Single PEMFC Research Articles

Impact of Cell Compression on Resistance, Mass Transport, and Ultimate PEMFC Performance

The gas diffusion layer (GDL) plays multiple roles in the performance of a PEMFC: it provides pathways for fuel transport to and water away from the catalyst layer via the tortuous void/pore structure and it ensures a good electronic contact between the catalyst layer and the current collector of the PEMFC stack. A balancing act in cell assembly must be struck for the GDL to simultaneously offer the best transport pathways and electronic contact; different PEMFC operating conditions can require different assembly in terms of compression. To gain a better understanding of this balancing act and to optimize the performance of the PEMFC, we systematically varied the compression of a single cell PEMFC and evaluated it under different operating conditions to extract the impact on contact resistance and mass transport. Scanning electron microscopy of the GDL and catalyst layers post mortem reveal changes in the overall pore/void structure and provide further clues on the implications of compression on performance.

Constructing proton-conductive highways within an ionomer membrane by embedding sulfonated polymer brush modified graphene oxide

Sulfonated polymer brush modified graphene oxide (SP-GO) fillers with controllable brush length are synthesized via the facile distillation–precipitation polymerization, and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate composite membranes. The influences of SP-GO upon the microstructures, including thermal and mechanical properties, water uptake/swelling, proton conduction, H2 permeability and single PEMFC performances of composite membranes are intensively investigated. It is found that the SP-GO fillers are uniformly dispersed and tend to lie perpendicularly to the cross-section surface of the whole membrane, which allow SP-GO fillers creating inter-connected and broad ionic pathways through the sulfonic acid groups in polymer brushes. Meanwhile, the SP-GO fillers connect the ionic clusters in SPEEK matrix via interfacial interactions. In such a way, proton-transfer highways are constructed along the SPEEK/SP-GO interface, which lower the proton transfer activation energy and enhance the proton conductivities of the composite membranes under both hydrated and anhydrous conditions. Furthermore, elevating the brush length on SP-GO could further enhance the proton conductivity. Compared to SPEEK control membrane, a 95.5% increase in hydrated conductivity, an 178% increase in anhydrous conductivity and a 37% increase in maximum power density are obtained for the optimal composite membrane.

Enhancement of PEM fuel cell performance at higher temperatures and lower humidities by high performance membrane electrode assembly based on Nafion/zeolite membrane

This work reports the preparation of Nafion/zeolite composite membranes with different zeolite loading. The structure of the Nafion/zeolite composite membranes are investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and by thermogravimetric analysis (TGA). The introduction of zeolite particles into the Nafion matrix helps to improve the water uptake, proton conductivity and thermal stability of the nanocomposite membranes compared to the virgin Nafion membrane. The SEM analyses have proved the uniform and homogeneous distribution of zeolite in composite membranes. The composite membranes are tested in a single PEMFC with a 5 cm2 active area operating at the temperature range of 75–120 °C and in humidified under 50% relative humidity (RH) and fully humidified conditions. Single PEMFC tests show that Nafion/zeolite composite membrane is more stable and also performed better than virgin Nafion membrane at low humidity condition. The results indicate the Nafion/zeolite composite membranes could be utilized as the proton exchange membranes for PEMFC.

Experimental investigation on uniform and zigzag positioned porous inserts on the rib surface of cathode flow channel for performance enhancement in PEMFC

The designs of flow channels are highly influencing the performance of PEMFC. A serpentine flow channel with Uniform and Zigzag positioned porous carbon inserts on cathode flow plate is experimentally analyzed in this paper. Addressing the flooding problem, a single PEMFC having an active area of 25 cm2 with various flow channel designs on the cathode flow plate namely serpentine, uniform and zigzag pin type; and flow channel with 2 mm cubical porous inserts on the uniform and zigzag pin type is experimentally investigated. The influence of porosity of carbon inserts on the cell performance is also studied by varying the porosity of carbon inserts in the range of 60–70%, 70–80%, 80–90% respectively. The results show that the flow channel with zigzag positioned porous inserts having 80–90% porosity has improved the power density and current density by 11.5% and 7% respectively when compared to the conventional serpentine flow channel. The reason for the increase in such performance is that, the porous insert on the rib surface removes the accumulated liquid water from the rib surface through the capillarity of its porous structure and eliminates the stagnant regions under the rib, thereby reducing liquid flooding in the interface between rib and GDL.

