Air-breathing Proton Exchange Membrane Fuel Cell Research Articles

Development of planar, air-breathing, proton exchange membrane fuel cell systems using stabilized sodium borohydride solution

A planar, air-breathing, proton-exchange membrane fuel cell (PEMFC) system using a humidified H 2 gas released from the hydrolysis of a stabilized sodium borohydride (NaBH 4) solution with a selected solid catalyst is extensively investigated as a promising energy storage system for mobile power sources. In economic terms, the passive air-breathing PEMFC is quite attractive because can its reliability, fuel utilization, and specific energy can be enhanced by removing auxiliary devices such as the air pump and the humidifier. The rate of hydrogen generation can be manually controlled by adjusting the amount of NaBH 4 solution passed through the selected catalyst. In this study, the rate of hydrogen generation is varied from 0 to 18 cm 3 min −1 by controlling the mass transport of stabilized NaBH 4 solution. The open-circuit voltage (OCV) and maximum power density are, respectively, 0.9 V and 128 mW cm −2 at ambient temperature and pressure. Assuming a fuel conversion efficiency of 100%, the Faradic efficiency and energy efficiency of this system estimated to be 75% and 46%, respectively. In a planar 8-cell series-connected format, the maximum power density and cathode temperature are 3.1 W (103 mW cm −2) at 103 mW cm −2 and 46 °C, respectively.

Numerical study of a novel micro-diaphragm flow channel with piezoelectric device for proton exchange membrane fuel cells

Previous studies have shown that the amplitude of the vibration of a piezoelectric (PZT) device produces an oscillating flow that changes the chamber volume along with a curvature variation of the diaphragm. In this study, an actuating micro-diaphragm with piezoelectric effects is utilized as an air-flow channel in proton exchange membrane fuel cell (PEMFC) systems, called PZT-PEMFC. This newly designed gas pump, with a piezoelectric actuation structure, can feed air into the system of an air-breathing PEMFC. When the actuator moves outward to increase the cathode channel volume, the air is sucked into the chamber; moving inward decreases the channel's volume and thereby compresses air into the catalyst layer and enhancing the chemical reaction. The air-standard PZT-PEMFC cycle is proposed to describe an air-breathing PZT-PEMFC. A novel design for PZT-PEMFCs has been proposed and a three-dimensional, transitional model has been successfully built to account for its major phenomena and performance. Moreover, at high frequencies, PZT actuation leads to a more stable current output, more drained water, higher sucked air, higher hydrogen consumption, and also overcomes concentration losses.

Improvement of water management in air-breathing and air-blowing PEMFC at low temperature using hydrophilic silica nano-particles

This study examined the effect of the hydrophilicity of an anode catalyst layer on the performance of a proton exchange membrane fuel cell (PEMFC). Hydrophilic SiO 2 particles were added to the anode catalyst layer in an attempt to improve the water management and performance in an air-blowing and air-breathing PEMFC operated at low temperature. The SiO 2 -doped membrane electrode assemblies (MEAs) were prepared using a spraying method and the contact angle was measured using the sessile drop method at room temperature. Each MEA was tested at 35 ∘ C in an air-blowing and air-breathing PEMFC. Pure dry hydrogen as fuel was fed in the electrode using graphite plate with serpentine channels. Air, as the oxidant, was diffused in the electrode through an open window made from gold-plated stainless steel with 70% opening for the air-breathing PEMFC. In case of the air-blowing PEMFC, a graphite plate with serpentine channels was used for the cathode instead of an open window. The polarization curves, impedance spectra and fraction of water from the anode outlet were measured. The hydrophilic anode catalyst layer contributed to the hydration of the anode in the air-blowing system and water removal from the cathode in air-breathing system, respectively. For both the air-blowing and air-breathing systems, the performances of the cell were improved by 26.9% and 44.4%, respectively, using the 40 wt% SiO 2 -doped MEAs compared with the MEA without SiO 2 .

