PEM fuel cell performance improvement through numerical optimization of the parameters of the porous layers

A numerical model for a PEM fuel cell has been developed and used to investigate the effect of some of the key parameters of the porous layers of the fuel cell (GDL and MPL) on its performance. The model is comprehensive as it is three-dimensional, multiphase and non-isothermal and it has been well-validated with the experimental data of a 5 cm2 active area-fuel cell with/without MPLs. As a result of the reduced mass transport resistance of the gaseous and liquid flow, a better performance was achieved when he GDL thickness was decreased. For the same reason, the fuel cell was shown to be significantly improved with increasing the GDL porosity by a factor of 2 and the consumption of oxygen doubled when increasing the porosity from 0.40 to 0.78. Compared to the conventional constant-porosity GDL, the graded-porosity (gradually decreasing from the flow channel to the catalyst layer) GDL was found to enhance the fuel cell performance and this is due to the better liquid water rejection. The incorporation of a realistic value for the contact resistance between the GDL and the bipolar plate slightly decreases the performance of the fuel cell. Also the results show that the addition of the MPL to the GDL is crucially important as it assists in the humidifying of the electrolyte membrane, thus improving the overall performance of the fuel cell. Finally, realistically increasing the MPL contact angle has led to a positive influence on the fuel cell performance

Carbon Nanotubes and Carbon Nanotube Structures Used for Temperature Measurement

Accurate measurement of temperatures with low power consumption with the highest sensitivity and smallest possible elements is still a challenge. The thermal, electrical, and mechanical properties of carbon nanotubes (CNTs) have suggested that their use as a very sensitive sensing element will allow the creation of different sensors, far superior to other devices of similar size. In this paper, we present a short review of different constructive designs of CNTs based resistive sensors used for temperature measurement, available in literature, assembled using different processes, such as self-assembly, drop-casting from a solution, thin films obtained by gluing, printing, spraying, or filtration over a special membrane. As particular cases, temperature sensors obtained from CNT-polymer nanocomposite structures, CNTs filled with uniformly dispersed Fe3O4 nanoparticles or with gallium, and carbon nanotube wires (CNWs) hybrids are presented. Using these preparation procedures, mixtures of CNTs with different dimensions and chirality, as well as with a variable level of impurities and structural defects, can be produced. The sensors’ performance charts are presented, highlighting a number of aspects regarding the applicability of CNT structures for temperature measurement ranging from cryogenic temperatures to high temperatures, the limitations they have, their characteristics and advantages, as well as the special situations that may arise given the particular structure of these new types of materials, together with basic relationships and parameters for CNTs characterization. Further research will be required to develop the techniques of manipulating and depositing individual CNTs on supports and electrodes for the development of temperature sensors

Graphene Modified Fluorinated Cation-Exchange Membranes for Proton Exchange Membrane Water Electrolysis

One of major current technical challenges in proton exchange membrane water electrolysis (PEMWE) is the limited proton conductivity. Nowadays, graphene is considered one of the most promising candidates for improving the ionic transport properties, isotopic selectivity and proton conductivity throughout the unique two-dimensional structure. In this paper, we report on the development of graphene modified commercial membranes (Fumapem®) containing different graphene loadings for PEMWE applications. The membranes are characterized by Scanning Electron Microscopy (SEM) and thermo-gravimetrical and differential thermal analysis (TGA-DSC). Properties of composite membranes are investigated, including water uptake and ion-exchange capacity (IEC). In plane four-electrode arrangement is used to determine the proton conductivity of the composite membranes. It is found that composite membranes show an improved behaviour when compared to pristine commercial membranes and graphene loading can improve proton conductivity. In our conditions, the calculated activation energy (Ea) for proton conduction is found to be about 3.80 kJ mol−1 for the composite Fumapem®/graphene membrane with 10 mg graphene loading, lower than of the pristine polymer proton exchange membrane

Effects of geometrical dimensions of flow channels of a large-active-area PEM fuel cell: A CFD study

