Air-breathing PEMFC Research Articles

Modeling the Effect of Cell Orientation on the Performance of an Air-Breathing Polymer Electrolyte Fuel Cell with a Columnar Cathode Plate

Air-breathing polymer electrolyte fuel cells (PEMFCs) are expected to play an important role in the development of sustainable portable and mobile devices, such as unnamed aerial vehicles, motorbikes or laptops. In this work, the performance of air-breathing PEMFCs with a columnar cathode plate design is examined by means of a 3D two-phase, non-isothermal model, and compared against experimental data. The results show that the performance is highly influenced by the cell orientation, namely horizontal (material plane perpendicular to gravity) versus vertical (material plane parallel to gravity). Oxygen transport in horizontal cells is mainly dominated by diffusion, leading to oxygen shortage toward the cell center and an inhomogeneous current density distribution. In contrast, oxygen transport in vertical cells is assisted by natural convection, enhancing oxygen transport throughout the cell and increasing the current density homogeneity. Water saturation is preferentially accumulated close to the cell center, being larger in horizontal cells due to the lower water removal rate of the cathode plate.

Modeling the Effect of Cell Orientation on the Performance of an Air-Breathing Polymer Electrolyte Fuel Cell with a Columnar Cathode Plate

Air-breathing polymer electrolyte fuel cells (PEMFCs) are expected to play an important role in the development of sustainable portable and mobile devices, such as unnamed aerial vehicles, motorbikes or laptops. In this work, the performance of air-breathing PEMFCs with a columnar cathode plate design is examined by means of a 3D two-phase, non-isothermal model, and compared against experimental data. The results show that the performance is highly influenced by the cell orientation, namely horizontal (material plane perpendicular to gravity) versus vertical (material plane parallel to gravity). Oxygen transport in horizontal cells is mainly dominated by diffusion, leading to oxygen shortage toward the cell center and an inhomogeneous current density distribution. In contrast, oxygen transport in vertical cells is assisted by natural convection, enhancing oxygen transport throughout the cell and increasing the current density homogeneity. Water saturation is preferentially accumulated close to the cell center, being larger in horizontal cells due to the lower water removal rate of the cathode plate.

Biomimetic integrated gas diffusion layer inspired by alveoli for enhanced air-breathing fuel cell performance and stability

Inspired by the structure of alveoli, a biomimetic integrated GDL was carefully designed. The biomimetic integrated GDL structure enhances the performance and durability of PEMFC while also making its structure more compact.

Design, simulation and experimental characterization of a high-power density fuel cell

This research proposes a novel design of a millimeter-sized air-breathing proton exchange membrane fuel cell (AB-PEMFC). The producing method of the air-breathing PEMFC consisted of the sequential deposition of the elements in layers: 1) endplate of a flat polymer, 2) fuel flow channel with gas diffusion layers (GDL), 3) silicone seal with embedded micro Pt (platinum) wires, 4) membrane electrode assembly (MEA) with high platinum load, 5) GDL with micro Pt wires. Performance tests were done using an AB-PEMFC and the stack of two mono cells under different conditions. The results obtained by the computational fluid dynamics (CFD) allowed analyzing the current collector (CC) position. The performance results show 110 W L−1 for the cell power density and 2200 W kg−1 for the specific power density.

Performance improvement of air-breathing proton exchange membrane fuel cell stacks by thermal management

Air-breathing is known as a way to reduce the weight, volume, and the cost of PEMFCs. In this study, the thermal management of the high-powered air-breathing PEMFC stacks by applying different cathode flow channel configurations is carried out to improve the stack performance. In order to verify the thermal management results, numerical simulation is also performed. The research results show that a combination of the 50% and 58.3% opening ratios in the air-breathing stack reduces the stack temperature and enhances the temperature distribution uniformity, leading to a better and more stable stack performance. In addition, it is found that the stack performance is significantly improved under the assisted-air-breathing condition. Moreover, the simulation results and the experimental data are basically consistent. It is suggested to adopt the average temperature over the cross-sectional flow region from simulation as fitting the simulation results and the measured data.

