Dynamic modeling of high temperature PEM fuel cell start-up process

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are considered to be the next generation fuel cells. Compared with standard low temperature proton exchange membrane fuel cells (LT-PEMFCs) the electrochemical kinetics for electrode reactions are enhanced by using a polybenzimidazole based membrane at an operation temperature between 160 °C and 180 °C. However, starting HT-PEMFCs from room temperature to a proper operation temperature is a challenge in application where a fast start of the fuel cell is required such as in uninterruptible power supply systems. There are different methods to start-up HT-PEMFCs. Based on a 3D physical model of a single HT-PEMFC, the start-up process is analyzed by comparing the start-up duration of the different start-up concepts. Furthermore, the temperature distribution in the HT-PEMFC is also analyzed. Finally, an optimal start-up method is proposed for the given cell configuration.     

Parameter study of high-temperature proton exchange membrane fuel cell using data-driven models

In this paper, a numerical model of high-temperature proton exchange membrane fuel cell (HT-PEMFC) was developed, in which the thermal and electrical properties were treated as temperature dependent. Based on the numerical simulation, the needed training data was acquired and used for the development of data-driven model via the artificial neural network (ANN) algorithm. The developed data-driven model was then used to predict the performance of HT-PEMFC. The simulation results indicated that the deviation of ANN prediction was less than 2.48% compared with numerical simulation. The effects of various influential factors, such as the geometry size of the gas flow channel, the thickness of the membrane and the operating temperature, could be predicted easily by using the ANN model. The ANN model prediction results showed that the more compact fuel cell and the higher operating temperature improved the performance of HT-PEMFC. The proposed ANN model and the parameters study will contribute to the further design and operation of HT-PEMFC.     

Effects of leak current density and doping level on energetic,exergetic and ecological performance of a high-temperature PEM fuel cell

This paper presents a one-dimensional and semi-empirical model of a high-temperature PEM fuel cell (HT-PEMFC) to determine the performance characteristics through energy, exergy, and ecological analysis. The proposed model is compared with different experimental studies and supported by a few statistical approaches to prove its accuracy. As a result, the minimum and maximum R² values are determined to be 99.67% and 99.97%, respectively. In addition, the performance of the fuel cell is investigated under varying leakage current densities and doping levels. Accordingly, increasing the leak current density decreases the power density, net output voltage, energy efficiency, and exergy efficiency by 5.77%, 5.88%, 5.44%, and 5.48%, respectively, whereas increasing the doping level boosts these parameters by 23.07%, 11.76%, 30.25%, and 32.52%, respectively. In addition, increasing the leak density decreases all ecological functions. In contrast, raising the doping level increases the ecological parameters considerably and reduces the improvement potential.     

Consistent modeling of a single PEM fuel cell using Onsager's principle

In this paper a novel approach is proposed for a three-dimensional (3D) modeling of a High Temperature Exchange Membrane Fuel Cell (HTPEMFC). This new modeling is based on Onsager's principle of minimum energy dissipation that is applicable for near equilibrium and coupled irreversible systems. In particular, for low conductivity membranes, this leads to a one directional proton movement through the membrane. The resulting equations are numerically solved for a real single cell geometry, using a 3D finite volume discretization. Results are analyzed and validated against experimental data.     

Numerical and experimental investigation of cascade type serpentine flow field of reactant gases for improving performance of PEM fuel cell

The distribution of reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) plays a pivotal role in current density distribution, temperature distribution, and water concentration. Problems such as flooding or drying of the membrane are caused by the non-uniformity of the above mentioned parameters resulting in a reduced membrane electrode assembly (MEA) life time. In this study, a new cascade type serpentine flow field is introduced and the concept of design is explained. The simulation results are in good agreement with the literature. The optimal channel to rib ratio is obtained using simulation results. The results show that the proposed flow field produces a uniform current density and local stoichiometry as well as an improved water management. It is also determined that the two phase numerical method can estimate experimental results correctly.     

Micro-cogeneration application of a high-temperature PEM fuel cell stack operated with polybenzimidazole based membranes

High temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC) have attracted the attention of researchers in recent years due to their advantages such as working with reformed gases, easy heat management and compatibility with micro-cogeneration systems. In this study, it is aimed to designed, manufactured and tested of the HT-PEMFC stack based on Polybenzimidazole/Graphene Oxide (PBI/GO) composite membranes. The micro-cogeneration application of the PBI/GO composite membrane based stack was investigated using a reformat gas mixture containing Hydrogen/Carbon Dioxide/Carbon Monoxide (H₂/CO₂/CO). The prepared HT-PEMFC stack comprises 12 cells with 150 cm² active cell area. Thermo-oil based liquid cooling was used in the HT-PEMFC stack and cooling plates were used to prevent coolant leakage between the cells. As a result of HT-PEMFC performance studies, maximum 546 W and 468 W power were obtained from PBI/GO and PBI membranes based HT-PEMFC stacks respectively. The results demonstrate that introducing GO into the PBI membranes enhances the performance of HT-PEMFC technology and demonstrated the potential of the HT-PEMFC stack for use in micro-cogeneration applications. It is also underlined that the developed PBI/GO composite membranes have the potential as an alternative to commercially available PBI membranes in the future.     

