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.     

Modeling and simulation of a single direct carbon fuel cell

A mathematical model was developed to simulate the performance of a direct carbon fuel cell. The model takes account of the electrochemical reaction dynamics, mass-transfer and the electrode processes. An improved packed bed anode was adopted. Polarization losses for the cell components were examined supposing graphite as the fuel and molten carbonate as the electrolyte. The results indicated that the anode activation polarization was the major potential loss in 923–1023 K. The effects of temperature, anode dimension, and carbon particle size on the cell performance were investigated. The model predicted that the power density can be as high as 200–500 W m⁻², with carbon particle size in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ m and in 923–1023 K and that the overall efficiency of the cell is higher than 55% for low current density and is 45–50% for high current density.     

Modeling and simulation of a simple glass window

This paper presents a mathematical model with numerical simulations of the heat transfer across a simple glass window. The model is two-dimensional, transient based upon the energy equation with a source term to account for the solar radiation absorbed through the glass sheet. Variable incident solar radiation and external ambient temperature are considered in the numerical simulations. The governing equations and the associated boundary conditions are discretized by the finite difference approach and the ADI scheme. Numerical simulations are realized for the cases of clear and absorbing glass to show the effect of the glass thickness on the total heat gain, the solar heat gain and the shading coefficient.     

Modeling of hybrid photovoltaic/wind/fuel cells power system

In this paper, identification and modeling of a hybrid photovoltaic/wind/fuel cells power system is presented. This system comprises also a battery storage supplying a load via an inverter. The identification of each subsystem has been made and then the proposed system is modeled and simulated under Matlab/Simulink Package. The power control of the hybrid system is introduced by using LabVIEW Software. The mathematical model topology and its power management of the global system with battery bank system are significant contributions of our work. The proposed control strategy has been experimentally implanted and practical results are compared to those obtained by simulation under the same metrological conditions, showing the effectiveness of the proposed hybrid system.     

A 5 kWt catalytic burner for PEM fuel cells: Effect of fuel type,fuel content and fuel loads on the capacity of the catalytic burner

For proton exchange membrane fuel cell systems (PEMFC) integrated with fuel processors, the calorific value of reformate gases produced during the start-up phase must be recovered. An appropriate exhaust after treatment system has crucial importance for PEMFC systems. Catalytic combustion is a promising alternative regarding its total oxidation capability of low calorific value gases at low temperatures, thereby reducing environmentally hazardous emissions. The aim of the study is to develop an after treatment system using a catalytic burner with a nominal capacity of 5 kW_t, which is also adaptive to partial loads of PEM fuel cell capacity. Fuel type, fuel composition and fuel loads are important parameters determining the operating window of the catalytic burner. Precious metal based catalysts, as proved to be the most active catalysts for the oxidation of hydrocarbons, can withstand temperatures of about 1073 K without exhibiting a rapid deactivation. This is the main barrier dictating the operating window and thereby determining the capacity of the burner. In this work, 1.5% natural gas (NG) alone was found to be the upper limit to control the catalyst bed temperature below 1073 K. In the case of catalytic combustion of hydrogen–NG mixture, 7% of hydrogen with NG up to 0.6% could be totally oxidized below 1073 K. Within the experimented ranges of fuel loads, between 2.5 kW_t and 5.5 kW_t, the temperature of the catalyst bed was seen to increase with increasing the fuel load at constant fuel percentages. It has been observed that fuel type was another parameter affecting the exhaust gas temperature.     

Modeling and simulation of a proton exchange membrane fuel cell using computational fluid dynamics

An isothermal, three dimensional, single phase model was presented to evaluate a proton exchange membrane fuel cell (PEMFC) with serpentine flow. The mass, momentum and electrochemical equations were solved simultaneously for the steady state condition using computational fluid dynamics (CFD) software based on the finite element method. The model considered reactions as mass source/sink terms, and electron transport in the catalyst layers and GDLs. To validate the model, the numerical results were compared to the experimental data collected from the fabricated membrane electrode assemblies. The exchange current density parameter of the catalysts was fitted by the model to calibrate the results. The model showed good agreement with experimental data and predicted a higher current density for the catalyst with a higher surface area and Pt content. The oxygen, hydrogen and water mass fraction distribution, velocity magnitude and pressure distribution were estimated by the model. Moreover, the effect of pressure and temperature, as two important operating conditions, on the current density was predicted by the validated model.     

