Electrolyte Membrane Fuel Cell Electrodes Research Articles

Local ageing effects of polymer electrolyte fuel cell membrane electrode assemblies due to accelerated durability testing

AbstractAccelerated durability test (ADT) protocols are useful tools to reduce testing time and development costs of automotive polymer electrolyte fuel cell stacks. Established accelerated stress tests allow comparing individual cell components. However, such tests in general do not allow drawing reliable conclusions on the expected lifetime for a complete stack. In this work, we examine the influence of combined stressors on the ageing behavior of individual cell components operated on stack level. We combine known main stressors for mobile fuel‐cell operation such as dynamic load, temperature and humidity cycling or hydrogen/air fronts during start‐up to develop a new accelerated test protocol. It was applied to an automotive 5‐cell short stack for 460 operating hours (OpH). A second stack was operated in a reference long‐term test for 2300 OpH. Several in situ characterization techniques, such as cyclic voltammetry, and recording the local current density distribution were employed. In addition, post‐mortem analyses, such as focused ion beam scanning electron microscopy imaging, was applied in order to better understand the degradation mechanisms. The results presented here provide an excellent basis for the further development of a new ADT protocol, which will accelerate ageing processes in the fuel cell in a realistic way, i.e. leading to similar degradation characteristics as in long term testing.

Recovery of Pt and Ru from Spent Low-Temperature Polymer Electrolyte Membrane Fuel Cell Electrodes and Recycling of Pt by Direct Redeposition of the Dissolved Precursor on Carbon

Recovery of Pt and Ru from Spent Low-Temperature Polymer Electrolyte Membrane Fuel Cell Electrodes and Recycling of Pt by Direct Redeposition of the Dissolved Precursor on Carbon

Platinum Encapsulated within a Bacterial Nanocellulosic–Graphene Nanosandwich as a Durable Thin-Film Fuel Cell Catalyst

Developing cost-effective electrocatalysts for proton electrolyte membrane fuel cell electrodes has proven challenging because of the difficulty in finding inexpensive alternatives to platinum that...

Particle Size-Controlled Growth of Carbon-Supported Platinum Nanoparticles (Pt/C) through Water-Assisted Polyol Synthesis.

A water-assisted control of Pt nanoparticle size during a surfactant-free, microwave-assisted polyol synthesis of the carbon-supported platinum nanoparticles (Pt/C) in a mixture of ethylene glycol and water using (NH4)2PtCl6 as the Pt precursor is demonstrated. The particle size was tuned between ∼2 and ∼6 nm by varying either the H2O volume percent or the Pt precursor concentration during synthesis. The electrochemical surface area (ECSA) and the oxygen-reduction reaction activity obtained for the Pt/C electrocatalyst show a catalytic performance competitive to that of the state-of-the-art commercial Pt/C electrocatalysts used for polymer electrolyte membrane fuel cell electrodes (ECSA: ∼70 m2/g; half-wave potential for oxygen reduction reaction: 0.83 V vs reversible hydrogen electrode). The synthesized Pt/C electrocatalysts show durability equivalent to or better than that of the commercial Pt/C. The durability was found to improve with increasing particle size, with the ECSA loss values being ∼70 and ∼55% for the particle sizes of 2.1 and 4.3 nm, respectively. The study may be used as a route to synthesize Pt/C electrocatalysts from a convenient and economic Pt precursor (NH4)2PtCl6 and avoiding the use of alkaline media.

Zoom in Catalyst/Ionomer Interface in Polymer Electrolyte Membrane Fuel Cell Electrodes: Impact of Catalyst/Ionomer Dispersion Media/Solvent.

Large-scale applications of polymer electrolyte membrane fuel cells (PEMFCs) are throttled primarily by high initial cost and durability issues of the electrodes, which essentially consist of the nanoparticulate catalysts (e.g., Pt) having accessibility to electrons (e-), protons (H+), and fuel/oxidant through catalyst support, polymer electrolyte ionomer, and porous gas diffusion layer, respectively. Hence, to achieve high electrode performance in terms of activity and/or durability, understanding and optimization of the catalyst/support and catalyst/ionomer interfaces are of significant importance. Present study demonstrates an alternative route to inspect the catalyst/ionomer interface through an accelerated stress test combined with electrochemical impedance spectroscopy. Various interfaces are created through catalyst inks prepared using commercial Pt/C catalyst powder dispersed in different solvents. Electrode degradation pattern turns out to be a very useful tool to interpret a catalyst/ionomer interface structure. Variations of interfacial impedance, electrochemical surface area (ECSA), and double layer capacitance with the number of potential cycles suggested significant impact of catalyst/ionomer interface on the catalyst performance. A quantification of the degradation mechanisms responsible for ECSA loss during AST was employed to further understand the correlations between the electrochemical performance of the electrodes and their catalyst/ionomer interface structures. The knowledge may be implied to further optimize the electrode structure and hence to advance the PEMFC technology.