Experimental and numerical investigation on effects of cathode flow field configurations in an air-breathing high-temperature PEMFC

Air-breathing high-temperature proton exchange membrane fuel cell (HT-PEMFC) gets rid of the cumbersome air supplying systems and avoids the water flooding problem by directly exposing the cathode to air and operating the fuel cell at elevated temperature. Performance of the air-breathing HT-PEMFC is dependent on many factors particularly the cathode flow field configurations. However, studies about air-breathing HT-PEMFCs are quite limited in the literature. In the present study, an experimental testing system was setup for the performance measurement of the air-breathing HT-PEMFC. A 3D numerical model was established and validated by the experimental data. Effects of the cathode flow field configurations including the opening shape, end plate thickness, open ratio and opening direction on performance of the air-breathing HT-PEMFC were experimentally and numerically investigated. It was found that the cathode end plate thickness and upward or sideways orientation have the least effect on the performance. The maximum power density of 160 mW/cm2 at the current density of 394 mA/cm2 can be achieved for the cathode flow field with slot holes and an open ratio of 75%.

A CFD Simulation for an Air Breathing PEMFC for Power Source Portable Applications

This paper presents a numerical investigation for a 44 cm2 air breathing PEM fuel cell. We analyzed the influence of some operating and design parameters on the cell performance. The numerical solution based on ANSYS Multiphysics software and Fuel Cell Module offered an optimal performance at a cell with the cathode channel dimensions of 1.5 mm x 1.5 mm. Analyzing the polarization curves it can be noticed that for operating voltages greater than 0.75V, the channel width and depth has only a small influence on the performance, while at lower operating voltages the influence of the channels size on the performance become significant. In identifying the critical parameters and for having an insight into physical mechanisms that can influence the fuel cell we analyzed the water mass fraction and membrane protonic conductivity distributions, the relative humidity and temperature in the anode and the pressure and temperature in the cathode side.

A CFD Simulation for an Air Breathing PEMFC for Power Source Portable Applications

Air breathing PEM fuel cells are a promising and a potential power source for portable applications. The challenges that air breathing fuel cells has to overcome in order to be used in portable applications and to be cost competitive are related to the ability to use logistic fuels, to the prevention of cathode contamination with impurities from the used air (supplied by active or passive methods), to the reduction of the size and weight. In this context, the development of a mathematical model for a better understanding of the fundamental processes and characteristics associated with air breathing cathode operation is required. The three-dimensional model developed in this paper based on the ANSYS Multiphysics software was used to analyse the influence of the factors that influence the PEM fuel cell performance (flow field configuration, operating conditions). Regarding the flow field configuration a 3 step-serpentine was used for the anode channel and parallel channels were used in the cathode side for the forced air supply. In this respect, for the cathode side channels, the width, depth and the space between two adjacent channels was varied (1 mm, 1.5 mm, and 2 mm) in order to see their influence on the uniformity of the reactant distribution (particularly water) and on heat management. Regarding the operating parameters that can have a significant influence on the performance, our numerical analysis took into consideration the air flow rate, the humidity and temperature and the results are discussed in the paper. The analysis was intended to identify critical parameters and give an insight into physical mechanisms that can influence this type of air breathing PEM fuel cell.