Dependence of high-temperature PEM fuel cell performance on Nafion® content

Operating a proton exchange membrane (PEM) fuel cell at elevated temperatures (above 100 °C) has significant advantages, such as reduced CO poisoning, increased reaction rates, faster heat rejection, easier and more efficient water management and more useful waste heat. Catalyst materials and membrane electrode assembly (MEA) structure must be considered to improve PEM fuel cell performance. As one of the most important electrode design parameters, Nafion^® content was optimized in the high-temperature electrodes in order to achieve high performance. The effect of Nafion^® content on the electrode performance in H₂/air or H₂/O₂ operation was studied under three different operation conditions (cell temperature (°C)/anode (%RH)/cathode (%RH)): 80/100/75, 100/70/70 and 120/35/35, all at atmospheric pressure. Different Nafion^® contents in the cathode catalyst layers, 15–40 wt%, were evaluated. For electrodes with 0.5 mg cm⁻² Pt loading, cell voltages of 0.70, 0.68 and 0.60 V at a current density of 400 mA cm⁻² were obtained at 35 wt% Nafion^® ionomer loading, when the cells were operated at the three test conditions, respectively. Cyclic voltammetry was conducted to evaluate the electrochemical surface area. The experimental polarization curves were analyzed by Tafel slope, catalyst activity and diffusion capability to determine the influence of the Nafion^® loading, mainly associated with the cathode.     

Impact of high frequency current ripples on the degradation of high-temperature PEM fuel cells (HT-PEMFC)

In order to achieve the goal of reducing the environmental footprint of the transport sector, new low-carbon energy systems including fuel cells and power converters are proposed. The sizing and operation of such systems have to take into account the aging of the fuel cell. This paper focuses on the study of a potential impact of high frequency current ripples (HFCR) on the degradation of a high-temperature proton exchange membrane fuel cell (HT-PEMFC). A 2600 h long endurance test was carried out on 4 HT-PEMFC single cells with and without HFCR. The degradation of two cells operated with a triangular current waveform of frequency 20 kHz and amplitude 20 %_pp of the mean current density (0.2 A/cm²) is compared to the degradation of two cells operated at the same constant mean current density. In addition to endurance phase, several characterization phases (polarization curves, electrochemical impedance spectroscopy and cyclic voltammetry) are used to analyse the impact of the current harmonics. The obtained results show that the high frequency current ripples do not seem to accelerate the degradation of the HT-PEMFC single cells.     

Modeling charge transfer in a PEM fuel cell using solar hydrogen

Hydrogen is an energy carrier that can be used in industry, residences, transportation, and mobile applications. One of the main attractions for hydrogen is the environmental advantage over fossil fuels. However, Polymer Electrolyte Membrane Fuel Cells, (PEMFC), is an integral part of the future hydrogen economy, they are highly efficient and a low-polluting technology. Numerous applications exist; one of the promising applications is the automotive industry. For this report a comprehensive literature survey is conducted. The findings of the literature survey include hydrogen production and fuel cell models that fit into two broad categories, that is, analytical and empirical. This work is a presentation of our original research and development regarding the production and utilization of a solar hydrogen and its use in a PEM single cell. In order to facilitate the understanding of the charge transfer phenomena in the PEM single cell, a modeling tool with visual basic was developed. All the experiences and results were illustrated in this work.     

Effects of gas-diffusion layer properties on the performance of the cathode for high-temperature polymer electrolyte membrane fuel cell

The role of the gas-diffusion layer (GDL) in high-temperature polymer electrolyte fuel cell (HT-PEMFC) differs from that in low-temperature PEMFC GDL due to operating conditions and environment. Determining the GDL's structural parameters that affect its transport properties, and how these properties impact HT-PEMFC performance was urgently required. Four commercial GDLs were employed in HT-PEMFC cathode's GDE and was examined using X-μCT, mercury intrusion porosimetry, and an optical microscope to analyze structural parameters and characteristics. Fractal theory was applied to comprehend the gas transmission property of GDL, and the validity of the theory was confirmed through ex-situ through-plane gas permeability measurement. The analysis indicated that the porosity of GDL influenced by the crack region of the MPL has more impact on the GDL's gas transmission than its thickness. After that, we established a correlation between HT-PEMFC cathode performance and GDL porosity and theoretical gas transmission properties using R² coefficient of determination.     

