology on the polarization behavior of a PEM fuel cell membrane electrode assembly has been investigated in this communication. Nanometer sized platinum electrocatalyst particles were deposited on lower surface area fibrous (carbon nanofibers) and particulate carbon supports (carbon blacks) by the well-documented ethylene glycol route for supported electrocatalyst synthesis. These supported catalyst systems were subsequently utilized to prepare catalyst inks and membrane electrode assemblies (MEA) in conjunction with a perflurosulfonated ionomeric membrane-Nafion ®. Level of liquid Nafion binder in the supported catalyst inks was varied and the ramifications of such a variation on polarization behavior of the MEA determined. The trend in polarization performance was found to be independent of the carbon support morphology in the various ink compositions. The two varieties of carbon supports were also mixed together in various weight ratios and platinum was deposited by the glycol method. Key parameters such as the platinum content on carbon and platinum particle size were determined to be independent of the nature of the supports on which the particles had been deposited. The results indicate that lower surface area carbon supports of vastly contrasting morphologies can be interchangeably employed as catalyst support materials in a PEM fuel cell MEA.

A Simple Alternative to the Expression of Finite Warburg Diffusion Impedance in Porous Electrodes by Considering Oxygen Consumption Along the Air Channel

The classical expression of the finite Warburg element used for analysing electrochemical impedance spectroscopy (EIS) spectra is obtained assuming that the reaction occurs at the electrode/membrane interface and that the oxygen concentration at the gas channel/gas diffusion layer interface is constant. An alternative to this expression is proposed: it takes into account the variation in oxygen concentration along the gas channel due to the oxygen-reduction reaction (ORR). This pseudo-2D approach is well suited for investigating mass transfer limitations in the fuel cell membrane-electrode assemblies (MEA). Simple numerical applications starting from data already published by different authors show that with this new expression, conclusions about the mass transfer limiting layer and its main characteristics can be significantly modified. This improvement to the usual Warburg impedance could contribute to a better understanding of mass transfer limitation in fuel cells and eventually, to the design of MEAs in which diffusion losses are minimal.

Optimization of a proton exchange membrane fuel cell membrane electrode assembly

A computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on a two-dimensional through-the-channel isothermal, isobaric and single phase membrane electrode assembly (MEA) model. The model input parameters are the manufacturing parameters used to build the MEA: platinum loading, platinum to carbon ratio, electrolyte content and gas diffusion layer porosity. The governing equations of the fuel cell model are solved using Netwon’s algorithm and an adaptive finite element method in order to achieve near quadratic convergence and a mesh independent solution respectively. The analysis module is used to solve the optimization problem of finding the optimal MEA composition for maximizing performance. To solve the optimization problem a gradient-based optimization algorithm is used in conjunction with analytical sensitivities. By using a gradient-based method and analytical sensitivities, the framework presented is capable of solving a complete MEA optimization problem with state-of-the-art electrode models in approximately 30 min, making it a viable alternative for solving large-scale fuel cell problems.

Analysis of Oxygen Reduction Reaction Activity of Pt/C Catalysts for Actual PEFC MEAs

The dependence of the oxygen reduction reaction (ORR) activity of Pt/C catalysts used in actual polymer electrolyte fuel cell membrane electrode assemblies (PEFC MEAs) on cell temperature, O2 partial pressure and catalyst loading has been investigated. Based on physical chemistry and electrochemistry points of view, the charge transfer coefficient (α) was demonstrated to vary with potential over a narrow range of 0.5–0.6. The double Tafel slope occurring at potentials above 0.8 V vs. RHE was considered to be caused by the effect of adsorption or reaction of oxygen-containing species sourced by water. As a result, the α was assumed constant at 0.5 irrespective of the potential, and used in the estimation of the ORR activity [A/cm2-Pt]. The ORR activity was observed to increase linearly with increasing temperature. It was also found to be dependent on O2 partial pressure (considered as O2 concentration) until it reached a plateau at an O2 concentration of 40%, and then remained almost constant. This finding implies that in gas-phase PEFC MEAs, adsorption of O2 as a reactant can influence and govern the electrochemical reaction. In addition, the ORR activity is demonstrated to be independent of the Pt/C ratio of the catalyst not only for Pt plate electrodes in liquid-phase systems, but also for MEA electrodes in the gas-phase system of actual single-cell PEFCs. The ORR activity was found to be almost constant at 2.6 × 10–6 A/cm2-Pt at 60°C for Pt/C ratios from 19.3 to 55.8 wt%.