Model development and optimization of operating conditions to maximize PEMFC performance by response surface methodology

Optimization of operating conditions to obtain maximum power in PEMFCs could have a significant role to reduce the costs of this emerging technology. In the present experimental study, a single serpentine PEMFC is used to investigate the effects of operating conditions on the electrical power production of the cell. Four significant parameters including cathode stoichiometry, anode stoichiometry, gases inlet temperature, and cathode relative humidity are studied using Design of Experiment (DOE) to obtain an optimal power. Central composite second order Response Surface Methodology (RSM) is used to model the relationship between goal function (power) and considered input parameters (operating conditions). Using this statistical–mathematical method leads to obtain a second-order equation for the cell power. This model considers interactions and quadratic effects of different operating conditions and predicts the maximum or minimum power production over the entire working range of the parameters. In this range, high stoichiometry of cathode and low stoichiometry of anode results in the minimum cell power and contrary the medium range of fuel and oxidant stoichiometry leads to the maximum power. Results show that there is an optimum value for the anode stoichiometry, cathode stoichiometry and relative humidity to reach the best performance. The predictions of the model are evaluated by experimental tests and they are in a good agreement for different ranges of the parameters.

3D CFD modeling and experimental characterization of HT PEM fuel cells at different anode gas compositions

A numerical and experimental characterization of the performance of a High Temperature Polymer Electrolyte Membrane Fuel Cell (HT PEM FC) is presented.Starting from the fluid dynamic optimization performed in a previous work, a detailed 3D CFD-electrochemical model of a single HT PEM FC is developed, in order to describe the internal fluid dynamic fields coupled to the electrochemical reactions.To validate the numerical activity, an experimental campaign has been conducted on a single-cell prototype built ad-hoc, with both pure H2 and Syngas anodic feeding.The results of both the numerical and experimental investigations are compared to the performance of commercial HT PEM Fuel Cells, proving the good accuracy of our numerical method as well as the consistency of the experimental setup.

Fabrication and Performance Evaluation of Hybrid Membrane based on a Sulfonated Polyphenyl Sulfone/Phosphotungstic acid/Silica for Proton Exchange Membrane Fuel Cell at Low Humidity Conditions

Sulfonated polyphenyl sulfone/phosphotungstic acid/silica (sPPS/PWA/silica) hybrid membranes were prepared and characterized as alternative materials for PEMFC operation at high temperature and low humidity conditions. Polyphenyl sulfone polymer (PPS) was sulfonated with trimethylsilyl chlorosulfonate in 1,2 dichloroethane at ambient temperatures. The degree of sulfonation was determined by 1H-NMR analysis. Sulfonation levels from 25 to 45% were easily achieved by varying the content of the sulfonation agent. The hybrid membrane was composed of the mixture of sPPS solution, PWA/silica particles. The structures of the membranes were investigated by Scanning Electron Microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and by thermogravimetric analysis (TGA). The composite membranes gained good thermal resistance with insertion of PWA/silica. SEM results have proven the uniform and homogeneous distribution of PWA/silica in hybrid membrane. The existence PWA/silica has improved the water uptake, proton conductivity and oxidative stability of hybrid membrane. Gas diffusion electrodes (GDE) were fabricated by ultrasonic coating technique. Catalyst loading was 0.4mg Pt/cm2 for both anode and cathode sides. The membranes were tested in a single cell with a 5cm2 active area operating at the temperature range of 70 to 120°C and 100 and 30% relative humidity conditions. Single PEMFC tests performed at different operating temperatures indicated that sPPS/PWA/silica hybrid membrane was more stable and also performed better than pristine sPPS membrane. At the overall, the sPPS/PWA/silica hybrid membrane seems to be a promising alternative membrane for the possible utilization in PEMFC.