Modeling and simulation of net energy gain by dark fermentation

For dark fermentation (DF) to be accepted as a sustainable process for biohydrogen production, the net energy gain should be positive and as high as possible. A theoretical approach is proposed in this study to evaluate the net energy gain possible from hydrogen generated by the DF process as well as from the end products of DF via anaerobic digestion (AD) and microbial fuel cells (MFC). Experimental data on hydrogen evolution and aqueous end products formation from sucrose and from sucrose/dairy manure blends were used to validate the proposed approach for estimating net energy gain via DF, DF + AD, DF + MFC. Good agreement was found between the experimental and predicted net energy gain values, with overall correlation coefficient of 0.998. Based on the results of this study, DF + MFC is recommended as the best combination to maximize net energy gain.     

Modeling of an air cathode for microfluidic fuel cells: Transport and polarization behaviors

Air-cathode microfluidic fuel cells are promising micro-scale power sources that unfortunately undergo substantial performance loss at the cathode. This study therefore develops a mathematical model to gain a better understanding of the fundamental processes and polarization characteristics associated with the MFC air cathode operation so as to find strategies to minimize the cathode polarization. The model is solved for the four regions of an MFC cathode compartment (i.e. gas channel, gas diffusion layer, catalyst layer and electrolyte microchannel), and considers microfluidic flow, species transport, charge transport and multi-step oxygen reduction reactions. Relying on the model, transport and chemical patterns inside the MFC cathode compartment are examined. Corresponding electrode polarization behaviors are analyzed over a wide operating potential range including different forms of resistance. Through a series of model-based parametric studies, it is found that the internal transfer resistance slightly decreases with increasing catalyst layer porosity but can be effectively reduced through a proper control of electrolyte hydrodynamic conditions, indicating microfluidic technology is a powerful tool for enhancing electrochemical cells.     

Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

Static and dynamic modeling of a diesel fed fuel cell power supply

Fuel cell supplied auxiliary power units could ease the development of fuel cell systems in transportation application if they are fed by conventional hydrocarbons like diesel. Then a fuel processor has to be used to convert the hydrocarbon in a hydrogen rich gas mixture with a low rate of contaminant. The temperatures of the fuel processor modules and the mass flows have to be controlled. The energetic macroscopic representation (EMR) is a causal, graphic modeling tool for complex multi-domain systems that can be used for the design of the control structure through the inversion of model. In this work EMR is used to model a diesel supplied low temperature fuel cell unit including the fuel processor, the fuel cell stack (HTPEM) as well as the supply system of the mass flows. The presented fuel processor and HTPEM models are validated against experimental results. The structure of the temperature and mass flow controls in the fuel processor and supply system are derived. Both the model and the control are implemented in Matlab/Simulink™ and validated.     

Modeling and control of a wind fuel cell hybrid energy system

This paper describes a hybrid energy system consisting of a 5 kW wind turbine and a fuel cell system. Such a system is expected to be a more efficient, zero emission alternative to wind diesel system. Dynamic modeling of various components of this isolated system is presented. Selection of control strategies and design of controllers for the system is described. Simnon is used for the simulation of this highly nonlinear system. Transient responses of the system for a step change in the electrical load and wind speed are presented. System simulation results for a pre-recorded wind speed data indicates the transients expected in such a system. Design, modeling, control and limitations of a wind fuel cell hybrid energy system are discussed.     