Polyol synthesis of reduced graphene oxide supported platinum electrocatalysts for fuel cells: Effect of Pt precursor, support oxidation level and pH

In this work, a comprehensive study on the polyol synthesis of platinum supported on reduced graphene oxide (Pt/rGO) catalysts, including both ex-situ and in-situ characterizations of the prepared Pt/rGO catalysts, was performed. The polyol synthesis was studied considering the influence of the platinum precursor, oxidation level of graphite oxide and pH of reaction medium. The as-prepared catalysts were analyzed using thermo-gravimetric (TG) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and cyclic voltammetry (CV). The best results in terms of platinum particle size and distribution were obtained when the synthesis was performed in acidic medium, using chloroplatinic acid as precursor and using graphene oxide with high oxidation level. The most promising graphene-supported catalyst was used to prepare a polymer electrolyte membrane fuel cell electrode. The membrane electrode assembly (MEA) prepared with graphene-based electrode was compared with a MEA prepared with catalyst based on commercial platinum supported in carbon black (Pt/C). Single cell characterization included polarization curves and in-situ electrochemical impedance spectroscopy (EIS). The graphene-based electrode presented promising albeit unstable electrochemical performance due to water management issues. Additionally, EIS measurements revealed that the MEA made with Pt/rGO catalyst presented a lower mass transport resistance than the commercial Pt/C.

Gas-leak-induced pinhole formation at polymer electrolyte membrane fuel cell electrode edges

Pinhole formation in the membrane is a polymer electrolyte membrane fuel cell (PEMFC) failure mode typically due to mechanical causes. This study reports the discovery of thermal pinhole formation caused by a gas leak.The study was prompted by an unexpected cell failure of a real PEMFC stack during its initial conditioning. A little gas leak had been detected in the stack, and the gas leak was suspected to generate pinholes. However, in spite of the large gas leak, pinholes did not appear in the normal cells with a GDL-covered catalyst layer. Additional cells with a GDL-uncovered catalyst layer simulating an uneven electrode edge of the failed stack were then tested under the gas leak conditions. Pinholes were demonstrated to appear at the GDL-uncovered catalyst layer position near the gas leak path during the initial conditioning and the phenomena were reproducible. A gas-leak-induced thermal pinhole formation is suggested in which the leaked gas hits the GDL-uncovered low-heat-dissipation catalyst, a hot spot occurs by catalytic combustion, generating the pinhole.

Twenty years of operando IR, X-ray absorption, and Raman spectroscopy: Direct methanol and hydrogen fuel cells

Mixed metal catalysts in polymer electrolyte fuel cell membrane electrode assemblies were characterized by operando infrared, X-ray absorption and Raman spectroscopy. Windowed direct methanol and hydrogen-air fuel cell assemblies allow for spectral acquisition with controlled potential, temperature and flowing reactant streams to the graphite flow fields. Johnson Matthey Pt and PtRu (1:1), in-house prepared PtRu (1:1 and 3:1), PtRuOs (65:25:10), PtNi (1:1), and a melamine-synthesized FeNC catalyst were studied. The near invariant core structure of phase segregated alloy catalysts over practical fuel cell potentials enable a simultaneous fit of metal component EXAFS to quantitatively characterize core structures: JM PtRu is a face centered cubic lattice with 50% of the Ru in an amorphous phase. Stark tuning of COads as a reaction intermediate and as a surface structure probe elucidates potential dependent co-adsorption of Nafion functional groups on Pt. Operando Raman spectroscopic tracking of membrane hydration at a fuel cathode is facilitated by symmetry-based group mode assignments of Nafion IR bands. Fully hydrated Nafion sulfonate groups have C3V local symmetry. Dehydrated sulfonic acid groups have C1 local symmetry. C3V and C1 IR bands coexist at intermediate states of membrane hydration.

Influence of the polytetrafluoroethylene content on the performance of high-temperature polymer electrolyte membrane fuel cell electrodes

In high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), the properties of the catalyst layers (catalyst and binder materials) are critical for the performance of membrane electrode assemblies (MEAs). Here we report the optimization of the polytetrafluoroethylene (PTFE) content in the catalyst layers in terms of the fuel cell performance. Investigations with scanning electron microscopy (SEM) showed fewer PTFE filaments in catalyst layers containing a lower amount of PTFE. Spatially resolved conductive atomic force microscopy (AFM) revealed the higher electric conductivity of catalyst layers with reduced PTFE content. Ex-situ measurements indicated optimized phosphoric acid uptake of catalyst layers containing less PTFE. The PTFE content in the catalyst layers was found to have a large effect on the performance of MEAs in single cell experiments. Reduced PTFE content resulted in a decrease of the high frequency and charge-transfer resistance as well as an improved phosphoric acid uptake of the catalyst layers which resulted in enhanced fuel cell performance. The highest performance was obtained with catalyst layers containing 5% PTFE. The break-in behavior of the cells was significantly improved by addition of the non-ionic surfactant Triton X-100 to the catalyst layers.