Various flow field designs have been numerically investigated to evaluate the effect of pattern and the cross-sectional dimensions of the channel on the performance of a large active area PEM fuel cell. Three types of multiple-serpentine channels (7-channels, 11-channels and 14-channels) have been chosen for the 200 cm2 fuel cell investigated and numerically analysed by varying the width and the land of the channel. The CFD simulations showed that as the channel width decreases, as in the 14-channels serpentine case, the performance improves, especially at high current densities where the concentration losses are dominant. The optimum configuration, i.e. the 14-channels serpentine, has been manufactured and tested experimentally and a very good agreement between the experimental and modelling data was achieved. 4 channel depths have been considered (0.25, 0.4, 0.6 and 0.8 mm) in the CFD study to determine the effects on the pressure drop and water content. Up to 7% increase in the maximum reported current density has been achieved for the smallest depth and this due to the better removal of excess liquid water and better humidification of the membrane. Also, the influence of the air flow rate has been evaluated; the current density at 0.6 V increased by around 25% when air flow rate was increased 4 times; this is attributed to better removal of excess liquid water

PEM fuel cell performance improvement through numerical optimization of the parameters of the porous layers

A numerical model for a PEM fuel cell has been developed and used to investigate the effect of some of the key parameters of the porous layers of the fuel cell (GDL and MPL) on its performance. The model is comprehensive as it is three-dimensional, multiphase and non-isothermal and it has been well-validated with the experimental data of a 5 cm2 active area-fuel cell with/without MPLs. As a result of the reduced mass transport resistance of the gaseous and liquid flow, a better performance was achieved when he GDL thickness was decreased. For the same reason, the fuel cell was shown to be significantly improved with increasing the GDL porosity by a factor of 2 and the consumption of oxygen doubled when increasing the porosity from 0.40 to 0.78. Compared to the conventional constant-porosity GDL, the graded-porosity (gradually decreasing from the flow channel to the catalyst layer) GDL was found to enhance the fuel cell performance and this is due to the better liquid water rejection. The incorporation of a realistic value for the contact resistance between the GDL and the bipolar plate slightly decreases the performance of the fuel cell. Also the results show that the addition of the MPL to the GDL is crucially important as it assists in the humidifying of the electrolyte membrane, thus improving the overall performance of the fuel cell. Finally, realistically increasing the MPL contact angle has led to a positive influence on the fuel cell performance

Graphene inclusion effect on anion-exchange membranes properties for alkaline water electrolyzers

The main issues facing the development of Anion Exchange Membranes (AEM) are the low hydroxide ion (OH−) conductivity compared to protons (H+), and the thermal and chemical stability. Based on the its unique two-dimensional structure, graphene is estimated to be one of the best solutions for the hydrogen ions (H+ and OH−) selectivity and conductivity improvement. This work presents the graphene-composite membranes (AEMGrs) preparation and characterization in comparison with commercial FAA3-20® and FAA3-30® membranes from Fumatech. Various amounts of commercial graphene were incorporated into the Fumion® FAA-3 in NMP (10%), solutions which were then used to fabricate new AEMs by the Doctor-Blade (DB) method. Commercial and graphene-composite AEMs were studied by infrared spectroscopy with Fourier Transformation (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), water uptake (WU), ion exchange capacity (IEC), and in plane four-points electrochemical impedance spectroscopy (4p-EIS). The results indicated that the composite membranes containing 50 mg of graphene exhibited an improved IEC (3.16 mmol g−1) and OH− conductivity (113.27 mS cm−1) at 80 °C measured in 0.01 M KOH (pH = 12)

Effects of geometrical dimensions of flow channels of a large-active-area PEM fuel cell: A CFD study

Various flow field designs have been numerically investigated to evaluate the effect of pattern and the cross-sectional dimensions of the channel on the performance of a large active area PEM fuel cell. Three types of multiple-serpentine channels (7-channels, 11-channels and 14-channels) have been chosen for the 200 cm2 fuel cell investigated and numerically analysed by varying the width and the land of the channel. The CFD simulations showed that as the channel width decreases, as in the 14-channels serpentine case, the performance improves, especially at high current densities where the concentration losses are dominant. The optimum configuration, i.e. the 14-channels serpentine, has been manufactured and tested experimentally and a very good agreement between the experimental and modelling data was achieved. 4 channel depths have been considered (0.25, 0.4, 0.6 and 0.8 mm) in the CFD study to determine the effects on the pressure drop and water content. Up to 7% increase in the maximum reported current density has been achieved for the smallest depth and this due to the better removal of excess liquid water and better humidification of the membrane. Also, the influence of the air flow rate has been evaluated; the current density at 0.6 V increased by around 25% when air flow rate was increased 4 times; this is attributed to better removal of excess liquid water