Exchange Membrane Fuel Cell Performance Research Articles

Insight on Single Cell Proton Exchange Membrane Fuel Cell Performance of Pt-Cu/C Cathode

The oxygen reduction reaction (ORR) properties of a proprietary PtCu3/C alloy electrocatalyst produced on a multi-gram scale are characterized by the conventional rotating disc electrode (RDE) method and by constructing a membrane electrode assembly (MEA) proton exchange membrane (PEM) single cell. The PtCu3 nanoparticles become porous, enriched in Pt on the surface, and exhibit a high RDE activity. The single cell electrochemical study reveals that, contrary to most advanced catalysts, the high ORR activity can be transferred from the RDE to the MEA. In the latter case, at 0.9VIRfree, a mass activity of 0.53 A/mgPt, at a Pt electrode loading of 0.2 mg/cm2, is achieved. However, at high current density, oxygen transport becomes limited. This is proven by the analysis of polarization curves and electrochemical impedance spectroscopy (EIS) data with a Kulikovsky (physical) model. These indicate that this limitation is caused by the non-optimal microporosity of our catalyst, which hinders the mass transport of oxygen during ORR. Based on our prospective results, one can realistically plan for further efforts to bridge the gap between the RDE and MEA measurements completely and achieve high power densities for Pt-alloy electrocatalysts.

Evolution and degradation phenomena of electrode for proton exchange membrane fuel cells (PEMFCs)

Electrode degradation is the main problem of the lifetime for proton exchange membrane fuel cell performance. The operating conditions with different parameters, as high and low flow rates, high and low pressures for hydrogen and oxygen and the aggressive operating which the results show the distribution of the catalyst in the cathode by scanning electron microscopic (SEM) and degradation, especially in the catalyst. This shows the detachment of catalyst from the support as shown by X-ray diffraction (XRD) peaks and transmission electron microscopy (TEM). The XRD showed the decrease in intensity peaks after operating, which increase in the degradation of cathode as crystallinities phases, and increasing the particle size of catalyst from 4.14 to 5.57 nm for more than 100 h operating in a single cell of 25 cm2 with different operating conditions as shown by the TEM.
 Keywords: Electrode fabrication, degradation; characterisation.

Model based evaluation of alkaline anion exchange membrane fuel cells with water management

The aim of this work is to improve alkaline anion exchange membrane fuel cell performance with water management. The mathematical model of alkaline anion exchange membrane fuel cells was developed with consideration of the water transport inside the membrane. The effects of key operating parameters such as the cathode relative humidity, anode relative humidity, cathode pressure, anode pressure on the net water flux across the membrane and the cell performance were analyzed with the unbalanced pressure concept to enhance the water back diffusion from the anode side to the cathode side. The increasing of the anode and cathode relative humidity leads to high water content, enhancement of membrane conductivity and reduction of ohmic loss resulting in a significant improvement of cell performance, especially an increase in the anode relative humidity. The high cell performance can achieve with the unbalanced pressure operation and the use of thin membrane is also preferred to facilitate water back diffusion from the anode to the cathode and enhance the cell performance.

Single cell induced starvation in a high temperature proton exchange membrane fuel cell stack

Fuel and oxidant starvation are amongst the most critical phenomena affecting fuel cell durability. Reactant starvation during proton exchange membrane fuel cell operation can cause serious irreversible damages. In the present research, the effect of a selective induced starvation of reactant gases on the performance and degradation of a high-temperature PEM fuel cell is studied. A specifically designed 5-cell stack is used, which enables varying the gas supplied to any of the individual cells. The particularity of selectively starving only one cell in a controlled manner is one of the novelties of this study. Two different tests are performed actuating on the central cell (cell 3). They are denoted as moderate and severe starvation, depending on the intensity of the limitation imposed to the gases flowrate. Some relevant and novel results are obtained. It is verified that the performance degradation caused by a moderate starvation of the reactant gases in a cell is reversible. On the contrary, the damages caused by an aggressive gas starvation, which is also maintained in time (30 min), are irreversible. However, the behavior of the rest of the cells is barely affected by the gas starvation to cell 3. Thus, the other major novelty of the present work is the evidence/proof of the ability of a stack with a starved and highly degraded cell, to continue operating, although with a drastic reduction in the total generated current.