The Impact of Operating Conditions on the Performance effect of Selected Airborne PEMFC Contaminants

The effects of the airborne contaminants naphthalene, acetonitrile, and propene on the performance of a single PEMFC were investigated at different operating conditions. The results indicated that higher contaminant concentrations resulted in higher performance losses and faster degradations, while the rate of performance recovery was more rapid. Lower temperatures caused increased performance losses, more rapid degradations, slower recoveries, and irrecoverable losses. Higher contaminant concentrations and lower temperatures caused voltage oscillations when the PEMFC was contaminated with naphthalene. The exposure of the PEMFC to propene at higher temperatures resulted in performance recovery to a level that was temporarily greater than its performance prior to propene exposure. The PEMFC performance loss at different current densities was dependent on specific contaminants. At higher current densities, naphthalene and propene caused greater performance losses as well as faster degradation and recovery. Acetonitrile caused similar performance losses at all current densities. The performance degradation caused by naphthalene and acetonitrile may be dependent on the cathode potential. EIS analysis indicated that contaminant exposure affected catalytic and mass transport processes for all the impurities tested and that acetonitrile increased the membrane resistance.

Experimental investigation of pinhole effect on MEA/cell aging in PEMFC

The effect of MEA pinhole size on the aging of single (10 × 10 cm2) PEMFC was investigated. Two MEAs were perforated by two pins of different diameters (0.7 and 1.2 mm), in both cases in the H2 inlet zone. The performance losses and the degradation rates of the MEA components were compared to those exhibited by a healthy, not perforated MEA. Perforation by the smaller pin did not promote immediate cell voltage decay and the hydrogen crossover increased only slightly. Perforation by the larger pin resulted in immediate reduction in cell voltage and one decade increase of the hydrogen crossover. LSV and CV voltammograms performed for determination of the crossover and the electrode active surface were changed abruptly by the larger perforation, which confirmed the existence of an internal short circuit within the MEA. Besides, the perforation affected the time variations of the diffusion and charge transfer resistances.

Effect of rheology controller agent addition to Micro-Porous Layers on PEMFC performances

Formulations of carbon-based inks for doctor blade applications were considered and the use of Carboxymethylcellulose (CMC) as rheology modifier and suspension stabilizer was proposed. Rheological measurement evidenced that CMC addition guarantees a good dispersion of the carbon powder which results in a higher stability of the ink. The electrical performances of Gas Diffusion Layer (GDL) coated with Micro-Porous Layers (MPLs) prepared with and without CMC were compared. A single PEMFC was used to assess the properties of these GDLs: electrochemical performances were tested in terms of I–V curves and of AC Electrochemical Impedance Spectroscopy (EIS) of the running cell. CMC-containing GDLs showed improved performances when the cell was operated at 80°C and RH 80–60. Analysis of the EIS spectra demonstrated that, at high Current Density (CD), the CMC-based GDLs suffer for water management. Such a behavior was ascribed to a hydrophilic character of the GDL due to residual amounts of CMC in MPL coating.

Optimization of platinum/iridium ratio in thin sputtered films for PEMFC cathodes

The paper presents an investigation on the electrocatalytic activity of co-sputtered PtIr thin films towards the ORR. The catalyst composition was controlled by varying the sputtering power of the Ir target in the range 20–100W at constant power of 100W for the Pt target. The films were analyzed applying SEM, XRD, EDX, XPS (physical characterization); stationary and quasi-stationary polarization curves, cyclic voltammetry and ac impedance (“in situ” tests performed in single PEMFC). The influence of the Pt/Ir ratio on the atomic interaction, morphology, and the resulting electrocatalytic activity was studied in detail. The contribution of the film content, morphology and the Pt/Ir electrocatalytic synergism to the electrode performance was evaluated. The optimal balance between the favourable effect of Ir addition and the lost of active surface sites due to substitution of Pt for Ir was established.