Three-dimensional heat and mass transfer analysis in an air-breathing proton exchange membrane fuel cell

There is strong interaction between heat/mass transfer and electrode dynamics in an air-breathing proton exchange membrane fuel cell (PEMFC). To investigate the heat/mass transfer characteristics of PEMFC, their effect on oxygen transport and then on the performance of the cell, a coupled three-dimensional (3D) mathematical model has been developed for an air-breathing PEMFC using non-dimensional heat/mass transfer coefficients, and a detailed interpretation of heat/mass transfer parameters in it has been done. The full elliptic Navier Stokes and energy equations are simultaneously solved in the composite domain with commercial CFD tool STAR-CD based on the finite volume numerical method. And the model has been confirmed by experimental results. From the numerical simulation results obtained, a simple equation has been suggested on the function of the sum of Grashof number and diffusional Grashof number for the calculation of dimensionless mass transfer coefficient Sherwood number. The equation is believed to be useful for a profound understanding of the nature of oxygen transport limitation coupled with the heat/mass transfer in the air-breathing PEMFC, and further for the optimum design of the air-breathing PEMFCs. The concentration over-potential as a function of limited oxygen mass transfer rate, as well as profiles of velocity, temperature, reactant and water concentration, current density are presented and discussed to analyze the coupling problems between heat/mass transfer and electrode dynamics in an air-breathing PEMFC.

A model for a vertical planar air breathing PEM fuel cell

This paper presents a two-dimensional, steady state, single phase, non-isothermal and complete model for a vertical, fully planar, Air Breathing Proton Exchange Membrane Fuel Cell (AB-PEMFC) with hydrogen fuel supplied by forced convection at the anode. It is applied to a cell with an active area of 6 cm 2 operating at ambient atmospheric conditions of 23 °C and 20% relative humidity. The transport characteristics in terms of the velocity, and heat and mass transfer coefficients in the various components of the fuel cell are reported for several values of the operating current density. The effect of cathode height (1–5 cm) and operating atmospheric conditions (10–40 °C and 20–80% relative humidity), on the cell performance is also reported. Further, the applicability of the model to a non-planar AB-PEMFC is examined by comparison with available experimental data. The average mass transfer coefficients for oxygen and water vapor at the cathode GDL surface are found to be of the order of 10 −3 m s −1. The operating current density is seen to substantially affect the variation of the local current density distribution and the cathode surface temperature along the height of the fuel cell as also the temperature variation across the MEA thickness. The maximum power density and the corresponding current density, herein defined as the optimum current density, are found to increase with decreasing height of the fuel cell, decreasing ambient temperature and increasing ambient relative humidity. However, the local cell temperature at high current densities is found to increase beyond the safe operating limits for short fuel cells. Comparison of the model predictions with available experimental data points to its applicability in the ohmic polarization zone of a non-planar cell. The cell performance at high current densities deteriorates due to mass transport limitation and electrolyte dehydration.

Dynamic modeling of proton exchange membrane fuel cell using non-integer derivatives

The modeling of proton exchange membrane fuel cells (PEMFC) may work as a powerful tool in the development and widespread testing of alternative energy sources in the next decade. In order to obtain a suitable PEMFC model, which can be used in the analysis of fuel cell-based power generation systems, it is necessary to define the values of a specific group of modeling parameters. In this paper, the authors propose a dynamic model of PEMFC, the originality of which lays on the use of non-integer derivatives to model diffusion phenomena. This model has the advantage of having least number of parameters while being valid on a wide frequency range and allows simulating an accurate dynamic response of the PEMFC. In this model, the fuel cell is represented by an equivalent circuit, whose components are identified with the experimental technique of electrochemical impedance spectroscopy (EIS). This identification process is applied to a commercially available air-breathing PEMFC and its relevance is validated by comparing model simulations and laboratory experiments. Finally, the dynamic response derived from this fractional model is studied and validated experimentally.

Pin head diode: Anon., New Scientist, 10 (241), 29 June 1961, 786

It is well recognized that pore structure and the hydrophilicity/hydrophobicity balance are key factors for the cathodes of air-breathing proton exchange membrane fuel cells (AB-PEMFCs). In this work, we attempted to adjust the pore structure and hydrophilicity of an air-breathing cathode by using two types of catalysts, Pt/C and Pt/CNT, to prepare the catalyst layer for the air-breathing cathode instead of using a single catalyst. An MEA with the dual-catalyst cathode exhibited significantly improved single-cell performance, which was affected by the ratio of Pt/C to Pt/CNT. Our optimized MEA, which had a ratio of 54:46 in the cathode catalyst layer, achieved a current density of up to 290 mA cm−2 at 0.6 V, which was 14% higher than that of a MEA without Pt/CNT. The Pt/CNT in the catalyst layer played the key role in the overall performance of the AB-PEMFC. We propose that the CNT improved charge transfer and enabled better electrical conductivity than carbon black. In addition, the tubular structure of Pt/CNT made the catalyst layer more porous and permeable to gas. Furthermore, the addition of Pt/CNT may have changed the cathode's hydrophilicity/hydrophobicity balance, giving the cathode better water balance and consequently yielding better performance.