Optimization of the performance, operation conditions and purge rate for a dead-ended anode proton exchange membrane fuel cell using an analytical model

Operating proton exchange membrane fuel cells in dead-ended anode mode results in fewer subsystem components and a lower cost and less complex system. However, dead-ended operation results in a gradual accumulation of water and impurities within the anode compartment, which leads to performance degradation. Therefore, anode purging is required to partially remove impurities and water from the anode and to recover performance. In the present study, a mathematical model, incorporating nitrogen crossover from the cathode to the anode and water build-up in the anode is developed. This model simulates the dead-ended anode proton exchange membrane fuel cell performance during the purge and the subsequent performance recovery. The model is in good agreement with experimental results. By using this model and introducing the concept of the ‘total wasted energy’, the purge parameters (purge interval and purge duration) can be optimized. The predicted optimum purge duration and purge interval for a sample single cell are 25 ms and 260 s, respectively. The effect of operating condition parameters on this optimization are investigated, showing that the hydrogen purity has a strong effect on the total wasted energy. By increasing the hydrogen purity from 99.5% to 99.99%, the efficiency increases by 2.4%.

Anion Exchange Membrane Fuel Cell Performance in the Presence of Carbon Dioxide: An Investigation into the Self-Purging Mechanism

In this study we investigate the commonly observed phenomenon whereby carbon dioxide (CO2) in the cathode gas stream (e.g., air) is absorbed and released from the anion exchange membrane fuel cell (AEMFC). Often described as “self-purging” due to the emission of the CO2 gas from the AEMFC with increased current, the mechanisms of this process are still largely unknown. Herein we provide evidence that this self-purging occurs through an electrochemical mechanism, in which bicarbonate and carbonate ions directly participate in the hydrogen oxidation reaction. After determining the nature of the self-purging mechanism, we present a series of parametric studies that investigate the fundamental effects of CO2 on the AEMFC, and discuss certain operating parameters that can be manipulated to improve cell performance.

Effect of contaminant mixtures in air on proton exchange membrane fuel cell performance

The effects of single, binary and ternary contaminant mixtures containing propene (C3H6), acetonitrile (CH3CN), and bromomethane (CH3Br) on proton exchange membrane fuel cells have been studied. Changes in polarization curves, electrochemical impedance spectroscopy spectra, electrochemical catalyst surface areas by cyclic voltammetry, and hydrogen crossover through the membrane by chronoamperometry are used to define the extent of recovery and irrecoverable losses after the contamination period and to understand the contaminant interactions. CH3CN in the contaminant mixture mitigates the decrease in oxygen reduction reaction kinetics and the increase in oxygen and water mass transport resistance, while C3H6 speeds up the above situations. The hydrolysis of CH3CN results in the formation of ammonium ions, which exchange with membrane protons, leading to an increase in the membrane resistance. CH3Br increases the decomposition of the Nafion® ionomer. Bromide accumulation on the catalyst surface leads to large catalyst area losses for the mixtures containing CH3Br. Competitive adsorption on Pt active sites exists between CH3CN and CH3Br. However, there is noncompetitive adsorption between C3H6 and CH3Br or CH3CN.