Improving the performance of high-temperature PEM fuel cells based on PBI electrolyte

This paper describes the testing of the gas-diffusion electrodes for polymer electrolyte membrane fuel cells utilizing phosphoric acid doped polybenzimidazole (PBI) electrolyte, which allows for an operating temperature as high as 200 °C. In order to determine the optimum structure of our anodes and cathodes, the platinum content in the Pt/C catalyst and catalyst loading were varied, as well as the loading of the PBI electrolyte dispersed in the catalyst layer. The different MEAs were tested in terms of their performance by recording polarization curves using pure oxygen and hydrogen. It was found that a high platinum content and a thin catalyst layer on both anode and cathode, gave the overall best performance. This was attributed to the different catalyst surface areas, the location of the catalyst in relation to the electrolyte membrane and particularly the amount of PBI dispersed in the catalyst layer. Scanning electron microscopy (SEM) was used in order to examine the cross-section of the MEAs and measure the thickness of the catalyst layers. With this information, it was possible to give an estimate of the porosity of the catalyst layer.     

The effects of porosity distribution variation on PEM fuel cell performance

Gas diffusion layers (GDL) are one of the important parts of the PEM fuel cell as they serve to transport the reactant gases to the catalyst layer. Porosity of this layer has a large effect on the PEM fuel cell performance. The spatial variation in porosity arises due to two effects: (1) compression of the electrode on the solid landing areas and (2) water produced at the cathode side of gas diffusion layers. Both of these factors change the porosity of gas diffusion layers and affect the fuel cell performance. To implement this performance analysis, a mathematical model which considers oxygen and hydrogen mass fraction in gas diffusion layer and the electrical current density in the catalyst layer, and the fuel cell potentials are investigated. The porosity variation in the GDL is calculated by considering the applied pressure and the amount of the water generated in the cell. The validity of the model is approved by comparing the computed results with experimental data. The obtained results show that the decrease in the average porosity causes the reduction in oxygen consumption, so that a lower electrical current density is generated. It is also shown that when the electrical current density is low, the porosity variation in gas diffusion layer has no significant influence on the level of polarization whereas at higher current density the influence is very significant. The porosity variation causes non-uniformity in the mass transport which in turn reduces the current density and a lower fuel cell performance is obtained.     

Relating the N-shaped polarization curve of a PEM fuel cell to local oxygen starvation and hydrogen evolution

In this study, we experimentally investigate the appearance of a local negative differential resistance (N-NDR) branch in polarization curves of a segmented 7 by 7 cell measured under the steady and highly-dynamic conditions. Under both conditions, a comma shaped polarization curve, corresponding to depletion of oxygen, was followed by an increase in current as the cell voltage was lowered. This characteristic was measured under potentiostatic mode, where no current is forced through the cell, and at a positive cell voltage (<100 mV in steady-state and ∼300 mV in dynamic condition). With a theoretical model, we show that at these positive cell voltages and upon the depletion of oxygen, a shift in the Nernst potential occurs allowing for the hydrogen evolution reaction to take place in the cathode catalyst layer. The results of the model are complemented with experimental measurements of produced hydrogen at the cathode outlet.     

The effects of mine conditions on the performance of a PEM fuel cell

Proton exchange membrane fuel cells (PEMFC) have been selected to replace conventional underground power sources such as diesel engines, to improve underground air quality, to reduce green house gas emissions and operating costs and to facilitate equipment automation. The effects of underground mining conditions, gases, dust and shock and vibration on the performance of PEMFC’s were investigated during extensive testing in an operating underground metal mine. Neither the voltage–amperage nor the power–amperage curves showed significant damage effects, and a post-testing stack inspection showed minor pressure drop, at the higher current density and airflow rate. With the use of an air intake filter, little particle accumulation was registered in the stack, and effluent water testing revealed the presence of rock-derived particles, showing that the stack was able to purge itself of low particle concentrations. No physical damage was imposed to the stack, auxiliary system and hydrogen metal hydride storage unit. Fuel cell performance compared well to pre-test and initial construction power plant data generation. Further tests are recommended to study individual mine gas and particle mineralogy type effects.     