Inorganic–organic membranes based on Nafion, [(ZrO2)·(HfO2)0.25] and [(SiO2)·(HfO2)0.28]. Part I: Synthesis, thermal stability and performance in a single PEMFC

This work reports the preparation, characterization and test in a single fuel cell of two families of hybrid inorganic-organic proton-conducting membranes, each based on Nafion and a different “core-shell” nanofiller. Nanofillers, based on either a ZrO2 “core” covered with a HfO2 “shell” (ZrHf) or a HfO2 “core” solvated by a “shell” of SiO2 nanoparticles (SiHf), are considered. The two families of membranes are labelled [Nafion/(ZrHf)x] and [Nafion/(SiHf)x], respectively. The morphology of the nanofillers is investigated with high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and electron diffraction (ED) measurements. The mass fractions of nanofiller x used for both families are 0.05, 0.10 or 0.15. The proton exchange capacity (PEC) and the water uptake (WU) of the hybrid membranes are determined. The thermal stability is investigated by high-resolution thermogravimetric measurements (TGA). Each membrane is used in the fabrication of a membrane-electrode assembly (MEA) that is tested in single-cell configuration under operating conditions. The polarization curves are determined by varying the activity of the water vapour (aH2O) and the back pressure of the reagent streams. A coherent model is proposed to correlate the water uptake and proton conduction of the hybrid membranes with the microscopic interactions between the Nafion host polymer and the particles of the different “core–shell” nanofillers.

Performance of proton exchange membrane fuel cells at elevated temperature

The polarization curves of a single PEMFC having a Nafion membrane fed with H 2/O 2 with relative humidity (RH) of 35%, 70% and 100% were measured at cell temperatures ranging from 65 °C to 120 °C at back pressures of 0 atm and 1 atm, respectively. Measured results showed that the best cell performance at 0.6 V operated within 65–120 °C at zero back pressure was 1000 mA cm −2 at 65 °C and RH = 100%, while the best cell performance at 1 atm back pressure was 1300 mA cm −2 at 100 °C and RH = 100%. Based on the analysis of impedance data measured at anode and cathode humidification temperatures of 90 °C and cell temperature of 100 °C at back pressures of 0 and 1 atm (90–100p0 and 90–100p1), it could be found that the membrane resistance was reduced and the catalyst became more active as the back pressure increases. The present results showed that increasing back pressure was able to dramatically improve cell performance and the effect of the back pressure surpassed that of humidification in the internal resistance of cell.

고분자전해질 연료전지(PEMFC)와 PEMFC/SCB의 동적 Matlab/Simulink 모델링 및 독립운전특성에 관한 연구

The available power generated from the FC power plant may not be sufficient to meet sustained load demand, peak demand or transient events. An supercapacitor bank(SCB) can supply a large burst of power, but it cannot store a significant amount of energy. The combined use of FC and SCB has the potential for the better energy efficiency, reducing the cost of FC technology and improved dynamic response. In this paper, A single PEMFC and PEMFC operated in parallel with a SC bank are presented, A new dynamic model of PEMFC system, the converter and controller has been developed for stand-alone applications. The simulation results are presented using Matlab/Simulink, and SimPowerSystems environments. It is confirmed that the results show a good performance and stable DC-link voltage for proposed dynamic and mathematical models developed for the combined FC/SCB.

Spontaneous oscillations of cell voltage, power density, and anode exit CO concentration in a PEM fuel cell

The spontaneous oscillations of the cell voltage and output power density of a PEMFC (with PtRu/C anode) using CO-containing H(2) streams as anodic fuels have been observed during galvanostatic operating. It is ascribed to the dynamic coupling of the CO adsorption (poisoning) and the electrochemical CO oxidation (reactivating) processes in the anode chamber of the single PEMFC. Accompanying the cell voltage and power density oscillations, the discrete CO concentration oscillations at the anode outlet of the PEMFC were also detected, which directly confirms the electrochemical CO oxidation taking place in the anode chamber during galvanostatic operating.

Development of gas diffusion layer using water based carbon slurry for proton exchange membrane fuel cells

The micro-porous layer of gas diffusion layers (GDLs) was fabricated with the carbon slurry dispersed in water containing sodium dodecyl sulfate (SDS), by wire rod coating process. The aqueous carbon slurry with micelle-encapsulation was highly consistent and stable without losing any homogeneity even after adding polytetrafluoroethylene (PTFE) binder for hundreds of hours. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. GDLs fabricated with various SDS concentrations were assembled into MEAs and evaluated in a single cell PEMFC under diverse operating relative humidity (RH) conditions using H 2/O 2 and H 2/air as reactants. The peak power density of the single cell using the GDLs with optimum SDS concentration was 1400 and 500 mW cm −2 with H 2/O 2 and H 2/air at 90% RH, respectively. GDLs were also fabricated with isopropyl alcohol (IPA) based carbon slurry for fuel cell performance comparison. It was found that the composition of the carbon slurry, specifically SDS concentration played a critical role in controlling the pore diameter as well as the corresponding pore volumes of the GDLs.