Carbon Black and Multi-Walled Carbon Nanotube Supported Cobalt for Anion Exchange Membrane Fuel Cell

Carbon black (CB) and multi-wall carbon nanotube (MWCNTs) supported cobalt, namely, CoPc/CB and CoPc/MWCNTs, respectively, with different metal loads was synthesized and used as the cathode catalyst for anion exchange membrane fuel cells. The prepared catalysts were characterized using X-ray diffraction and scanning electron microscopy. The surface morphology analysis revealed heterogeneous cobalt distribution on the carbon support. Cyclic Voltammetry was also studied to investigate the best combination ratio. The results indicated that the electrochemically largest active surface area was observed when 30 and 40 wt% cobalt was combined with 70 wt% CB and 60 wt% MWCNTs, respectively. The anion exchange membrane fuel cell performance showed that both cathode catalysts exhibited the highest peak power density at 40 wt%t. Co load. The peak power density of 55 mW/cm2 at 0.4 volts was obtained using CoPc/CB. Meanwhile, the promising catalyst CoPc/MWCNTs only produced 35mW/cm2, which did not meet the expectation. According to some references, the alkaline fuel cell performance might be bothered by the acid residues, sulfates and nitrates produced by the MWCNT purification process.

Transport phenomena of convergent and divergent serpentine flow fields for PEMFC

Reactive species and water transport are crucial for the proton exchange membrane fuel cell operation and performance, and for this, effective flow field design can facilitate the desired transport characteristics of species. From this motivation, the conventional single serpentine flow field pattern is modified by convergent and divergent design concepts and the complex transport phenomena of the newly developed flow field designs are investigated by a numerical approach. For the numerical analyses, an experimentally validated mathematical model is developed to predict the current density, oxygen mass transport, water concentration and pressure distribution. The different configurations of modified convergent and divergent serpentine flow fields are then numerically solved and the results are compared with the conventional serpentine flow field pattern. The transport of reactive species and water concentration are analyzed from the different perspectives including cathode domains and surfaces with a quantitative formulation of the transport species. The numerical results reveals that the modified convergent serpentine flow fields yield to a uniform current density due to the lower mass fraction of water concentration over the reaction zone facilitating better oxygen mass transport and also higher channel pressure distribution along the flow field comparing the conventional and divergent type serpentine flow fields.

(Invited) Reaching New Heights in Anion Exchange Membrane Fuel Cell Performance and Stability: Catalysts, Membranes, Water, and Beyond

Anion exchange membrane fuel cells (AEMFCs) have seen a massive surge in interest in recent years to displace incumbent proton exchange membrane fuel cells (PEMFCs) because of their possible advantages: the possibility to eliminate platinum group metals (PGM) in the catalyst layers; lower cost cell components (i.e. bipolar plates); lower cost membranes; and lower cost balance of plant (i.e. humidification and air circulation systems) [1-2]. Unfortunately, an overwhelming majority of AEMFCs studied in the literature i) achieve extremely low performance that is not competitive with PEMFCs; ii) use higher PGM loadings than modern PEMFC; and/or iii) use catalysts and membranes whose elaborate synthesis limits their applicability. All of these limitations have stifled the practical application of AEMFC, leaving nearly all of them far away from automotive OEM and DOE targets for activity, stability and PGM loading. This talk will focus on recent work by our group, our collaborators and other groups that has led to new records in the literature with regards to the achievable current and peak power density for Pt-containing AEMFCs, Pt-free AEMFCs, low PGM loading AEMFCs and completely PGM-free AEMFCs [2-6]. AEMFCs have also been demonstrated that are able to i) achieve high peak power densities (> 2 W cm-2); ii) operate stably for several hundred hours of operation; and iii) meet strategic DOE targets – including meeting performance targets while reducing the total PGM loading to 0.1 mg cm-2. It is intended that this talk will provide a roadmap to guide the future direction of AEMFC components and their operation. The advances and demonstrations that will be discussed show that despite the fact that AEMFCs are still in their infancy relative to PEMFCs, they are nearing a point where they are ready to be taken seriously in the open market.