Effect of compression on the performance of a HT-PEM fuel cell

This paper shows by thorough electrochemical investigation that (1) the performances of high-temperature polymer electrolyte fuel cell membrane electrode assem- blies of three suppliers are differently affected by com- pressive forces. (2) Membrane thickness reduction by compressive pressure takes place less than expected. (3) A contact pressure cycling experiment is a useful tool to distinguish the impact of compression on the contact resistances bipolar plate/gas diffusion layer (GDL) and GDL/catalytic layer. A detailed visual insight into the structural effects of compressive forces on membrane and gas diffusion electrode (GDE) is obtained by micro-com- puted X-ray tomography (l-CT). l-CT imaging confirms that membrane and GDEs undergo severe mechanical stress resulting in performance differences. Irreversible GDL deformation behavior and pinhole formation by GDL fiber penetration into the membrane could be observed.

A Carbon Corrosion Model to Evaluate the Effect of Steady State and Transient Operation of a Polymer Electrolyte Membrane Fuel Cell

A carbon corrosion model is developed based on the formation of surface oxides on carbon and platinum of the polymer electrolyte membrane fuel cell electrode. The model predicts the rate of carbon corrosion under potential hold and potential cycling conditions. The model includes the interaction of carbon surface oxides with transient species like OH radicals to explain observed carbon corrosion trends under normal PEM fuel cell operating conditions. The model prediction agrees qualitatively with the experimental data supporting the hypothesis that the interplay of surface oxide formation on carbon and platinum is the primary driver of carbon corrosion.

Correction to “Tuning the Performance of Low-Pt Polymer Electrolyte Membrane Fuel Cell Electrodes Derived from Fe2O3@Pt/C Core–Shell Catalyst Prepared by an in Situ Anchoring Strategy”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to “Tuning the Performance of Low-Pt Polymer Electrolyte Membrane Fuel Cell Electrodes Derived from Fe2O3@Pt/C Core–Shell Catalyst Prepared by an in Situ Anchoring Strategy”Vishal M Dhavale and Sreekumar Kurungot*Cite this: J. Phys. Chem. C 2012, 116, 22, 12377Publication Date (Web):May 25, 2012Publication History Published online25 May 2012Published inissue 7 June 2012https://doi.org/10.1021/jp3045803Copyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views688Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Tuning the Performance of Low-Pt Polymer Electrolyte Membrane Fuel Cell Electrodes Derived from Fe2O3@Pt/C Core–Shell Catalyst Prepared by an in Situ Anchoring Strategy

Tuning the Performance of Low-Pt Polymer Electrolyte Membrane Fuel Cell Electrodes Derived from Fe₂O₃@Pt/C Core–Shell Catalyst Prepared by an in Situ Anchoring Strategy

Surface Chemistry of Carbon Black Electrocatalyst Supports as a Result of a Commercial Synthethic Route

A common electrocatalyst support, Vulcan XC72, was taken through a commercial catalyst synthetic route by Tanaka Kikinzoku Kogyo without depositing platinum and subsequently heat treated to produce samples of various surface-modified blacks. These support materials, which are used in polymer electrolyte membrane fuel cell electrode layers, were characterized by both surface and bulk characterization techniques to understand the impact of process steps on formation and removal of oxygen-containing functional groups and their effect on surface acidity of the supports. We present a rigorous cleaning procedure of the processed samples to eliminate free ions and synthesis precursors present on the support surfaces that prohibit accurate data collection. It is shown that strongly acidic functional groups are introduced during the catalyzation process by sacrificing only about 10% of the C–C bonding. Subsequent heat-treatment slowly destroys these functional groups, and while heat-treatment to 1000°C brings the elemental surface composition back to that of the base carbon, the oxygen containing moieties are different.

Nanomaterials-Based PEM Electrodes by Combining Chemical and Physical Depositions

The real market penetration of polymer electrolyte fuel cells is hindered by the high cost of this technology mainly due to the expensive platinum catalyst. Two approaches are followed to reduce the cost: one way is to increase the Pt utilization efficiency reducing at the same time the total load and the other way is to increase the catalytic activity of the catalyst/support assembly. In this work, the increase of utilization efficiency is addressed by optimizing the catalyst distribution on the uppermost layer of the electrode via electrodeposition and sputter deposition, while the improvement of the catalyst activity is pursued by nanostructuring the catalysts and the carbon-based supports. A very low Pt loading (0.006 mg cm−2) was obtained by sputter deposition on electrodes that exhibited a mass specific activity for methanol oxidation reaction better than a commercial product. Carbon nanofibers used as catalyst support of electrodeposited platinum nanoparticles resulted in improved mass specific activity and long term stability compared to conventional carbon-based supports. Finally, PtAu alloys developed by sputter deposition were found more efficient than commercial PtRu catalyst for the methanol oxidation reaction. In conclusion, polymer electrolyte membrane fuel cell electrode based on nanomaterials, developed by combining physical and chemical deposition processes, showed outstanding electrochemical performance.