Enhanced water management in the cathode of an air-breathing PEMFC using a dual catalyst layer and optimizing the gas diffusion and microporous layers

In an air-breathing proton exchange membrane fuel cell (ab-PEMFC), large amounts of water are generated and condensed on the cathode at high current densities due to the low operating temperature. Water management for ab-PEMFCs remains a challenge. In this paper, a cathode with a dual catalyst layer structure is designed, and the gas diffusion layer (GDL) and microporous layer (MPL) are optimized to improve the water management of an ab-PEMFC. A thin hydrophilic layer using perfluorosulfonate (Nafion) as the catalyst binder is coated on the electrolyte membrane to form an inner layer that maintains a good proton transfer rate, while a hydrophobic outer layer is prepared using a mixture of Nafion and polytetrafluoroethylene as the binder, preventing the removal of water under low-humidity conditions and expelling the excess water generated in the high current density area. A membrane electrode assembly (MEA) with this dual catalyst layer cathode exhibits excellent air-breathing performance, as the MEA's water management is greatly improved by the dual layer structure. We also find that the thickness of the MPL and the hydrophobicity of the GDL significantly affect the air-breathing performance of the MEA, and we attempt to optimize these parameters.

Forced Air-Breathing PEMFC Stacks

Air-breathing fuel cells have a great potential as power sources for various electronic devices. They differ from conventional fuel cells in which the cells take up oxygen from ambient air by active or passive methods. The air flow occurs through the channels due to concentration and temperature gradient between the cell and the ambient conditions. However developing a stack is very difficult as the individual cell performance may not be uniform. In order to make such a system more realistic, an open-cathode forced air-breathing stacks were developed by making appropriate channel dimensions for the air flow for uniform performance in a stack. At CFCT-ARCI (Centre for Fuel Cell Technology-ARC International) we have developed forced air-breathing fuel cell stacks with varying capacity ranging from 50 watts to 1500 watts. The performance of the stack was analysed based on the air flow, humidity, stability, and so forth, The major advantage of the system is the reduced number of bipolar plates and thereby reduction in volume and weight. However, the thermal management is a challenge due to the non-availability of sufficient air flow to remove the heat from the system during continuous operation. These results will be discussed in this paper.

Performance enhancement of air-breathing proton exchange membrane fuel cell through utilization of an effective self-humidifying platinum–carbon catalyst

One issue with air-breathing proton exchange membrane fuel cells (AB-PEMFCs) is that the reactants are not externally humidified, and thus the membrane or the catalyst layers might dry out due to electro-osmotic drag, diffusion and evaporation at the opening cathode. This results in a drop in internal ionic conductivity and thus in cell performance. Here, the preparation and characterization of self-humidifying carbon-supported Pt catalyst using citric acid modified carbon black (CA-CB) as the catalyst support are reported. Pt/CA-CB is highly hydrophilic due to the functional groups attached on the carbon support, which endows the ability to retain water in the membrane electrolyte assembly (MEA) and thereby help to improve the performance of AB-PEMFCs. A maximum power density of 204 mW cm −2 can be achieved in an air-breathing PEMFC stack using Pt/CA-CB, a thick polymer membrane (NRE212) and a circular opening cathode. A 23.4% enhancement in the output power density is obtained by using Pt/CA-CB in place of a commercial catalyst when oblique slit cathodes are employed. This self-humidifying catalyst is particularly suitable for portable PEMFC applications.

Hydrogen generation from solid NaBH 4 with catalytic solution for planar air-breathing proton exchange membrane fuel cells

In the pursuit of the development of alternative mobile power sources with high energy densities, this study elucidated a new hydrogen generation approach from solid NaBH 4 using a new catalyst, sodium hydrogen carbonate (NaHCO 3), which was placed in a small and compact cartridge. A planar air-breathing PEMFC system fitted with the cartridge has been investigated for testing hydrogen generation from NaBH 4 and NaHCO 3. NaHCO 3 allowed the hydrogen cartridge to control hydrogen generation and to improve the power density, fuel efficiency, energy efficiency, and cell response. The cell performance of solid NaBH 4 air-breathing PEMFC system strongly depended on the operating conditions: the feeding rates and concentrations of catalytic solutions for NaBH 4 hydrolysis. In various concentrations (5 - 12 wt %) of NaHCO 3 aqueous solutions, 10 wt % NaHCO 3 aqueous solution exhibited the highest maximum power density of 128 mW cm −2 at 0.7 V, which was estimated to be a Faradic efficiency of 78.4% and an energy efficiency of 46.3%. The data illustrated that NaHCO 3 was an effective catalyst for hydrogen generation with the solid NaBH 4, which is considered as a hydrogen carrier for air-breathing micro PEMFCs operated without auxiliary hydrogen controller or devices.