Analyzing the impact of Temperature on Proton Exchange Membrane Fuel Cell performance Using Matlab

The Proton Exchange Membrane Fuel cell (PEMFC) is an electrochemical engine that converts the chemical energy of hydrogen into electrical energy. It receives hydrogen at anode and oxygen at the cathode side, due to chemical reaction at electrodes electronic current, water, and heat are produced. Heat produced causes problem for current produced, cell performance and may lead to a phase change of water produced. Water produced causes flooding at electrodes and membrane which requires a specific amount of water only. This study uses Mat lab to analyze the impact of temperature on different parameters which have a significant effect on heat and mass flow. This study shows the performance of Proton Exchange Membrane fuel cell reduces with increase in temperature significantly during operation of the cell. Proton Exchange Membrane fuel cell is suitable for transport, automobile, and other applications.

Impact of manufacturing processes on proton exchange membrane fuel cell performance

Commercial success for proton exchange membrane fuel cell (PEMFC) requires manufacturing of its core component, membrane electrode assembly (MEA), with consistent and reliable performance. In this study, three common methods for the MEA manufacturing are investigated systematically for their impact on the cell performance under consistent preparation and cell test conditions, including catalyst coated substrate (CCS), catalyst coated membrane (CCM), and low temperature decal method (LTDM). The variations in each of these methods studied include applying an extra Nafion layer, hot press, and Pt loading. It is found that MEA manufacturing process has a significant impact on the cell performance, and this impact is significantly affected by the Pt loading. At the high Pt loading of 0.5 mg/cm2, CCM without hot press involving gas diffusion layers (GDLs), referred to as CCM-Wo, results in the best performance with the maximum power density of 0.95 W/cm2, although both LTDM and CCS with an extra Nafion layer (hence called N-LTDM and N-CCS) are just slightly less with the maximum power density of 0.91 W/cm2. Hot press with GDLs is essential for CCS method to achieve a good performance, while it is not the case for CCM and N-LTDM. Applying an extra layer of Nafion on catalyst layers as in N-LTDM and N-CCS methods has a positive impact on the cell performance; whereas it is negative when it is applied on the membrane as in the N-CCM method. When the Pt loading is reduced to 0.125 mg/cm2 (75% reduction in the Pt loading), cell performance is reduced for all the MEAs made by the three methods, but significant reduction (about 75%) is observed for CCS method, while it is less than 30% for the other two methods. Therefore, care should be taken in the MEA manufacturing for MEAs with low Pt loadings.

Pt-supported C–MnO2 as a catalyst for polymer electrolyte membrane fuel cells

C–MnO2 is an alternative catalyst support in polymer electrolyte membrane fuel cells. In this study, C–MnO2 was prepared by hydrothermal method using KMnO4 as the Mn source. Meanwhile, Pt/C–MnO2 electrocatalyst was prepared by impregnation chemical reduction using ethylene glycol as reducing agent and H2PtCl6 as Pt precursor. The structure and morphology of C–MnO2 and Pt/C–MnO2 were characterized by X-ray diffraction energy-dispersive spectroscopy and transmission electronic microscopy analyses. Electrochemical performance was investigated by cyclic voltammetry analyses. A rotating disk electrode (RDE) was used to examine catalytic oxygen reduction reactions (ORRs) to explore the oxygen reduction of Pt/C–MnO2. The Pt/C–MnO2 exhibited better activity and stability than those of Pt/C. In contrast to Pt/C, MnO2 possessed unique characteristics; the oxide functions as an effective Pt support and hence enhances ORR activity and durability. The RDE results for the ORR indicated that the main reaction of the Pt/C–MnO2 catalyst was the direct reduction of O2–H2O. This reaction is similar to the mechanism of the Pt/C catalyst and both with a four-electron charge transfer. The results of the single cell polarization experiment and the ON–OFF cycling test revealed that MnO2 improves proton exchange membrane fuel cells performance and durability. This paper also investigated the mechanism through which MnO2 promotes oxygen reduction.