Model-based power control strategy development of a fuel cell hybrid vehicle

An integrated procedure for math modeling and power control strategy design for a fuel cell hybrid vehicle (FCHV) is presented in this paper. Dynamic math model of the powertrain is constructed firstly, which includes four modules: fuel cell engine, DC/DC inverter, motor-driver, and power battery. Based on the mathematic model, a power control principle is designed, which uses full-states closed-loop feedback algorithm. To implement full-states feedback, a Luenberger state observer is designed to estimate open circuit voltage (OCV) of the battery, which make the control principle not sensitive to the battery SOC (state of charge) estimated error. Full-states feedback controller is then designed through analyzing step responding of the powertrain and test data. At last of the paper, the results of simulation and field test are illustrated. The results show that the power control strategy designed takes into account the performance and economy characteristics of components of the FCHV powertrain and achieves the control object excellently.     

Convergence criteria establishment for 3D simulation of proton exchange membrane fuel cell

A validated 3 dimensional (3D) computational fluid dynamics model of a single cell proton exchange membrane fuel cell (PEMFC) was used for investigating convergence criteria. The simulation study was carried out using the commercial PEMFC simulation module built in to ANSYS FLUENT 12.1 software package and compared with published experimental data. Convergence data up to 19,000 iterations were collected in order to establish expectations for convergence errors and differences in convergence rates for different boundary conditions. Species mass fluxes and current density were used to perform a dual verification of experimentally verifiable simulation predictions. The results of the simulation showed that convergence trends were consistent for different boundary conditions and that the solution trends asymptotically to a final value with species mass flux errors approaching to constant values. The data were used to establish convergence criteria for future 3D PEMFC simulations where residual monitoring alone is insufficient to ensure convergence.     

Modeling and simulation of methane steam reforming in a thermally coupled membrane reactor

A distributed mathematical model for thermally coupled membrane reactor that is composed of three channels is developed for methane steam reforming. Methane combustion takes place in the first channel on a Pt/δ–Al₂O₃$\text{Pt}/\delta \text{–}{\text{Al}}_2{\text{O}}_3$ catalyst layer that supplies the necessary heat for the endothermic steam reforming reaction. In the second channel, catalytic steam reforming reactions take place in the presence of Ni/MgO–Al₂O₃ catalyst. The combustion catalyst forms a thin layer next to the reactor wall to minimize the heat transfer resistance. Selective permeation of hydrogen through the palladium membrane is achieved either by co-current or counter-current flow of sweep gas through the third channel. The burner is modeled as a monolith reactor and the reformer is assumed to behave as a pseudo-homogenous reactor. The mass and energy balance equations for the thermally coupled membrane reactor form a set of 22 coupled ordinary differential equations. With the application of appropriate boundary conditions, the distributed reactor model for steady-state operation is solved as a boundary value problem. The model equations are discretized using spline collocation on finite elements. The discretized nonlinear modeling equations, along with the boundary conditions, form a system of algebraic equations that are solved using the trust region dogleg method. The performance of the reactor is numerically investigated for various key operating variables such as inlet fuel concentration, inlet steam/methane ratio, inlet reformer gas temperature and inlet reformer gas velocity. Simulations for both the co-current and the countercurrent flow modes are also performed using different sweep gas flow rates. For each case, the reactor performance is analyzed based on methane conversion and hydrogen recovery yield.     

Simulation of a fuel reforming system based on catalytic partial oxidation

Catalytic partial oxidation (CPO) has potential for producing hydrogen that can be fed to a fuel cell for portable power generation. In order to be used for this purpose, catalytic partial oxidation must be combined with other processes, such as water-gas shift and preferential oxidation, to produce hydrogen with minimal carbon monoxide. This paper evaluates the use of catalytic partial oxidation in an integrated system for conversion of a military logistic fuel, JP-8, to high-purity hydrogen. A fuel processing system using CPO as the first processing step is simulated to understand the trade-offs involved in using CPO. The effects of water flow rate, CPO reactor temperature, carbon to oxygen ratio in the CPO reactor, temperature of preferential oxidation, oxygen to carbon ratio in the preferential oxidation reactor, and temperature for the water-gas shift reaction are evaluated. The possibility of recycling water from the fuel cell for use in fuel processing is evaluated. Finally, heat integration options are explored. A process efficiency, defined as the ratio of the lower heating value of hydrogen to that of JP-8, of around 53% is possible with a carbon to oxygen ratio of 0.7. Higher efficiencies are possible (up to 71%) when higher C/O ratios are used, provided that olefin production can be minimized in the CPO reactor.     

