Biomimetic flow fields for proton exchange membrane fuel cells: A review of design trends

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.Ministerio de Ciencia, Innovación y Universidades ENE2017-91159-EXPMinisterio de Economía y Competitividad UNSE15-CE296

Distributed and Lumped Parameter Models for Fuel Cells

The chapter presents a review of modeling techniques for three types of fuel cells that are gaining industrial importance, namely, polymer electrolyte membrane (PEMFC), direct methanol (DMFC), and solid oxide (SOFC) fuel cells (FCs). The models presented are both multidimensional, suitable for investigating distributions, gradients, and inhomogeneities inside the cells, and zero-dimensional, which allows for fast analyses of overall performance and can be easily interfaced with or embedded in other numerical tools, for example, for studying the interaction with static converters needed to control the electric power flow. Thermal dependence is considered in all models. Some special numerical approaches are presented, which allow facing specific problems. An example is the Proper Generalized Decomposition (PDG) that allows overcoming the challenges arising from the extreme aspect ratio of the thin electrolyte separating anode and cathode. The use of numerical modeling as part of identification techniques, particularly by means of stochastic optimization approaches, for extracting the material parameters from multiple in situ measurements is also discussed and examples are given. Merits and demerits of the different models are discussed

Transport phenomena in direct methanol fuel cells : modelling and experimental studies

Tese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 200

Modelling and simulation of the laboratory low temperature proton exchange membrane and direct methanol fuel cells

PhD ThesisProton exchange membrane fuel cells (PEMFCs) are promising candidates as power sources due to their high energy conversion efficiency, power density and low pollutants emission. Water management is of vital importance to achieve maximum performance and durability from PEMFCs. The main object of this work was to develop a mathematic model to better understand the water transport in PEMFCs under practical conditions. The aim is to enhance the output power of fuel cells by establishing effective water removal and distribution strategies. A single-phase flow, along the channel, isothermal model of a PEMFC is developed and validated against experimental data. Reactant flow and diffusion are simulated using the Navier-Stokes equation and Maxwell-Stefan equation, respectively. Water transport through the membrane is described by the combinational mechanism in which electro-osmotic drag, back diffusion and hydraulic permeation are all included. Agglomerate assumption is applied for the catalyst layer structure. This model is used to study the effects of the catalyst layer properties on cell performance. The model indicates that the rapid decrease in current density at lower cell voltage is due to an increased oxygen diffusion resistance through the ionomer film. A two-phase flow, across the channel, isothermal model is developed. The water phase transfers between water vapour, dissolved water and liquid water are taken into account and liquid water formation and transport are introduced. Liquid water occupies the secondary pores of the cathode catalyst layer to form a liquid water film on the outer boundary of the ionomer film. This model is used to study the influence of catalyst layer parameters and operating conditions on the cell performance. The model provides useful guidance for optimisation of the ionomer volume fraction in the cathode catalyst layer and the relative humidity of the cathode gas inlet. A two-phase flow, across the channel, non-isothermal model is developed. The model considered the non-uniform temperature distribution within the fuel cell. The modelling results show that heat accumulates within the cathode catalyst layer under the channel. Higher operating temperatures improved the fuel cell performance by increasing the kinetic rate, reducing the liquid water saturation on the cathode and increasing the water carrying capacity of the anode gas. Applying higher temperature on the anode and enlarging the width ratio of the channel/rib could improve the cell performance. A multi-variable optimisation of the cathode catalyst layer composition is represented by a surrogate modelling. Five design parameters, platinum loading, platinum mass ratio, ionomer volume fraction, catalyst layer thickness and agglomerate radius, are optimised by a multiple surrogate model and their sensitivities are analysed by a Monte Carlo method based approach. Two optimisation strategies, maximising the current density at a fixed cell voltage and within a specific range, are implemented for the optima prediction. At higher current densities, cell performance is improved by reducing the ionomer volume fraction and increasing the catalyst layer porosity. The one-dimensional, isothermal, time dependent and steady state models for the anode of a direct methanol fuel cell (DMFC) are developed. The two models are based on the dual-site mechanism, in which the coverage of intermediate species of methanol, OH and CO on the surface of platinum and ruthenium are included. Both the effect of operating conditions and electrode parameters are investigated. The distributions of methanol concentration and overpotential inside the electrode are represented and the current densities predicted by the intrinsic and macro kinetics are compared. From the analysis of the different models developed in this thesis, the main results can be summarised as: (1) Mass transport resistance resulted from the oxygen diffusion through the ionomer film surrounding the agglomerate is the main reason for the rapid fall of current density at lower cell voltage. (2) Ionomer swelling has a significant effect on fuel cell performance because it resulted in a decrease in the porosity and an increase in the ionomer film thickness, leading to an increase in the oxygen transport resistance. (3) Catalyst layer composition has a vital impact on the utilisation of the platinum catalyst and cell performance. (4) Heat accumulates within the cathode catalyst layer under the channel. Applying higher temperatures on the anode optimises the temperature distribution within the MEA and improves the cell performance. (5) Cell performance is improved by enlarging the width ratio of channel/rib. However, the improvement is limited by the sluggish oxygen reduction reaction. (6) For the methanol oxidation reaction in a Pt-Ru anode, the intrinsic current density is determined by the coverage ratios of the intermediate species. The structure and property of the electrode also play an important role in determining the anode performance of a DMFC.EPSR