Impact of ionomer in the catalyst layers on proton exchange membrane fuel cell performance under different reactant flows and pressures

To achieve a good performance, proton exchange membrane fuel cells (PEMFCs) require a delicate water balance through the design of cells and selection of operating conditions. In this study, the impact of ionomers with different side-chain lengths, having different water retention capability, serving as binder in the catalyst layers is investigated experimentally for both catalyst layer structure and the resulting cell performance under a wide range of reactant flows and cell operating pressures. The results show that cells with the short side-chain (SSC) ionomers, having a higher water retention capability, achieve a higher cell performance, active surface area, platinum utilization, and porosity than the cells made by the conventional long side-chain (LSC) even under fully humidified condition, in contrast with studies reported in literature. This is achieved for the high reactant flow, which has a higher water removal capability. The SSC ionomer with the low equivalent weight of 720 results in a significantly higher cell performance with the maximum power density of 1.3 W/cm2 at the high reactant flow. SSC with the equivalent weight of 790 has a good balance between water retention and water removal in the catalyst layer at a lower airflow. The performance of the cells with the SSCs is better, and it is far less sensitive than, the cells with the LSC when the operating pressure is increased.

Development of Electrocatalysts for Anion Exchange Membrane Fuel Cells

Recent development of chemically stable anion exchange membranes and ionomers resulted in substantial increase in research and development in the field of Anion Exchange Membrane Fuel Cells (AEMFCs) [1]. One of the advantages of AEMFC technology is the possibility to use completely platinum group metal-free (PGM-free) electrocatalysts for the cathode (Oxygen Reduction Reaction, ORR) and the anode (Hydrogen Oxidation Reaction, HOR) [2, 3]. High performance of Membrane Electrode Assemblies (MEAs) with PGM-free catalysts was achieved using M-N-C type of materials (M=Fe, Co or Ni) [4]. The cathodic electrocatalysts consisted of transition metal, nitrogen and carbon matrix can be prepared by several methods: treatment of carbons with transition metal in ammonia atmosphere, high temperature pyrolysis of Metal Organic Framework (MOF) compounds or through templating approach (Sacrificial Support Method, SSM) [5, 6]. In contrast to massive research in the ORR for AEMFCs, the development of PGM-free catalysts for HOR is still in the early stage, with majority of electrocatalysts tested in Rotating Disk Electrode (RDE) conditions. The only publications in open literature on integration of PGM-free anodic materials (nickel-based) are limited to NiW and NiMo supported on carbon blacks [7, 3]. In a present contribution the design, synthesis and scale-up of different Ni-based anodic materials for AEMFC application is reported. The electrocatalysts were synthesized by thermal reduction of nickel and second metal precursors on the surface of commercial and in house