Preparation,characterization, and high performance of RuSe/C for direct methanol fuel cells

RuSe/C catalysts prepared by different methods have been tested for oxygen reduction and the results analyzed based on the active species and particle size distribution. Inorganic precursor methods exhibit higher catalytic performance than the carbonyl method. Selenious acid is an excellent inorganic precursor. X-ray photoelectron spectra indicate that selenium in a high oxidation state is more active than that with zero valence. The effect of operating conditions is analyzed for catalysts prepared by the inorganic precursor method. The optimum heat-treatment temperature for both active phase formation and particle size distribution is 300 °C. A performance of 62 mW cm⁻² at 80 °C is obtained using 80 wt.% RuSe/C in the cathode.     

Dynamic modeling and simulation of a proton exchange membrane electrolyzer for hydrogen production

Computational model of a proton exchange membrane (PEM) water electrolyzer is developed to enable investigation of the effect of operating conditions and electrolyzer components on its performance by expending less time and effort than experimental investigations. The work presents a dynamic model of a PEM electrolyzer system based on MATLAB/Simulink software. The model consists mainly of four blocks - anode, cathode, membrane and voltage. Mole balances on the anode and cathode blocks form the basis of the model along with Nernst and Butler-Volmer equations. The model calculates the cell voltage by taking into account the open circuit voltage and various over-potentials. The model developed predicted well the experimental data on PEM water electrolyzer available in the literature. The dynamic behavior of the electrolyzer system is analyzed and the effects of varying electrolyzer temperature and pressure on electrolyzer performance and over-potentials are presented.     

Synchrotron-based structural and spectroscopic studies of ball milled RuSeMo and RuSnMo particles as oxygen reduction electrocatalyst for PEM fuel cells

Particles of RuSeMo and RuSnMo have been produced by ball milling; they present catalytic activity towards the oxygen reduction reaction (ORR) in acid media. A Tafel slope close to 120 mV/dec was found for both materials. Their morphology was first characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images reveal particles in the sub-micrometer range. The structure of the materials was further probed with synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption spectroscopy (XAS). SR-PXD reveals the existence of metallic Ru as the main phase and the formation of phases such as RuSe₂ in RuSeMo and Ru₃Sn₇ in RuSnMo. Mo was found to form solid solution into the RuSe₂ phase in ball milled RuSeMo. Finally, The Ru L₃-edge and Mo L₃-edge XAS fingerprints were correlated with the catalytic activity towards ORR.     

MATLAB-based simulator of a 5 kW fuel cell for power electronics design

In the last few years, renewable energies have been encouraged by worldwide governments to meet energy saving policies. Among renewable energy sources, fuel cells have attracted much interest for a wide variety of research areas. Since combined heat-power generation is allowed, household appliances are still the most promising applications. Fuel cell-based residential-scaled power supply systems take advantage by simultaneous generation of power and heat, reducing the overall fossil fuel consumption and utilities cost. Modelling is one of the most important topic concerning fuel cell use. In this paper, a measurement-based steady-state and dynamic fuel cell model is presented. The parameters identification procedure is analyzed and the MATLAB/Simulink implementation is shown. The proposed modelling approach is implemented on a 5 kW Proton Exchange Membrane Fuel Cell. As shown by the comparison between experimental and simulation results, the model error is restricted to ±1%, corresponding to a maximum absolute model error of 0.6 V.