Pore-scale simulation of fluid flow through the electrodes of high temperature PEMFC using Lattice Boltzmann Method

Polymer electrolyte membrane fuel cells (PEMFC) have received attention as new power sources for residential, transportation, as well as portable applications. Despite the tremendous progress in PEM fuel cell technology, namely development of the phosphoric acid doped PBI-based high temperature (> 100 oC) PEMFC with improved properties, reduced production cost, high efficiency and sufficient tolerance of Pt based hydrogen oxidation catalysts to CO impurity in hydrogen fuel (up to 2% at 180 oC) [1], degradation issues still remain. Loss of phosphoric acid by different processes, especially in high current density and elevated temperature (> 160 oC) [2], is thought to be one of the major mechanisms of degradation. Deep insight into this degradation mechanism, leading to irreversible or reversible performance loss and the relation with other degradation mechanisms and operating conditions, can come by pore-scale modelling of the mass transport phenomena, which provides detailed information at the microscopic scale. In order to optimize the mass transport properties of the electrodes of high temperature PEMFC, firstly, the microstructure of a fiber-based gas diffusive layer (GDL) and a carbon-supported catalyst layer (CL) are reconstructed. Concerning GDL, two different commercial materials are considered and investigated by 2D Scanning Electron Microscopy images: woven GDL (Toray Graphite Paper, TGPH-120, BASF Fuel Cell) and non-woven GDL (Freudenberg Plain H2315, Freudenberg Non-wovens Technical Division). Different reconstruction techniques have been developed to deal with these materials. Woven GDL has been described by a deterministic algorithm [3], while non-woven GDL by a stochastic algorithm. On the other hand, in case of the catalyst layer reconstruction, different degrees of clustering have been investigated in order to match the actual properties of commercial materials [3]. Secondly, pore-scale flow simulations by the Lattice Boltzmann Method (PALABOS [4]) have been done to estimate the permeabilities. Rarefied gas effects are taken into account by a simplified approach, relying on a good agreement with experimental data. A model is proposed to link the permeabilities with degradation processes occurring during the high temperature PEMFC operation and, in particular, with the loss of phosphoric acid. Furthermore, the effects of the micro-morphology and the catalyst particles distribution on the durability of the electrolyte membrane are studied. Some optimization strategies are proposed in order to improve fuel cells durability. This work is part of the on-going European ARTEMIS project, within the Fuel cells and Hydrogen Joint Undertaking (FCH-JU). The purpose of ARTEMIS is to develop and optimise alternative materials for a new generation of European membrane electrolyte assembly, while reducing cost and increasing durability. [1] Q. Li, J.O. Jensen, R.F. Savinell, N.J. Bjerrum. High temperature proton exchange membranes based on polybenzimidazoles for fuel cells. Prog. Polym. Sci. 34 (2009) 449. [2] S. Yu, L. Xiao, and B. C. Benicewicz. Durability Studies of PBI-based High Temperature PEMFCs. FUEL CELLS 08, 2008, No. 3–4, 165–174 [3] U. Salomov, E. Chiavazzo and P. Asinari, Pore-scale modeling of fluid flow through electrodes for high temperature proton exchange membrane (HT-PEM) fuel cells, submitted to Computers and Mathematics with Applications, 2012. [4] www.palabos.or

Multi-scale modeling to boost fuel cell performance: From pore-scale simulations to better efficiency and durability

According to the European Commission, Europe has set itself a goal to reduce CO2 emission levels by 2050 to 80% of what they were in 1990. Fuel cells and hydrogen have potential to contribute to overcoming the energy challenges that accompany this change. In particular, fuel cells based on proton-exchange membranes (PEM) and fuelled by hydrogen and air have many attractive features, including high power density, rapid start-up and high efficiency. However, among the major technology issues that must be addressed for their commercialization and widespread use, the degradation phenomena of the membrane electrode assembly (MEA) plays a key role. In this talk, we present multi-scale morphological models and simulation tools for detailed understanding of degradation phenomena. This kind of modeling techniques can take strong advantage by recent progresses in dual-beam focused ion beam scanning electron microscopy (FIB-SEM). As an example, we investigate the effects of the catalyst distribution in the electrodes on the local fluid flow and on the loss of phosphoric acid from the membran