prepared carbon supports (in house carbon supports are denoted as Engineered Catalyst Supports, ECS). Several important synthetic parameters such as ratio between metals, type of carbon support, reduction temperature etc. were optimized in order to achieve the highest performance in fuel cell tests. As-obtained electrocatalytically active anodic materials were integrated into the catalyst layer by proprietary method practiced at EWII Fuel Cells [8]. The catalyst layer variations included different catalyst:ionomer ratio, loading of the Ni-based catalysts in the MEA and other parameters. Fuel cell tests performed at Pajarito Powder and EWII Fuel Cells revealed high performance of PGM-free materials similar to reported earlier (Figure 1) [3]. Figure 1. Fuel cell performance of MEA with NiCu/C anode using different loadings in catalyst layer. Conditions: A: NiCu/C, C: Pt/C, Tcell = 60°C, 100% RH, flow rates = 200 ccm, backpressure = 10 psig. The future directions on improvement of fuel cell performance will be discussed. Acknowledgements: Department of Energy, Hydrogen Oxidation Reaction in Alkaline Media, Control Number: 0966-1624, Award Number: DE-EE0006962 (PI A. Serov) and ARPA-E DE-AR0000688 (PI B. Zulevi). References. [1] A. Serov, I. V. Zenyuk, C. G. Arges, M. Chatenet "Hot topics in alkaline exchange membrane fuel cells" J. of Power Sources (2017) DOI: doi.org/10.1016/j.jpowsour.2017.09.068 [2] Md M. Hossen, K. Artyushkova, P. Atanassov, A. Serov "Synthesis and characterization of high performing Fe-NC catalyst for oxygen reduction reaction (ORR) in Alkaline Exchange Membrane Fuel Cells" J. Power Sources (2017) DOI: 10.1016/j.jpowsour.2017.08.036 [3] S. A. Kabir, K. Lemire, K. Artyushkova, A. Roy, M. Odgaard, D. Schlueter, A. Oshchepkov, A. Bonnefont, E. Savinova, D. Sabarirajan, P. Mandal, E. Crumlin, I. V. Zenyuk, P. Atanassov, A. Serov "Platinum Group Metal-free NiMo Hydrogen Oxidation Catalysts: High Performance and Durability in Alkaline Exchange Membrane Fuel Cells" J. Mater. Chem. A (2017) DOI: 10.1039/C7TA08718G [4] R. Janarthanana, A. Serov, S. Kishore Pilli, D. A. Gamarra, P. Atanassov, M. R. Hibbs, A. M. Herring "Direct Methanol Anion Exchange Membrane Fuel Cell with a Non-Platinum Group Metal Cathode based on Iron-Aminoantipyrine Catalyst", Electrochim. Acta 175 (2015) 202-208. [5] J. K. Dombrovskis, A. E. C. Palmqvis "Recent Progress in Synthesis, Characterization and Evaluation of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction" Fuel Cells 16 (2016) 4–22. [6] A. Serov, M. J. Workman, K. Artyushkova, P. Atanassov, G. McCool, S. McKinney, H. Romero, B. Halevi, T. Stephenson "Highly stable precious metal-free cathode catalyst for fuel cell application", J. Power Sources 327 (2016) 557-564. [7] Q. Hu, G. Li, J. Pan, L. Tan, J. Lu, L. Zhuang "Alkaline polymer electrolyte fuel cell with Ni-based anode and Co-based cathode" Int. Journal of Hydrogen Energy 38 (2013) 16264-16268. [8] T. Reshetenko, M. Odgaard, D. Schlueter, A. Serov "Analysis of alkaline exchange membrane fuel cells performance at different operating conditions using DC and AC methods" J. of Power Sources (2017) DOI: /doi.org/10.1016/j.jpowsour.2017.11.030 Figure 1