Experimental study of a novel piezoelectric proton exchange membrane fuel cell with nozzle and diffuser

The newly designed proton exchange membrane fuel cell with a piezoelectric actuation structure, called a PZT-PEMFC, can force air into an air-breathing PEMFC system. Previous studies indicated the PZT-PEMFC may solve the water-flooding problem and improve cell performance. In this experimental study, a PZT-PEMFC with nozzle and diffuser, PZT-PEMFC-ND, is built to verify the previous theoretical study. This innovative design may direct air flow into the cathode channel through the diffuser and prevent air backflow without valves. The performance test includes an analysis of PZT vibration frequencies, cell operation temperatures, gravity effect, and designs of the nozzle and diffuser. The optimal operating temperature for the PZT-PEMFC-ND is 323 K to avoid the risk of higher temperatures drying out the membrane electrode assembly (MEA). The optimal vibration frequency of the PZT-PEMFC-ND is 180 Hz, which may pump in enough air and solve the water-flooding problem in the cathode channel. This study also concludes that the innovative design of the PZT-PEMFC-ND, may reach the performance of an open cathode stack configuration, 0.18 W cm −2, without an external air supply device.

Planar air breathing PEMFC with self-humidifying MEA and open cathode geometry design for portable applications

In this paper, planar air breathing PEMFCs without the need for endplates are proposed for low power portable applications. PEMFCs with 3 different cathode designs (parallel slit, circular open and oblique slit) with the same opening ratio and employing self-humidifying MEAs were investigated. Performance and stability tests were conducted in hydrogen dead-end operation under both self-breathing and forced convection condition. It was found that rib geometry and hydraulic diameter have significant impact on oxygen transportation. It was concluded that circular opening design yields the best performance and highest limiting current. This is because this design provides the shortest rib distance and smallest hydraulic diameter. However, fuel cell instability was observed under self-breathing and forced convection condition. This is due to the water accumulation that could not be removed by natural-evaporation at the opening cathode. Overall, our proposed air breathing PEMFC achieves a specific power of 150 W kg−1 and a power density of 347 mW cm−3.

The formation of water droplets in an air-breathing PEMFC

Air-Breathing Proton Exchange Membrane Fuel Cells (AB-PEMFC) have the potential to supersede lithium-ion batteries in portable electronics. However, their water management issue has yet to be resolved to ensure optimum cell performance and safe system operation. In this paper, the formation of water droplets and their aggregation in the cathode flow channels of an operating AB-PEMFC is investigated by direct visualisation under various operating conditions. The developed optical set-up enables observation of droplet formation on the surface of the membrane from the top and side view of the channels simultaneously. The two orthogonal views reveal that during formation the receding and advancing droplet contact angles are almost identical with values that increase, in a similar trend to the droplet height, with increasing droplet diameter. Water films were able to develop and maintain direct contact with the side wall of the channels even under the effect of gravitational force. The aggregation of water droplets in the channels was strongly influenced by the change in the air and hydrogen stoichiometry conditions. However, these operating parameters appear to have no significant effect on the water extraction from the channels contrary to load and temperature, where temperature has proved to be the most effective water removal mechanism with minimum reduction in the current density of AB-PEMFC.