Gravity effect on the performance of PEM fuel cell stack with different gas manifold positions

The importance of gravity effect on the performance of proton exchange membrane fuel cell (PEMFC) has recently been recognized. In this paper, the effect of gravity on the performance of PEMFC has been investigated associating with different gas intake modes. The polarization curves of the stack with different positions of reaction gas inlet and outlet at varied gravitational angles are addressed in detail. The results indicate that the output power of PEMFC stack can be greatly enhanced at the optimized gravitational angle. Gas intake modes that were realized by varying the gas inlet and outlet positions strongly affect the stack performance as well. The optimized performance can be reached at the tilted angle of 90° when both air and hydrogen inlets are placed at the upper side of the stack, whereas the worst performance occurs at the tilted angle of 90° when air and hydrogen flow into the channel from the bottom side of the stack. These results have important implications for PEM fuel cell design and operational strategies. In order to improve the performance, fuel cells should be designed and operated at the optimized gravitational angle and gas inlet/outlet position. Copyright © 2011 John Wiley & Sons, Ltd.     

Three-dimensional multi-phase simulation of PEM fuel cell considering the full morphology of metal foam flow field

It is well-known that flow field design is of primary importance to optimization of proton exchange membrane (PEM) fuel cell. Traditional channel-rib flow fields, e.g. parallel or serpentine channels, always lead to non-uniform distributions of reactant gas, liquid, current density and so on between the channel and rib regions. Metal foam materials with high porosity (>90%) have been proposed as alternative flow fields for PEM fuel cells. In this study, influences of metal foam flow field on the transport phenomena coupled with the electrochemical reactions in PEM fuel cell are investigated using a three-dimensional (3D) multi-phase non-isothermal model. Specifically, the full morphology of metal foam flow field is taken into account in the 3D simulation after validated against experimental permeability data. The full morphology inclusion enables capture of the detailed gas flow from the flow field into the gas diffusion layer (GDL) and the current collection at the metal foam/GDL interface. In addition, compared with the conventional channel-rib flow fields, the metal foam design greatly increases fuel cell performance in the high current density regime. In addition, the oxygen and current density distributions in PEM fuel cell with the metal foam flow field are more uniform than those in the conventional one. Though the current collection area at the GDL surface is much smaller in the metal foam flow field, the relevant Ohmic loss won't increase significantly due to the improved physical contact by the fine pore structure of metal foam over the GDL.     

A numerical investigation of the effects of compression force on PEM fuel cell performance

In the present study we report on numerical investigations into the effects of compression on the performance of a unit cell. The focus of this study is how the transport properties of the gas diffusion layer (GDL) material, specifically porosity and permeability, affect numerical predictions of cell performance. Experimental data of porosity and permeability of uncompressed and compressed GDLs were obtained using a porometer, and used in numerical simulations. A 3D model with two parallel channels and an membrane electrode assembly (MEA) is constructed for the calculations. Three different configurations of transport properties were tested, i.e. uniform uncompressed GDL properties, uniform compressed GDL properties, and non-homogeneous GDL properties. It is found that the non-homogeneous case shows noticeable differences in predicted cell performance. For the non-homogenous case, simulations with a pressure difference between two cathode channels were carried out to gain insight into the effect of cross-channel flow on the overall prediction of cell performance. We found that the cross-channel flow changes local current density distribution primarily on the high-pressure channel. The present study demonstrates the importance of the proper use of transport properties for the compressed portion of the GDL.     

PEM fuel cell degradation effects on the performance of a stand-alone solar energy system

After comparing fresh and degraded performances of Polymer Electrolyte Membrane (PEM) based components of a hydrogen cycle with the help of computational fluid dynamics simulations, recently established stand-alone solar energy system producing hydrogen for energy storage is investigated focusing on the effects of degradation of fuel cells on the overall performance of the system. A complete model of the system has been developed using TRNSYS, and a degraded PEM Fuel Cell Subsystem has been incorporated into the model. Then, the effects of the PEM fuel cell degradation on the overall performance of the energy system are estimated. After reviewing the simulation results, the model shows that the PEM Fuel Cell degradation has a substantial impact on the overall system performance causing a system down time of approximately one month in a typical simulation year. Consequently, the stand-alone system is not capable of operating continuously for a complete year when the PEM fuel cells are degraded. Furthermore, an economic analysis is performed for a project lifetime of 25 years and the Levelized Cost of Electricity (LCE) value of the degraded system is found to be 0.08 $/kWh higher than the newly established system. Nevertheless, LCE calculations that are repeated for declining PV panel costs show that the considered hybrid system may be an economically competitive alternative to conventional diesel generators, even when the degradation of PEM based components and their regular maintenance are considered.     

Research progress on performance of fuel cell system utilized in vehicle

The application of fuel cells was an important approach for vehicle industry to deal with the challenges of Energy shortage and environment pollution caused by traditional power machines. Fuel cells, which generate power and torque with zero emissions and high efficiency, are considered as an promising future power machine for vehicles. This paper reviewed previous research model and method for fuel cell, effect of state parameters and structural parameters on the performance of fuel cell,power density and life cycle of fuel cell systems in recent years,Prospected development and application of fuel cell system in the future.