A Facile Route for Polymer Electrolyte Membrane Fuel Cell Electrodes with in situ Grown Pt Nanowires

Novel Gas Diffusion Electrodes (GDEs) for Polymer Electrolyte Membrane Fuel Cells (PEMFCs) were prepared by in situ growing Pt nanowires on carbon paper using a facile deposition method at room temperature. Pt nanowires, with a length 100–150 nm, were uniformly coated on the carbon fiber surfaces in carbon paper. This route was much simpler than the traditional method for preparing GDEs because there were no processes needed to make the ink or print the catalysis layer. Membrane Electrode Assemblies (MEAs) were made with the as-prepared GDEs and tested in a 25 cm 2 PEMFC fed by hydrogen/air. The impedance spectroscopy and polarization curve measurement showed that the as-prepared GDE possessed a lower charge transfer resistance and a higher power density than did the conventional one with ELAT ® GDE LT120EW. The excellent performance obtained and the simple steps made the process a promising technique for preparing GDEs in PEMFCs for commercial applications.

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%.

Modeling for PEFC MEAs Based on Reaction Rate on Pt Surface and Microstructures of Catalyst Layers

A polymer electrolyte fuel cell membrane electrode assembly (PEFC MEA) model that focuses on the structural and reaction parameters of catalyst layers has been developed. The reaction and structural parameters were modeled independently by considering the oxygen reduction reaction (ORR) activity in terms of current per unit active surface area of Pt [A cm–2-Pt]. The catalyst layer models were constructed based on an assumption of cylindrical secondary pore structure, which was verified by measuring the primary pore size using mercury porosimetry. We found that penetration of Nafion® electrolyte into the primary pores of Pt/C catalysts was restricted, and thus diffusion and reaction in primary pores became negligible. Moreover, the experimental results demonstrated that for the same catalyst, ORR activity remained almost constant, irrespective of the agglomerate size (i.e., 2.7 × 10–6 A cm–2-Pt at 60°C for Pt/C TEC10E50E in this study). This supported our idea that reaction parameters and structural parameters should be considered independently in PEFC modeling. The cell performance predicted with the developed model was satisfactorily accurate as compared to that obtained from experiments. As a result, the modeling developed in this study can be used to construct simple PEFC models that yield results with good accuracy and can be a useful tool for the development of PEFCs in future.

Quantitative analysis of oxygen-containing species adsorbed on the Pt surface of a polymer electrolyte fuel cell membrane electrode assembly electrode using stripping voltammetry

The quantity of oxygen-containing species adsorbed on Pt surface of a single-cell polymer electrolyte fuel cell membrane electrode assembly (PEFC MEA) in the gas-phase system was measured by stripping voltammetry (SV), of which the adsorbed amount is considered in terms of the quantity of electric charge required for stripping. The effect of different experimental parameters on the adsorption quantity was analyzed and an optimum condition for applying SV to a PEFC MEA electrode was then suggested. The electric charge required for stripping was observed to be linearly proportional to the potential and arose from 0.7 V vs. RHE. The adsorption amount of oxygen-containing species for the PEFC MEA at a cell temperature of 60 °C was 384 μC cm −2-Pt at a potential of 1.0 V vs. RHE. More importantly, considering the effect of O 2 partial pressure on the adsorption in the gas-phase PEFC MEAs, water is suggested to be the main source of the oxygen in adsorbed oxygen-containing species. The present method is well applicable to quantitative studies of the oxygen-containing species adsorbed on electrodes of PEFC MEAs.

Multi-objective optimization of a polymer electrolyte fuel cell membrane electrode assembly

A multi-objective multi-variable gradient-based fuel cell optimization framework is presented in order to optimize fuel cell membrane electrode assembly fabrication. The optimization target is to simultaneously maximize the cell current density at a given voltage and minimize its production costs. The design variables are electrode composition parameters such as platinum loading and porosity. To develop this framework, a two-dimensional through-the-channel single-phase membrane electrode assembly model is implemented and coupled to an optimization algorithm. In order to solve the optimization problem in a reasonable time, a gradient-based optimization method in conjunction with analytical sensitivities of the electrode model with respect to design parameters such as amount of electrolyte are used. Results show the trade-offs between performance and cost and illustrate that large gains in performance and reductions in production costs are possible. They also highlight the problems associated with formulating the optimization problem without taking into account production costs.