Optimization of Ru xSe y electrocatalyst loading for oxygen reduction in a PEMFC

The synthesis, characterization and optimization of Ru xSe y catalyst loading as a cathode electrode for a single polymer electrolyte membrane fuel cell, PEMFC were investigated. Ru xSe y catalyst was synthesized via a decarbonylation of Ru 3(CO) 12 and elemental selenium in 1,6-hexanediol under refluxing conditions for 2 h. The powder electrocatalyst was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and examined for the oxygen reduction reaction (ORR) in 0.5M H 2SO 4 by rotating disk electrode (RDE) and in membrane-electrode assemblies, MEAs for a single PEMFC. Results indicate the formation of agglomerates of crystalline particles with nanometric size embedded in an amorphous phase. The catalyst exhibited high current density and lower overpotential for the ORR compared to that of Ru x cluster catalyst. Dispersed Ru xSe y catalyst loading on Vulcan carbon was optimized as a cathode electrode by performance testing in a single H 2–O 2 fuel cell.

A numerical investigation on multi-phase transport phenomena in a proton exchange membrane fuel cell stack

In this study, the simulation of a fuel cell stack is performed by applying a general numerical model with VOF method that has been successfully applied to single PEMFC model to investigate the fluid dynamics, mass transport, flooding phenomenon and the effects of liquid water on the stack performance. The performance of three single cells in series connection in the fuel cell stack is examined according to the presence of liquid water in different single cells. The distributions of fluid flow, species concentration and the current density are presented to illustrate the effects of liquid water on the performance of each single cell. The numerical results locate that the low distributions of species in the flooding cell certainly degrade the performance of this cell. Moreover, it can be seen that the performance of the flooding cell will significantly affect the whole stack performance since the values of average current density must be identical in all single cells.

Effect of carbon paper substrate of the gas diffusion layer on the performance of proton exchange membrane fuel cell

Gas diffusion layers (GDLs) were fabricated using non-woven carbon paper substrates with various thicknesses developed by Hollingsworth & Vose Co. Highly consistent carbon slurry containing Pureblack carbon and vapor grown carbon fiber (3:1 ratio) with 25 wt.% Teflon was prepared by using a dispersion agent, Novec-7300 in isopropyl alcohol. Micro-porous layer was coated by using a fully automated Coatema coating tool with a uniform carbon loading of 2.6–3 mg cm −2 using carbon slurry. The surface morphology, contact angle and pore size distribution of the GDLs were examined using SEM, Goniometer and Hg Porosimeter, respectively. Various cathode GDLs assembled into MEAs were evaluated in a single cell PEMFC under various operating relative humidity (RH) conditions using H 2/O 2 and H 2/air as reactants. The peak power density of the single cell using the optimum carbon paper substrate thickness was about 1400 and 700 mW cm −2 with H 2/O 2 and H 2/air at 60% RH, respectively. It was found that the pore diameter as well as the corresponding pore volumes of the GDLs played a key role in exhibiting the optimum fuel cell performance.

Codes and Standards for Stationary Fuel Cell Installations and Testing of Single PEMFC as Applicable in the USA

With the proliferation of the various distributed power plants including fuel cell for mobility and stationary applications, there is a need to address the issues of codes and standards by all the players. At the moment, various states in the U.S. and the Federal Government agencies are expanding their infrastructural networks to accommodate the vast growing demand for alternative energy and soon, various nations will expand their fuel cell installations too. Knowledge of the fuel cell installation's codes and standards will reduce incidents and accidents and makeovers and streamline the quality of installation. The relevance of codes and standards is that the infrastructure will satisfy the applicable regional or national codes. The second part of this report addresses the applicable test protocol for testing single proton exchange membrane- PEM fuel cell as developed by the U.S. Fuel Cell Council (USFCC). This enables test results from various laboratories and institutions to be compared on the same basis. This work addresses mechanical and electrical installation codes requirements and low temperature PEM operating below 80 oC.