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[en] 'Full text:' In February 2005, Ballard announced its most recent advances in PEMFC stack technology. This technology development exhibited, we believe, for the first time the capability of a single PEMFC stack design to demonstrate combined excellence in cost reduction, freeze start capability from -20 C and durability under an automotive OEM defined dynamic operating cycle, comparable to that experienced by a fuel cell stack in an actual vehicle. One month later, building on the above technology leadership demonstration, Ballard announced a technology 'oad map' that defined a path to commercially viability for a PEMFC stack by 2010. The key target parameters for cost reduction, durability, freeze start and stack power density are described in detail along with demonstrated historical capability and a clear path as to how Ballard will achieve the required targets. (author)
[en] 'Full text:' Mathematical modeling is an important tool for PEM fuel cell commercialization. Mathematical models can illustrate the effect of the different processes on the overall performance of a PEM fuel cell; thus, mathematical models can be used to as a design tool to find optimal designs and operating conditions. A general formulation for a comprehensive fuel cell model, based on the conservation principle and volume-averaging, is presented. The model formulation includes the electro-chemical reactions, proton migration, and the mass transport of the gaseous reactants and liquid water. Additionally, the model formulation can be applied to all regions of the PEM fuel cell: the bipolar plates, gas flow channels, electrode backing, catalyst, and polymer electrolyte layers. Numerical results, showing the effect of water flooding on PEM fuel cell performance, are presented. (author)
[en] Bipolar plate for Proton Exchange Membrane (PEM) fuel cell was fabricated with various materials and characterized by different techniques. Two types of gas flow fields, serpentine and parallel, were designed for bipolar plates and their effect on the functioning of fuel cells was investigated. Pressure drop between the two designs, at inlet and outlet of gases was different and its effect was reported. In the fabrication process of membrane electrode assemblies (MEA), the platinum catalyst was synthesized in the laboratory and this catalyst was deposited on the Nafion membrane with the help of ionomer emulsion. Then gas diffusion layers were placed on both sides of the membrane. Different MEAs versions (imported and indigenous) were assembled and tested in the fuel cells and their efficiency was evaluated in terms of current, voltage and power, A fuel cell test stand was developed to operate and test the working of single cell and fuel cell stack is also described. Polarization curves were drawn to evaluate the performance of fuel cells. These studies are directed at the development of different fuel cell components which are tested under the same conditions for comparison. (author)
[en] In this paper we combine a stochastic 3D microstructure model of a fiber based gas diffusion layer of polymer electrolyte fuel cells with a Lattice Boltzmann model for fluid transport. We focus on a simple approach of compressing the planar oriented virtual geometry of paper-type gas diffusion layer from Toray. Material parameters – permeability and tortuosity – are calculated from simulation of one phase, one component gas flow in stochastic geometries. We analyze the statistical spread of simulation results on ensembles of the virtual geometry, both uncompressed and compressed. The influence of the compression is discussed with regard to the Kozeny–Carman equation. The effective transport properties calculated from transport simulations in compressed gas diffusion layers agree well with a trend based on the Kozeny–Carman equation
[en] Highlights: • Covers a comprehensive review of available flow field channel configurations. • Examines the main design considerations and limitations for a flow field network. • Explores the common materials and material properties used for flow field plates. • Presents a case study of step-by-step modeling for an optimum flow field design. - Abstract: This study investigates flow fields and flow field plates (bipolar plates) in proton exchange membrane fuel cells. In this regard, the main design considerations and limitations for a flow field network have been examined, along with a comprehensive review of currently available flow field channel configurations. Also, the common materials and material properties used for flow field plates have been explored. Furthermore, a case study of step-by-step modeling for an optimum flow field design has been presented in-details. Finally, a parametric study has been conducted with respect to many design and performance parameters in a flow field plate.