Gas-dynamic and electro-chemical optimization of catalyst layers in high temperature polymeric electrolyte membrane fuel cells

We investigate the impact of catalyst (Pt) particle distribution on gas dynamics, electro-chemistry and consequently the performance of high temperature polymeric electrolyte membrane (HTPEM) fuel cells. We demonstrate that optimal distribution of catalyst can be used as an effective mitigation strategy for phosphoric acid loss and crossover of reagents through the membrane. First, we recognize that one of the reasons for performance degradation of HTPEM fuel cells originates from the gas dynamic pulling at the interface between the catalyst layer and membrane. Hence, we show that this can be greatly alleviated by choosing a proper catalyst particle distribution within the catalyst layer (CL). A simplified three-dimensional macroscopic model of the membrane electrode assembly (MEA) with catalyst layer made of three or five sublayers with different catalyst loadings, have been developed to analyze the effect of the proposed mitigation strategy on gas dynamics within the catalyst layer and the overall cell performance. This simplified macroscopic model predicts significant reduction (up to 4 times) in pulling using a feasible mitigation strategy, at the cost of only 9% efficiency reduction at high current densities

Numerical investigation of multiphase flow in a channel

Due to the occurrence of failures are divided into design, production and operational. Structural failures occur due to imperfection or violation of the established rules and (or) norms for the design of an object. Production - arise as a result of improper assignment of technological processes for the manufacture or restoration of parts and assembly of a car or are the result of a violation of the accepted technology, unsatisfactory quality of the material of parts or coatings applied to them, the use of insufficiently accurate measuring instruments, failure to meet technical requirements for the manufacture and assembly of elements, as well as the manufacture and assembly of elements and the object as a whole. In the article, basic information about the principles of calculations for solving a system of multiphase Navier–Stokes equations using the control volume method is provided. It is shown that the relationship between velocities and pressure is found using the procedure of SIMPLE. For the numerical solution of this problem, the McCormack scheme was applied. A comparison has been made between each other and with the experimental data. For turbulence, the Spalart–Allmares model was used. And also in the work the movement of sedimentary fluid in different diameters and different Reynolds numbers was studied

Calculation of the water flow rate of Micro HPP depending on the water fall angle in ideal cases

The paper describes the technology for generating electrical energy in small hydroelectric power plants, in the absence of a natural descent of water flows. It is known that the main parameter for obtaining electrical energy is the water flow, which includes the speed of the water. Along with this, the paper theoretically considers the calculation of the resulting velocities of water flows in small hydropower structures. The calculations took into account the ideal, natural and real model of the process of increasing the efficiency in the hydraulic system when using artificial reservoirs with a dam. At the same time, the pattern of modeling various vectors from the initial flow, a term with the potential energy of the accumulated total mass in the cavity of the hydropower structure itself, was considered. This ensured growth and increase in modulus and in other parameters of the vector and force characteristics of the flow, leading to an increase in the overall efficiency of the complete structure. And this already led to an increase in the generation of electrical energy in the installation itself, which has a direct dependence on the momentum and on the flow rate. In conclusion, an output expression is given for calculating the resulting velocity in the system. It is concluded that the construction of the proposed hydropower structures increases the efficiency of hydroelectric power generation

Selection of technical components of Micro HPP

The purpose of this work is to study and design the technical characteristics and design parameters necessary for the design of a micro-hydroelectric power station. Due to the complexity and long process of designing all the components of the system, only the Kaplan turbine and the permanent magnet generator were used in this study. Other power source and turbine designs are beyond the scope of this study and therefore were chosen based on design criteria from the literature alone. Despite these shortcomings, the selection of technical sleeves for Micro HPP has been developed and can be used in practice