Geometry optimization for proton-exchange membrane fuel cells with sequential quadratic programming method

Integration between COMSOL Multiphysics™ and MATLAB™ offers a useful option for the self-automated geometry optimization in proton-exchange membrane fuel cells (PEMFCS). It overcomes the difficulties of automatically re-generating high-quality computational meshes and subsequently running the simulations to evaluate the objective function values using commercial software in computational fuel cell dynamics-based designs. Geometry optimization studies of an air-breathing PEMFC searching for the optimum channel ratio at the anode and the optimum open ratio at the cathode, are undertaken. A sequential quadratic programming method is selected to deal with the constrained design problems, while the objective functions are evaluated by running the three-dimensional simulation script of COMSOL™ under the MATLAB™ environment. Simulation results show that for the air-breathing PEM fuel cell operated at 353 K and one standard atmosphere pressure, when the anode channel ratio is fixed at 10%, the optimum cathode open ratios are very similar for the cell operated at voltages of 0.7 and 0.4 V, namely, 49.8% for 0.7 V and 49.5% for 0.4 V. When the cathode open ratio is set at 80% with a cell voltage of 0.7 V, the optimum anode channel ratio is found to be 34.7%.

Effect of Three Dimensional Shape of Cathode Opening on the Performance of Air-Breathing PEMFCs

not Available.

A study on cathode structure and water transport in air-breathing PEM fuel cells

For portable electronics, air-breathing PEMFCs are being developed without external air-feeding and humidification systems. To optimize the cathode structure and to investigate characteristics of such air-breathing PEMFCs, the effects of catalyst loading and gas diffusion layer (GDL) properties on the cell performance are examined. Water transport in air-breathing PEMFCs is interpreted in terms of the net water drag coefficient, which was obtained by changing the current density, relative humidity, temperature and the hydrogen stoichiometry to understand the water transport phenomena under various conditions.

Influence of cathode opening size and wetting properties of diffusion layers on the performance of air-breathing PEMFCs

Air-breathing PEMFCs consist of an open cathodic side to allow an entirely passive supply of oxygen by diffusion. Furthermore, a large fraction of the produced water is removed by evaporation from the open cathode. Gas diffusion layers (GDLs) and the opening size of the cathode have a crucial influence on the performance of an air-breathing PEMFC. In order to assure an unobstructed supply of oxygen the water has to be removed efficiently and condensation in the GDL has to be avoided. On the other hand good humidification of the membrane has to be achieved to obtain high protonic conductivity. In this paper the influence of varying cathodic opening sizes (33%, 50% and 80% opening ratios) and of GDLs with different wetting properties are analysed. GDLs with hydrophobic and hydrophilic properties are prepared by coating of untreated GDLs (Toray ® carbon paper TGP-H-120, thickness of 350 μm). The air-breathing PEMFC test samples are realised using printed circuit board (PCB) technology. The cell samples were characterised over the entire potential range (0–0.95 V) by extensive measurements of the current density, the temperature and the cell impedance at 1 kHz. Additionally, measurements of the water balance were carried out at distinct operation points. The best cell performance was achieved with the largest opening ratio (80%) and an untreated GDL. At the maximum power point, this cell sample achieved a power density of 100 mW cm −2 at a moderate cell temperature of 43 °C. Furthermore, it could be shown that GDLs with hydrophilic or intense hydrophobic properties do not improve the performance of an air-breathing PEMFC. Based on the extensive characterisations, two design rules for air-breathing PEMFCs could be formulated. Firstly, it is crucial to maximise the cathode opening as far as an appropriate compression pressure of the cell assembly and therewith low contact resistance can be assured. Secondly, it is advantageous to use an untreated, slightly hydrophobic GDL.

Effects of cathode open area and relative humidity on the performance of air-breathing polymer electrolyte membrane fuel cells

For portable applications, the, characteristics of passive air-breathing PEMFCs were investigated by examining effects of cathode open area and relative humidity on the cell performance. Among the single cells with cathode open area from 52 to 94%, the single cell with the open area of 77% exhibited the highest performance. The cell performance was improved with increasing RH of atmosphere from 20 to 100% in the low current region while lowered in high current region. Those results were related with the mass transport of oxygen from the atmosphere to the catalyst layer and the degree of membrane hydration determining the ionic conductivity of the membrane.