Computational fluid dynamics study of 3-pass serpentine flow field configuration on proton exchange membrane fuel cell performance

ABSTRACTA 3-D PEM fuel cell model with 3-pass serpentine flow field was developed to analyse the performance of the fuel cell. Simulations were carried out in the commercial ANSYS FLUENT 15.0 software with species concentration on the anode side as H2 – 0.8, O2 – 0, H2O – 0.2 and on the cathode side H2 – 0, O2 – 0.2, and H2O – 0.1. Along with the performance of the cell, key parameters like pressure drop, hydrogen mass fraction, oxygen mass fraction, liquid water activity and the membrane water content have been analysed. The results showed that when the cell was operated at a lower voltage of 0.4 V, i.e. a higher current density, hydrogen and oxygen consumption rates are high as well as water production rate. Finally, the proposed fuel cell model performance characteristics are compared with the available experimental data that shows good agreement.

Gas diffusion layer development using design of experiments for the optimization of a proton exchange membrane fuel cell performance

Gas Diffusion Layer (GDL) was optimized to maximize the performance of a Proton Exchange Membrane Fuel Cell (PEMFC) using design of experiments (DoE). The fabrication of the GDLs consisted of using a non-woven carbon paper substrate, coated with a mixture (slurry) of Pureblack Carbon (PB), Vapor Grown Carbon Fiber (VGCF) and the polytetrafluoroethylene (PTFE), all dispersed in water containing Sodium Dodecyl Sulfate (SDS). The concentration of PB and the PTFE in the slurry was organized through the application of a 22 full factorial design of experiments, with the quantity of PB and the quantity of PTFE as the factors. For each GDLs a Membrane-Electrodes Assemblies (MEA) were fabricated using Catalyst Coated Nafion Membrane CCM, in a single cell PEMFC, then the polarization curve was evaluated using H2/Air as well as H2/O2 at various relative humidity (RH) conditions. In addition, each GDLs were characterized by pore size distribution and contact angle using SEM, Goniometer and Hg Porosimeter. It was found that the optimized GDLs exhibited a power density of 487 mW/cm2 (H2/Air, 70 °C, 70% RH,) and 995 mW/cm2 (H2/O2,70 °C, 100% RH) for the optimum composition of 73% PB and 34% PTFE.

Analysis of alkaline exchange membrane fuel cells performance at different operating conditions using DC and AC methods

Membrane electrode assemblies (MEAs) for anion exchange membrane fuel cells (AEMFCs) were manufactured from commercial materials: Pt/C catalyst, A201 AEM and AS4 ionomer by using an industrial mass-production digital printing method. The MEA designs selected are close to those recommended by US Department of Energy, including low loading of platinum on the cathode side (0.2 mg cm−2). Polarization curves and electrochemical impedance spectroscopy (EIS) were applied for MEA evaluation in fuel cell conditions with variation of gas humidification and oxygen partial pressure (air vs oxygen). The typical impedance curves recorded at H2/O2 gas configuration consist of high- and medium-frequency arcs responsible for hydrogen oxidation and oxygen reduction, respectively. Operation with air as a cathode feed gas resulted in a decrease in AEMFC performance due to possible CO2 poisoning and mass transfer losses. At the same time, EIS demonstrated formation of a low frequency loop due to diffusion limitations. Despite the low loading of platinum on the cathode (0.2 mg cm−2), a peak power density of ∼330 mW cm−2 was achieved (at 50/50% of RH on anode and cathode), which is substantially higher performance than for AEMFC MEAs tested at similar conditions.

Effect of flow field with converging and diverging channels on proton exchange membrane fuel cell performance

In this study, a novel bipolar flow field design is proposed. This new design consists of placed sequentially converging and diverging channels. Numerical simulation of cathode side is used to investigate the effects of converging and diverging channels on the performance of proton exchange membrane fuel cells. Two models of constant and variable sink/source terms were implemented to consider species consumption and production. The distribution of oxygen mole fraction in gas diffusion and catalyst layers asa result of transverse over rib velocity is monitored. The results indicate that the converging channels feed two diverging neighbors. This phenomenon is a result of the over rib velocity which is caused by the pressure difference between the neighboring channels. The polarization curves show that by applying an angle of 0.3° to the channels, the net electrical output power increases by 16% compared to the base case.

Nanocatalysts for Low Temperature Fuel Cells

Zeolitic Imidazolate Frameworks (ZIFs) are one of the potential candidates as highly conducting networks with surface area with a possibility to be used as catalyst support. In the present study, highly active state-of-the-art Pt-NCNTFs catalyst was synthesized by pyrolyzing ZIF-67 along with Pt precursor under flowing Ar-H2 (90-10 %) gas at 700 °C. XRD analysis indicated the formation of Pt-Co alloy on the surface of the nanostructured catalyst support. The high resolution TEM examination showed the particle size range of 7 to 10 nm. Proton exchange membrane fuel cell performance was evaluated by fabricating membrane electrode assemblies using Nafion-212 electrolyte using H2/O2 gases (100 % RH) at various temperatures. The peak power density of 630 mW.cm2 was obtained with Pt-NCNTFs cathode catalyst and commercial Pt/C anode catalyst at 70 °C at ambient pressure.