Efficient steam generation by inexpensive narrow gap evaporation device for solar applications

Technologies for solar steam generation with high performance can help solving critical societal issues such as water desalination or sterilization, especially in developing countries. Very recently, we have witnessed a rapidly growing interest in the scientific community proposing sunlight absorbers for direct conversion of liquid water into steam. While those solutions can possibly be of interest from the perspective of the involved novel materials, in this study we intend to demonstrate that efficient steam generation by solar source is mainly due to a combination of efficient solar absorption, capillary water feeding and narrow gap evaporation process, which can also be achieved through common materials. To this end, we report both numerical and experimental evidence that advanced nano-structured materials are not strictly necessary for performing sunlight driven water-to-vapor conversion at high efficiency (i.e. ≥85%) and relatively low optical concentration (≈10 suns). Coherently with the principles of frugal innovation, those results unveil that solar steam generation for desalination or sterilization purposes may be efficiently obtained by a clever selection and assembly of widespread and inexpensive materials

Crystal structure and magnetic properties ferrites Ba-Fe-O, Bi-Fe-O, synthesized in NGO “Physics-Sun”

Alloys based on Ba-Fe-O have been synthesized in a large solar furnace NGO “Physics-Sun”. The obtained barium hex ferrite with magnetic characteristics suitable for solving technical problems for the manufacture of protective coatings. The experimentally observed increase in the specific magnetization of BiFe0.75Ni0.25O3 with respect to the data obtained in nominally pure bismuth ferrite is associated both with the suppression of the cycloidal spin structure due to the partial substitution of nickel cations for iron cations and with the establishment of ferromagnetic exchange interaction between neighboring Fe3+ and Ni3+ ions. The results of ab initio (LSDA + U approximation of the DFT method) calculations of the band structure suggest that in the ground state BiFe0.75Ni0.25O3 is a semiconductor with a band gap of 1.94 eV

Pore-scale modeling of fluid flow through gas diffusion and catalyst layers for high temperature proton exchange membrane (HT-PEM) fuel cells

This work represents a step towards reliable algorithms for reconstructing the micromorphology of electrode materials of high temperature proton exchange membrane fuel cells and for performing pore-scale simulations of fluid flow (including rarefaction effects). In particular, we developed a deterministic model for a woven gas diffusion layer (GDL) and a stochastic model for the catalyst layer (CL) based on clusterization of carbon particles. We verified that both of the models developed accurately recover the experimental values of the permeability, without any special ad hoc tuning. Moreover, we investigated the effect of catalyst particle distributions inside the CL on the degree of clusterization and on the microscopic fluid flow, which is relevant for the modeling of degradation (e.g. loss of phosphoric acid). The three-dimensional pore-scale simulations of the fluid flow for the direct numerical calculation of the permeability were performed by the lattice Boltzmann method (LBM

Calculation of the water flow rate of Micro HPP depending on the water fall angle in ideal cases

The paper describes the technology for generating electrical energy in small hydroelectric power plants, in the absence of a natural descent of water flows. It is known that the main parameter for obtaining electrical energy is the water flow, which includes the speed of the water. Along with this, the paper theoretically considers the calculation of the resulting velocities of water flows in small hydropower structures. The calculations took into account the ideal, natural and real model of the process of increasing the efficiency in the hydraulic system when using artificial reservoirs with a dam. At the same time, the pattern of modeling various vectors from the initial flow, a term with the potential energy of the accumulated total mass in the cavity of the hydropower structure itself, was considered. This ensured growth and increase in modulus and in other parameters of the vector and force characteristics of the flow, leading to an increase in the overall efficiency of the complete structure. And this already led to an increase in the generation of electrical energy in the installation itself, which has a direct dependence on the momentum and on the flow rate. In conclusion, an output expression is given for calculating the resulting velocity in the system. It is concluded that the construction of the proposed hydropower structures increases the efficiency of hydroelectric power generation