[en] This paper addresses the importance of the boundary conditions for the charge conservation equation in the modeling of fuel cells. In this context, we analyze the charge transport in an electric conductor, aiming to determine whether constant current and constant potential boundary conditions can be interchanged without disturbing the local current density distribution in the cell. Their interchangeability can be described with a dimensionless number, referred to as the “interchangeability number”, which captures the relevant operating, geometrical and material parameters. The effect of the interchangeability number is further explored in a model for non-isothermal two-phase flow in a proton exchange membrane fuel cell, for which is it verified that the interchangeability number should be much less than 3, in order to ensure that the prediction for the local current density distribution at the catalyst layers remains the same regardless of galvanostatic or potentiostatic boundary conditions
[en] This paper presents a model of the Proton Exchange Membrane Fuel Cell (PEMFC) suitable for system simulation and optimisations using physically meaningful parameters. It is capable of modelling the transient behaviour and distributed nature of the cell. The model of the PEMFC is built up using discrete model elements representing subcomponents of the cell. Built in PSPICE, MATLAB/Simulink and VTB, the proposed model closely follows the physical layout of the actual cell. The interactions of chemical reactants, products and the main electrical circuit are represented in an electrochemically and physically accurate manner. The interactions include those of the water and protons, electrode-electrolyte charge double layer, reactant diffusion induced voltage drops and cross-over currents. Results are given for steady-state and transient operation and compared to experimental results. Conclusions are drawn concerning the ease of use of the model. (author)
[en] In this paper, an innovative robust prediction algorithm for performance degradation of proton exchange membrane fuel cell (PEMFC) is proposed based on a combination of model-based and data-driven prognostic method. A novel approach using the moving window method is applied, in order to 1) train the developed models; 2) update the weight factors of each method and 3) further fuse the predicted results iteratively. In the proposed approach, both model-based and data-driven methods are simultaneously used to achieve a better accuracy. During the prediction process, each dataset in the proposed moving window are divided into three sections respectively: training, evaluation and prediction. The training data are used first to identify the models parameters. The evaluation data are then used to measure the weight of each method, which represents the degree of confidence of each method in the actual state. Based on these dynamically adjusting weight factors, the prediction results from different methods are then fused using weighted average methodology to calculate the final prediction results. In order to verify the proposed method, three experimental validations with different aging testing profiles have been performed. The results demonstrate that the proposed hybrid prognostic approach can achieve a higher accuracy than conventional prediction methods. In addition, in order to find the satisfactory trade-off between the prediction accuracy and forecast time for optimizing on-line prognostic, the performance variation of proposed approach with different moving window length is further showed and discussed. - Highlights: • Long-term aging trend of PEMFC is captured by a degradation empirical model. • Nonlinear characteristics of PEMFC degradation are predicted by a NARNN model. • Both model-based and data-driven prognostic approaches are simultaneously used. • Moving window method iteratively updates the prediction process. • Performance variation of hybrid prognostic with different prediction horizon is shown.
[en] This study deals with the thermodynamic modeling of a polymer electrolyte membrane (PEM) fuel cell power system for transportation applications. The PEM fuel cell performance model developed previously by two of the authors is incorporated into the present model. The analysis includes the operation of all the components in the system, which consists of two major modules: PEM fuel cell stack module and system module and a cooling pump. System module includes air compressor, heat exchanger, humidifier and a cooling loop. A parametric study is performed to examine the effect of varying operating conditions (e.g., temperature pressure and air stoichiometry) on the energy and exergy efficiencies of the system. Further, thermodynamic irreversibilities in each component of the system are determined. It is found that, with the increase of external load (current density), the difference between the gross stack power and net system power increases. The largest irreversibility rate occurs in the fuel cell stack. Thus, minimization of irreversibility rate in the fuel cell stack is essential to enhance the performance of the system, which in turn reduces the cost and helps in commercialization of fuel cell power system in transportation applications. (author)
[en] Fuel cells are electrochemical energy converters. They convert the chemical energy contained in the fuel into electricity while producing water and heat. Compared to the traditional energy converters, such as batteries and internal combustion engines, fuel cells are marked by high conversion efficiency and very low emissions.This work contains a computer study of optimization and control of fuel cells systems. An analytical study of the fuel (Hydrogen and air) supply system was performed taking into account compressor, cooling and humidification subsystems. In addition, the stack system, which consists of a lot of cells, was analyzed using the experimental equations of Nafion 117 membrane. The model of the whole system was then implemented in MATLAB/Simulink environment. The effect of the cathode pressure and the membrane water content on the polarization curves of the cell was examined. To validate the model, the responses of the model to step changes in the compressor voltage and the current drawn from the stack, were used. More attention was given to the net power which can be provided by the system, taking into account the power wasted by the compressor. (author)