Preparation, Proximate Composition and Culinary Properties of Yellow Alkaline Noodles from Wheat and Raw/Pregelatinized Gadung (Dioscorea Hispida Dennst) Composite Flours

The steady increase of wheat flour price and noodle consumptions has driven researchers to find substitutes for wheat flour in the noodle making process. In this work, yellow alkaline noodles were prepared from composite flours comprising wheat and raw/pregelatinized gadung (Dioscorea hispida Dennst) flours. The purpose of this work was to investigate the effect of composite flour compositions on the cooking properties (cooking yield, cooking loss and swelling index) of yellow alkaline noodle. In addition, the sensory test and nutrition content of the yellow alkaline noodle were also evaluated for further recommendation. The experimental results showed that a good quality yellow alkaline noodle can be prepared from composite flour containing 20% w/w raw gadung flour. The cooking yield, cooking loss and swelling index of this noodle were 10.32 g, 1.20 and 2.30, respectively. Another good quality yellow alkaline noodle can be made from composite flour containing 40% w/w pregelatinized gadung flour. This noodle had cooking yield 8.93 g, cooking loss 1.20, and swelling index of 1.88. The sensory evaluation suggested that although the color, aroma and firmness of the noodles were significantly different (p ≤ 0.05) from wheat flour noodle, but their flavor remained closely similar. The nutrition content of the noodles also satisfied the Indonesian National Standard for noodle. Therefore, it can be concluded that wheat and raw/pregelatinized gadung composite flours can be used to manufacture yellow alkaline noodle with good quality and suitable for functional food

Mass transport in polymer electrolyte membrane fuel cells using natural convection for air supply

A fuel cell converts chemical energy into electricity and heat through electrochemical reactions. Polymer electrolyte membrane fuel cells (PEMFCs) are approaching commercialization in many applications, including transportation, stationary power, and portable devices. In this thesis, the focus was on small-scale PEMFCs, in which natural convection is used as the air supply method. A cell design with straight vertical cathode channels was studied using experimental and modeling methods, in order to obtain a quantitative insight into mass transport phenomena and to identify the performance limiting processes. The variation of mass transport conditions over the active area of the cell was studied using a current distribution measurement system, which was based on the use of a segmented current collector. The accuracy of the method was analyzed by experimental work and numerical simulation. In order to quantify the local mole fractions of water and oxygen, and the velocity of buoyancy-driven air flow in the cathode channel, a numerical model was developed to describe mass transport in the cathode channel and the gas diffusion layer. Water transport across the polymer membrane was studied by measuring the fraction of product water exiting through the anode. The results give indication of the variation of net water transport coefficient across the active area. The redistribution of water along with the hydrogen flow was also observed. The effect of ambient temperature and relative humidity on cell performance was investigated in a climate chamber. For stack research, a measurement approach was developed for determining the ohmic voltage losses of individual cells in a stack by the current interruption method. As an overall conclusion, it was found that the cell design should be improved especially from the point of view of water management. In order to reduce flooding problems, the cross-section and length of the cathode channels were identified as key parameters to be optimized. It was also found that mechanically rigid gas diffusion layer materials are advantageous for designing an optimized geometry. In addition, it was found that the choice of the anode flow geometry can be used to control the distribution of water across the active area.reviewe

Policies and Motivations for the CO2 Valorization through the Sabatier Reaction Using Structured Catalysts. A Review of the Most Recent Advances

The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions has been defined as mandatory, but for carrying out this, a smart strategy is proposed. This is the application of a circular economy model, which seeks to minimize the generation of waste and maximize the efficient use of resources. From this point of view, CO2 recycling is an alternative to reduce emissions to the atmosphere, and we need to look for new business models which valorization this compound which now must be considered as a renewable carbon source. This has renewed the interest in known processes for the chemical transformation of CO2 but that have not been applied at industrial level because they do not offer evident profitability. For example, the methane produced in the Sabatier reaction has a great potential for application, but this depends on the existence of a sustainable supply of hydrogen and a greater efficiency during the process that allows maximizing energy efficiency and thermal control to maximize the methane yield. Regarding energy efficiency and thermal control of the process, the use of structured reactors is an appropriate strategy. The evolution of new technologies, such as 3D printing, and the consolidation of knowledge in the structing of catalysts has enabled the use of these reactors to develop a wide range of possibilities in the field. In this sense, the present review presents a brief description of the main policies that have motivated the transition to a circular economy model and within this, to CO2 recycling. This allows understanding, why efforts are being focused on the development of different reactions for CO2 valorization. Special attention to the case of the Sabatier reaction and in the application of structured reactors for such process is paid